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