T. A. Stromnova

Mechanism of reaction of palladium(II) carboxylates with carbon monoxide in nonaqueous media

Abstract The reduction of Pd II carboxylates by carbon monoxide in benzene and AcOH solutions has been studied. In the case of Pd II acetate the reaction is found to proceed through an intermediate complex with a Pd-CO-CH 3 group and the Pd I carbonylacetate [Pd(CO)(OAc)] 4 (PCA). A reductive condensation type of mechanism is suggested for the PCA decomposition on the base of kinetic data. The metal cluster skeleton is proposed to increase stepwise as the oxidation state of Pd decreases. A number of Pd I complexes, PCA analogs having composition [Pd(CO)(OCOR)] 4 , where R = C 2 H 5 , C 6 H 5 , CF 3 , CCl 3 , CH 2 Cl, have been prepared.

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.

Palladium carbene cluster : synthesis, structure and reactivity

Abstract The first palladium carbene cluster, μ-tetrakis(diphenylmethyliden)-μ-tetraacetato-quadro-tetrapalladium (4Pd-Pd) Pd 4 (μ-CPh 2 ) 4 (μ-OAC) 4 (I), has been synthesized by substitution of diphenylcarbene ligands for CO-groups in μ-tetrakis(carbonyl)-μ-tetraacetato-quadro-tetrapalladium (4Pd-Pd) Pd 4 (μ-CO) 4 (μ-OAc) 4 (II) and characterized with EXAFS data. Reactivity of I, II and related clusters is discussed. Thermolysis of the clusters has been found to involve inner-sphere oxidation of carbene or carbonyl ligands during which an oxygen atom is transferred from the carboxylate group to the carbene or carbonyl ligand. Thermolysis of carbonyl clusters in benzene or toluene solutions gives rise to the products of CO 2 insertion into the CH bond of the solvent forming benzoic acid from benzene and a mixture of phenylacetic and tolyl acids from toluene.

Metallation of the methyl group ino-nitrosotoluene: synthesis and the molecular structure of the binuclear complex [o-(NO)(CH2)C6H4)]2Pd2(μ-OOCCF3)2

The reaction of the tetranuclear cluster Pd4(CO)4(OOCCF3)4 witho-nitrosotoluene afforded the Pd11-containing complex [o-(NO)(CH2)C6H4]2Pd2(μ-OOCCF3)2. The elimination of CO2 and the formation of organic products of transformation of tolylnitrene species (azotoluene, ditolylamine, and tolylisocyanate) were observed in the course of the reaction. The title complex was characterized by IR and1H NMR spectroscopy. Its structure was established by X-ray diffraction analysis. It was suggested that the reaction proceeds through intermediate formation of nitrene complexes.

Palladium nitrosoarene complexes in reductive carbonylation of nitroarenes

The reactions of carbon monoxide with the palladium nitrosoarene complexes Pd2(μ-OCOR)2(—CH2C6H4NO)2 (1, R = Me, CF3, But, or Ph) and Pd2(μ-OCOR)2(PhNC6H4NO)2 (2, R = Me, CF3, But, or Ph) were studied. Complexes 1 contain the o-nitrosotoluene molecule metallated at the methyl group. In complexes 2, the phenyl-o-nitrosophenylamide ligand coordinated via two nitrogen atoms can be considered as a nitrosobenzene derivative bearing the NPh group in the ortho position of the Ph ring. It all cases, carbonylation of the complexes afforded the corresponding aryl isocyanates Ar—N=C=O or the products of their further transformations. The mechanism of reductive carbonylation of nitroarenes catalyzed by palladium compounds and the role of palladium nitrosoarene complexes as possible intermediates in this process are discussed.

Low-valence palladium complexes: Stoichiometric reactions and catalysis

New data on the structure and reactivity of palladium clusters are surveyed. The mechanisms of stoichiometric and catalytic reactions of the palladium cluster complexes with alkenes, alcohols, aldehydes, formic acid, CO, and phenol are discussed.

Kinetics of the reductional decomposition of palladium (I) clusters under the action of sodium acetate

Conclusions1.The carbonylacetate of Pd(I) is an intermediate product in the reduction of Pd(II) acetate by carbon monoxide in acetic acid solutions containing sodium acetate.2.The kinetic data, indicate that reductional decomposition of Pd(I) clusters is a reductional condensation process, in which a decrease in the oxidation state of the atomic palladium and stepwise growth of the metallic cluster skeleton proceed simultaneously.

Reduction of nitrosoarene ligands in binuclear palladium(ii) complexes

Reduction of the binuclear PdII complexes Pd2(OCOR)2(o-CH2C6H4—NO)2 (1) and Pd2(OCOR)2(o-PhN—C6H4—NO)2 (2) (where R = Me, CF3, But, or Ph) by sodium borohydride, an ethanolic solution of KOH, or molecular hydrogen was examined. The first stage of reduction was demonstrated to afford metallic palladium and aromatic amines, viz., o-toluidine o-Me—C6H4—NH2 from complex 1 and aniline Ph—NH2 from complex 2. The reactions with molecular hydrogen involve deeper stages to yield cyclic ketones (o-methylcyclohexanone and cyclohexanone) and then cycloalkanes (methylcyclohexane and cyclohexane, respectively). The latter reactions are accompanied by elimination of N2. The mechanism of reduction of complexes 1 and 2 with molecular hydrogen was proposed.

Reactions of palladium(I) carbonylacetate cluster with alcohols

Reactions of a tetranuclear palladium cluster [Pd(CO)(OAc)[4 with C1-C3 alcohols have been found to proceed simultaneously via several routes to form CO, and dialkyl carbonates, the products of oxidation of coordinated CO ligands, along with carbonyl compounds which form due to oxidation of the corresponding alcohols. Alkoxy, alkoxycarbonyl, and acyl palladium derivatives are shown to be the intermediates of the reactions studied.