Reactions of 2-indolylphosphines with Ru3(CO)12: cluster capping with μ3,η2-indolylphosphine as an anionic six-electron P,N-donor ligand

Abstract

Stepwise bidentate coordination of the novel indolylphosphine ligands HL (1, HL = P(C₆H₅)₂(C₉H₈N) (diphenyl-2-(3-methylindolyl)phosphine); 2, HL = P(C₆H₅)(C₉H₈N)₂ (phenyldi-2-(3-methylindolyl)phosphine); and 3, HL = P(C₆H₅)(C₁₇H₁₂N₂) (di(1H-3-indolyl)methane-(2,12)-phenylphosphine)) to the ruthenium cluster Ru₃(CO)₁₂ is demonstrated. Reactions of 1–3 with Ru₃(CO)₁₂ led to the formation of Ru₃(CO)₁₁(HL) (4–6), in which HL is mono-coordinated through the phosphorus atom. The X-ray structures of 4–6 show that the phosphorus atom is equatorially coordinated to the triruthenium core. In all cases, gentle heating of Ru₃(CO)₁₁(HL) resulted in the formation of Ru₃(CO)₉(μ-H)(μ₃,η²-L) (7–9) in which the NH proton of the indolyl substituent had migrated to the ruthenium core to form a bridging hydride ligand. The X-ray structure of Ru₃(CO)₉(μ-H)[μ₃,η²-P(C₆H₅)₂(C₉H₇N)] (7) shows the deprotonated nitrogen atom of the indolyl moiety bridging over the face of the triruthenium core, bonding to the two ruthenium metal centers to which the phosphorus atom is not bound. The phosphorus atom is forced to adopt an axial bonding mode due to the geometry of the indolylphosphine ligand. Cluster electron counting and X-ray data suggest that the indolylphosphine behaves as a six-electron ligand in this mode of coordination. Compounds 4–9 have been characterized by IR, ¹H, ¹³C and ³¹P NMR spectroscopy.