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’.