Add time:07/26/2019         Source:sciencedirect.com

The reaction of tetrafluoroethylene with Co2(CO)8 under mild conditions was reported to give (OC)4CoCF2CF2Co(CO)4. This compound readily undergoes decarbonylation with accompanying fluorine migration to give the trifluoromethylfluorocarbene complex (μ-CF3CF)Co2(CO)6(μ-CO) and eventually the cluster CF3CCo3(CO)9. In order to understand the chemistry of these cobalt carbonyl complexes obtained from tetrafluoroethylene, the structures and thermochemistry of the (C2F4)Co2(CO)n (n = 8, 7, 6, 5) systems have been investigated by density functional theory. The lowest energy (C2F4)Co2(CO)8 isomer is the experimentally observed (OC)4CoCF2CF2Co(CO)4, lying ∼6 kcal/mol in energy below the isomeric (CF3CF)[Co(CO)4]2. Loss of CO from (OC)4CoCF2CF2Co(CO)4 with accompanying fluorine migration to give (μ-CF3CF)Co2(CO)6(μ-CO) is essentially thermoneutral within ∼1 kcal/mol. The higher energy of ∼20 kcal/mol for the isomeric (μ-CF2CF2)Co2(CO)6(μ-CO) structure, where fluorine migration has not occurred, suggests a significant activation energy for this process. Further loss of CO from (μ-CF3CF)Co2(CO)6(μ-CO) gives low-energy (μ-CF3CF)Co2(CO)n(μ-CO) isomers (n = 5, 4) containing CoCo multiple bonds and/or vacant coordination sites. Such structures are possible intermediates to form CF3CCo3(CO)9 by reaction with excess Co2(CO)8 followed by Co(CO)nF elimination.

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