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 Fe-2(CO)(9) or CO2(CO)(8) led to the synthesis of Fe-2(CO)(5)Pn* (1) and CO2(CO)(4)Pn* (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; I contains mu-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.