The reaction of allene with diketonato Ir complexes: synthesis, properties and crystal structure of bis(allylic) Ir(III) compl and cyclopentane deriv

Allene reacts with compounds of the type (&diketonato)Ir(q-C,H,.& (I) to give iridium(II1) derivatives of formula (&diketonato)IrC1zHIG (II) in which an allene tetramer, i.e. .the 2,3,6,'7-tetramethyleneoctane-l&diyl group, is bonded to the iridium atom by two q3-allylic groups. The molecular structures of these complexes were deduced by 'H NMR studies and by single-crystal X-ray analysis of (hfacac)IrCI,Hle (IIb)_ The reactions of the complexes II with hydrogen and with CO are described_ The reaction of (acac)Ir(q-C&H,,), with alIene, at -7S"C, gives a thermally unstable~compound of probable stoichiometry (aizac)Ir(C3H& (VI). Its lowtemperature IR spectrum and its reaction with bromine indicate that VI contains two i2-bonded allene molecules and the 3,44imethyleneiridocyclopentane moiety_ VI reacts with pyridine with loss of an allene molecule to give an iridium- (III) derivative of formula (acac)Ir(C6Hs)(CsH4)py (IX). Complex IX was shown by single-crystal X-ray analysis to contain the 3,4-dimethyleneirid~clopentane moiety and one q'-bonded @lene molecule. The roll of i&do cycles qs precursors of the bis(aUylic) complexes II is dis- .crlss&i..