Binuclear Acetoniminato Derivatives of Iron and Chromium Carbonyls: A Theoretical Study

The structures and energetics of binuclear acetoniminato metal carbonyl derivatives of the types (Me2C═N)2Fe2(CO)n and (Me2C═N)2Cr2(CO)n have been investigated by density functional theory. The (Me2C═N)2Fe2(CO)6 structure, with bridging Me2C═N ligands using only their nitrogen atoms to bridge an Fe═Fe bond related to experimentally known species, as well as a related (Me2C═N)2Cr2(CO)8 structure, appear to be energetically preferred. Among carbonyl-richer systems, the iron system energetically prefers a {Me2C═NC(O)}2Fe2(CO)6 structure with bridging Me2C═NC(O) ligands, whereas the chromium system energetically prefers a structure with a 2,3-diazabutadiene ligand having each nitrogen atom bonded to a Cr(CO)5 moiety. Preferred structures for systems with fewer CO groups include the tetracarbonyl (Me2C═N)2Fe2(CO)4 in which one of the bridging Me2C═N uses its C═N double bond to bond to an iron atom, as well as (Me2C═N)2Cr2(CO)n (n = 7, 6) structures with chromium–chromium multiple bonds bridged by Me2C═N groups.