Specific C-C coupling of the labile diruthenium bridging methylene complex, Cp2Ru2(μ-CH2)(CO)2(MeCN), with diazoalkanes (R2C=N2) leading to alkenyl complexes, Cp2Ru2(μ-CH=CR2)(μ-H)(CO)2, and alkenes, CH2=CR2

Treatment of the labile mu-methylene species, Cp2Ru2(mu-CH2)(CO)(2)(MeCN) 1, with diazoalkanes results in C-C coupling of the alkylidene units. The reaction of monosubstituted diazoalkanes (N-2=CHR) and 4-t-butyldiazocyclohexane gives the mu-alkenyl-mu-hydride complexes, Cp2Ru2(mu-CH=CR2)(mu-H)(CO)(2) 2, as sole products, whereas the reaction of disubstituted aryldiazoalkanes (N-2=(CRR2)-R-1) produces olefins (CH2=(CRR2)-R-1) together with mixtures of unidentified organometallic compounds. Labeling experiments using 1-d(2) (mu-CD2) and 1-C-13 (mu-(CH2)-C-13) reveal that the methylene bridge in 1 is converted to the alpha-CH and mu-H parts in 2 and the alkylidene part of diazoalkane is incorporated into the B-CR, part of the alkenyl bridge. The olefinic products should come from a eta(2)-olefin intermediate, Cp2Ru2(eta(2)CH(2)=CHR)(CO)(2) 7, resulting from coupling of the two alkylidene fragments within the coordination sphere of the diruthenium core. It is notable that C-H oxidative addition in 7 takes place prior to free rotation of the eta(2)-olefin ligand as judged by the regiospecificity of the labeling experiments. Thus specific coupling of alkylidene units proceeds under mild conditions and this C-C coupling reaction serves as a model system for the carbon chain propagation step of surface-catalyzed reactions such as catalytic CO hydrogenation. (C) 1998 Elsevier Science S.A. All rights reserved.