Synthesis of Ir Catalysts Featuring Amide‐functionalized NHC Ligands and Survey of their Activity on Formic Acid Dehydrogenation

Abstract

2 a and 2 b, [Ir(CI)(COD)(NHC)] (COD=1,5‐cyclooctadiene), have been prepared via transmetallation from NHC−Ag complexes. [Rh(CI)(COD)(NHC)] (4) was prepared analogously. [Ir({κ‐C,N‐(NHC‐acetamide−1H)}(COD)] (3 c) has been synthesized via transmetallation from the deprotonated NHC−Ag complex. [IrCp*({κ‐C,N‐(NHC‐acetamide−1H)}] (5) (Cp*=pentamethylcyclopentadienyl), has been obtained analogously. [Ir(CI)(CO)2(NHC)] (6) and [Ir({κ‐C,N‐(NHC‐acetamide−1H)}(CO)2] (7) have been prepared by carbonylation of 2 b and 3 c, respectively. The catalytic activity of these complexes has been evaluated in the dehydrogenation of formic acid, under solventless conditions, in the presence of water as a cosolvent, and in a 5 : 2 HCOOH/Et3N mixture, with the best TOF values being obtained in the case of the latter. Stoichiometric experiments suggest COD hydrogenation as the preactivation step.