Attaching metal-capped sp carbon chains to metal clusters: Synthesis, structure, and reactivity of rhenium/triosmium complexes of formula [(5-C5Me5)Re(NO)(PPh3)(CC)(n)Os3(CO)(y)(X)(Z)]m+, including carbon geometries more distorted than planar tetracoordinate
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Reaction of [(5-C5Me5)Re(NO)(PPh3)(CCH)] (1) and [Os3(CO)10(NCCH3)2] (CH2Cl2, room temperature) gives the ReC2Os3 complex [(5-C5Me5)Re(NO)(PPh3)(CC)Os3- (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 ReCC(Os3) and +Re=C=C=(Os3)- 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 [(5-C5Me5)Re(NO)(PPh3)(CCCC)Os3(CO)9(H)] (7, 57 %), in which the ReCCCC terminus binds to three osmium atoms, and the adjacent carbon (and hydride) to two. Reaction of 2 and HBF4Et2O gives [(5/C5Me5)Re(NO)(PPh3)(CC)Os3(CO)10(H)2]+BF4/- (8+ BF4/-, 69%). The crystal structure of the SbF6/- salt shows an ReC2Os3 unit very similar to that of 2, but with the hydrides bridging different osmium-osmium bonds. The C3OMe complex [(5-C5Me5)Re(NO)(PPh3)(CCC(OMe)=)Os3(CO)11] (9) decarbonylates in refluxing heptane to give [(5-C5Me5)Re(NO)(PPh3)(CCC)Os3(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.
