Synthesis and properties of tetramethyl(η 5 -pentamethylcyclopentadienyl)iridium( V ), dimethyl-di-µ-methylene-bis[(η 5 -pentamethylcyclopentadienyl)iridium( IV )], and related complexes from reactions of di-µ-chloro-dichlorobis[(η 5 -pentamethylcyclopentadienyl)iridium( III )] with hexamethyldialuminium

The intermediate [{(C5Me5)IrMe3}2AlMe](2b) from reaction of [{(C5Me5)Ir}2Cl4] and Al2Me6 in pentane, reacted with ligands (L = PPh3 or C2H4) to give [(C5Me5)IrMe2L], and with a hydrogen-acceptor (acetone) to give the dimethyl-di-µ-methylene complex [{(C5Me5)IrMe}2(µ-CH2)2]. The most unusual reaction of (2b) was the oxygenation to give a 40% yield of the iridium(V) complex [(C5Me5)IrMe4]. Other complexes which were formed in these reactions in lower yields include the chloro(methyl)-di-µ-methylene complex [{(C5Me5)Ir}2Me(Cl)(µ-CH2)2] and the trinuclear di-µ3-methylidyne complex [{(C5Me5)Ir}3(µ3-CH)2]. The complexes have been characterised spectroscopically and by comparison with their rhodium analogues. Mechanisms for the reactions are proposed.