Catalytic Carbodiimide Guanylation by a Nucleophilic, High Spin Iron(II) Imido Complex

Reduction of the three-coordinate iron­(III) imido [Ph2B­(tBuIm)2FeNDipp] (1) affords [Ph2B­(tBuIm)2­FeNDipp]­[K­(18-C-6)­THF2] (2), a rare example of a high-spin (S = 2) iron­(II) imido complex. Unusually for a late metal imido complex, the imido ligand in 2 has nucleophilic character, as demonstrated by the reaction with DippNH2, which establishes an equilibrium with the bis­(anilido) complex [Ph2B­(tBuIm)2­Fe­(NHDipp)2]­[K­(18-C-6)­THF2] (3). In an unusual transformation, formal insertion of iPrNCNiPr into the FeN­(imido) bond yields the guanidinate [Ph2B­(tBuIm)2­Fe­(iPrN)2­CNDipp]­[K­(18-C-6)­THF2] (4). Reaction of 4 with excess DippNH2 provides 3, along with the guanidine (iPrNH)2CNDipp. As suggested by these stoichiometric reactions, 2 is an efficient catalyst for the guanylation of carbodiimides, converting a wide range of aniline substrates under mild conditions.