Allenylphosphonium Complexes of Rhodium and Iridium

The propargylic salt [Ph3PCH2CCH]­PF6 ([1]­PF6) undergoes a facile rearrangement to the allenyl isomer [Ph3PCHCCH2]­PF6 ([2]­PF6) upon coordination to rhodium and iridium. The η2-allenylphosphonium salts [IrX­(η2-CH2CCHPPh3)­(CO)­(PPh3)2]­PF6 (X = Cl, [4]­PF6; X = Br, [5]­PF6) and [RhCl­(η2-CH2CCHPPh3)­(PPh3)2]­PF6 ([7]­PF6) have been synthesized and characterized, including X-ray crystallographic analyses. In the case of rhodium, it was found that [7]­PF6 was also formed by the reaction of the α-alkynylphosphonium salt [Ph3PCCCH3]­PF6 ([3]­PF6) with [RhCl­(PPh3)3]. The complex [RhCl­(CO)­(PPh3)2] was found to catalyze the isomerization of [1]+ to [2]+.