Natalia V. Cherkashina

Unexpected participation of nucleophiles in the reaction of palladium(II) acetate with divalent 3d metals

The kinetics of reactions of palladium(II) acetate with cobalt(II), nickel(II), and copper(II) acetates were studied by spectrophotometry. These reactions produce heterobimetallic complexes PdII(μ-OOCMe)4MII(OH2)(HOOCMe)2, where M = Co, Ni, or Cu. These reactions are very slow in carefully dehydrated (<0.01% H2O) acetic acid, but are considerably enhanced by water or acetonitrile. Our data indicate that the activation of the kinetically inert ring structure of the initial palladium complex Pd3(μ-OOCMe)6 by means of the nucleophilic attack of an H2O or acetonitrile molecule is the key step of the reaction mechanism.

Preparative synthesis of palladium(II) acetate: Reactions, intermediates, and by-products

Comparison of various laboratory procedures for the synthesis of palladium acetate demonstrated that the purest product containing no nitrite or nitrate impurities is formed in up to 90% yields upon the reaction of palladium nitrate with alkali metal acetates in aqueous acetic acid. Other laboratory syntheses are more labor-consuming and do not ensure high purity of the product. The synthesis by-products are described and possible reaction schemes are proposed.

On the nature of the chemical bond in heterobimetallic palladium(II) complexes with divalent 3d metals

The complex Pd(μ-OOCMe)4Cu(OH2) · 2Pd3(μ-OOCMe)6 was synthesized and characterized by X-ray crystallography. In the heterometallic moiety of this complex, the PdII and CuII atoms are at an extraordinary short distance (2.521(3) Å). DFT quantum-chemical calculations of the geometric and electronic structure of a series of heterobinuclear paddlewheel complexes PdIIMII(μ-OOCMe)4L (M = ZnII, NiII, CuII, CoII, FeII; L = OH2 and NCH) and their formate analogues PdIIMII(μ-OOCH)4L (M = ZnII, NiII, FeII) showed that the extraordinary short Pd⋯M distance in all these complexes is caused only by the tightening effect of carboxylate bridges rather than by the metal-metal bond. The direct Pd-M interaction becomes possible only after removal of electrons from the antibonding orbitals and formation of oxidized complexes of the [PdIII(μ-OOCMe)4NiIII]2+ type.

Polymeric low-valence platinum-phenanthroline complexes as precursors of platinum colloids

It was found that the reduction of Pt(II), Pt(III) and Pt(I,III) acetates with H2 in the presence of 1,10-phenanthroline (phen), according to the standard procedure for the synthesis of palladium-561 giant clusters, resulted, unexpectedly, in the high-nuclear Pt(I) complex of the empirical composition Pt8phen3(OAc)4(OH)4(H2O)6 instead of the expected platinum colloid. Data of electron microscopy (TEM, HREM), small-angle X-ray scattering (SAXS), EXAFS and thermal analysis (DTA-TG) combined with elemental microanalysis all point to a loose structure of the obtained complex, with a minor PtPt bonding (average coordination number for the PtPt bonds is about 1). Variation of the preparation procedure resulted in a series of polymeric phen-platinum complexes, containing Pt atoms in oxidation states ranging from (+1) to (+0.3), and whose main structural features were established by the above-mentioned techniques. Giant clusters with dense PtPtOx cores (coordination number for the PtPt bonds is about 6) were obtained by gradual heating of the precursor Pt complex to about 200°C as well as by a modified preparation procedure at 20°C.

Platinum acetate blue: synthesis and characterization.

Platinum acetate blue (PAB) of the empirical formula Pt(OOCMe)2.5±0.25, a byproduct in the synthesis of crystalline platinum(II) acetate Pt4(OOCMe)8, is an X-ray amorphous substance containing platinum in the oxidation state between (II) and (III). Typical PAB samples were studied with X-ray diffraction, differential thermal analysis-thermogravimetric, extended X-ray absorption fine structure, scanning electron microscopy, transmission electron microscopy, magnetochemistry, and combined quantum chemical density functional theory-molecular mechanics modeling to reveal the main structural features of the PAB molecular building blocks. The applicability of PAB to the synthesis of platinum complexes was demonstrated by the preparation of the new homo- and heteronuclear complexes Pt(II)(dipy)(OOCMe)2 (1), Pt(II)(μ-OOCMe)4Co(II)(OH2) (2), and Pt(III)2(OOCMe)4(O3SPhMe)2 (3) with the use of PAB as starting material.

The Role of Water Molecules in Formation of Heterometallic Palladium Acetate Complexes with Cerium and Neodymium

The reactions of palladium(II) acetate with neodymium(III) and cerium(III) acetates in acetic acid containing a specified amount of water have been studied. The following homo- and heterometallic complexes have been synthesized and characterized by X-ray diffraction: Nd2(μ-OOCMe)2(μ,η2-OOCMe)2(η2-OOCMe)2(HOOCMe)2(OH2)2 · 4HOOCMe, [Pd(μ-OOCMe)4Ce(OH2)2(μ,η2-OOCMe)]2 · 2HOOCMe · 6H2O, [Pd(μ-OOCMe)4Ce(OH2)2(μ,η2-OOCMe)]2 · 14H2O, [Pd(μ-OOCMe)4M(HOOCMe)2(OH2)2]+ [Pd(μ-OOCMe)4M(μ-OOCMe)4Pd]− · 2MeCOOH · 1.5H2O (M = Nd, Ce), and {[Pd(μ-OOCMe)4Ce(OOCMe)4]2 [Pd4(μ-OOCMe)4]2(μ4-O)8CePd4}(OH)3 · 27H2O. From kinetic and structural data and optical spectra of reaction solutions, the conclusion was drawn that hydrolytic processes play a decisive role in complexation reactions.

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 platinum complexes in the gas phase

Previously unknown cationic platinum complexes Pt(C5H4N)(C5H5N)+ and Pt(C5H4N)+, where platinum atom forms an unusual three-membered metallacycle with a deprotonated pyridine molecule, were detected in the gas phase by mass spectrometry and structurally characterized by DFT quantum-chemical calculations.

Unusual sandwich platinum(II) complex: [Pt(phen)2]2+ cation between two Pt(phen)(OOCMe)2 molecules

New carboxylate platinum(II) complexes: syn and anti isomers of Pt(phen)(OOCMe)2 molecular complex, [Pt(phen)(NCMe)2](O3SCF3)2, as well as unusual sandwich complex [Pt(phen)2]2+ · 2syn-[Pt(phen)(OOCMe)2] where [Pt(phen)2]2+ cation is inserted between two syn-Pt(phen)(OOCMe)2 molecules were synthesized and structurally characterized by X-ray diffraction analysis. As distinct from syn- and anti-Pt(phen)(OOCMe)2 and [Pt(phen)(NCMe)2](O3SCF3)2 complexes with flat phenanthroline ligand, the phen ligands in [Pt(phen)2]2+ cation have a curved configuration. Comparative DFT analysis of geometry of model structures phen, phen+, phenH+, and [Ptphen2]n+ (n = 1, 2) showed that electron removal from phen molecule had no effect on its geometry in both free state and platinum(II) complexes.