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

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({kappa-C,N-(NHC-acetamide-1H)}(COD)] (3 c) has been synthesized via transmetallation from the deprotonated NHC-Ag complex. [IrCp*({kappa-C,N-(NHC-acetamide-1H)}] (5) (Cp*=pentamethylcyclopentadienyl), has been obtained analogously. [Ir(CI)(CO)(2)(NHC)] (6) and [Ir({kappa-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.

Automated summary

Two Ir complexes, 2a and 2b, with the ligand [Ir(CI)(COD)(NHC)] (COD=1,5-cyclooctadiene), were synthesized through transmetallation from NHC-Ag complexes. Analogously, another Rh complex, 4, was prepared using the same method. By transmetallation from the deprotonated NHC-Ag complex, another Ir complex, 3c, with the ligand [Ir({kappa-C,N-(NHC-acetamide-1H)}(COD)], was synthesized. Similarly, [Ir(CI)(CO)(2)(NHC)] (6) and [Ir({kappa-C,N-(NHC-acetamide-1H)}(CO)(2)] (7) were obtained through carbonylation of 2b and 3c respectively. The catalytic activity of these complexes in formic acid dehydrogenation was evaluated, with the highest turnover frequency (TOF) observed in the presence of a 5:2 HCOOH/Et3N mixture. Stoichiometric experiments suggested COD hydrogenation as the preactivation step.