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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.

The reaction of equimolar trimethylsilyldiazomethyllithium (LiTMSD) with high spin ( S = 2) PhB(AdIm) 3 FeCl (PhB(AdIm) 3 - = tris(3-adamantylimidazol-2-ylidene)phenylborate) affords the corresponding N- nitrilimido complex PhB(AdIm) 3 Fe-N═N═C(SiMe 3 ). This complex can be converted to the thermodynamically more favorable C -isocyanoamido isomer PhB(AdIm) 3 Fe-C═N═N(SiMe 3 ) by reaction with an additional equivalent of LiTMSD. While the iron(II) complexes are four-coordinate, the diazomethane is bound side-on in the iron(I) congener PhB(AdIm) 3 Fe( N , N '-κ 2 -N 2 C(H)Si(CH 3 ) 3 ). The latter complex adopts high spin ( S = 3/2) ground state and features an unusually weak C-H bond. Photolysis of the iron(II) complexes induces N═N bond cleavage, with the iron(II) cyanide PhB(AdIm) 3 Fe-C≡N and iron(IV) nitride PhB(AdIm) 3 Fe≡N complexes being the major products of the reaction. The same products are obtained when the iron(I) complex is photolyzed or treated with a fluoride source. The trimethylsilyldiazomethane-derived ligand disassembly reactions are contrasted with those observed for related tris(carbene)amine complexes.