Dehydrogenation of Alcohols by Bis(phosphinite) Benzene Based and Bis(phosphine) Ruthenocene Based Iridium Pincer Complexes

Dehydrogenation of alcohols by three iridium pincer complexes, IrH(Cl)[2,6-(tBu2PO)2C6H3] (1), {IrH(acetone)[2,6-(tBu2PO)2C6H3]}{BF4} (2), and IrH(Cl)[{2,5-(tBu2PCH2)2C5H2}Ru(C5H5)] (3), is reported, in both the presence and the absence of a sacrificial hydrogen acceptor. Dehydrogenation of secondary alcohols proceeds in a catalytic mode with turnover numbers up to 3420 (85% conversion) for acceptorless dehydrogenation of 1-phenylethanol. Primary alcohols are readily decarbonylated even at room temperature to give catalytically inactive 16e Ir–CO adducts. The mechanism of this transformation was studied in detail, especially for EtOH; new intermediates were isolated and characterized.