Effect of Transition Metal Variability in NNN-Pincer Complexes on Catalytic CO2 Reduction to Methanol.

The catalytic efficiency of M-H2tpda pincer complexes (M=Mn(I), Fe(II), Co(III)) in CO2 hydrogenation, emphasizing the role of transition metal variability have been discussed. The DFT analysis demonstrates that complexes with low αR values form weaker M-H bonds, enhancing catalyst reactivity with the elongation of M-H bond. The analysis further displays excellent catalytic performance for Mn-H2tpda (ΔE=20.3 kcal/mol), Fe-H2tpda (ΔE=21.0 kcal/mol) and Co-H2tpda (ΔE=23.6 kcal/mol) for CO2 to formic acid formation. The Co-H2tpda (ΔE=16.7 kcal/mol) is comparatively better than Mn-H2tpda (ΔE=20.7 kcal/mol) and Fe-H2tpda (ΔE=19.6 kcal/mol) in formaldehyde formation. All three catalysts exhibit excellent catalytic performance in the conversion of formaldehyde to methanol. The condensed Fukui function calculations of these catalyst complexes establish direct relationship between the ΔE for the rate limiting catalytic cycle and the electrophilicity of the metal centers. The TOF calculations further helped to understand the catalytic performance of the catalysts at various temperatures.