New Pre-Catalysts for Olefin Polymerisation and Ring-Opening Polymerisation of Lactides/Lactones
A number of pre-catalysts featuring phenoxyimine, phenolate and calixarene ligand systems have been synthesized, characterised and screened for their ability to polymerize α-olefins or ring open polymerize (ROP) cyclic esters. The treatment of a number of related phenoxyimine ligands (L1H – L3H, L6H – L14H) and bridged phenoxyimines (L4H2 and L5H2) with vanadium trichloride (VCl3), vanadium oxytrichloride (VOCl3) or vanadium oxytripropoxide (VO(OnPr)3) afforded the compounds 1 – 20. Compounds 21, 22 and 23 were isolated from the reaction between VO(OnPr)3 and diphenolate ligand (L15H2) or bridged diphenolates (L16H4 or L17H4) respectively. Treatment of the alkali vanadium compound (LiVO(OtBu)4) with tert-butylcalix[6]arene (L18H6) afforded compound 24, while on a number of syntheses, the minor 1D polymeric compound 25 was also obtained. Whilst the reaction between tert-butylcalix[8]arene (L19H8) and NaVO(OtBu)4 led to the formation of compound 26, the use of the alkali free VO(OtBu)3 resulted in the formation of two solvates of compound 27. Imidazole (L20H), oxazole (L21H), α-diimine (L22), iminopyridine (L23, L24) and phenoxyimine (L25H – L29H) ligand sets have been treated with group 5 (Nb or Ta) chlorides or oxytrichlorides to afford compounds 28 – 50, which have been fully characterised. The screening of group 5 compounds 1 – 50 for the polymerisation of α-olefins revealed high activity, significantly in the case of the niobium precatalysts which were two orders of magnitude above the previously reported compounds. The reactions between 1,3-dipropoxy-p-tert-butyl-calix[4]arene (L30H2), hexahomotrioxacalix[3]arene (L31H3) or tripropoxy-p-tert-butylcalix[4]arene (L32H) with zinc or magnesium alkyls has been explored, resulting in the isolation of compounds 51 – 58, which includes a number of heterobimetallic compounds. While all of the zinc and magnesium compounds screened were found to be active for the ring opening polymerisation of either ε-caprolactone or rac-lactide, compound 58, featuring a tripropoxy-p-tert-butylcalix[4]arene (L32H) ligand with a magnesium n-butyl group was found to exhibit exceptional activity and immortal character.
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