Sterically (un)encumbered mer-tridentate N-heterocyclic carbene complexes of titanium(iv) for the copolymerization of cyclohexene oxide with CO2

Abstract

Titanium(IV) complexes bearing an unsubstituted tridentate bis(phenolate) N-heterocyclic carbene (NHC) were synthesized and structurally identified. While sterically unencumbered NHC–Ti(IV) complexes bearing chloro and alkoxy co-ligands tend to dimerize in solution and in solid-state, the use of a bulky aryloxy as co-ligand favors the monomeric species. Upon activation by onium salts, all these complexes were found to be highly selective towards the copolymerization of cyclohexene oxide (CHO) with CO₂ under mild conditions (P_CO2 < 1 bar), albeit the sterically unencumbered NHC–Ti(IV) complexes are less stable and active than their structural analogues bearing bulkier substituents.