Transition metal complexes of the chelating phosphine boraneligand Ph2PCH2Ph2P·BH3

Abstract

Chromium and ruthenium complexes of the chelating phosphine borane H₃B·dppm are reported. Addition of H₃B·dppm to [Cr(CO)₄(nbd)] (nbd = norbornadiene) affords [Cr(CO)₄(η¹-H₃B·dppm)] in which the borane is linked to the metal through a single B–H–Cr interaction. Addition of H₃B·dppm to [CpRu(PR₃)(NCMe)₂]⁺ (Cp = η⁵-C₅H₅) results in [CpRu(PR₃)(η¹-H₃B·dppm)][PF₆] (R = Me, OMe) which also show a single B–H–Ru interaction. Reaction with [CpRu(NCMe)₃]⁺ only resulted in a mixture of products. In contrast, with [Cp*Ru(NCMe)₃]⁺ (Cp* = η⁵-C₅Me₅) a single product is isolated in high yield: [Cp*Ru(η²-H₃B·dppm)][PF₆]. This complex shows two B–H–Ru interactions. Reaction with L = PMe₃ or CO breaks one of these and the complexes [Cp*Ru(L)(η¹-H₃B·dppm)][PF₆] are formed in good yield. With L = MeCN an equilibrium is established between [Cp*Ru(η²-H₃B·dppm)][PF₆] and the acetonitrile adduct. [Cp*Ru(η²-H₃B·dppm)][PF₆] can be considered as being “operationally unsaturated”, effectively acting as a source of 16-electron [Cp*Ru(η¹-H₃B·dppm)][PF₆]. All the new compounds (apart from the CO and MeCN adducts) have been characterised by X-ray crystallography. The solid-state structure of H₃B·dppm is also reported.