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The article presents results of residue analysis, based on Gas Chromatograph Mass Spectrometer (GC-MS) measurements, conducted on 13 ceramic storage jars unearthed in the Babylonian destruction layer (586 BCE) in Jerusalem. Five of the jars bear rosette stamp impressions on their handles, indicating that their content was related to the kingdom of Judah's royal economy. The identification of the original contents remains is significant for the understanding of many aspects related to the nutrition, economy and international trade in the ancient Levant. The study shed light on the contents of the jars and the destruction process of the buildings in which they were found. The jars were used alternatively for storing wine and olive oil. The wine was flavored with vanilla. These results attest to the wine consumption habits of the Judahite elite and echo Jerusalem's involvement in the trans-regional South Arabian trade of spices and other lucrative commodities on the eve of its destruction by Nebuchadnezzar.

The selective catalytic oxidative monofunctionalization of gaseous alkanes found in natural gas and commodity chemicals such as benzene and cyclohexane is an important objective in the field of carbon–hydrogen bond activation. Past research has demonstrated the possibility of stoichiometric oxyesterification of such substrates using lead­(IV) trifluoroacetate (PbIV(TFA)4) as oxidant, which is driven by the high 2-electron redox potential of lead­(IV). However, this redox potential then precludes reoxidation of lead­(II) by a convenient oxidant such as O2, nullifying an effective catalytic cycle. In order to utilize renewable energy resources as alternatives to high-temperature thermocatalysis, we demonstrate the room-temperature electrocatalytic oxyesterification of alkanes and benzene with PbIV(TFA)4 as catalysts. At 1.67 V versus SHE, alkanes and benzene yielded the corresponding trifluoroacetate esters at room temperature; typically, good yields and high faradaic efficiencies were observed. High intrinsic turnover frequencies were obtained, for example, of >1000 min–1 for the oxyesterification of ethane at 30 bar. An analysis of the possible mechanistic pathways based on previously investigated stochiometric reactions, cyclic voltammetry measurements, kinetic isotope effects, and model compounds led to the conclusion that catalysis involves lead-mediated proton-coupled electron transfer of alkanes at and to the anode, followed by reductive elimination through an SN2 reaction to yield the alkyl-TFA products. Similarly, lead-mediated electron transfer from benzene at and to the anode leads to phenyl-TFA. Cyclic voltammetry also shows the viability of in situ reoxidation of Pb­(II) species. The synthesis results obtained as well as the mechanistic insight are important advances towards the realization of selective alkane and arene oxidation reactions.

Host-guest solution chemistry with a wide range of organic hosts is an important and established research area, while the use of inorganic hosts is a more nascent area of research. In the recent past in a few cases, Keplerate type molybdenum oxide based porous, spherical clus-ters, shorthand notation {Mo132}, have been used as hosts for organic guests. Here we demonstrate the synthetically controlled encapsula-tion of first row transition metals (M = Mn, Fe, and Co) within a Keplerate cluster that was lined on the inner core with phosphate ani-ons, {Mo132PO4}. The resulting M2+x{Mo132PO4} host-guest complexes were characterized by 31P NMR and ENDOR spectroscopy that substantiated the encapsulation of the first-row transition metal guest. Magnetic susceptibility measurements showed that the encap-sulation of up to 10 equivalents showed little magnetic interaction between the encapsulated metals, indicating that each guest atom occupied a single site. Visualization of the capsules and differentiation of the Mo atoms of the capsule framework and the encapsulated transition metal was possible using spherical and chromatic double aberration-corrected electron microscopy combined with energy-filtered TEM (EFTEM) elemental maps. In addition, use of visible light induced XPS for chemically resolved electrical measurements (CREM) confirmed the successful encapsulation of M within {Mo132PO4} and furthermore showed photoinduced electron transfer from M to Mo. In the future such targeted electron transfer between host {Mo132} and a transition metal guest could be used as photo-initiated switches using inorganic compounds and for single site photocatalytic reactions in confined space.

Four small ceramic juglets that had been used as containers for offerings in an elite Middle Bronze Age III (ca. 1650-1550 BCE) masonry tomb uncovered at Tel Megiddo in the Jezreel Valley, Israel were tested using organic residue analysis. Notably, residues of vanillin, 4-hydroxybenzaldehyde, and acetonvanillone were identified in three of the four juglets examined. These are the major fragrance and flavour components of natural vanilla extract. To date, it has been commonly accepted that vanilla was domesticated in the New World and subsequently spread to other parts of the globe. Our research first ruled out all possibility of sample contamination and then conducted a post-organic residue analysis investigation of various species within the plant kingdom from which these principle compounds could have been exploited. The results shed new light on the first known exploitation of vanilla in an Old World context, including local uses, the significance and employment in mortuary practices, and possible implications for understanding trade networks in the ancient Near East during the second millennium BCE.

The selective oxidation of light hydrocarbons and their valorization with only dioxygen (O-2) are important transformations toward development of efficient chemical processes. Monooxygenase enzymes can catalyze selective aerobic reactions under reducing and protic conditions. The translation of such enzymatic pathways to the practical electrocatalytic oxidation of light, gaseous hydrocarbons, using O-2 as sole oxidant is now reported. An iron tungsten oxide inorganic molecular catalyst with a capsular structure {Fe30W72} stabilized inside by sulfate/bisulfate anions provides a protic environment where three iron atoms are located at each of the pores of the capsule leading to a unique and potent active site for the oxidation reactions. Under mild electrochemical conditions, 1.8 V, in water at room temperature, using O-2 from air, we demonstrate the low-pressure (1-2 bar) hydroxylation of alkanes, notably ethane to acetic acid, and the ozone like cleavage of the carbon carbon double bonds of alkenes. Typical turnover frequencies were 300-400 min(-1). Initial mechanistic studies support a reaction through a very active iron-oxo species.

In this review article, we consider the use of molecular oxygen in reactions mediated by polyoxometalates. Polyoxometalates are anionic metal oxide clusters of a variety of structures that are soluble in liquid phases and therefore amenable to homogeneous catalytic transformations. Often, they are active for electron transfer oxidations of a myriad of substrates and upon reduction can be reoxidized by molecular oxygen. For example, the phosphovanadomolybdate, H5PV2Mo10O40, can oxidize Pd(0) thereby enabling aerobic reactions catalyzed by Pd and H5PV2Mo10O40. In a similar vein, polyoxometalates can stabilize metal nanoparticles, leading to additional transformations. Furthermore, electron transfer oxidation of other substrates such as halides and sulfur containing compounds is possible. More uniquely, H5PV2Mo10O40 and its analogues can mediate electron transfer-oxygen transfer reactions where oxygen atoms are transferred from the polyoxometalate to the substrate. This unique property has enabled correspondingly unique transformations involving carbon carbon, carbon hydrogen, and carbon metal bond activation. The pathway for the reoxidation of vanadomolybdates with O-2 appears to be an inner-sphere reaction, but the oxidation of one-electron reduced polyoxotungstates has been shown through intensive research to be an outer-sphere reaction. Beyond electron transfer and electron transfer oxygen transfer aerobic transformations, there a few examples of apparent dioxygenase activity where both oxygen atoms are donated to a substrate.

How molecules in solution form crystal nuclei, which then grow into large crystals, is a poorly understood phenomenon. The classical mechanism of homogeneous crystal nucleation proceeds via the spontaneous random aggregation of species from liquid or solution. However, a non-classical mechanism suggests the formation of an amorphous dense phase that reorders to form stable crystal nuclei. So far it has remained an experimental challenge to observe the formation of crystal nuclei from five to thirty molecules. Here, using polyoxometallates, we show that the formation of small crystal nuclei is observable by cryogenic transmission electron microscopy. We observe both classical and non-classical nucleation processes, depending on the identity of the cation present. The experiments verify theoretical studies that suggest non-classical nucleation is the lower of the two energy pathways. The arrangement in just a seven-molecule proto-crystal matches the order found by X-ray diffraction of a single bulk crystal, which demonstrates that the same structure was formed in each case.

The photoreduction mechanism of carbon dioxide to carbon monoxide by the Re-organic hybrid polyoxometalates (POMs) {NaH[PW₁₂O₄₀]^3-Re^IL(CO)₃DMA}^na (L = 15-crown-5 phenanthroline, DMA = N,N-dimethylacetamide) has been investigated by means of DFT and TD-DFT calculations. The reaction mechanism can be divided into several steps, including (i) photoexcitation and charge transfer, (ii) DMA release, (iii) CO₂ addition, (iv) protonation, and (v) CO release and regeneration of the catalyst. The charge transfer (CT) states, POM to Re complex, are efficiently induced by metal-centered (MC) excitations occurring on the reduced POM. Once one electron is transferred to the organometallic unit from the excited POM, the Re is able to bind and activate the CO₂ substrate. Subsequent steps that involve protonation of CO₂ and CO release are favorable thermodynamically and are induced by a second electron transfer from the POM to the Re complex. In this reaction, the POM acts as photosensitizer, electron reservoir, and electron donor.

The electrochemical properties of Keggin type polyoxometalates Qn[XW12O40] (X = P, Si, B; Q = n-tetraoctylammonium and n-trioctylmethylammonium) in organic solvents were investigated in order to understand the interrelation between the redox potentials, solvents and ion pairing. A logarithmic correlation between the dielectric constant of the solvent (epsilon ranged from 4.8 to 46.6) and the reduction potential of the [PW12O4](3-)/[PW12O4](4-) couple was found. This reduction potential increased significantly when the surface charge of the polyoxometalate went from 3- to 5-. The investigation of the ion pairing properties by diffusion NMR revealed the presence of intimate ion pairs in less polar solvents (e.g. dichloromethane) and less compact ion pairs in more polar solvents (e.g. DMSO). Using a V atom within the polyoxometalate an NMR experiment showed that a n-trioctylmethyl ammonium cation bonded to the polyoxometalate anion more intimately than a n-tetraoctyl ammonium cation.

