Group 4 bis(chelate) metal complexes of monoanionic bidentate [E,O−] ligands (E = O, S): synthesis and application as α-olefinpolymerizationcatalysts

Abstract

Monoanionic bidentate phenoxy–ether [O⁻,O] and phenoxy–thioether [O⁻,S] ligands were synthesized and used to prepare octahedral group 4 metal complexes with general formula [O⁻,E]₂ML₂ (complex 1: E = S, M = Hf, L = Bn; complex 2: E = O, M = Ti, L = NMe₂; complex 3: E = S, M = Ti, L = NMe₂; complex 4: E = S, M = Ti, L = Cl). Variable-temperature ¹H NMR studies were performed on all the complexes 1–4 in the range of +20 to −70 °C. For the hafnium complex 1 a dynamic interchange of the Δ and Λ enantiomers for a C₂-symmetric isomer was revealed. Eyring analysis indicated that rearrangement of the ligands occurs via a non-dissociative mechanism. In the range of the explored temperatures, a broadening of the signals was observed for complexes 2–3. Finally, a reversible fluxional process between several isomers was revealed for complex 4. Complexes 1–4 were tested as pre-catalysts for ethylene and propene polymerization in combination with different activators and under variable conditions. Complex 1 was found to be inactive whereas complexes 2–4 showed moderate activities in the polymerization of ethylene and propene. A mixture of polymers with different microstructure was obtained in all cases, coherently with the fluxional behaviour of the pre-catalysts observed in solution.