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

The cobalt carbonyl complexes (CF3NC)(2)Co-2(CO)(n) (n = 7, 6, 5, 4) and (CF3NC)Co(CO)(n) (n =4, 3, 2) of the strongly pi-accepting trifluoromethyl isocyanide ligand have been investigated by density functional theory. The lowest energy (CF3NC)(2)Co-2(CO)(6) structures are doubly bridged structures with the global minimum having two bridging CF3NC ligands. The lowest energy unbridged (CF3NC)(2)Co-2(CO)(6) structure lies similar to 19 kcal/mol in energy above this global minimum. This differs from unsubstituted Co-2(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)(2)Co-2(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 eta(2)-mu-CF3NC groups are found in higher energy structures. Coupling of CF3NC groups to form a coordinated bis(trifluoromethyldiimine) ligand, CF3N=C=C=NCF3 is observed in carbonyl-rich (CF3NC)(2)Co-2(CO)(2) structures. However, such (CF3NC)(2)Co-2(CO)(7) structures do not appear to be viable since CO dissociation from the lowest energy such structure to give (CF3NC)(2)Co-2(CO)(6) is predicted to be essentially thermoneutral. (C) 2013 Elsevier B.V. All rights reserved.