Preference for trihapto/monohapto over bis(dihapto) metal–ligand bonding in binuclear hexafluorocyclopentadiene cobalt carbonyls

The reaction of hexafluorocyclopentadiene with Co2(CO)8 is reported to lead to the structurally characterized trihapto/monohapto ligand complex (η3,η1-C5F6)Co2(CO)7. The structures and thermochemistry of the related (C5F6)Co2(CO)n systems with n from 8 to 4 have been investigated using density functional theory. For the octacarbonyl (C5F6)Co2(CO)8 all three low-energy structures have the hexafluorocyclopentadiene ligand bonded to two Co(CO)4 units as monohapto ligands leaving an uncomplexed CC double bond. The local environments of the cobalt atoms in these species are similar to the very stable perfluoro alkylcobalt tetracarbonyls such as (CF3)Co(CO)4. The lowest energy (C5F6)Co2(CO)n (n = 7, 6, 5, 4) structures all have the hexafluorocyclopentadiene ligand bonded to one cobalt atom as a trihapto ligand and to the other cobalt atom as a monohapto ligand. Cobalt–cobalt bonds are found in the unsaturated (C5F6)Co2(CO)n (n = 6, 5, 4) systems. The thermochemistry of the (C5F6)Co2(CO)n systems is consistent with the heptacarbonyl (C5F6)Co2(CO)7 being the experimentally observed product from the reaction of hexafluorocyclopentadiene with Co2(CO)8. However, the octacarbonyl (C5F6)Co2(CO)8 might be viable under sufficiently mild conditions or in the presence of CO to inhibit decarbonylation.