On [(1,2,3,4,5-η)-6-(1-ethoxyethyl)-3-mesityl-2,4,6-trimethylcyclohexa-2,4-dienyl]dimesityliridium(III)

Abstract

The interaction of an aberrant batch of ‘iridium trichloride hydrate’ that had been treated with SOCl2 in Et2O gave, on interaction with mesityllithium, a cherry red, substituted cyclohexadienyl compound 1 of stoichiometry Ir(mes)2(C22H31O), mes = 2,4,6-trimethylphenyl, whereas previous arylations of hydrated iridium(III) chloride ‘IrCl3·nH2O’ gave Ir(mes)4. Compound 1 has exo and endo isomers separable by column chromatography. The study of various treated iridium chlorides has given reproducible syntheses of 1; a halide with water co-ordinated to iridium appears necessary. An X-ray crystal structure determination of the major isomer 1b shows that the C22H31O moiety bound to Ir comprises a cyclohexadienyl ring with a mesityl group at position 3, methyl groups at positions 2,4 and 6 and an exo EtOC(H)Me group at position 6. Detailed variable-temperature 1H and 13C NMR studies have allowed almost complete assignments for both exo and endo isomers; additional diasteroisomers were detected in solution and activation parameters for dynamic processes were determined. Alternative syntheses of Ir(mes)3 and Ir(mes)4 as well as syntheses of 1 are discussed in relation to thermal and SOCl2 treatments of IrCl3·nH2O, (H3O)2IrCl6·2H2O and ‘sodium hexachloroiridate hydrate’.