Reactions of pentaborane(9) with electron-rich molybdenum and tungsten phosphine polyhydrides

Reaction of [W(PMe2Ph)3H6] with pentaborane(9) gives nido-2-[W(PMe2Ph)3H2B4H8] (1) as well as nido-2-[W(PMe2Ph)3HB5H10] (2). The crystal structure of (2) has been determined. Compound (2) has a novel metallaborane structure containing an edge-bridging {BH3} group between the tungsten atom and one of the basal boron atoms in a “nido-WB4” pyramid. Reaction of [W(PMe3)4(η2-CH2PMe2)H] with pentaborane(9) gives nido-2-[W(PMe3)3H2B4H8] (3) whilst reaction of [Mo(L)4H4] with pentaborane(9) gives nido-2-[Mo(L)3H2B4H8] [L = PMe3 (4), PMe2Ph (5)]. Treatment of [Mo(PMe3)4H4] with excess BH3 · thf gives the known borohydride [Mo(PMe3)4H(η2-BH4)].