Oxygen-Atom Transfer from Carbon Dioxide to a Fischer Carbene at (PNP)Ir

Abstract

Dehydrogenation of the dihydride (PNP)IrH_2 with norbornylene in the presence of t-butyl methyl ether leads to formation of an iridium(I) Fischer carbene complex, (PNP)Ir═C(H)O^tBu, by double C−H activation and loss of H_2. The square planar pincer-type carbene effects quantitative oxygen-atom transfer from CO_2 (1 atm) at ambient temperature to generate t-butyl formate and (PNP)Ir−CO. The iridium carbene reacts similarly with carbonyl sulfide and phenyl isocyanate, causing sulfur-atom and nitrene-group transfer, respectively. In the absence of a hydrogen acceptor, thermolysis of (PNP)IrH_2 in t-butyl methyl ether under an atmosphere of CO_2 also results in the formation of (PNP)Ir−CO and oxidation of t-butyl methyl ether to t-butyl formate via an iridium carbene. Preliminary mechanistic studies indicate that these reactions proceed through an intermediate four-membered metallalactone.

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