Mechanism of Catalytic Nitrene Transfer Using Iron(I)–Isocyanide Complexes

Low-spin iron­(I) complexes supported
by bulky β-diketiminate
ligands catalyze the formation of unsymmetric carbodiimides (RNCNR′,
R ≠ R′) from
isocyanides and organoazides. In situ EPR studies
indicate that the catalytic resting state in these reactions is the
tris­(isocyanide)­iron­(I) complex LFe­(CNR)3, and kinetic
experiments show that the reaction is inverse second-order in isocyanide
concentration, suggesting that two isocyanide molecules dissociate
prior to the rate-determining step. An unusual iron–carbodiimide
complex can be isolated independently, and facile displacement of
the coordinated carbodiimide by both isocyanide and N2 demonstrate
that product release is not kinetically limiting during catalysis.
These experimental data fit a coherent mechanism for the catalytic
C–N coupling reaction, and the implications for catalytic nitrene
transfer are discussed.