The epoxidation of alkenes with peroxides by W-VI, Mo-VI, V-V, and Ti-IV compounds is well established, and it is well accepted that the active intermediate peroxo species are electrophilic toward nucleophilic substrates. Polyoxotungstates, for example, those of the sandwich structure, [WZn(TML)(2)(ZnW9O34)(2)](q-) in which TM = transition metal and L = H2O, have in the past been found to be excellent epoxidation catalysts. It has now been found that substituting the Lewis basic Bi-III into the terminal position of the sandwich polyoxometalate structure to yield [Zn2Bi2III(ZnW9O34)(2)](14-) leads to an apparent umpolung of the peroxo species and formation of a nucleophilic peroxo intermediate. There are two lines of evidence that support the formation of a reactive nucleophilic peroxo intermediate: (1) More electrophilic sulfoxides are more reactive than more nucleophilic sulfides, and (2) nonfunctionalized aliphatic alkenes and dienes showed ene type reactivity rather than epoxidation pointing toward dark formation of singlet oxygen from the nucleophilic intermediate peroxo species. Allylic alcohols reacted much faster than alkenes but showed chemoselectivity toward C-H bond activation of the alcohol and formation of aldehydes or ketones rather than epoxidation. This explained via alkoxide formation at the Bi-III center followed by oxidative beta-elimination.

The investigation of new oxidative transformations for the synthesis of carbon-heteroatom and heteroatom-heteroatom bonds is of fundamental importance in the synthesis of numerous bioactive molecules and fine chemicals. In this context, NaIO₄, an exciting reagent, has attracted increasing attention enabling the development of these unprecedented oxidative transformations that are difficult to achieve otherwise. Thus, NaIO₄ has been successfully explored as a versatile oxidant for a variety of fundamental organic transformations such as C-H activation, oxidative functionalization of alkenes and other interesting oxidative transformations and its application in the synthesis of bioactive natural products. This review summarizes recent developments in this area with NaIO₄ as a versatile oxidant and brings out many challenges that still remain elusive for the future.

A new aerobic carbon-carbon bond cleavage reaction of linear di-substituted alkenes, to yield the corresponding aldehydes/ketones in high selectivity under mild reaction conditions, is described using copper(II)-substituted polyoxometalates, such as {α₂-Cu(L)P₂W ₁₇O₆₁}^8- or {[(Cu(L)]₂WZn(ZnW ₉O₃₄)₂}^12-, as catalysts, where L = NO₂. A biorenewable-based substrate, methyl oleate, gave methyl 8-formyloctanoate and nonanal in >90% yield. Interestingly, cylcoalkenes yield the corresponding epoxides as products. These catalysts either can be prepared by pretreatment of the aqua-coordinated polyoxometalates (L = H ₂O) with NO₂ or are formed in situ when the reactions are carried with nitroalkanes (for example, nitroethane) as solvents or cosolvents. Nitroethane was shown to release NO₂ under reaction conditions. ³¹P NMR shows that the Cu-NO₂-substituted polyoxometalates act as oxygen donors to the C-C double bond, yielding a Cu-NO product that is reoxidized to Cu-NO₂ under reaction conditions to complete a catalytic cycle. Stoichiometric reactions and kinetic measurements using {α₂-Co(NO₂)P₂W₁₇O ₆₁}^8- as oxidant and trans-stilbene derivatives as substrates point toward a reaction mechanism for C-C bond cleavage involving two molecules of {α₂-Co(NO₂)P₂W ₁₇O₆₁}^8- and one molecule of trans-stilbene that is sufficiently stable at room temperature to be observed by ³¹P NMR.

The tri-rhenium(VI) capped Wells-Dawson polyoxometalate, [Re₃P₂W₁₅O₆₂]^6- with quaternary ammonium cations was synthesized by reacting the trivacant lacunary species, [P₂W₁₅O₅₆]^12- with [ReOCl₃(PPh₃)₂] in an organic solvent. Elemental analysis by thermogravimetry and inductively coupled plasma mass spectroctrometry confirmed the substitution of three rhenium atoms, single-crystal X-ray diffraction as well as infra red spectroscopy showed the complete Wells-Dawson structure. The presence of all three rhenium atoms in one cap is indicated by ³¹P nuclear magnetic resonance spectroscopy and the electron spin resonance spectrum shows that the tri-rhenium(V) species with three unpaired electrons is low spin, S = 1/2.

Crystallization of the {HW₉O₃₃} isopolyanion in the presence of M^II(DMSO)₄Cl₂ (where M = Ru, Os) and Na and K cations yielded one-dimensional chains, {K[HW₉O ₃₃M₂(C₂H₆SO)₆] ^6-}_n. The {HW₉O₃₃} isopolyanion is capped by M^II(DMSO)₃ moieties, which are, in turn, linked by potassium cations. The chains for the Ru^II-based compound show a prismatic coordination around the K⁺ linker and {HW₉O ₃₃} moieties that are eclipsed relative to each other along the chain, while the Os^II-based compound has an octahedral coordination around the K⁺ linker and {HW₉O₃₃} moieties that are staggered relative to each other along the chain. The three-dimensional arrangement of the two compounds is quite different. For the Ru^II compound, channels are obtained by the arrangement of six {K[HW ₉O₃₃Ru₂(C₂H₆SO) ₆]^6-}_n chains along the c axis. The channel is stabilized by the binding of sodium cations, which interlock the chains through coordination of different oxygen atoms and leads to a tight staggered arrangement between the chains of {K[HW₉O₃₃Ru ₂(C₂H₆SO)₆]^6-} _n. The channels have an approximate diameter of 8 Å and are occupied by layers of six sodium cations that form chair-like hexagons with Na-Na interatomic distances of 2.807 Å. There are five water molecules that separate the layers of the Na⁺ cations. For the osmium compound, two different types of channels, defined by the arrangement three {K[HW ₉O₃₃Os₂(C₂H₆SO) ₆]^6-}_n chains, are formed. The channels are formed through interchain bonding through a bridge formed by connecting sodium atoms to the terminal atoms of the {HW₉O₃₃} unit. Here, the {K[HW₉O₃₃Os₂(C₂H ₆SO)₆]^6-}_n chains are eclipsed relative to one another. Water molecules occupy one channel, while the other channel is occupied by K⁺ cations hexacoordinated to aqua ligands. The approximate diameter of the channels is 5.5 Å.

Chiral cross-linked polyethylenimines were used to intercalate MnIII salen catalysts, thereby inducing a chiral environment upon an achiral metal complex. The synzyme, dispersed in water, catalyzes the aqueous biphasic asymmetric epoxidation of styrene derivatives (see structure; L=Cl, OAc, R=isopropyl, phenyl). In the presence of the chiral catalyst there is a significant synergistic effect that increases the enantioselectivity of epoxidation.

Copper(I) complexes with perfluorinated tails, (Cu^IL ²AcN)BF₄ and (Cu^IL³AcN)BF ₄, where L² = 6,6′-bis(perfluorohexyl)-2,2′: 6′,2′-terpyridine and L³ = 6,6′-bis(2,2,3,3,4,4,5, 5,6,6,7,7,7-tridecafluoroheptyl)-2,2′-bipyridine and AcN = acetonitrile, were synthesized and their rather unique crystal structures were elucidated. (Cu^IL²AcN)BF₄ crystallizes in a low-symmetry space group, P$\bar {1}$, with a very large unit cell that required synchrotron radiation to locate all atoms. The molecular structure of (Cu^IL²AcN)BF₄ has an asymmetric tetrahedrally distorted square-planar coordination sphere around Cu^I. Eight similar but distinct molecular structures were found. The crystal packing of (Cu ^IL²AcN)(BF₄) has a layered structure with a clear segregation between the terpyridine moieties and the fluorous chains. The terpyridine units are arranged in a "back to back" fashion and tilted 20-25° relative to the interlayer plane, and the layered structure is staggered with offsets of approximately 4 Å between layers. The molecular structure of (Cu^IL³AcN)(BF₄) features a Y-shaped trigonal planar coordination sphere around copper(I). Comparison of the structure with analogous Cu^I(neocuproine)AcN showed that the fluorous tails with the CH₂CH₂ spacers basically have no effect on the bond lengths and angles to Cu¹. The crystal structure of (Cu^IL³AcN)(BF₄) shows a "herring bone" conformation with an approximately 96° angle in the CubipyAcN units. The "herring bone" conformation leads to an accordion-type fluorous layer. Copper(I) complexes of bipyridine (Y-shaped trigonal planar) and terpyridine (tetrahedrally distorted square-planar) with fluorous tails showed crystal packing with segregation of the aromatic units and the fluorous tails. Layered structures that are tilted in two different dimensions as well as "herring bone" structures with accordion-like fluorous layers were observed.

An insoluble, porous, amorphous, homochiral material based on a polypeptide titanium–phosphonate scaffold with an encapsulated achiral Mn^III–salen was prepared and characterized. Consecutive epoxidation and hydration of styrene and its derivatives by aqueous hypochlorite in THF showed the highly enantioselective (>99%) formation of styrene diol derivatives.

