syn-Permethylpentalene Iron and Cobalt Carbonyl Complexes: Proximity Bimetallics Lacking Metal−Metal Bonding

Reaction of 1,3,4,5,6-pentamethyl-2-methylene-1,2-dihydropentalene (Pn*‘) with Fe2(CO)9 or Co2(CO)8 led to the synthesis of Fe2(CO)5Pn* (1) and Co2(CO)4Pn* (2), respectively, in good yields. 1 and 2 have been structurally characterized by X-ray crystallography and are examples of syn-facial 34-electron dinuclear permethylpentalene complexes; 1 contains a μ-CO moiety with an unusual orientation, and NMR data indicate rapid terminal-bridging CO exchange. Theoretical investigations support the structures found in the solid state and also suggest an absence of metal−metal bonding in these compounds, despite the proximity of the metal centers.