Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 104. Trimetal molybdenum and tungsten complexes containing η5-C2B9H9R′2(R′= H or Me) ligands; crystal structure of [NEt4][Mo2W(µ3-CC6H4Me-4)(µ-CO)(CO)7(PMe3)(η5-C2B9H9Me2)]

Abstract

Solutions of the salts [NEt₄][M(CR)(CO)₂(η⁵-C₂B₉H₉R′₂)](M = Mo or W, R = C₆H₄Me-4 or CCBu^t, R′= H or Me), in thf (tetrahydrofuran) at room temperature, react with the compound [Mo(CO)₃(NCMe)₃] to afford the trimetal complexes [NEt₄][Mo₂M(µ₃-CR)(µ-CO)(CO)₈(η⁵-C₂B₉H₉R′₂)](M = W, R = C₆H₄Me-4, R′= H or Me; M = Mo, R = C₆H₄Me-4, R′= H; M = W, R = C CBu^t, R′= Me). A single-crystal X-ray diffraction study was carried out on the PMe₃ derivative [NEt₄][Mo₂W(µ₃-CC₆H₄Me-4)(µ-CO)(CO)₇(PMe₃)(η⁵-C₂B₉H₉Me₂)]. The metal triangle [Mo–Mo 2.968(3), Mo–W 2.881 (3) and 2.867(3)Å] in the anion is capped on one side by the p-tolylmethylidyne group [µ₃-C–Mo av. 2.26(2), µ₃-C–W 2.01 (2)Å], and is bridged on the other by the C₂B₉H₉Me₂ cage. The latter is η⁵ co-ordinated to the tungsten atom and linked to the molybdenum atoms via two exopolyhedral B–H⇀Mo bonds. The bond to one molybdenum centre involves a BH fragment α to a CMe group in the CCBBB face of the cage, while the bond to the other molybdenum centre employs a BH fragment β to the CMe groups. Moreover, the molybdenum atom linked to the cage via the β BH group carries the PMe₃ ligand [Mo–P 2.489(7)Å]. This metal atom is also ligated by two terminally bound CO groups, and by a CO molecule that asymmetrically bridges to the other molybdenum [Mo–C–O 156(2) and 124(2)°]. The latter is co-ordinated by three CO groups, and the tungsten atom by two CO molecules. In the formation of [NEt₄][Mo₂W(µ₃-CC₆H₄Me-4)(µ-CO)(CO)₇(PMe₃)(η⁵-C₂B₉H₉Me₂)] there was n.m.r. evidence for the formation of a second isomer (ca. 15%) in which the PMe₃ group occupies a different site. Attempts to protonate the salts [NEt₄][Mo₂M(µ₃-CR)(µ-CO)(CO)₈(η⁵-C₂B₉H₉R′₂)] in order to obtain stable neutral complexes were unsuccessful, but treatment of [NEt₄][Mo₂W(µ₃-CCCBu^t)(µ-CO)(CO)₈(η⁵-C₂B₉H₉Me₂)] in thf with [AuCl(PPh₃)] in the presence of TIPF₆ gives [Mo(CO)₆] and the dimetal complex [WAu(µ-CCCBu^t)(CO)₂(PPh₃)(η⁵-C₂B₉H₉Me₂)]. The latter reacts with [Pt(nb)(PMe₂Ph)₂](nb = bicyclo[2.2.1]heptene) to afford the trimetal complex [WPtAu(µ₃-CCCBu^t)(CO)₂(PPh₃)(PMe₂Ph)₂(η⁵-C₂B₉H₉Me₂)]. The n.m.r. data (¹H, ¹³C-{¹H}, ¹¹B-{¹H}, and ³¹P-{¹H}) for the new compounds are reported and discussed.