A ditopic 1,2-bis(2,2′-bipyridyl-6-yl)ethyne ligand, L, has been synthesized for the first time by consecutive Suzuki and Sonogashira coupling reactions either in a one- or two-step synthesis. Coordination of L with some first-row transition metals, Fe, Mn and Co showed a very rich structural diversity that can be obtained with this ligand. Reaction of L with Mn ^II(OAc)₂ yielded a dimanganese(ii) complex, [Mn ₂L(μ-OAc)₃]PF₆, (1) where the two somewhat inequivalent trigonal-bipyramidal Mn atoms separated by 3.381 Å are bridged by L and three acetate moieties. A similar reaction of L with Mn ^III(OAc)₃ yielded a very different dimanganese complex [Mn₂L′(OH)(OAc)₂(DMF)₂]PF ₆·DMF (2) where L′ is a E-1,2-bis(2,2′-bipyridyl- 6-yl)ethene fragment that was formed in situ. The L′ ligand bridges between the two Mn centers, despite its trans configuration, which leads to a very strained ethene bridging moiety. The Mn atoms are also bridged by two acetate ligands and a hydroxy group that bridges between the Mn atoms and the ethene fragment; DMF completes the octahedral coordination around each Mn atom which are separated by 3.351 Å. A comproportionation reaction of L with Mn^II(OAc)₂ and n-Bu₄NMnO₄ yielded a tetramanganese compound, [Mn₄(μ₃-O)₂(OAc) ₄(H₂O)₂L₂](PF₆) ₂·2CH₃CN (3). Compound 3 has a dimer of dimers structure of the tetranuclear Mn core that consists of binuclear [Mn ₂O(OAc)₂L]⁺ fragment and a PF₆ anion. BVS calculations indicate that 3 is a mixed-valent 2Mn^II plus 2Mn^III compound where two [Mn^II₂O(OAc) ₂L]⁺ fragments are held together by Mn^III-O inter-fragment linkers which have a distorted octahedral geometry. The Mn atoms in the [Mn₂O(OAc)₂L]⁺ fragments have a capped square-pyramid configuration where an aqua ligand is capped on one of the faces. Although the aqua ligand is well within a bonding distance to a carbon atom of the proximal ethyne bridge, there does not appear to be an oxygen-carbon bond formation, rather the ligand is constrained in this position, as deduced by the observation that the bond lengths and angles of the ligand are essentially the same as those for the free ligand, L. Reaction of L with perchlorate or triflate salts of Fe(ii), Mn(ii) and Co(ii) in dry acetonitrile yielded binuclear triple helicate structures (2:3 metal to L ratios) [Fe₂L ₃](CF₃SO₃)₄·CH₃CN (4), [Mn₂L₃](ClO₄)₄·1. 7CH₃CN·1.65EtOEt (5) and [Co₂L₃] (ClO₄)₄·2CH₃CN·2EtOEt (6) where each M(ii) center with a slightly distorted octahedral geometry is bridged by three of the ditopic ligands. The M-M distances varied; 5.961 Å (Mn), 6.233 Å (Co) 6.331 Å (Fe). Reaction of L with Co(ClO ₄)₂·6H₂O in wet acetonitrile yielded a dicobalto(iii) compound, [Co₂L′₃(O) ₂](ClO₄)₂·H₂O (7), with two types of L′ fragments; one bridging between the two Co centers and two non-bridging ligands, each bonded to a Co atom via one bipyridyl group where the other is non-bonding. The octahedral coordination sphere around each Co atom is completed by the formation of a cobalt-carbon bond from the two carbon atoms of the ethene moiety of the bridging ligand and by a hydroxy moiety that is also bonded to the ethene group of the non-bridging ligand. Reaction of L with Co(ClO₄)₂·6H₂O in dry acetonitrile in the presence of Et₃N yielded the tetracobalto(ii) complex {[Co ₂L₄(OH)₄](ClO₄)₄} ₂ (8) with a unique twisted square configuration of cobalt ions with Co-Co distances of 3.938 to 4.131 Å. In addition to the L bridging ligand the Co atoms are linked by hydroxy moieties. Some preliminary catalytic studies showed that the Mn compounds 1 and 2 were active (high yield within 3 min) for alkene epoxidation with peracetic acid and hydrogen peroxide dismutation (catalase activity).

In this Forum Article, we discuss the use of dioxygen (O₂) in oxidations catalyzed by polyoxometalates. One- and two-electron-transfer oxidation of organic substrates is catalyzed by H₅PV ₂Mo₁₀O₄₀ and often occurs via an outer-sphere mechanism. The reduced polyoxometalate is reoxidized in a separate step by O₂ with the formation of water. H₅PV₂Mo ₁₀O₄₀ also catalyzes electron transfer-oxygen transfer reactions. Here, in contrast to the paradigm that high-valent oxo species are often stronger oxygen-transfer species than lower-valent species, the opposite occurs. Thus, oxygen transfer from the catalyst is preceded by electron transfer from the organic substrate. The monooxygenase-type reduction of O₂ with polyoxometalates is also discussed based on the formation of a stable iron(III) hydroperoxide compound that may have implications for the oxidation of other lower-valent polyoxometalates such as vanadium(IV)- and ruthenium(II)-substituted polyoxometalates. Finally, the formation of hybrid compounds through the attachment of electron-accepting polyoxometalates to coordination compounds can modify the reactivity of the latter by making higher-valent oxidation states more accessible.

A polyoxometalate of the Keggin structure substituted with Ru(III), (6)Q(5)[Ru(III)(H(2)O)SiW(11)O(39)] in which (6)Q=(C(6)H(13))(4)N(+), catalyzed the photoreduction of CO(2) to CO with tertiary amines, preferentially Et(3)N, as reducing agents. A study of the coordination of CO(2) to (6)Q(5)[Ru(III)(H(2)O)SiW(11)O(39)] showed that 1) upon addition of CO(2) the UV/Vis spectrum changed, 2) a rhombic signal was obtained in the EPR spectrum (g(x)=2.146, g(y)=2.100, and g(z)=1.935), and 3) the (13)C NMR spectrum had a broadened peak of bound CO(2) at 105.78 ppm (Delta(1/2)=122 Hz). It was concluded that CO(2) coordinates to the Ru(III) active site in both the presence and absence of Et(3)N to yield (6)Q(5)[Ru(III)(CO(2))SiW(11)O(39)]. Electrochemical measurements showed the reduction of Ru(III) to Ru(II) in (6)Q(5)[Ru(III)-(CO(2))SiW(11)O(39)] at -0.31 V versus SCE, but no such reduction was observed for (6)Q(5)[Ru(III)(H(2)O)SiW(11)O(39)]. DFT-calculated geometries optimized at the M06/PC1//PBE/AUG-PC1//PBE/PC1-DF level of theory showed that CO(2) is preferably coordinated in a side-on manner to Ru(III) in the polyoxometalate through formation of a Ru-O bond, further stabilized by the interaction of the electrophilic carbon atom of CO(2) to an oxygen atom of the polyoxometalate. The end-on CO(2) bonding to Ru(III) is energetically less favorable but CO(2) is considerably bent, thus favoring nucleophilic attack at the carbon atom and thereby stabilizing the carbon sp(2) hybridization state. Formation of a O(2)C-NMe(3) zwitterion, in turn, causes bending of CO(2) and enhances the carbon sp(2) hybridization. The synergetic effect of these two interactions stabilizes both Ru-O and C-N interactions and probably determines the promotional effect of an amine on the activation of CO(2) by [Ru(III)(H(2)O)SiW(11)O(39)](5-). Electronic structure analysis showed that the polyoxometalate takes part in the activation of both CO(2) and Et(3)N. A mechanistic pathway for photoreduc

The H₅PV₂Mo₁₀O₄₀ polyoxometalate and Pd/AI₂O₃ were used as co-catalysts under anaerobic conditions for the activation and oxidation of CO to CO ₂ by an electron transfer-oxygen transfer mechanism. Upon anaerobic reduction of H₅PV₂Mo₁₀O₄₀ with CO in the presence of Pd(0) two paramagnetic species were observed and characterized by continuous wave electron paramagnetic resonance (CW-EPR) and hyperfine sublevel correlation (HYSCORE) spectroscopic measurements. Major species I (65-70%) is assigned to a species resembling a vanadyl cation that is supported on the polyoxometalate and showed a bonding interaction with ¹³CO. Minor species II (30-35%) is attributed to a reduced species where the vanadium(IV) atom is incorporated in the polyoxometalate framework but slightly distanced from the phosphate core. Under aerobic conditions, CO/O₂, a nucleophilic oxidant was formed as elucidated by oxidation of thianthrene oxide as a probe substrate. Oxidation reactions performed on terminal alkenes such as 1-octene yielded a complicated mixture of products that was, however, clearly a result of alkene epoxidation followed by subsequent reactions of the intermediate epoxide. The significant competing reaction was a hydro-carbonylation reaction that yielded a ∼1:1 mixture of linear/branched carboxylic acids.

Primary alcohols such as 1-butanol were oxidized by the H₅PV₂Mo₁₀O₄₀ polyoxometalate in an atypical manner. Instead of C-H bond activation leading to the formation of butanal and butanoic acid, C-C bond cleavage took place leading to the formation of propanal and formaldehyde as initial products. The latter reacted with the excess 1-butanol present to yield butylformate and butylpropanate in additional oxidative transformations. Kinetic studies including measurement of kinetic isotope effects, labeling studies with ¹⁸O labeled H₅PV₂Mo₁₀O₄₀, and observation of a prerate determining step intermediate by ¹³C NMR leads to the formulation of a reaction mechanism based on electron transfer from the substrate to the polyoxometalate and oxygen transfer from the reduced polyoxometalate to the organic substrate. It was also shown that vicinal diols such as 1,2-ethanediol apparently react by a similar reaction mechanism.

It has been found that in apolar reaction media the nitrosonium cation (NO⁺) activated alkenes under mild conditions toward electrophilic substitution of arene substrates to yield the alkylated arene with Markovnikov orientation. In the absence of arenes the alkenes react with themselves to yield a mixture of dimeric alkenes. The nitrosonium cation can be dissolved in the reaction medium by using the tetrakis-(bis-(3,5-trifluromethyl)phenyl) borate anion, where upon the reactions occur effectively at 30 °C. Alternatively an insoluble, heterogeneous catalyst was prepared so as to yield a NO⁺ cation with a polyoxometalate (PW₁₂O₄₀^3-) anion. This catalyst was generally more effective and selective toward a broader range of substrates at 70 °C.

