A radical mechanism for C–H bond cross-coupling and N2 activation catalysed by β-diketiminate iron complexes

Abstract

Our density functional theory calculations reveal a radical mechanism for N₂ fixation and conversion to N(SiMe₃)₃ and PhN(SiMe₃)₂ catalysed by a diketiminate-supported iron system. We found that the Na(15-crown-5)˙ radical plays an essential role as a co-catalyst in the reaction for the formation of the Me₃Si˙ radical and a stable intermediate. The attack of two Me₃Si˙ radicals to distal nitrogen and the phenyl migration to proximal nitrogen gradually weaken and activate the NN bond. The turnover-limiting step in the whole catalytic reaction is the activation of the C–H bond with a free energy barrier of 20.3 kcal mol⁻¹. Molecular orbital analysis of dinitrogen complexes indicates that the π back-bonding interactions between iron and N₂ orbitals have major contributions to N₂ fixation.