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-(Pr2C6H3)-Pr-i)N=C(3,5-(Bu2C6H2)-Bu-t)OH] in toluene at -30 degrees C to 25 degrees C cleanly affords the corresponding achiral (imino)phenoxy-tribenzyl complexes, [(2,6-(Pr2C6H3)-Pr-i)N=C(3,5-(Bu2C6H2)-Bu-t)OH] Zr-( Bn)(3) (1)and [(2,6-(Pr2C6H3)-Pr-i)N=C(3,5-(Bu2C6H2)-Bu-t)OH] Ti(Bn)(3) (2). A chiral dibenzyl complex 3 incorporating the unsymmetric, tetradentate amino(imino)bis(phenoxy)ligand, [(2,6-Br2C6H2(O)(6-CH2(NC5H9))-Ch(2)N=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)center dot THF in CD2Cl2 at room temperature (RT)affords clean, quantitative formation of the corresponding zirconium cation [(2,6-(Pr2C6H3)-Pr-i)N=C(3,5-(Bu2C6H2)-Bu-t)O)Ti(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-(Pr2C6H3)-Pr-i)N=C(3,5-(Bu2C6H2)-Bu-t)OH]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 a-methylene-.-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.