The reaction of a quaternary ammonium salt of the tin chloride-substituted polyoxometalate, [PSn(Cl)W₁₁O₃₉]^4-, with a variety of n-nucleophiles including primary, secondary, and tertiary amines and a tertiary phosphine, yielded tin-centered Lewis acid-base adducts, [PSn(Cl)W₁₁O₃₉]^4--n-nucleophile; with more nucleophilic secondary amines such as diisopropylamine, apparently some [PSnN[CH(CH₃)₂]₂W₁₁O ₃₉]^4- was formed as a minor product. The compounds were identified by ¹H, ¹¹⁹Sn, ¹⁵N, ³¹P, and ¹⁸³W NMR, ESI-MS, and elemental analyses. The key connectivity of the Sn-Cl center with the amine was clarified by the observation of ³J Sn-H couplings (Sn from the polyoxometalate cluster and H from the amine moiety) in a 2D ¹¹⁹Sn-¹H heteronuclear multiple-bond correlation NMR experiment. This new, rather simple synthetic method was also utilized for preparing amino acid-polyoxometalate hybrid compounds.

Polyoxometalates of the ε-Keggin structure [Mo₁₂^VO₃₉(μ₂-OH)₁₀H₂{X^II(H₂O)₃}₄] (X = Ni, Co, Mn and Cu), have been synthesized. While the nickel substituted compound was known, the cobalt, manganese and copper analogs are new. These ε-Keggin polyoxometalates are insoluble and, except for the nickel analog, could not be obtained in crystalline form. The IR spectra indicate that for cobalt and manganese substitution the compounds are isostructural to the nickel derivative. The ε-Keggin polyoxometalates were used as heterogeneous catalysts for the aerobic oxidation of aldehydes to carboxylic acids. The selectivity of the reaction was highly dependent on the identity of the aldehyde. Aliphatic linear aldehydes, e.g. octanal, and benzaldehyde react quantitatively and selectively to the respective carboxylic acids. 2-Methyl-undecanal reacted quite selectively yielding as minor product 2-undecanone by decarboxylation. 2-Phenylpropanal showed more significant β-methyl cleavage. Substrates with a variety of functional moieties such as myrtenal and 5-norbornene-2-carboxaldehyde yielded considerable amounts of formates via a Dakin type reaction and allylic oxidation products.

Palladium nanoparticles were prepared, stabilized, and dispersed in water by alkylated branched polyethyleneimine. The palladium nanoparticles were effective aqueous biphasic catalysts for the chemoselective hydrogenation of alkenes with preferential reduction of less hindered double bonds, such as reduction of 3-methylcyclohexene in the presence of 1-methylcyclohexene and 1-octene in the presence of 2-methyl-2-heptene.

Na₁₂[WZn₃(H₂O)₂[ZnW₉O₃₄)₂], easily self assembled from Na₂WO₄ and Zn(NO₃)₂, catalyses the in situ oxidation of ammonia with hydrogen peroxide to hydroxylamine, which further reacts with ketones and aromatic aldehydes in an aqueous biphasic medium without organic solvent to yield oximes as valuable intermediates.

The synthesis of a new vanadium phosphonate material (TPPhA-V), prepared by the non-hydrolytic condensation of a vanadium(V) alkoxide with an arylphosphonic acid, is presented. Transmission electron microscopy (TEM) of TPPhA-V showed the specimen to be granular with small highly contrasting dots situated within the a more poorly contrasting substance, while the scanning electron microscopy (SEM) examination revealed formation of spongelike amorphous material as the only type of the specimen morphology. Room-temperature electron spin resonance measurement of the TPPhA-V isotropic broad singlet resonance line indicated strong interaction between neighboring vanadium (IV) atoms. The test of the catalytic properties of TPPhA-V showed that the oxidation generally proceeded smoothly with the formation of corresponding benzylic aldehydes at high conversion and selectivity.

This paper reviews our work on oxidations with aqueous hydrogen peroxide catalyzed by inorganic catalysts devoid of organic ligands. In the first part of the review, the use of the [WZn₃(ZnW₉O₃₄)₂] ^12- "sandwich" polyoxometalate as a multi-purpose oxidation catalyst is described. Attention is paid to practical aspects that are of relevance for large-scale, industrial use of this catalyst, such as catalyst preparation, handling, and recycling. Its activity in cyclooctene epoxidation compared to other W-based catalyst systems has been determined under ceteris paribus conditions. The second part of the review deals with homogeneous and heterogeneous inorganic catalysts for "dark" singlet oxygenation, i.e., singlet oxygenation by catalytic disproportionation of hydrogen peroxide into singlet oxygen and water. The industrial advantages of "dark" singlet oxygenation compared to conventional photo-oxidation are described. It is pointed out that the reaction medium and nature of the catalyst strongly influence the selectivity and scope of the method.

An organic-inorganic hybrid material. TPPhA-Ti, was constructed by non-hydrolytic condensation of a dendritic tetrakis-1,3,5,7-(4- phosphonatophenyl)adamantane precursor and titanium(iv) isopropoxide. One preparative pathway yielded insoluble materials with a Ti/P ratio of ∼1 which was confirmed by a combination of FT-IR, TGA, and EDS measurements. N ₂ sorption experiments showed that TPPhA-Ti is a porous solid (micro pores ∼13 Å; mesopores ∼38 Å) with a high surface area, ∼550 m²g^-1. The structure and morphology of the TPPhA-Ti as investigated by transmission and scanning electron microscopy showed a layered-type material. Additional X-ray diffraction data suggest a paracrystalline material; an optimization of possible molecular arrangements of TPPhA-Ti was simulated that was in agreement with the experimental data. A second preparative pathway yielded a Ti oxide-phosphonate with a Ti/P ratio of ∼3.4. Both TEM and SEM revealed that hollow nanospheres were formed with diameters of ∼180- 300 nm.

(Chemical Equation Presented) [cis-Ru(II)(dmp)₂(H ₂O)₂]²⁺ (dmp = 2,9-dimethylphenanthroline) was found to be a selective oxidation catalyst using hydrogen peroxide as oxidant. Thus, primary alkenes were very efficiently oxidized via direct carbon-carbon bond cleavage to the corresponding aldehydes as an alternative to ozonolysis. Secondary alkenes were much less reactive, leading to regioselective oxidation of substrates such as 4-vinylcyclohexene and 7-methyl-1,6-octadiene at the terminal position. Primary allylic alcohols were chemoselectively oxidized to the corresponding allylic aldehydes, e.g., geraniol to citral.

Nitrobenzene was regioselectively oxidized to 2-nitrophenol with oxygen in a reaction catalyzed by the H5PV2Mo10O40 polyoxometalate. The reaction was first order in oxygen and catalyst. 15N NMR showed the interaction between nitrobenzene and the polyoxometalate. Use of labeled 18O2, H218O, a competitive kinetic isotope experiment, and use of phenyl-tert-butylnitrone as a spin-trap and identification by EPR provided evidence for formation of a radical intermediate involving a selective intramolecular interaction at the ortho position due to formation of a H5PV2Mo10O40−nitrobenzene complex.

A basic premise behind the use of polyoxometalates in oxidation chemistry is the fact that polyoxometalates are oxidatively stable. This, a priori, leads to the conclusion that for practical purposes polyoxometalates would have distinct advantages over widely investigated organometallic compounds that are vulnerable to decomposition due to oxidation of the ligand bound to the metal center. Since polyoxometalate synthesis is normally carried out in water by mixing the stoichiometrically required amounts of monomeric metal salts and adjusting the pH to a specific acidic value many structure types are accessible by variation of the reaction stoichiometry, replacement of one or more addenda atoms with other transition or main group metals, and pH control. The structural variety available has enabled the use of polyoxometalates as catalysts for oxidation of hydrocarbons and functionalized organic substrates (alcohols, amines, sulfides, etc.) with a wide range of oxygen donors ranging from molecular oxygen, hydrogen peroxide, nitrous oxide, ozone, alkyl hydroperoxides, periodate, sulfoxide and others. The wide purview of oxidation reactions is enabled because the structural variety leads to oxidation through a number of different mechanistic motifs.From a synthetic organic point of view, the most applicable uses of polyoxometalates as catalysts involve the “green” oxygen donors – hydrogen peroxide and molecular oxygen. Since practical applications are in hand in this area, practical considerations concerned with catalyst recycle and/or recovery and the elimination of environmentally problematic solvents are also coming to the forefront. In this paper, we will present some of our activities in the area of “catalyst engineering” for catalytic synthetic applications by polyoxometalates including: (a) catalytic mesoporous solids from organic-polyoxometalate hybrid materials, (b) fluorous phase polyoxometalates with and without fluorous solvents and (c) the use of aqueous biphasic media for oxidation with hydrogen peroxide.

Two new paradigms for separating the homogeneous catalyst from the substrate and products of oxidation were reviewed. The first example demonstrated the functionalization in water of hydrophobic substrates, i.e., hydrocarbons, with methane monooxygenase biomimetic complexes embedded in a derivatized surface silica system using tert-butyl hydroperoxide/O₂ as the oxidants. For example, cyclohexane was oxidized to a mixture of cyclohexanone, cyclohexanol, and cyclohexyl-tert-butyl peroxide, in a ratio of ∼ 3:1:2. The balance between polyethylene oxide and polypropylene oxide, tethered on the silica surface, was crucial for maximizing the catalytic activity. The mechanism for the silica-based catalytic assembly occurred via the Haber-Weiss process. The second precatalyst separation paradigm, the use of the fluorous solvents, which was predicted on solubilizing the precatalyst in a fluorocarbon solution, allowed the functionalization of alkanes and alkenes, while selective oxidation of alcohols to aldehydes was also possible; both precatalyst and product were in separate solvent phases.

