Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 103. Carbaborane molybdenum and tungsten dimetal complexes

Treatment of the complex [Mo(CO)2(NCMe)2(η5-C9H7)][BF4](C9H7= indenyl) with the salts [NEt4][W(CCCBut)(CO)2(η5-C2B9H9Me2)]and [NEt4][Mo(CC6H4Me-4)(CO){P(OMe)3}(η5-C2B9H9Me2)] in CH2Cl2 affords, respectively, the dimetal compounds [MoW(µ-CCCBut)(CO)3(η5-C9H7)(η5-C2B9H9Me2)]and[Mo2(µ-CC6H4Me-4)(CO)2{P(OMe)3}(η5-C9H7(η5-C2B9H9Me2)]. Similarly, reactions between the salts [NEt4][M(CR)(CO)2(η5-C2B9H9R′2)](M = Mo or W, R = C6H4Me-4, R′= H; M = W, R = C6H4Me-4 or C6H4Me-2, R′= Me; M = W, R = CCBut, R′= Me) and [Mo(CO)2(NCMe)(η7-C7H7)][BF4] yield the dimetal complexes [MMo(µ-CR)(CO)2(η7-C7H7)(η5-C2B9H9R′2)](M = W, R = C6H4Me-4, C6H4Me-2, or CCBut, R′= Me; M = Mo or W, R = C6H4Me-4, R′= H). The compounds [MoW(µ-CC6H4Me-4)(CO)2(η7-C7H7)(η5-C2B9H10Me)] and [MoW(µ-CC6H4Me-4)(CO)2(η7-C7H7)(η6-C2B10H10Me2)] have also been prepared using the reagents [NEt4][W(CC6H4Me-4)(CO)2(η5-C2B9H10Me)] and [NEt4][W(CC6H4Me-4)(CO)2(η6C2B10H10Me2)]. All the dimetal compounds have structures in which the metal–metal bonds are bridged by an alkylidyne group and by a B–H⇀Mo three-centre two-electron bond. The latter involves a boron atom lying in the face of the nido-carbaborane fragment which is co-ordinated to the other metal centre in the η5(for C2B9H9R′2) or η6(for C2B10H10Me2) bonding mode. The n.m.r. data (1H, 13C-{1H}, 11B-{1H}, 11B, and 31P-{1H}) for the new compounds are reported and discussed in the context of the structures proposed.