DFT Investigation of the Potential of [H‐M{(NHCH2CH2)3X}] Catalysts (M = Mo, Ru, Os; X = N, P) for the Reduction of N2 to NH3 by H2

Abstract

AbstractDFT calculations of model complexes [H‐M{(NHCH2CH2)3X}] (M = Mo, Ru, Os; X = N, P) were carried out to investigate the catalytic potential of these complexes towards the reduction of N2 to NH3 using only H2 as the reducing agent. Closed catalytic cycles were calculated for all three metal hydrides. The calculations showed that [H‐Mo{(NHCH2CH2)3N}], 1‐Mo, is not an appropriate catalyst due to very high activation barriers for several steps of the reaction (ΔH‡max = 69.1 kcal/mol). Much lower activation barriers were found for the Ru and Os catalysts [H‐Ru{(NHCH2CH2)3N}], 1‐Ru, and [H‐Os{(NHCH2CH2)3P}], 1‐Os(P). With ΔH‡max/ΔG‡max = 29.3/35.7 kcal/mol, 1‐Os(P) shows potential for future theoretical work. QM/MM calculations were used to investigate some properties of the Ru system empolying the hexaisopropylterphenyl ligand (HIPT). The results indicate that an HIPT substituent at the ligand core has a benefical influence on some reaction steps by lowering the activation barriers, while for other steps the activation energies increase. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)