The reaction of allene with β-diketonatoiridium(I) complexes: synthesis,properties and crystal structures of bis(η3-allyllic) complexes of iridium(III) and of iridocyclopentane derivatives

Allene reacts with compounds of the type (β-diketonato)Ir(η-C₈H₁₄)₂| (I) to give iridium(III) derivatives of formula (β-diketonato)IrC₁₂H₁₆ (II) in which an allene tetramer i.e. the 2,3,6,7-tetramethyleneoctane-1,8-diyl group, is bonded to the iridium atom by two η₃-allylic groups. The molecular structures of these complexes were deduced by ¹H NMR studies and by single-crystal X-ray analysis of (hfacac)IrC₁₂H₁₆ (IIb). The reactions of the complexes II with hydrogen and with CO are described.The reaction of (acac)Ir(η-C₈H₁₄)₂ with allene, at -78°C, gives a thermally unstable compound of probable stoichiometry (acac)Ir(C₃H₄)₄ (VI). Its low-temperature IR spectrum and its reaction with bromine indicate that VI contains two η²-bonded allene molecules and teh 3,4-dimethyleneiridocyclopentane moiety. VI reacts with pyridine with loss of an allene molecule to give an iridium(III) derivative of formula (acac)Ir(C₆H₈)(C₃H₄)py (IX). Complex IX was shown by single-crystal X-ray analysis to contain the 3,4-dimethyleneiridocyclopentane moiety and one η²-bonded allene molecule.The role of irido cycles as precursors of the bis(allylic) complexes II is discussed.