Iridium isonitrile complex

Organometallic Compounds. The predominant oxidation states of iridium in organometallics are +1 and +3. Iridium forms mononuclear and polynuclear carbonyl complexes including IrCl(P(C6H5)3)2(CO)2] [14871-41-1], [Iu,Cl4(CO)2] [12703-90-1], [Ir4(CO)12] [18827-81-1], and the conducting, polymeric [IrCl(CO)3]K [32594-40-4]. Isonitrile and carbene complexes are also known. 

Mixed donor tridentate [NPS] ligated derivatives, chromium(III) complexes, 5, 370 Mixed iridium carbonyl dimers, preparation, 7, 289 Mixed isonitrile acetylides, liquid crystals, 12, 281 Mixed isonitrile phenyl complexes, liquid crystals, 12, 282 Mixed ligand triangular Pt carbonyl clusters, characteristics, 8, 411... 

A problem is that the Pauson-Khand reaction uses two equivalents of cobalt. More efficient versions, many of them catalytic, using other metals have been developed. These include carbonyl complexes of titanium, molybdenum, tungsten (Scheme 7.15), rhodium and ruthenium (Scheme 7.16). Rhodium, iridium and iron (Scheme 7.17) have also been used with two alkynes to give cyclopentadienones, often as complexes 7.59. A version of the Pauson-Khand reaction employing a nickel catalyst and an isonitrile in place of CO has been developed. The product is an imine, which can be hydrolysed to a cyclopentenone. 

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