Yu.S. Varshavsky

Carbon-13 nuclear magnetic resonance spectra of rhodium carbonyl complexes

Abstract The 13C NMR spectra of a series rhodium carbonyl complexes were measured. An approximate correlation of δ(13CO) chemical shifts with carbonyl group stretching frequencies ν(CO) was observed. For square planar complexes the variations in ν(CO) parallel that of the coupling constants 1J(RhC). The oxidative addition to planar rhodium(I) complex with formation of octahedral rhodium(III) complex results in opposite trends for ν(CO) and J. The greater ν(CO) value reflects the diminished electron density on the central atom and a lower coupling constant is due to the reduced contribution of the rhodium 5s orbital in the RhCO bond.

Mixed carbonylcyclooctene complexes of rhodium(I). cis-cyclooctene as ligand

Abstract The substitution reactions of carbonyl groups in [Rh(CO) 2 Cl] 2 , Rhacac(CO) 2 , Rhoxq(CO) 2 (acac = acetylacetonate, oxq = 8-hydroxyquinolinate) by cis -cyclooctene, leading to the formation of [Rh(C 8 H 14 )(CO)Cl] 2 , Rhacac- (C 8 H 14 )CO, Rhoxq(C 8 H 14 )CO respectively, are described. Other monoolefins examined do not displace carbonyl groups from rhodium(I) complexes. Mixed carbonylcyclooctene complexes are also formed in the ligand exchange reactions [Rh(CO) 2 Cl] 2 + [Rh(C 8 H 14 ) 2 Cl] 2 and Rhacac(CO) 2 + Rhacac(C 8 H 14 ) 2 . On reaction with triphenylphosphine and triphenylstibine the mixed complexes give Rhacac(L)CO and Rhoxq(L)CO. (Stibine derivatives of this type have not previously been obtained). The chemical and spectroscopic evidence, as well as the thermodynamic data cited from the literature indicate that cyclooctene exhibits comparatively strong donor properties.

Mild decarbonylation of transition metal carbonyls by rhodium(I) complexes

Abstract Transition metal carbonyls have been found to react with rhodium(I) complexes under mild conditions with resultant transfer of carbonyl to rhodium. Partial decarbonylation of Mo(CO)6 and Fe(CO)5 gives Mo(PPh3)2(CO)4, Mo(Arene)(CO)3 (Arene = benzene, toluene or mesitylene, Fe(PPh3)(CO)4, Fe(PPh3)2(CO)3, Fe(Diene)(CO)3 (Diene = butadiene or isoprene). In the absence of ligands capable of stabilizing partially decarbonylated moieties the decarbonylation goes to completion. In hexamethylphosphoramide the exhaustive decarbonylation of Cr(CO)6, Mo(CO)6, W(CO)6, Fe(CO)5 and Ni(CO)4 induced by [Rh(C8H14)2Cl]2 (C8H14 = cyclooctene) proceeds homogeneously and with retention of the oxidation state of rhodium (+1).

Spectral characteristics of products formed by reaction between Rhacac(PPh3)(CO) and methyl iodide

Abstract 13C, 31P and 1H NMR spectra revealed that in reaction mixtures Rhacac(PPh3)(CO) and MeI there were present two methylcarbonyl (MC) complexes of RhIII. These were presumably isomers of Rhacac(PPh3)(CO)(Me)I: MC-I (δ 13C 185. 3 ppm, 1J(CRh) 64.0 Hz, 2J(CRhP) 18.1 Hz; δ 31P 33.7 ppm, 1J(PRh) 124.4 Hz; δ 1H (MeRh) 1.36 ppm, 2J(HCRh) 1.9 Hz, 3J(HCRhP) 2.1 Hz) and MC-II (δ 13C 185.6 ppm, 1J(CRh) 62.5 Hz, 2J(CRhP)11.0 Hz; δ 31P 28.4 ppm, 1J(PRh) 117.4 Hz δ 1H (MeRh) 1.65 ppm, 2J (HCRh) 1.9 Hz, 3J(HCRhP) 3.8 Hz). The third product is an acetyl complex, presumably the dimer [Rhacac(PPh3)(MeCO)I] 2 (δ 13C 212.4 ppm, 1J(CRh) 28.0 Hz, 2J(CRhP) ∼ 7 Hz; δ 31P 37.6 ppm, 1J(PRh) 153.0 Hz; δ 1H (MeCO) 2.94 ppm, 2J(HCC) 5.9 Hz). The MC-I complex is able to transform partially into MC-II. Oxidative addition of MeI to Rhacac (AsPh3)(CO) and to Rhoxq(PPh3)(CO) (hoxq = 8-hydroxyquinoline; oxq its residue) yielded similar methylcarbonyl and acetyl complexes. All species present in the reaction mixtures are identified spectroscopically without isolation.

The nature of the product of the reaction [Rh(CO)2Cl]2 with PPh3 at 11 mole ratio of PPh3/Rh

Oxidation of the compounds1 RhAcac(CO)2 and RhAcacPPh3CO with halogens affords rhodium(III) carbonyl chloride, [Rh(CO)2Cl3]3, and binuclear phosphine-containing complexes (RhPPh3COX3)2 (X = Cl, Br). The nature of the reaction product of [Rh(CO)2Cl]2 with triphenylphosphine at a 11 mole ratio of PPh3/Rh is discussed.

Oxidation of the [Rh(CO)2Cl2] anion in aqueous solution

Abstract The reaction of rhodium(I) carbonyl chloride, [Rh(CO)2Cl]2, with dichromate, cerium(IV) sulfate, hexachloroplatinic acid or p-benzoquinone in aqueous hydrochloric acid proceeds by consumption of 4 equivalents of oxidizing agent per mole or rhodium(I) in accordance with the equation RhI(CO)2  4e + H2O → RhIII(CO) + 2H+ + CO2 A “cyclic” oxidation mechanism is suggested.

Interfragment transmission of electronic effects of π-acceptor ligands in heterometallic triad complexes with trans-[Ru(Py)4(CN)2] as a central unit

The complex trans-[RuPy4(CN)2] cleaves chloride bridges in the binuclear rhodium(i) and palladium(ii) complexes [Rh(CO)2Cl]2, [Rh(η4-C8H12)Cl]2, [(η4-C8H12)Rh(μ-Cl)2Rh(CO)2], [Pd(η3-C3H5)Cl]2, and [(η3-C3H5)Pd(μ-Cl)2Rh(CO)2] to form heterometallic triad complexes [(CO)2ClRh(NC)RuPy4(CN)RhCl(CO)2] (1), [(η4-C8H12)ClRh(NC)RuPy4(CN)RhCl-(η4-C8H12)] (2), [(CO)2ClRh(NC)RuPy4(CN)RhCl(η4-C8H12)] (3), [(η3-C3H5)ClPd(NC)-Ru(Py)4(CN)PdCl(η3-C3H5)] (4), and [(CO)2ClRh(NC)Ru(Py)4(CN)PdCl(η3-C3H5)] (5), respectively. In solutions, complex 3 coexists with equilibrium amounts of compounds 1 and 2; complex 5 is in the equilibrium with compounds 4 and 1. In both cases, the ratio of concentrations is close to binomial. Complexes 2 and 5 treated with [Rh(CO)2Cl]2 are converted into 1 with the simultaneous formation of [Rh(η4-C8H12)Cl]2 and [Pd(η3-C3H5)Cl]2, respectively. The δH and δC values for the ligands η4-C8H12, η3-C3H5, and CO are sensitive to the nature of the remote triad unit. The ligand effects are shown to be transmitted along the chain L′-M′-(NC)-Ru-(CN)-M″-L″.