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.