Metal carbonyl anions readily react with imidoyl halides through nucleophilic displacement of the halide atom to produce complexes containing η1-iminoacyl ligands. However, weakly nucleophilic anions, such as tetracarbonylcobaltate, induce a head-to-tail coupling reaction of two imidoyl groupings via the incorporation of two anions. This has been established by an X-ray crystallographic analysis of the compound CO2(CO)5(P(CH3)2C6H5)[(C6H5)CN(C6H5)]2. The bis-imidoyl ligand chelates one cobalt atom while one of the carbon atoms bridges the two mutually bonded cobalt atoms. Photolytic decarbonylation of the complexes containing η1-iminoacyl ligands may proceed by either of three processes. When the substituent on the nitrogen atom is an alkyl group, either a migration with formation of an isocyanide ligand or formation of an η2-iminoacyl ligand can occur. When the substituent is an aryl group, ortho-metallation of the N-aryl ring occurs. This has been demonstrated by an X-ray crystallographic analysis of the compound (C5H5)Fe-(CO)[C(C6H5)N(H)p-CH3C6H3)] which contains a phenyl-N-p-tolylaminocarbene ligand in which the p-tolyl ring is bonded to the iron atom in an ortho position. © 1979, All rights reserved.