Catalytic ethylene polymerisation in carbon dioxide as a reaction medium with soluble nickel(II) catalysts

A series of neutral Ni-II-salicylaldiminato complexes substituted with perfluorooctyl- and trifluoromethyl groups, [Ni{kappa(2)-N, O-6-C(H)=NAr-2,4R'2C6H2O}(Me)(pyridine)] (6a: Ar= 2,6-{4-(F17C8)C6H4}(2)C6H3, R' =I; 6b: Ar = 2,6-{4-(F3C)C6H4}(2)C6H3, R'= I; 6c: Ar = 2,6-{3,5-(F3C)(2)C6H3}(2)C6H3, R'=3,5-(F3C)(2)C6H3; 6d: Ar=2,6-{4-(F17C8)C6H4}(2)C6H3, R'= 3,5-(F3C)(2)C6H3; 6e: Ar=2,6-{3,5-(F3C)(2)C6H3}(2)-C6H3, R'=I) were studied as catalyst precursors for ethylene polymerisation in supercritical CO2. Catalyst precursors 6a and 6c, which are soluble in scCO(2), afford the highest polymer yields, corresponding to 2x 10(3) turnovers. Semicrystalline polyethylene (M-n typically 10(4) g mol(-1)) is obtained with variable degrees of branching (11 to 24 branches per 1000 carbon atoms, predominantly Me branches) and crystallinities (54 to 21%), depending on the substitution pattern of the catalyst.