Synthesis and reactivity of copper(I) complexes with an ethylene-bridged bis(imidazolin-2-imine) ligand

A series of copper(I) complexes with a sterically hindered, bidentate ligand, BLiPr, derived from an N-heterocyclic carbene precursor have been isolated, characterized and their reactivity studied. The ethylene-bridged bis(imidazolin-2-imine) ligand (BLiPr) provides strongly donating N-donor atoms for the stabilization of a copper(I) metal center, priming it for reactivity. The complexes [(BLiPr)Cu(XyNC)]PF6 (4) and [(BLiPr)CuCl] (5) were characterized by X-ray crystallography and exhibit trigonal coordination at the copper centers. The reactivity of [(BLiPr)Cu] SbF6 toward dioxygen was studied at low temperature, indicating formation of a thermally sensitive intermediate with intense UV/Vis features and an isotope-sensitive vibration at 625 cm(-1) (599 cm(-1) with O-18(2)). The intermediate is assigned as containing the bis(mu-oxo) dicopper(III) core, [2](PF6)(2), and the related, stable hydroxo form was crystallized as [{(BLiPr)Cu}(2)(mu-OH)(2)](PF6)(2), [3](PF6)(2). The reactivity of 5 as a catalyst for the ATR polymerization of styrene was assessed in terms of reaction kinetics and polymer properties, with low PDI values achieved for polymers with molecular weights up to 30000 g mol(-1).