Synthesis, characterization, and reactivity of rhodium carboxylate dimers [Rh(.mu.-OOCCR3)(CO)(PCy3)]2 (R = H, F). X-ray crystal structure of [Rh2(.mu.-OOCCH3)(.mu.-.eta.1:.eta.2-C2Ph)(CO)2(PCy3)2]

Abstract

The synthesis of dinuclear complexes of formulas [Rh(μ-OOCCR3)(CO)(PCy3)]2 (R = H (7), F (8)) and [Rh2(μ-OOCCR3)2(CO)3(PCy 3)] (R = H (11), F (12)) is described. These dinuclear compounds react with dimethyl acetylenedicarboxylate to form [Rh2(μ-OOCCR3)2(μ-MeO 2-CC=CCO2Me)(CO)2(PCy3)2] (R = H (13), F (14)) and [Rh2(μ-OOCCR3)2(μ-MeO 2CC=CCO2-Me)(CO)3(PCy3)] (R = H (16), F (17)), respectively. The subsequent treatment of 13 with this alkyne gives [Rh2(μ-OOCCH3)2(μ-MeO 2CC=CCO2Me)(η2-MeO2CC=CCO 2Me)(CO)2(PCy3)] (15) The addition of terminal alkynes to acetone solutions of 7 leads to the formation of compounds of the type [Rh2(μ-OOCCH3)(μ-η1:η 2-C2R)(CO)2(PCy3)2] (R = Ph (18), Cy (19), Me3-Si (20), MeO2C (21)). Similarly [Rh2(μ-OOCCF3)(μ-η1:η 2-C2Ph)(CO)2(PCy3)2] (22) and [Rh2(μ-OOCCH3)(μ-η1:η 2-C2Ph)(COD)2] (23) are prepared by the reaction of PhC≡CH with 8 and [Rh(μ-OOCCH3)(COD)]2 (1), respectively. The molecular structure of 18 was determined by X-ray investigations. 18 crystallizes in the space group P21/n with a = 16.418 (7) Å, b = 15.715 (3) Å, c = 20.117 (8) Å, and β = 112.92 (2)°. The complex can be described as a coordinatively unsaturated dinuclear compound, where the coordination geometry around each rhodium atom is approximately square-planar. The phenylacetylide ligand acts as a three-electron donor ligand which is bound σ to one rhodium atom and π to the other. In solution there is a rapid σ/π transformation of the alkynyl group between the metal atoms. ETH calculations on the fluxional movement in the model compound [Rh2(μ-OOCH)(μ-η1:η2-C 2H)(CO)2(PH3)2] suggest that the process has a low activation barrier (ca. 0.5 eV at the ETH level). The synthesis of the complexes [Rh2(μ-OOCCH3)(μ-pz)(CO)2(PCy 3)2] (24), [Rh(μ-pz)(CO)(PCy3)]2 (25), and [Rh-(OCOCF3)(CO)(Hpz)(PCy3)] (26) is also described.