Rhodium Complexes of a Chelating Bisphosphoniobenzophospholide Cation

The 1-(diphenyl(2-diphenylphosphinoethyl)phosphonio)-3-triphenylphosphoniobenzo[c]phospholide cation 1 reacts with [RhCl(C2H4)2]2 to form a dinuclear chelate complex, [RhCl(κ2-P(σ2),P‘(σ3)-1)]2 (5). Treatment of 5 with PPh3 affords mononuclear [RhCl(PPh3)(κ2-P(σ2),P‘(σ3)-1)] (8), whereas reaction with 1,5-cyclooctadiene proceeds via cleavage of the Cl bridges to give [RhCl(cod)(κ-P(σ3)-1)] (6). The chelating binding mode of 1 can be reconstituted by abstraction of chloride with TlOTf to give the dicationic complex [Rh(cod)(κ2-P(σ2),P‘(σ3)-1)]2+ (7). All complexes have been characterized by 1H, 31P, and 103Rh NMR spectroscopy, and 5[BPh4]2 was characterized as well by single-crystal X-ray diffraction. The structural parameters and metal NMR data confirm the different electronic properties of the two types of phosphorus centers in 1 and support in particular the assumption of distinct π-acceptor character for the σ2-P atom, which should render the complexes potentially interesting precatalysts for hydroform...