Four-membered chelate rings in complexes with 2,2-bis(diphenylphosphino)propane. Crystal and molecular structures of trans-[RuCl2{Me2C(PPh2)2}2], [RuCl{Me2C(PPh2)2}(η-C5H5)] and [(η-C5H5)Ru(µ-CO)2-{µ-Me2C(PPh2)2}RhCl2](Rh–Ru)

Abstract

The compound Me₂C(PPh₂)₂(2,2-dppp) reacted with 0.5 equivalent of [Rh₂Cl₂(CO)₄] to afford monomeric [RhCl(CO)(2,2-dppp-P,P′)]1. Metathesis with LiBr afforded [RhBr(CO)(2,2-dppp-P,P′)]2. With 0.25 equivalent of [Rh₂Cl₂(CO)₄] the rigid, square-planar [Rh(2,2-dppm)₂]Cl 3 was formed. These results are in sharp contrast to the chemistry seen with H₂C(PPh₂)₂ and H(Me)C(PPh₂)₂. With 0.5 equivalent of [RuCl₂(PPh₃)₃], 2,2-dppp reacted to give brown-orange trans-[RuCl₂(2,2-dppp)₂]4a. In solution this is in equilibrium with a green five-co-ordinate species [RuCl(2,2-dppp)₂]Cl 4b, the first such complex to be observed with a four-membered chelating diphosphine. With [RuCl(PPh₃)₂(η-C₅H₅)], 2,2-dppp reacted to form [RuCl(2,2-dppp)(η-C₅H₅)]5. Although its rhodium(I) chemistry suggests that 2,2-dppp favours chelation rather than bridging modes of co-ordination, when 5 was treated with 0.5 equivalent of [Rh₂Cl₂(CO)₄] it readily formed [(η-C₅H₅)Ru(µ-CO)₂(µ-2,2-dppp)RhCl₂](Rh–Ru)6. The structures of 4–6 have been determined by X-ray diffraction.