Synthesis and Photochemical Properties of Re(I) Tricarbonyl Complexes Bound to Thione and Thiazol-2-ylidene Ligands

Three Re(I) tricarbonyl complexes, with the general formulation Re(N^L)(CO)3X (where N^L is a bidentate ligand containing a pyridine functionalized at position 2 with a thione or a thiazol-2-ylidene group and X is either chloro or bromo), were synthesized and their reactivities explored in terms of solvent-dependent ligand substitution, in both the ground and excited states. When they were dissolved in acetonitrile, the complexes bound to the thione ligand underwent reversible ligand exchange with the solvent, resulting in the formation of Re(NCMe)2(CO)3X; the starting complex could be re-formed by precipitation following addition of diethyl ether. On the other hand, the complexes appeared to be inert in dichloromethane or acetone. Conversely, the complex bound to the thiazol-2-ylidene ligand did not display any ligand exchange reaction in the dark but underwent photoactivated ligand substitution on excitation to its lowest metal to ligand charge transfer manifold. Photolysis of this complex in acetonitrile generated multiple products, including Re(I) tricarbonyl and dicarbonyl solvato complexes as well as free thiazol-2-ylidene ligand.