A Transient Iron Carbide Generated by Cyaphide Cleavage

Abstract

Despite their potential relevance as molecular models for industrial and biological catalysis, well-defined mononuclear iron carbide complexes are unknown, in part due to the limited number of appropriate C 1 synthons. Here, we show the ability of the cyaphide anion (C�P − ) to serve as a C 1 source. The high spin (S = 2) cyaphide complex PhB( t BuIm) 3 Fe− C�P (PhB( t BuIm) 3 − = phenyl(tris(3-tert-butylimidazol-2-ylidene)borate) is readily accessed using the new cyaphide transfer reagent [Mg( Dipp NacNac)-(CP)] 2 ( Dipp NacNac = CH{C(CH 3 )N(Dipp)} 2 and Dipp = 2,6-di(iso-propyl)phenyl). Phosphorus atom abstraction is effected by the three-coordinate Mo(III) complex Mo(N t BuAr) 3 (Ar = 3,5-Me 2 C 6 H 3 ), which produces the known phosphide ( t BuArN) 3 Mo�P along with a transient iron carbide complex PhB( t BuIm) 3 Fe�C. Electronic structure calculations reveal that PhB( t BuIm) 3 Fe�C adopts a doublet ground state with nonzero spin density on the carbide ligand. While isolation of this complex is thwarted by rapid dimerization to afford the corresponding diiron ethynediyl complex, the carbide can be intercepted by styrene to provide an iron alkylidene.