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]⁺.