The Electronic Ground State of [Fe(CO)3(NO)]−: A Spectroscopic and Theoretical Study

During the past 10 years iron-catalyzed reactions have become established in the field of organic synthesis. For example, the complex anion [Fe(CO) 3(NO)]-, which was originally described by Hogsed and Hieber, shows catalytic activity in various organic reactions. This anion is commonly regarded as being isoelectronic with [Fe(CO)4]2-, which, however, shows poor catalytic activity. The spectroscopic and quantum chemical investigations presented herein reveal that the complex ferrate [Fe(CO)3(NO)]- cannot be regarded as a Fe-II species, but rather is predominantly a Fe0 species, in which the metal is covalently bonded to NO- by two π-bonds. A metal-N σ-bond is not observed. Even more complex: Spectroscopic and quantum chemical investigations show that the complex ferrate [Fe(CO) 3(NO)]- cannot be considered to be a Fe-II species, but rather is predominantly an Fe0 species, in which the metal is covalent bound to NO- by two π bonds. A metal=N σ bond is not observed.