Binuclear cobalt carbonyl complexes of the strong π-acceptor trifluoromethyl isocyanide

• The species (CF3NC)2Co2(CO)n (n = 7, 6, 5, 4) have been studied by density functional theory.
• Bridging CF3NC groups are energetically preferred over bridging CO groups.
• Four-electron donor bridging η2-μ-CF3NC groups are found in higher energy (CF3NC)2Co2(CO)n (n = 5, 4) structures.
• Coupling of two CF3NC groups to form a CF3NCCNCF3 ligand occurs in the (CF3NC)2Co2(CO)7 system.

The cobalt carbonyl complexes (CF3NC)2Co2(CO)n (n = 7, 6, 5, 4) and (CF3NC)Co(CO)n(n = 4, 3, 2) of the strongly π-accepting trifluoromethyl isocyanide ligand have been investigated by density functional theory. The lowest energy (CF3NC)2Co2(CO)6 structures are doubly bridged structures with the global minimum having two bridging CF3NC ligands. The lowest energy unbridged (CF3NC)2Co2(CO)6 structure lies ∼19 kcal/mol in energy above this global minimum. This differs from unsubstituted Co2(CO)8 for which the doubly bridged and unbridged isomers have similar energies so both can be observed experimentally. The lowest energy structures of the formally unsaturated (CF3NC)2Co2(CO)n (n = 5, 4) derivatives are also doubly bridged structures. Bridging CF3NC groups are energetically preferred over bridging CO groups. Four-electron donor bridging η2-μ-CF3NC groups are found in higher energy structures. Coupling of CF3NC groups to form a coordinated bis(trifluoromethyldiimine) ligand, CF3NCCNCF3 is observed in carbonyl-rich (CF3NC)2Co2(CO)7 structures. However, such (CF3NC)2Co2(CO)7 structures do not appear to be viable since CO dissociation from the lowest energy such structure to give (CF3NC)2Co2(CO)6 is predicted to be essentially thermoneutral.

The lowest energy (CF3NC)2Co2(CO)6 structures are doubly bridged structures with the global minimum having two bridging CF3NC ligands. The lowest energy structures of the formally unsaturated (CF3NC)2Co2(CO)n (n = 5, 4) derivatives are also doubly bridged structures with bridging CF3NC groups being energetically preferred over bridging CO groups. Four-electron donor bridging η2-μ-CF3NC groups are found in higher energy structures.Figure optionsDownload as PowerPoint slide