Combinations of alkylated polyethylenimine and polyoxometalates yield water-soluble synzymes with hydrophobic regions that allowed the aqueous biphasic selective oxidation of very hydrophobic, water-insoluble substrates with hydrogen peroxide. With the alkylated PEI/{PO₄[WO(O₂)₂]₄}³- highly effective C-C bond cleavage of alkenes to aldheydes was observed. The synzymes have both tertiary and quaternary amine centers as shown by a combination of ¹⁵N-¹H HMBC and XPS measurements. The existence of hydrophobic regions was concluded from the measurement of contact angles and a hypsochromic shift of a fluorescent probe.

A new high yield method for the synthesis of aromatic aldehydes has been developed. The procedure is based on an acid catalyzed hydroxymethylation of an arene substrate by paraformaldehyde with concurrent selective oxidation of the intermediate aromatic carbinol by 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) to the aldehyde product.

Alkylarenes were catalytically and selectively oxidized to the corresponding benzylic acetates and carbonyl products by nitrate salts in acetic acid in the presence of Keggin type molybdenum-based heteropolyacids, H_3+xPV_xMo_12-xO₄₀ (x = 0-2). H ₅PV₂Mo₁₀O₄₀ was especially effective. For methylarenes there was no over-oxidation to the carboxylic acid contrary to what was observed for nitric acid as oxidant. The conversion to the aldehyde/ketone could be increased by the addition of water to the reaction mixture. As evidenced by IR and ¹⁵N NMR spectroscopy, initially the nitrate salt reacted with H₅PV₂Mo₁₀O ₄₀ to yield a N^VO₂⁺[H ₄PV₂Mo₁₀O₄₀] intermediate. In an electron-transfer reaction, the proposed N^VO₂ ⁺[H₄PV₂Mo₁₀O₄₀] complex reacts with the alkylarene substrate to yield a radical-cation-based donor-acceptor intermediate, N^IVO₂[H₄PV ₂Mo₁₀O₄₀]-ArCH₂R^+.. Concurrent proton transfer yields an alkylarene radical, ArCHR^., and NO₂. Alternatively, it is possible that the N^VO ₂⁺[H₄PV₂Mo₁₀O ₄₀] complex abstracts a hydrogen atom from alkylarene substrate to directly yield ArCHR^. and NO₂. The electron transfer-proton transfer and hydrogen abstraction scenarios are supported by the correlation of the reaction rate with the ionization potential and the bond dissociation energy at the benzylic positions of the alkylarene, respectively, the high kinetic isotope effect determined for substrates deuterated at the benzylic position, and the reaction order in the catalyst. Product selectivity in the oxidation of phenylcyclopropane tends to support the electron transfer-proton transfer pathway. The ArCHR^. and NO₂ radical species undergo heterocoupling to yield a benzylic nitrite, which undergoes hydrolysis or acetolysis and subsequent reactions to yield benzylic acetates and corresponding aldehydes or ketones as final products.

A "sandwich" type polyoxometalate, Na₁₂[(WZn ₃(H₂O)₂][(ZnW₉O₃4) ₂], was used as an oxidation catalyst in aqueous biphasic reaction media to effect oxidation of alcohols, diols, pyridine derivatives, amines and aniline derivatives with hydrogen peroxide. The catalyst was shown by ¹⁸³W NMR to be stable in aqueous solutions in the presence of H ₂O₂ and showed only minimal non-productive decomposition of the oxidant. Secondary alcohols were selectively oxidized to ketones, while primary alcohols tended to be oxidized to the corresponding carboxylic acids, although secondary alcohols were selectively oxidized in the presence of primary alcohols. Vicinal diols yielded carbon-carbon bond cleavage products in very high yields. Pyridine derivatives were oxidized to the respective TV-oxides, but strongly electron-withdrawing moieties inhibited the oxidation reaction. Primary amines were oxidized to the oximes, but significantly hydrolyzed in situ. Aniline derivatives were oxidized to the corresponding azoxy or nitro products depending on the substitution pattern in the aromatic ring. Catalyst recovery and recycle was demonstrated.

The epoxidation of allylic alcohols is shown to be efficiently and selectively catalyzed by the oxidatively resistant sandwich-type polyoxometalates, POMs, namely [WZnM₂(ZnW₉O ₃₄)₂]^q- [M = OV(IV), Mn(II), Ru(III), Fe(III), Pd(II), Pt(II), Zn(II); q = 10-12], with organic hydroperoxides as oxygen source. Conspicuous is the fact that the nature of the transition metal M in the central ring of polyoxometalate affects significantly the reactivity, chemoselectivity, regioselectivity, and stereoselectivity of the allylic alcohol epoxidation. For the first time, it is demonstrated that the oxovanadium(IV)-substituted POM, namely [ZnW(VO)₂(ZnW ₉O₃₄)₂]^12-, is a highly chemoselective, regioselective, and also stereoselective catalyst for the clean epoxidation of allylic alcohols. A high enantioselectivity (er values up to 95:5) has been achieved with [ZnW(VO)₂(ZnW₉O ₃₄)₂]^12- and the sterically demanding TADOOL-derived hydroperoxide TADOOH as regenerative chiral oxygen source. Thus, a POM-catalyzed asymmetric epoxidation of excellent catalytic efficiency (up to 42 000 TON) has been made available for the development of sustainable oxidation processes. The high reactivity and selectivity of this unprecedented oxygen-transfer process are mechanistically rationalized in terms of a peroxy-type vanadium(V) template.

[Matrix presented] Polyfluorinated quaternary ammonium cations, [CF ₃(CF₂)₇(CH₂)₃] ₃CH₃N⁺ (R_FN⁺), were synthesized and used as countercations for the [WZnM₂(H ₂O)₂(ZnW₉O₃₄)₂] ^12- (M = Mn(II), Zn(II)) polyoxometalate. The (R_FN ⁺)₁₂[WZnM₂(H₂0)₂ (ZnW₉O₃₄)₂] compounds were fluorous biphasic catalysts for alcohol and alkenol oxidation, and alkene epoxidation with aqueous hydrogen peroxide. Reaction protocols with or without a fluorous solvent were tested. The catalytic activity and selectivity was affected by both the hydrophobicity of the solvent and the substrate.

Hybrid compounds with two functional centers consisting of a metallosalen moiety (M-salen; M = Mn, Co, Ni, and Pd) connected by an alkylene bridging group to a lacunary Keggin type polyoxometalate were synthesized and characterized. In these metallosalen-polyoxometalate compounds (M-salen-POM) it was shown by the use of a combination of UV-vis, H-1 NMR, EPR, XPS, and cyclic voltammetry measurements that the polyoxometalate exerts a significant intramolecular electronic effect on the metallosalen moiety leading to formation of an oxidized metallosalen moiety. For the Mn-salen-POM, the metallosalen center is best described as a metal-salen cation radical species; that is, a localized "hole" is formed on the salen ligand. For the other M-salen-POM compounds, the metallosalen moiety can be described as a hybrid of a metal-salen cation radical species and an oxidized metal-salen species, that is, a delocalized "hole" is formed at the metallosalen center. It is proposed that these oxidized metallosalen centers are best characterized as stabilized charge transfer (metallosalen donor-polyoxometalate acceptor) complexes despite the relatively large distance between the two functional centers.

A new heptamolybdate polyoxometalate structure containing ruthenium(II) or osmium(II) metal centers, [M(II)(DMSO)₃Mo₇O₂₄]^4- (M = Ru, Os), was synthesized by reaction between (NH₄)₆Mo₇O₂₄ and cis-M(DMSO)₄Cl₂. X-ray structure analysis revealed the complexes to contain a ruthenium/osmium center in a trigonal antiprismatic coordination mode bound to three DMSO moieties via the sulfur atom of DMSO and three oxygen atoms of the new heptamolybdate species. The heptamolybdate consists of seven condensed edge-sharing MoO₆ octahedra with C_2v symmetry. Three Mo atoms are in classic type II octahedra with a cis dioxo configuration. Two Mo atoms are also type-II-like, but one of the short Mo-O bonds is associated with bridging oxygen atoms rather than terminal oxygen atoms. Two molybdenum atoms are unique in that they are in a trigonally distorted octahedral configuration with three short Mo-O bonds and two intermediate-long M-O bonds and one long Mo-O bond. The [M(II)(DMSO)₃Mo₇O₂₄]^4- polyoxometalates were effective and in some cases highly selective catalysts for the aerobic oxidation of alcohols to ketones/aldehydes. The integrity of the polyoxometalate was apparently retained at high turnover numbers and throughout the reaction, and a variation of an oxometal type mechanism was proposed to explain the results.

(Matrix presented) The oxovanadium(IV) sandwich-type POM catalyzes the chemo-, regio-, and stereoselective epoxidation of allylic alcohols by chiral hydroperoxides with very high catalytic efficiency (up to 42 000 TON), a potentially valuable oxidation for the development of sustainable processes. By using the sterically demanding, TADDOL-derived hydroperoxide TADOOH as the chiral oxygen source, enantiomeric ratios (er) of up to 95:5 have been achieved.

Keywords: MANGANESE-CONTAINING POLYOXOMETALATE; ENVIRONMENTALLY BENIGN TECHNOLOGY; HYDROGEN-PEROXIDE; MOLECULAR-OXYGEN; ALKENE OXIDATION; LIQUID-PHASE; MULTIIRON POLYOXOANIONS; HETEROPOLY COMPOUNDS; OLEFIN EPOXIDATION; SOLID-STATE

(matrix presented) Palladium 15-20 nm particles stabilized by a Keggin-type polyoxometalate were prepared by reduction of K₅PPdW₁₁O₃₉ with H₂. The nanoparticles were shown to be effective catalysts for Suzuki-, Heck-, and Stille-type carbon-carbon coupling and carbon-nitrogen coupling reactions of bromoarenes in aqueous media. Chloroarenes were also reactive in reaction media without solvent.

