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

Reduction of the three-coordinate iron(III) imido [Ph 2 B( BuIm) 2 Fe═NDipp] ( 1 ) affords [Ph 2 B( BuIm) 2 Fe═NDipp][K(18-C-6)THF 2 ] ( 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 DippNH 2 , which establishes an equilibrium with the bis(anilido) complex [Ph 2 B( BuIm) 2 Fe(NHDipp) 2 ][K(18-C-6)THF 2 ] ( 3 ). In an unusual transformation, formal insertion of i PrN═C═N i Pr into the Fe═N(imido) bond yields the guanidinate [Ph 2 B( BuIm) 2 Fe( i PrN) 2 CNDipp][K(18-C-6)THF 2 ] ( 4 ). Reaction of 4 with excess DippNH 2 provides 3 , along with the guanidine ( i PrNH) 2 C═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.