(Arylimido)niobium(V)–Alkylidenes, Nb(CHSiMe<sub>3</sub>)(NAr)[OC(CF<sub>3</sub>)<sub>3</sub>](PMe<sub>3</sub>)<sub>2</sub>, That Enable to Proceed Living Metathesis Polymerization of Internal Alkynes
Itsuki Izawa, Kotohiro Nomura
Abstract
Living polymerizations of internal alkynes (2-hexyne, 3-hexyne, 4-methyl-2-pentyne, and 1-phenyl-1-propyne) have been demonstrated at 50 °C by (arylimido)niobium(V)–alkylidene complex catalysts, Nb(CHSiMe3)(NAr)[OC(CF3)3](PMe3)2 [Ar = 2,6-Me2C6H3 (4a), 2-MeC6H4 (4c), and 2,6-Cl2C6H3 (4d)], in the presence of PMe3, which plays an essential role to proceed the living polymerization without certain catalyst deactivation. The living nature of 4a was preserved even at 80 °C in the 2-hexyne polymerization under optimized conditions, and 4c and 4d showed higher activity than 4a. The living polymerizations of 4-methyl-2-pentyne by 4c,d and of 3-hexyne by 4c have also been achieved in the presence of PMe3 at 50 °C, and the effect of the internal alkynes toward the activity by 4c is in the order 2-hexyne > 4-methy-2-pentyne > 3-hexyne > 4-octyne ≫ 5-decyne (negligible). The living polymerization of 1-phenyl-1-propyne has also been demonstrated by 4d (at 25 and 50 °C) in the presence of PMe3.