The polyoxomolydate of the Keggin structure, PMo₁₂O₄₀^3-, catalyzes, under anaerobic conditions, oxygen transfer from sulfoxides to alkylarenes such as xanthene and diphenylmethane to yield xanthen-9-one and benzophenone, respectively. With use of ¹⁷O and ¹⁸O labeled phenylmethylsulfoxide it was shown that the sulfoxide is complexed by the polyoxometalate and the oxygen is transferred from the sulfoxide to the alkylarene. There is a good correlation between the reaction rate and the heterolytic benzylic C-H bond energy indicating a hydride transfer reaction from the alkylarene to the polyoxometalate-sulfoxide complex. In the case of triphenylmethane the resulting carbocation reacts to yield 9-phenylfluorene as the major product. The reaction kinetics supports such a reaction pathway.

A palladium-substituted polyoxometalate having a Keggin structure, supported on γ-alumina or active carbon, was used as a catalyst precursor for catalytic hydrogenation. The catalyst system enabled fast hydrogenation of arenes at 30 bar H₂ and 230°C. Most interesting was the finding that arenes could be selectively reduced in the presence of distal ketone groups under similar conditions, 30 bar H₂ and 200°C. For example, 1-phenyl-2-propanone yielded 1-cyclohexyl-2-propanone with no reduction of the ketone moiety. Additionally, aromatic compounds with vicinal (conjugated) ketone moieties underwent complete hydrogenation to saturated hydrocarbons and catalytic McMurry coupling was observed for aliphatic aldehydes.

The mechanism of aerobic oxidation of aromatic and alkyl aromatic compounds using anthracene and xanthene, respectively, as a model compound was investigated using a phosphovanadomolybdate polyoxometalate, H₅PV₂Mo₁₀O₄₀, as catalyst under mild, liquid-phase conditions: The polyoxometalate is a soluble analogue of insoluble mixed-metal oxides often used for high-temperature gas-phase heterogeneous oxidation which proceed by a Mars-van Krevelen mechanism. The general purpose of the present investigation was to prove that a Mars-van Krevelen mechanism is possible also in liquid-phase, homogeneous oxidation reactions. First, the oxygen transfer from H₅PV₂Mo₁₀O₄₀ to the hydrocarbons was studied using various techniques to show that commonly observed liquid-phase oxidation mechanisms, autoxidation, and oxidative nucleophilic substitution were not occurring in this case. Techniques used included (a) use of ¹⁸O-labeled molecular oxygen, polyoxometalate, and water; (b) carrying out reactions under anaerobic conditions; (c) performing the reaction with an alternative nucleophile (acetate) or under anhydrous conditions; and (d) determination of the reaction stoichiometry. All of the experiments pointed against autoxidation and oxidative nucleophilic substitution and toward a Mars-van Krevelen mechanism. Second, the mode of activation of the hydrocarbon was determined to be by electron transfer, as opposed to hydrogen atom transfer from the hydrocarbon to the polyoxometalate. Kinetic studies showed that an outer-sphere electron transfer was probable with formation of a donor-acceptor complex. Further studies enabled the isolation and observation of intermediates by ESR and NMR spectroscopy. For anthracene, the immediate result of electron transfer, that is formation of an anthracene radical cation and reduced polyoxometalate, was observed by ESR spectroscopy. The ESR spectrum, together with kinetics experiments, including kinetic isotope experiments and ¹H NMR, support a Mars-van Krevelen mechanism in which the rate-determining step is the oxygen-transfer reaction between the polyoxometalate and the intermediate radical cation. Anthraquinone is the only observable reaction product. For xanthene, the radical cation could not be observed. Instead, the initial radical cation undergoes fast additional proton and electron transfer (or hydrogen atom transfer) to yield a stable benzylic cation observable by ¹H NMR. Again, kinetics experiments support the notion of an oxygen-transfer rate-determining step between the xanthenyl cation and the polyoxometalate, with formation of xanthen-9-one as the only product. Schemes summarizing the proposed reaction mechanisms are presented.

A silane functionalized by octafluoroacetophenone was polymerized by the sol-gel method to form an insoluble silicate with perfluoroketone pendants; the silicate was used as a heterogeneous catalyst for the activation of aqueous hydrogen peroxide and the oxidation of aromatic amines and alkenes.

An antimony-substituted polyoxomolybdate, [PSb^III(H₂O) -Mo₁₁O₃₉]^4-, of the α-Keggin structure, has been synthesized. Although the molecular structure is typical, we have found from the analysis of the X-ray diffraction data that the crystal is anisotropic with alignment of the molecular units so that the substituted antimony atoms are all directed along the polar c axis and on the same side of the molecular unit. UV/Vis, ESR and magnetic susceptibility data support a formulation of [PSb^III(H₂O)Mo₁₁O₃₉]^4- whereby there is partial electron delocalization with some formation (10-20%) of Mo^V. Oxidation of [PSb^III(H₂O)Mo₁₁O₃₉]^4- with ozone or bromine yields the oxidized species [PSb^V(O)Mo₁₁O₃₉]^4- and [PSb^V(Br)Mo₁₁O₃₉]^3-. In the anaerobic oxydehydrogenation of alcohols, [PSb^V(O)Mo₁₁O₃₉]^4- is more active than [PSb^V(Br)Mo₁₁O₃₉]^3-. Catalytic aerobic oxidation of benzylic alcohols to aldehydes was also possible with no over-oxidation and formation of carboxylic̈ acids.

The catalytic electrophilic activation of hydrogen peroxide with transition metal compounds toward reaction with nucleophiles is a matter of very significant research and practical interest. We have now found that use of perfluorinated alcoholic solvents such as 1,1,1,3,3,3-hexafluoro-2-propanol in the absence of catalysts allowed electrophilic activation of hydrogen peroxide toward epoxidation of alkenes and the Baeyer−Villiger oxidation of ketones.

For the first time, mixed-addenda vanadium-substituted polyfluorooxometalates, PFOMs, have been synthesized. Depending on the workup procedure used, two types of compounds were prepared. The first PFOM was a quasi Wells-Dawson type compound, [H₂F₆NaV(V)W₁₇O₅₆]^8-, and the second a mixture of vanadium-substituted polyfluorooxometalates of the Keggin structure, XV(IV)W₁₁F(n)O(40-n) (X = H₂, V, W; n = 1-4). From the X-ray diffraction analysis, [H₂F₆NaV(V)W₁₇O₅₆]^8- has an elliptic (egg) shape with a central sodium atom surrounded by six fluorine atoms in a trigonal prism coordination. One may differentiate between two types of addenda atoms to be found in belt and capped positions. According to ¹H, ¹⁹F, and ⁵¹V NMR analysis, it is concluded that vanadium is isomorphically substituted in both the belt and capped position of [H₂F₆NaV(V)W₁₇O₅₆]^8-. The mixture of vanadium-substituted PFOMs of the Keggin structure was shown, by HPLC and ESR, to contain at least two species of different charge and of a different vanadium environment. The [H₂F₆NaV(V)W₁₇O₅₆]^8- PFOM was active for the catalytic aerobic oxidation of alkyl aromatic compounds in biphasic (water-catalyst and substrate) media. The reaction selectivity (autoxidation versus oxydehydrogenation) depended on the substrate and reaction conditions such as temperature and oxygen pressure. The selectivity to oxydehydrogenation was significantly higher compared to the prototypical cobalt acetate catalytic system.

The purpose of this study was to characterize the intraocular pressure (IOP) lowering activity and possible mechanism of action of the synthetic, non-psychotropic cannabinoid dexanabinol (HU-211) [(+)(3S,4S), 7-hydroxy-Delta-6-tetrahydrocannabinol 1, 1 dimethylheptyl], following intravenous (i.v.) administration in the rabbit. IOP (pneumatonometry), aqueous humor inflow rate (fluorophotometry), blood pressure, and heart rate (computerized physiograph system connected to central ear artery cannula) were measured in unanesthetized albino rabbits. Intravenous administration of HU-211 resulted in a dose-related reduction in IOP; a maximal IOP reduction of 5.0 +/- 0.2 mmHg was observed 4 hr after a 0.5 mg/kg dose. No significant changes in blood pressure or heart rate were observed during the first hr following this dose of HU-211. Pupil diameter did not change significantly during the 5 hr following the 0.5 mg/kg i.v. dose. No significant change in the rate of aqueous humor inflow occurred during the 6 hr after a 0.5 mg/kg dose of HU-211, thereby implicating outflow changes as the major source of IOP reduction. IOP reduction by HU-211 following pre-treatment with the alpha(2) adrenergic antagonist, yohimbine (1 mg/kg, i.v.), was only 30% of that of HU-211 alone. IOP reduction following pretreatment with the alpha(2) agonist, clonidine (0.5 mg/kg i.v.), was twice as large as that of HU-211 alone. Pretreatment with the beta-adrenergic antagonist, propranolol (0.5 mg/kg i.v.), resulted in a 50% reduction in the IOP-lowering effect of HU-211. In summary, HU-211, administered i.v., is an effective IOP-lowering agent, devoid of any significant side effects (blood pressure, heart rate or pupil diameter, all of which have been reported previously for cannabinoids). Involvement of the adrenergic system is indicated in mediating the IOP-lowering effects of HU-211 that appear to reflect a change in fluid outflow from the eye.

