Rhodium complexes of a chelating bisphosphoniobenzophospholide cation

The 1-(diphenyl(2-diphenylphosphinoethyl)phosphonio)-3-triphenylphosphoniob enzo[c]phospholide cation 1 reacts with [RhCl(C2H4)(2)](2) to form a dinucl ear chelate complex, [RhCl(kappa (2)-P(sigma (2)),P '(sigma (3))-1)](2) (5) . Treatment of 5 with PPh3 affords mononuclear [RhCl(PPh3)(kappa (2)-p(sigm a (2)),P '(sigma (3))-1)] (8) (8), whereas reaction with 1,5-cyclooctadiene proceeds via cleavage of the Cl bridges to give [RhCl(cod)(kappa -P(sigma (3))-1)] (6). The chelating binding mode of 1 can be reconstituted by abstr action of chloride with TlOTf to give the dicationic complex [Rh(cod)(kappa (2)-P(sigma (2)),P '(sigma (3))-1)](2+) (7). All complexes have been chara cterized by H-1, P-31, and Rh-103 NMR spectroscopy, and 5[BPh4](2) was char acterized as well by single-crystal X-ray diffraction. The structural param eters and metal NMR data confirm the different electronic properties of the two types of phosphorus centers in 1 and support in particular the assumpt ion of distinct pi -acceptor character for the sigma (2)-P atom, which shou ld render the complexes potentially interesting precatalysts for hydroformy lation. In accord with this hypothesis, complexes 5[BPh4](2) and 7[BPh4](2) display good activities and chemoselectivies as catalysts for the hydrofor mylation of 1-hexene at room temperature, even though the regioselectivitie s for n-aldehydes are low.