Attaching metal-capped sp carbon chains to metal clusters:: Synthesis, structure, and reactivity of rhenium/triosmium complexes of formula [(η5-C5Me5)Re(NO)(PPh3)(CC)nOs3(CO)y(X)z]m+, including carbon geometries more distorted than planar tetracoordinate

Reaction of [(eta(5)-C5Me5)Re(NO)(PPh3)(C=CH)] (1) and [Os-3-(CO)(10)(NCCH3)(2)] (CH2Cl2, room temperature) gives the ReC2Os3 complex [(eta(5)-C5Me5)Re(NO)(PPh3)(CC)Os-3(CO)(10)(H)] (2, 78%). The crystal structure shows that the hydride and ReCC terminus bridge the same two osmium atoms symmetrically. The Re-C and ReC-C bond lengths, and IR and NMR properties, indicate contributions by both ReC=C(Os-3) and Re+=C=C=(Os-3)(-) resonance forms. Analogous ReC4Os3 (4, 83 %) and ReC6Os3 (6, 61%)complexes are prepared similarly, and are increasingly less stable in solution and the solid state. Cyclic voltammograms of 2, 4, and 6 show partially reversible oxidations. Complex 4 decarbonylates in refluxing hexane to give [(eta(5)-C5Me5)Re(NO)(PPh3)(CCC)Os-3(CO)(9)(H)] (7, 57%), in which the ReCCCC terminus binds to three osmium atoms, and the adjacent carbon land hydride) to two. Reaction of 2 and HBF4. Et2O gives [(eta(5)-C5Me5)Re(NO) (PPh3)(CC)Os-3(CO)(10)(H)(2)](+). BF4- (8(+) BF4-, 69%). The crystal structure of the SbF6- salt shows an ReC2 Os-3 unit very similar to that of 2, but with the hydrides bridging different osmium-osmium bonds. The C3OMe complex [(eta(5)-C5Me5)Re(NO)(PPh3) (C=CC(OMe)=)-Os-3(CO)(11)] (9) decarbonylates in refluxing heptane to give [(eta(5)-C5Me5)Re(NO)(PPh3)(CCC)Os-3(CO)(9)(OMe)] (10, 63%), in which the ReCCC terminus binds to three osmium atoms, and the center carbon binds to the osmium that is not methoxide-bridged. The crystal structure shows the ReCCC carbon to be highly distorted, binding to four atoms that fall on one side of a plane through the carbon.