The cyclooctadiene ligand in [IrCl(COD)] 2 is hydrogenated under transfer hydrogenation conditions: A study in the presence of PPh 3 and a strong base in isopropanol

International audience; The interaction of [IrCl(COD)]2 with PPh3 in isopropanol has been investigated for various P/Ir ratios, in the absence or presence of a strong base (KOtBu), at room temperature and at reflux. At room temperature, PPh3 adds to the metal center to yield [IrCl(COD)(PPh3)] and additional PPh3 only undergoes rapid degenerative ligand exchange. Subsequent addition of KOtBu affords [IrH(COD)(PPh3)2] as the main compound, even for high P/Ir ratios, although very minor amounts of products having a “HIr(PPh3)3” core are also generated. Warming to the solvent reflux temperature results in a rapid (< 1 h) and quantitative COD removal from the system as hydrogenated products (54.4% of cyclooctene plus 32.2% of cyclooctane according to a quantitative GC analysis) and in the eventual generation of [IrH3(PPh3)3]. The latter is observed as a mixture of the fac and mer isomers in solvent-dependent proportions. Other minor products, one of which is suggested to be mer-cis-[IrH2(OiPr)(PPh3)3] by the NMR characterization, are also generated. These results show that, contrary to certain previously published assumptions, systems of this kind are unlikely to function via a COD-containing active species in transfer hydrogenation catalyses conducted in hot isopropanol in the presence of a strong base.