DFT Probe into the Mechanism of Formic Acid Dehydrogenation Catalyzed by Cp*Co, Cp*Rh, and Cp*Ir Catalysts with 4,4′-Amino-/Alkylamino-Functionalized 2,2′-Bipyridine Ligands

Abstract

The mechanistic landscape of H2 generation from formic acid catalyzed by Cp*M­(III) complexes (M = Co or Rh or Ir) with diamino-/dialkylamino-substituted 2,2′-bipyridine ligand architectures have been unveiled computationally. The calculations indicate that the β-hydride elimination process is the rate-determining step for all the investigated catalysts. The dialkylamino moieties on the 2,2′-bipyridine ligand were found to reduce the activation free energy required for the rate-limiting β-hydride elimination step and increase the hydridic nature of the Ir–hydride bond, which accounts for the experimentally observed enhanced catalytic activity. Furthermore, the protonation by H3O+ ion was found to be the kinetically most favorable route than the conventional protonation by formic acid. The origin for this preference lies in the increased electrophilicity of the proton from hydronium ion which facilitates easy protonation of the metal-hydride with low activation energy barrier. The Co and Rh analogues of the chosen iridium catalyst were computationally designed and were estimated to possess a rate-determining activation barrier of 16.9 and 14.5 kcal/mol, respectively. This illustrates that these catalysts are potential candidates for FAD. The insights derived in this work might serve as a vital knowledge that could be capitalized upon for designing cost-effective catalyst for FAD in future.

Cobalt-catalysed nucleophilic fluorination in organic carbonates

“…52–54 M06 and B3LYP are hybrid functionals very commonly used in catalysis, and have also been applied to related processes. 40,55–58 The Gibbs energy results for the reaction mechanism of the Co–F assisted nucleophilic fluorination reaction of benzoyl chloride ( vide infra ) are provided in Table S2,† and, as somehow expected, there is a relatively big dispersion in the results, B3LYP and M06-L providing similar activation barriers (15.3 and 16.7 kcal mol −1 , respectively), while M06 predicts an intermediate value (23.7 kcal mol −1 ), and TPSS and TPSSh provide the highest one (29.1 and 30.7 kcal mol −1 , respectively). The electronic and Gibbs energy difference between singlet and triplet states is shown in Table S3 †§…”

“…[52][53][54] M06 and B3LYP are hybrid functionals very commonly used in catalysis, and have also been applied to related processes. 40,[55][56][57][58] The Gibbs energy results for the reaction mechanism of the Co-F assisted nucleophilic fluorination reaction of benzoyl chloride…”

Formate dehydrogenase activity by a Cu(ii)-based molecular catalyst and deciphering the mechanism using DFT studies

“…where A = pre-exponential factor and R = gas constant. 49 For the [Cu(N3Q3)Cl]Cl complex, the activation energy was determined from the slope of the Arrhenius plot, i.e., E a /R, and approximated to be 86 kJ mol −1 by taking R = 8.3145 J K −1 mol −1 and slope = −10 300 in the presence of 1.0 mM [Cu (N3Q3)Cl]Cl, 15 mM formic acid, and 15 mM HCOONa. The Eyring plot is ln k/T plotted against 1/T to determine the thermodynamic parameters such as enthalpy, entropy, and free energy.…”

Understanding the Influence of Lewis Acids on CO2 Hydrogenation: The Critical Effect Is on Formate Rotation

“…However, this may not imply that TS1 becomes rate-limiting, as the subsequent catalyst regeneration may have a higher barrier, in line with results for other catalytic systems. 35,38,46,47,54,91,92 We computed the catalyst regeneration for 3 (SI, Figure S54), and our results indicate that H 2 association is overall rate-limiting (however, note that the model involves a charge-separation step making evaluation of relative energies challenging, see discussion in SI). Nonetheless, in line with our results for 1 and 2, we conclude that for 3, TS2 is more affected by LAs than TS1.…”

“…For insertion of CO 2 into metal–R bonds (R = hydride or alkyl/aryl), generally two mechanisms can be considered (Scheme A): i ) An inner sphere path , involving an interaction between CO 2 and the metal at the transition state for H–CO 2 bond formation (TS inn ). ,− Note that a precoordination of CO 2 is not required ,,,− Subsequently, the resulting η 1 -σ-intermediate rearranges (TS2) , to allow for formation of a κ 1 -O-(or κ 2 -O,O-)­carboxylate species. It is important to note that although TS inn and TS2 both are cyclic, they are entirely different transition states, whose optimized geometries will show distinct features.…”