Norbornadiene complexes of molybdenum(II) and their transformation to a catalyst for ring-opening metathesis polymerization: DFT calculations – X-ray crystal structure of a new norbornadiene complex [MoCl(GeCl3)(CO)3(η4-nbd)]

Photolysis of [Mo(CO)4(η4-nbd)] (nbd = norbornadiene) in n-heptane solution containing GeCl4 leads to the formation of a seven-coordinate compound with a direct Mo–Ge bond, [MoCl(GeCl3)(CO)3(η4-nbd)] (1). The molecular structure of compound 1 has been established by single-crystal X-ray diffraction studies. Similarly to the previously investigated heterobimetallic complexes of molybdenum(II), [MoCl(SnCl3)(CO)3(η4-nbd)] (2) and [MoCl(SnCl3)(CO)2(NCMe)(η4-nbd)] (3), the molybdenum–germanium compound 1 initiates the ring-opening metathesis polymerization (ROMP) of nbd. Density functional theory calculations at the B3LYP level have been performed to understand the mechanism of the rearrangement of the η4-nbd ligand to the species initiating the ROMP reaction in the coordination sphere of the molybdenum(II) complexes 2 and 3, which together with complex 1 are representative examples of experimental complexes in which such a transformation takes place.