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(Arylimido)niobium(V)–Alkylidenes, Nb(CHSiMe3)(NAr)[OC(CF3)3](PMe3)2, That Enable to Proceed Living Metathesis Polymerization of Internal Alkynes

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journal contribution
posted on 16.06.2020, 21:30 by Itsuki Izawa, Kotohiro Nomura
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.