(Arylimido)niobium(V)–Alkylidenes as the Catalysts for Ring-Opening Metathesis Polymerization (ROMP) of Cyclic Olefins: Z-Specific ROMP of Cyclooctene by Nb(CHSiMe3)(NC6H5)[OC(CF3)3](PMe3)2

Abstract

(Arylimido)niobium(V)–alkylidene complexes, Nb(CHSiMe3)(NAr)[OC(CF3)3](PMe3)2 (Ar = C6H5 (4), 2,6-F2C6H3, C6F5 (6)), Nb(CHSiMe3)(N-2,6-Cl2C6H3)(OC6F5)(PMe3)2 (7), and Nb(CHSiMe3)(N-2,6-F2C6H3)(OC6Cl5)(PMe3)2, have been prepared and identified. The pentafluorophenylimido analogue 6 and 7 showed superior catalytic activities for the ring-opening metathesis polymerization (ROMP) of norbornene (TOF = 56.1, 53.7 s–1, respectively, at 25 °C) and the activities increased at 50 °C (TOF ≥ 352 s–1). The prepared alkylidenes catalyzed the ROMP of cis-cyclooctene (COE), and the activity increased at high temperature (up to 80 °C). The Z-specific ROMP of COE has been demonstrated especially by the phenylimido analogue 4 at 80 °C, affording polymers possessing olefinic double bonds with exclusive cis selectivity (99%).