Chiral and achiral (imino)phenoxy-based cationic group 4 non-metallocene complexes as catalysts for polymerization of renewable α-methylene-γ-butyrolactones.

Protonolysis of M(Bn)4 (M = Zr, Ti; Bn = benzyl) with equimolar 2,4-di-tert-butyl-6-[(2,6-diisopropylphenylimino)methyl]phenol [(2,6-(i)Pr2C6H3)N=C(3,5-(t)Bu2C6H2)OH] in toluene at -30 °C to 25 °C cleanly affords the corresponding achiral (imino)phenoxy-tribenzyl complexes, [(2,6-(i)Pr2C6H3)N=C(3,5-(t)Bu2C6H2)O]Zr(Bn)3 (1) and [(2,6-(i)Pr2C6H3)N=C(3,5-(t)Bu2C6H2)O]Ti(Bn)3 (2). A chiral dibenzyl complex 3 incorporating the unsymmetric, tetradentate amino(imino)bis(phenoxy) ligand, [2,4-Br2C6H2(O)(6-CH2(NC5H9))CH2N=CH(2-adamantyl-4-MeC6H2O)]Zr(Bn)2 (3), has also been prepared using the same protonolysis protocol. Abstractive activation of 1 with B(C6F5)3·THF in CD2Cl2 at room temperature (RT) affords clean, quantitative formation of the corresponding zirconium cation ((2,6-(i)Pr2C6H3)N=C(3,5-(t)Bu2C6H2)O)Zr(Bn)2(THF)BnB(C6F5)3 (4). Likewise, benzyl abstraction of 2 with B(C6F5)3·THF in CD2Cl2 at RT generates the cationic titanium complex ((2,6-(i)Pr2C6H3)N=C(3,5-(t)Bu2C6H2)O)Ti(Bn)2(THF)BnB(C6F5)3 (5), accompanied by a small amount of decomposed species as a result of C6F5 transfer. The dibenzyl cations 4 and 5 have been characterized spectroscopically, and their structures have been confirmed by single crystal X-ray diffraction analysis. Characteristics of the coordination polymerization of renewable α-methylene-γ-butyrolactone monomers by the cationic catalysts derived from achiral complexes 1 and 2 as well as chiral complex 3 have been investigated, representing the first study of such polymerization by non-metallocene catalysts.