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.