Use of the sol-gel technique has allowed the preparation of silicates with polyfunctionalized surfaces. In this way, silicates containing combinations of hydrophilic poly(ethylene oxide) (PEO), hydrophobic poly(propylene oxide) (PPO) and cationic quaternary ammonium (Q⁺) groups were prepared. These silicates coupled with polyoxometalates led to active catalytic assemblies. In one application, H₅PV₂Mo₁₀O₄₀ was complexed to PEO-SiO₂ and used to catalyze the oxydehydrogenation of dihydroanthracene with improved activity and selectivity compared to the non-supported catalyst. Recycle of the assembly was possible. In a further use, [ZnWMn₂/(II)(ZnW₉O₃₄)₂]^12-, bound by a Q⁺ moiety to the silicate surface modified also with polyethers formed an assembly catalytically active, with excellent recycle for the epoxidation of alkenes with aqueous 30% H₂O₂. A silicate with a hydrophobic (PPO)/hydrophilic (PEO) balance showed the highest activity due to the optimal contact of the apolar hydrocarbon and the aqueous oxidant. Dispersion of the silicate in a solvent depended much on the polyether tether. Hydrophilic PEO-SiO₂ formed a homogeneous gel in water but was not dispersed in chloroform. For hydrophobic PPO-SiO₂, the opposite was observed. Maximal dispersion together with ease of recovery was possible with intermediate 10% PEO, 10% PPO-SiO₂.

The oxidation of alkanes with molecular oxygen using aldehydes as reducing agents (aldehydes are cooxidized) was studied using the α-H5PV2Mo10O40polyoxometalate as catalyst. Emphasis was placed on the initiation of the radical chain reaction by investigation of the aldehyde–polyoxometalate interaction. Using31P NMR and ESR spectroscopy one could differentiate between the reactivity of the five inseparable isomers of α-H5PV2Mo10O40. Contrary to previous belief, the 1,11 isomer with vanadium in distal positions is the most abundant. The31P NMR and ESR spectra supported by UV–vis absorption–time profiles of the reduction of α-H5PV2Mo10O40indicated that isomers with vanadium in vicinal positions were most kinetically viable in the alkane oxidation. Addition of isobutyraldehyde to α-H5PV2Mo10O40gave in the51V NMR spectrum a new downfield peak attributed to the formation of an aldehyde–polyoxometalate intermediate. The alkane/aldehyde/O2oxidizing system was found to be quite effective and selective for ketone formation. Reaction probes indicated that acyl peroxo radicals were the active oxidizing intermediates. Five pathways for its reaction were identified: chain propagation, alkane oxidation, decomposition to form oxygen, decomposition to acyl oxo radicals leading to CO2and ketone, and capture and inhibition by the polyoxometalate.

We report here on the fabrication and optimization of composites of conjugated polymer in Sol-Gel and PVA matrices. FTIR spectroscopy as well as other observations show that efficient phase and absorption holograms can be created in the material upon illumination, via the photochromic effect. The main contribution to the absorption change is chain scission and photo-oxidation mechanism. Optimized holographic composites with diffraction efficiencies as high as 26% are shown. Beam interaction between the writing beams is observed for these composites, while the diffraction efficiencies was improved by an order of magnitude.

The ruthenium substituted polyoxomolybdate of the Keggin structure, Q₄PRu^III(H₂O)Mo₁₁O₃₉ (Q=n-Bu₄N), has been synthesized and characterized. The IR spectra show that this compound is isostructural with the known manganese and cobalt analogs. The cyclic voltammogram showed similar redox potentials and the UV-vis spectra showed similar energies for the d-d transitions compared to the corresponding tungstate, Q₄PRu^III(H₂O)W₁₁O₃₉. The catalytic activity of the molybdate versus tungstate in reactions with molecular oxygen was, however, significantly different. IR and ³¹P NMR evidence indicated that treatment of Q₄PRu^III(H₂O)Mo₁₁O₃₉ with oxygen showed no structural changes whereas, for Q₄PRu^III(H₂O)W₁₁O39, a clear change was observed. This finding probably explains the lack of catalytic activity for the latter in the co-oxidation of cumene and 1-octene to cumyl alcohol and 1-octene oxide. For the molybdenum compound, this reaction took place by a kinetic balance of ruthenium metal-catalyzed autooxidation of cumene to cumene hydroperoxide and the molybdenum catalyzed oxygen transfer from cumene hydroperoxide to 1-octene to yield the products. High catalyst loading led to reaction inhibition whereas low loading and excess cumene led to increased autooxidation.

Macroporous, site isolated metal silicates are synthesized by a molecular route; the molybdenum silicate is especially active for the selective epoxidation of alkenes with tert-butyl hydroperoxide.

Poly(arylenevinylene) homopolymers and copolymers with polar hydroxy and carboxy moieties attached to the aromatic phenyl ring were prepared. The copolymers and the related homopolymers are copoly[5-(2-hydroxyethoxy)-2-methoxy-1,4-phenylenevinylene/1,4- phenylenevinylene], co(PHydroxyV-PV), and copoly(5-carboxymethoxy-2-methoxy-1,4-phenylenevinylene/1,4-phenylenevinylene), co(PCarboxyV-PV). For co(PHydroxyV-PV) the photoluminescence and electroluminescence spectra can be adjusted over a range of 100 nm as a function of the percentage of the hydroxy substituted phenyl ring. For co(PCarboxyV-PV) the observed spectral features are a function of the pH from which the final conjugated polymer was prepared. The optical density and photoluminescence of co(PCarboxyV-PV) films prepared from solutions at pH = 12 were significantly blue-shifted compared to polymers prepared from pH = 2 solutions at up to 30% substitution at the phenyl ring. The presence of the polar side chain was used to form self-assembled multilayer films, poly(ethyleneimine)/poly(styrenesulfonate)/co(PHydroxyV-PV), based on hydrogen bonding interactions rather than electrostatic forces. The luminescence spectra in the layered systems were blue-shifted compared to the spin coated films.

We have studied the current versus voltage (I-V) and the luminescence versus voltage (EL-V) characteristics in PPV-based LED devices for different film thickness, d. For voltages below the EL threshold voltage, the I-V curves exhibit a linear regime (I∼V) at low voltages and quadratic (I∼V²) regime for higher voltages. The later is attributed to the space charge limited current mechanism assuming a single shallow trap level. The fit of the model to the experimental results is very good with a single fitting parameter, namely, the effective mobility. The extracted mobilities are compared to those measured independently by time-of-flight (TOF) photoconductivity. The SCLC model gives a reasonable explanation for the voltage threshold in EL.

The oxidation of organic substrates catalyzed by 'sandwich' type transition metal substituted polyoxometalates of the general formula, Na(x)M₂Zn₃W₁₉O₆₈, (M = Ru, Mn, Zn, Pd, Pt, Co, Fe, Rh) was examined in three different reaction media. The manganese analog was dissolved in a 1,2-dichloroethane phase using a lipophilic quaternary ammonium counter cation. Various organic substrates were oxidized with 30% aqueous H₂O₂. Alkenes reactivity increased as a function of the nucleophilicity of the double bond, but decreased as a function of steric crowding in the cyclohexene series. Alkenols with primary hydroxyl groups reacted chemo- and stereoselectively to form the corresponding epoxy alcohols. On the other hand, alkenols with secondary hydroxyl units did not react chemoselectively; both ketones and epoxy alcohols were formed. Diols were oxidized in most cases to ketols, except for 1,4-butanediol which yielded γ-butyrolactone. Secondary amines yielded hydroxyl amines except for piperidine which reacted with the solvent. A manganese containing catalyst supported on a functionalized silica particle was as active and selective as the organic solvent containing biphasic system for the oxidation of alkenes and alkenols. Reactions were also carried out by dissolving Na(x)M₂Zn₃W₁₉O₆₈ in aqueous solutions of 30% H₂O₂, 70% t-butylhydroperoxide or 0.02 M potassium persulfate in the absence of solvent. Hydrogen peroxide degraded all the TMSP compounds. One degradation product was an effective and chemo- and stereoselective catalyst for the epoxidation of primary alkenols. In alcohol oxidation only the ruthenium precursor was active. For oxidations with 70% t-butylhydroperoxide all compounds were stable but only the Na₁₁Ru₂Zn₃W₁₉O₆₈ compound was active. Alcohols were oxidized selectively, however, alkenols yielded a mixture of products. With persulfate, some catalytic effects were observed in double bond oxidation.

Methyltrioxorhenium has been supported on silica functionalized with polyether tethers; in the absence of an organic solvent, this catalytic assembly catalysed the epoxidation of alkenes with 30% aqueous H₂O₂ in high selectivity compared to the ring opening products observed in homogeneous media.

The fabrication and characterization by means of photoluminescence (PL), UV-vis absorption, electro-luminescence (EL) and X-ray reflectivity of multilayer heterostructures consisting of alternate layers of conjugated and non-conjugated polymers are studied. The heterostructures are prepared by the layer-by-layer self-assembly technique, using two-types of polyelectrolytes. The thickness of bilayer or multilayer was controlled by changing the non-conjugated polymer layer. Fabrication of light emitting diodes (LEDs) which emit in the blue region is accomplished by using the assembly technique.

