Unveiling the mechanistic landscape of formic acid dehydrogenation catalyzed by Cp∗M(III) catalysts (M = Co or Rh or Ir) with bis(pyrazol-1-yl)methane ligand architecture: A DFT investigation

Abstract

The production of dihydrogen via formic acid dehydrogenation (FAD) has been gaining remarkable attention and advancement as an alternative, sustainable and clean energy source. Density functional theory (DFT) calculations have been utilized to probe the reaction mechanism of FAD catalyzed by a Cp∗Rh(III) complex reported by Fink and Laurenczy with bis(pyrazol-1-yl)methane ligand system. The calculated energetics show that the rate-limiting step is the β-hydride elimination step and protonation by hydronium ion was calculated to be the most favourable route requiring relatively less activation energy than the conventional process which entails formic acid as the proton source. The Co and Ir congeners of the chosen Rh catalyst were computationally designed and they were also found to follow the same mechanism. Interestingly, the three metal centres (Co, Rh and Ir) were estimated to possess nearly the same activation barrier of c.a. 14 kcal/mol at the rate determining step. Thus, the proposed Co complex with such a small rate determining activation barrier, could be considered as a cheap and propitious earth-abundant transition metal-based catalyst for FAD.