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

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.