Igor P. Stolarov

Oxidation, Redox Disproportionation and Chain Termination Reactions Catalysed by the Pd-561 Giant Cluster

Redox disproportionation of benzyl alcohol to benzaldehyde and toluene catalysed by the Pd561phen60(OAc)180 (phen=1,10-phenanthroline) giant cluster 1 under anaerobic conditions was found, whereas in an O2 atmosphere cluster 1 catalyses the oxidation of benzyl alcohol to benzaldehyde and inhibits further oxidation of the latter. A study of the AIBN-initiated and non-initiated oxidation of benzyl alcohol, sec-butyl alcohol and styrene in the presence of cluster 1 revealed that cluster 1 performs three functions in the oxidation reactions: 1) catalysis of polar oxidation of the substrates with O2, 2) termination of the chains of radical oxidation, and 3) catalysis of redox disproportionation.

Giant cluster catalysis: possible intermediacy of nitrene and carbene species

Abstract Coordinated carbene and nitrene species were suggested as the key intermediates in hydrogen-transfer reduction of multiple bonds and reduction of nitroaromatics by CO catalysed with giant Pd-561 clusters as well as in the reaction of Pd (I) carbonylacetate cluster with nitrosobenzene. In the last reaction, a palladium complex with phenyl- o -nitrosophenylamide was obtained whose structure gives evidence for the intermediacy of nitrene ligands in Pd-catalysed reactions.

IMIDO/NITRENE LIGANDS IN THE COMPLEXES OF PLATINUM METALS

A synthetic search for palladium and platinum complexes with nitrene ligands via reaction of tetranuclear cluster Pd 4 ( μ 2 -CO) 4 ( μ 2 -OAc) 4 with nitrosobenzene and reactions of mononuclear complexes [MX 4 ] 2− (M=Pt, Pd; X=Cl, NO 2 ) with o -phenylenediamine and its N -phenyl derivative have been carried out. The complexes obtained, [Pd(OAc) o -(PhN)(NO)C 6 H 4 ] 2 , Pd[ o -(NPh)(N)C 6 H 4 ] 2 , Pt[ o -(NPh)(N)C 6 H 4 ] 2 , Pt 2 [ o -(NPh)(N)C 6 H 4 ] 4 [O 3 SCF 3 ] 2 , and Pt 2 [ o -(NPh)(N)C 6 H 4 ] 4 Br 2 , have been structurally characterized by single crystal X-ray diffraction studies. The oxidation of complex Pt[ o -(NPh)(N)C 6 H 4 ] 2 by excess AgO 3 SCF 3 afforded a heterotricyclic quinoxaline derivative, whose structure has been determined by X-ray analysis. The data obtained suggest that labile nitrene species coordinated to Pd and Pt complexes are possible intermediates in the reactions under study.

Highly selective partial oxidation of methane to methyl trifluoroacetate

Methane has been oxidized stoicheiometrically by cobalt(III) trifluoroacetate in CF3CO2H solution at 150–180 °C and 10–40 atm to give methyl trifluoroacetate in 90 ± 10% yield based on CoIII, which is reduced to CoII; in the presence of O2(1–5 atm) the reaction becomes catalytic with respect to the cobalt(III) salt, giving methyl trifluoroacetate as the sole product of the oxidation of methane by dioxygen.

Oxidation of ethane and propane with cobalt(II) catalyst: unexpected formation of 1,2-diol esters and C–C bond cleavage

Ethane reacts with both cobalt(III) and O2–cobalt(II) in trifluoroacetic acid solution to form ethyl trifluoroacetate and 1,2-bistrifluoroacetoxyethane in successive reactions, along with the products of C–C bond cleavage; propane undergoes similar oxidative reactions.

Oxidations in the H2O2VvAcOH system. Evidence of vanadium (V) complexes with superoxide anion and singlet dioxygen molecule as ligands

Anthracene, its alkyl derivatives, and alkenes have been found to undergo oxidation by the VvH2O2AcOH catalytic system via a polar mechanism involving the transfer of singlet dioxygen from H2O2 to the unsaturated substrate molecule. The vanadium (V) complex with a singlet dioxygen molecule as ligand was suggested to be the only oxidant species active in the reaction. The Vv(O2•−) complex radical was detected as the only paramagnetic species in the system. Unusual acceleration of the styrene oxidation caused by the 2,6-di-tert-butyl-4-methylphenol additive (BHT) was observed and attributed to lowering the concentration of the Vv(O2•−) complex radical, which is assumed to be an active reductant toward the Vv complex with singlet dioxygen.

Scanning tunneling microscopy observation of giant palladium-561 clusters

Abstract STM observation showed giant palladium-561 clusters which are larger in size than observed earlier by TEM and HREM studies. The difference is presumably due to the ligand shell of the clusters, which is invisible to electron microscopy.

Heterometallic Palladium(II)–Indium(III) and −Gallium(III) Acetate-Bridged Complexes: Synthesis, Structure, and Catalytic Performance in Homogeneous Alkyne and Alkene Hydrogenation

The reaction of Pd3(OOCMe)6 with indium(III) and gallium(III) acetates was studied to prepare new PdII-based heterometallic carboxylate complexes with group 13 metals. The heterometallic palladium(II)-indium(III) acetate-bridged complexes Pd(OOCMe)4In(OOCMe) (1) and Pd(OOCMe)4In(OOCMe)·MeCOOH (1a) were synthesized and structurally characterized with X-ray crystallography and extended X-ray absorption fine structure in the solid state and solution. A similar Pd-Ga heterometallic complex formed by the reaction of Pd3(OOCMe)6 with gallium(III) acetate in a dilute acetic acid solution, as evidenced by atmospheric pressure chemical ionization mass and UV-vis spectrometry, was unstable at higher concentrations and in the solid state. Complex 1 catalyzes the liquid-phase-selective phenylacetylene and styrene hydrogenation (1 atm of H2 at 20 °C) in acetic acid, ethyl acetate, and N, N-dimethylformamide solutions, while no Pd metal was formed until alkyne and alkene hydrogenation ceased.

Unusual case of catalysis by palladium clusters

An unusual for Pd catalysts dehydration of α-alkyl and α, α′-dialkylbenzyl alcohols PhCR′R″OH (R′ = H, Me, Et, Bu; R″ = H, Me) occurs in the presence of the palladium(I) cluster [Pd4(CO)4(OAc)4] (1) in an inert atmosphere to form ethers PhCR′R″-O-CR′ R″ and water. The catalyst is an intermediate of cluster 1 reduction to Pd black, while neither the starting cluster 1, nor Pd black, which is the decomposition product, are active in the catalysis of this reaction.

Optical spectra of Pd-561 nanoclusters in aqueous solutions

Optical absorption spectra of aqueous solutions of the giant cluster Pd561Phen60(OAc)180 (1) were studied in air and after treatment with H2. The results obtained were compared with the corresponding data for 2—4-nm nanoparticles of colloidal palladium prepared by the radiochemical and chemical reduction of the PdII complexes in aqueous solutions. The optical spectra of cluster 1 and nanoparticles of colloidal palladium are of the same nature and are caused by the light absorption by free electrons in the metal.