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(pH2= 6 atm) at 50 °C.