This chapter contains sections titled:IntroductionThe Polyoxometalate Reduction-Substrate Oxidation Reaction Mode: Oxygen as Primary OxidantThe Polyoxometalate Oxidation-Substrate Oxidation Reaction Mode: Peroxygen Compounds as Primary OxidantsTransition Metal Substituted PolyoxometalatesOther Uses of Polyoxometalates in CatalysisA Final Word and a View to the FutureCiting Literature

TiO₂, MoO₃, and WO₃ have been dispersed in amorphous silica using the low temperature sol-gel procedure for xerogel preparation. These simply prepared amorphous compounds are proposed as possible alternatives to metal-substituted crystalline molecular sieves in H₂O₂ oxidations. The metallosilicate compounds are catalytically active in the 30% aqueous H₂O₂ oxidation of alkenes and alcohols provided the metal oxide precursor in the xerogel synthesis is a metal-dichlorodialkoxy compound yielding MO_x(Cl)-SiO₂, and not the tetraalkoxy derivative yielding MO_x-SiO₂. Catalyst efficiency is increased by using low loading of metal oxide in the silica framework. Excess H₂O₂ reduces yield due to the detrimental effect of water, so more hydrophobic silicates with phenyl-silicon units increases catalyst efficiency. IR studies show that in the xerogels, the absorption at ∼950 cm^-1 is mainly due to the Si-OH vibrations in (SiO)₃Si-OH units and not (SiO)₃Si-OM as has often been reported in studies of titanium-substituted zeolites. ²⁹Si MAS NMR spectra, sensitive to second neighbor atoms, of catalytically active MO_x(Cl)-SiO₂ versus inactive MO_x-SiO₂ reveals that the former have larger Q₃ peaks and therefore more (SiO)₃Si-OM units, indicating higher molecular dispersion of the metal oxide in the xerogels. Diffuse reflectance UV-vis measurements indicate, however, that this molecular dispersion is not complete as absorptions attributable to polymeric forms of metal oxide are observable. ESR spectra of the metal oxide substituted silicates in the presence of hydrogen peroxide or in the reduced form are not useful in differentiating between active and inactive xerogel compounds. Atomic force microscopy imaging of the xerogels at ∼10 nm resolution shows that the xerogel has a basically smooth surface. Large cylindrical pits of 500-700 nm diameter and depth of 15-40 nm are also observable as imperfections in the xerogel. There is also formation of small silicate droplets on the surface with dimensions similar to that of the pits. The catalytic xerogels are microporous with an average pore diameter of 15 Å and a surface area of 750 m²/g.

Polyoxometalates can be used as catalysts for the activation of molecular oxygen and 30% aqueous hydrogen peroxide for the selective transformation of various organic substrates. In this paper results are presented for the oxidation of alkenes, dienes, alkenols, and sulfides using 30% aqueous H₂O₂ as oxidant and [WZnMn(II)₂(ZnW₉O₃₄)₂] ¹²-as catalyst. In certain but not all cases high reactivity, chemoselectivity and sterospecificity has been observed especially in the epoxidation of alkenols with primary hydroxyl units.

A fluorinated poly(p-phenylenevinylene) analogue, co(TFPV-PV), has been prepared by copolymerization of fluorinated and nonfluorinated bissulfonium salt monomers. Conversion and yield decreased as a function of fluorine substitution. The UV - vis absorption was strongly shifted to the blue with increasing fluorine content. Complementary shifts in photoluminescence spectra were not observed, presumably because the fluorinated segments of the copolymer are very weakly luminescent relative to nonfluorinated segments. The photoluminescence spectra are therefore similar to those found for poly(p-phenylenevinylene) in the past. The co(TFPV-PV) compounds showed electroluminscence at an ac potential of ∼10 V (rms, 600 Hz) between ITO and Al electrodes. Maxima were shifted slightly to the blue with an increase in fluorine.

Color tuning of the electro‐ and photoluminescence from naphthalenevinylene–PPV–based light‐emitting diodes between yellow‐green and red is reported. Band structure considerations are employed to explain that chemical selectivity and selective band‐gap tuning are observed in some of the copolymers studied but not in others. It is also found that light emission can be tuned by changing the thickness of the copolymer film in the LED.

The disubstituted manganese polyoxometalate, [WZnMn₂(ZnW₉O₃₄)₂]^12-, has been used as a catalyst for the epoxidation of alkenes and the oxidation of secondary alcohols to ketones in biphasic (water—organic) reaction media using hydrogen peroxide (30% aqueous H₂O₂) as the oxygen donor. At subambient temperatures, epoxidations are highly selective with little dismutation of hydrogen peroxide by homolysis or formation of side products by allylic oxidation. Thus, cyclohexene was oxidized to cyclohexene oxide at 2 °C with 99% selectivity. At low catalyst loadings and depending on the substrate and reaction temperature, hundreds to thousands of catalytic turnovers were obtained with only a 2-fold excess of hydrogen peroxide over substrate. Kinetic measurements on a model epoxidation of cyclooctene showed that the reaction is first order in cyclooctene, hydrogen peroxide, and [WZnMn^II₂(ZnW₉O₃₄)₂]^12- catalyst. Magnetic susceptibility measurements along with ESR and atomic absorption spectroscopy reveal that the manganese atom is in a terminal position coordinated by five bridging oxygen atoms and one labile aquo ligand which is disassociated upon transfer of the polyoxometalate anion into an organic phase. Comparison of the [WZnMn^II₂(ZnW₉O₃₄)2]^12- anion with other mono-, tri-, or tetrasubstituted manganese polyoxometalates or catalysts having no manganese atoms showed that the catalytic activity of the former was unique. Kinetic evidence exhibited the absence of an induction period for catalyst activation or catalyst deactivation over a period of 12500 turnovers. IR spectra demonstrated that the original catalyst reacted with hydrogen peroxide to form a peroxo intermediate with a typical absorbance at 818 cm^-1. After completion of the reaction, the original IR spectrum was measured again. ESR and atomic aborption spectroscopy also revealed that the [WZnMn^II₂(ZnW₉O₃₄)₂]^12- anion is solvolytically stable to aqueous hydrogen peroxide. Cyclic voltammetry, IR and UV-vis, and a comparative reaction with iodosobenzene as the oxygen donor seem to exclude a high valent manganese—oxo compound as the reactive intermediate. Rather, high reactivity is probably due to a tungsten—peroxo intermediate somehow uniquely activated by an adjacent manganese atom.

Vanadium silicate xerogels (V₂O₅{single bond}SiO₂) were prepared by the sol-gel method by hydrolysis of vanadium and silicon alkoxides. The use of these xerogels as catalysts for oxidation of alkenes, alcohols and phenol was studied using 30% aqueous hydrogen peroxide as oxidant. It was found that the manner of xerogel preparation strongly influenced the catalytic activity of V₂O₅{single bond}SiO₂. Alcohols were the preferred solvents for the reaction and did not leach vanadium oxide into solution. For alkenes, epoxidation was the dominant oxidation reaction the yield and selectivity depending on the nucleophilicity and oxidizability of the substrate. For alkenes of intermediate nucleophilicity allylic oxidation was significant. Secondary alcohols were oxidized in low to fair yields whereas primary alcohols were inert. Phenol was oxidized selectively to a 2:1 mixture of hydroquinone/catechol. UV-vis and electron spin resonance spectra of V₂O₅{single bond}SiO₂ treated with hydrogen peroxide conclusively showed formation of vanadium-peroxo species with polarization of the O{single bond}O bond as seen by formation of vanadium (IV) electron spin resonance spectra leading to oxidation by both heterolytic and homolytic cleavage.

A concept has been presented whereby X‐ray irradiation can be used to induce visible luminescence of chromophores such as porphyrins. The essential aspects of the idea have been demonstrated in a supramolecular assembly consisting of a water‐dispersed polystyrene latex with an embedded scintillating compound, 2,5‐diphenyloxa‐zole, and an externally attached hematoporphyrin. X‐ray excitation of the assembly yields an emission spectra typical for hematoporphyrin with fluorescent yields. of up to 3% with respect to 2,5‐diphenyloxazole emission. Significant quenching in the presence of dioxygen indicates that singlet oxygen is formed at atmospheric conditions.

A membrane-spanning porphyrin has been synthesized by attaching four 3β-hydroxy-5-cholenic acid moieties to,β,α,β-meso-tetrakis(o-aminophenyl)porphyrin. The resulting steroidal porphyrin, H₂ChP, and the corresponding metalloporphyrins, MChP, were shown by gel permeation chromatography,³¹P NMR, and differential scanning calorimetry to intercalate into vesicle bilayers. The steroidal porphyrin was found to be in a well-defined and highly ordered microenvironment within the bilayer. The anisotropic ESR spectra of Cu¹¹(ChP) in orientated bilayer assemblies on Mylar film clearly indicated that the plane of the porphyrin ring was parallel to the plane defined by the bilayer-water interface. The porphyrin ring was also found to be in the middle of the bilayer with fluctuations of ±3-4 Å around the center. This was shown by use of tethered imidazole ligands of the general formula Im(CH₂)_nCOOH as molecular probes. Ligation to Co¹¹(ChP) could be monitored by ESR as a function of the length of the tethered ligand and conclusively demonstrated that only ligands where n > 6 were able to coordinate to the metal. Iron(III) and manganese(III) steroidal porphyrins were then used as regioselective epoxidation and hydroxylation catalysts. Diolefinic sterols were epoxidized exclusively at the side chain. Epoxidation of polyunsaturated fatty acids was preferred by a ratio of 2/1 at the more hydrophobic terminus and it was found that by increasing the rigidity of the bilayer by the addition of cholesterol the selectivity could be raised to 9/1. Finally, it was shown that cholesterol could be selectively hydroxylated at the C₂₅tertiary carbon.

Bis-tertiary diols accelerate bis-eliminations of HX from 1,2-dihalides in the presence of an onium salt as phase transfer catalyst and potassium hydroxide as base. PEG 400 catalyzes the same elimination, but isomerizations from 1-alkyne to mixtures with the 2-alkyne and the 1,2-diene occur easily.

Polyethylene glycol was found to undergo anionic 'catalyst poisoning' by lipophilic anions in a manner similar to that of quaternary ammonium salts, even though the interaction between alkali salts and the catalyst is generally considered to be influenced only by the cation. From reaction profiles which indicated catalyst poisoning, an exact kinetic equation describing the conversion as a function of time could be used to compute selectivity constants, K_s, by graphic iterations.

Benzyl alcohol was oxidized by aqueous sodium hypochlorite in a phase transfer catalysis reaction catalyzed by quaternary ammonium salts. Two products were obtained, benzaldehyde and benzyl benzoate. The concentration of the organic phase and the pH of the aqueous phase affected the product distribution: a dilute organic phase and low pH favored benzaldehyde as a product, whereas a concentrated organic phase and high pH favored benzyl benzoate as a product.