Vanadium(iii) phenoxyimine complexes for ethylene or ε-caprolactone polymerization: mononuclear versus binuclear pre-catalysts

Abstract

The mononuclear {[C₆H₄NCH(ArO)]₂VCl(THF)} (Ar = 2,4-t-Bu₂C₆H₂ (1), Ar = C₆H₄ (2)), {O[C₆H₄NCH(ArO)]₂}VCl(THF) (Ar = 2,4-t-Bu₂C₆H₂ (3), Ar = C₆H₄ (4)) and the binuclear vanadium(III) complexes {[C₆H₄NCH(ArO)]VCl₂(THF)₂}₂(μ-CH₂CH₂) (Ar = 2,4-t-Bu₂C₆H₂ (5), Ar = C₆H₄ (6)), have been synthesized and fully characterized. The compounds [C₆H₅NCH(ArO)]VCl₂(THF)₂ (Ar = 2,4-t-Bu₂C₆H₂ (7), Ar = C₆H₄ (8)), [2,4,6-Me₃–C₆H₂NCH(ArO)]VCl₂ (Ar = 2,4-t-Bu₂C₆H₂ (9), Ar = C₆H₄ (10)) and [2,6-i-Pr₂-C₆H₃NCH(ArO)]VCl₂(THF)₂ (Ar = 2,4-t-Bu₂C₆H₂ (11), Ar = C₆H₄ (12)), {μ-CH₂CH₂[NCH(C₆H₄O)]₂VCl(THF)} (14) and {C₆H₄[NCH(C₆H₄O)]₂VCl(THF)} (15) were synthesized for comparative polymerization studies. The dizwitterionic compound [2,6-i-Pr₂-C₆H₃N⁺(H)CH(C₆H₄O)]₂VCl₂O (13) was also isolated, and presumably formed via a fortuitous hydrolysis reaction. The complexes 2, 5 and 13 have been structurally characterized; the molecular structure of the parent ligand (L5) in 5 is also reported. All complexes have been screened for ethylene as well as ε-caprolactone polymerization, and results are compared against those for known related mono- and bi-nuclear counterparts to evaluate for possible cooperative effects. The compounds 10 and 12 have been supported on modified SiO₂, analysed by XPS and subjected to homo-polymerization (ethylene) and co-polymerization (1-hexene and ethylene) studies.