Synthesis, reactions and catalytic activities of cationic iridium(I) complexes of cycloocta-1,5-diene

Abstract

New cationic iridium(I) complexes, [Ir(cod)(PPh₃)L]ClO₄1[cod = cycloocta-1,5-diene; L = PhCN, PhCHCHCN, CH₂CHCN, CH₂C(Me)CN, MeCHCHCN or CH₂CHCH₂CN co-ordinated through the nitrogen atom], have been prepared by the reactions of [IrCl(cod)(PPh₃)] with AgClO₄ in the presence of L. Reaction of [Ir(cod)(PPh₃)(PhCN)]ClO₄1a with H₂ gives the cis-dihydridoiridium(III) complex [IrH₂(cod)(PPh₃)(PhCN)]ClO₄2a where the two hydrides are trans to PhCN and an olefinic group of cod, respectively. Complex 2a is stable both in solution and in the solid state at low temperature and decomposes at 15 °C to give cyclooctane and unidentified Ir–cod complex(es). The nitrile (L) in 1 is readily replaced by both PPh₃ and CO, while cod is replaced only by CO. In the presence of complexes 1, unsaturated alcohols such as CH₂CHCH₂OH, CH₂CHCH(Me)OH and CH₂CHCH(Ph)OH rapidly undergo isomerization to the corresponding saturated carbonyl compounds at room temperature. Complex 1a catalyses the hydrogenation of unsaturated aldehydes, PhCHCRCHO (R = H, Me or Cl) to give PhCHCRCH₂OH, PhCH₂CHRCHO and PhCH₂CHRCH₂OH under H₂(p_H2= 6 atm) at 50 °C.