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.