SYNTHESIS, CHARACTERIZATION, AND REACTIVITY OF THE 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]

The synthesis of dinuclear complexes of formulas [Rh(mu-OOCCR3)(CO)(PCy3)]2 (R = H (7), F (8)) and [Rh2(mu-OOCCR3)2(CO)3(PCY3)] (R = H (I 1), F (12)) is described. These dinuclear compounds react with dimethyl acetylenedicarboxylate to form [Rh2(mu-OOCCR3)2(mu-MeO2-CC=CCO2Me)(CO)2(PCy3)2] (R = H (13), F (14)) and [Rh2(mu-OOCCR3)2(mu-MeO2CC=CCO2-Me)(CO)3(PCY3)] (R = H (16), F (17)), respectively. The subsequent treatment of 13 with this alkyne gives [Rh2(mu-OOCCH3)2(mu-MeO2CC=CCO2Me)(eta2-MeO2CC=CCO2Me)(CO)2(PCy3)] (15). The addition of terminal alkynes to acetone solutions of 7 leads to the formation of compounds of the type [Rh2(mu-OOCCH3)(mu-eta1:eta2-C2R)(CO)2(PCy3)2] (R = Ph (18), Cy (19), Me3Si (20), MeO2C (21)). Similarly [Rh2(mu-OOCCF3)(mu-eta1:eta2-C2Ph)(CO)2(PCy3)2] (22) and [Rh2(mu-OOCCH3)(mu-eta1:eta2-C2Ph)(COD)2] (23) are prepared by the reaction of PhC=CH with 8 and [Rh(mu-OOCCH3)(COD)]2 (1), respectively. The molecular structure of 18 was determined by X-ray investigations. 18 crystallizes in the space group P2(1)/n with a = 16.418 (7) angstrom, b = 15.715 (3) angstrom, c = 20.117 (8) angstrom, and beta = 112.92 (2)-degrees. 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 sigma to one rhodium atom and pi to the other. In solution there is a rapid sigma/pi transformation of the alkynyl group between the metal atoms. ETH calculations on the fluxional movement in the model compound [Rh2(mu-OOCH)(mu-eta1:eta2-C2H)(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(mu-OOCCH3)(mu-pz)(CO)2(PCY3)2] (24), [Rh(mu-PZ)(CO)(PCy3)]2 (25), and [Rh(OCOCF3)(CO)(Hpz)(PCY3)] (26) is also described.