Synthesis, structure and oxidation of new ytterbium( ii ) bis(phenolate) compounds and their catalytic activity towards ε-caprolactone

Two ytterbium(II) bis(phenolate) complexes, [LRYb] where R=NMe2 and OMe have been synthesized and characterized, with being structurally defined to be a dimeric species with an unsymmetrical coordination of the bis(phenolate) ligand which is preserved in solution. Both and have been oxidized by a variety of oxidants (AgX, ROH) to form heteroleptic ytterbium(III) bis(phenolate) complexes: [(LNMe2)YbPF6], [(LNMe2)YbOSO2CF3(thf)], [(LNMe2)YbOBut], [(LNMe2)YbOPh], [(LOMe)YbOPh]. Compound has been structurally characterized as having a quasi-octahedral environment around ytterbium, with significant inter species hydrogen bonding between CHx and triflate fluorine atoms. Ligand exchange between Yb(N(SiMe3)2)3(thf)2 and H2LR yielded [(LNMe2)YbN(SiMe3)2] and [(LOMe)YbN(SiMe3)2], while metathesis from YbI2(thf)2 and K2LOMe reproducibly afforded the surprising oxidized product [(LOMe)2YbK(dme)2], which was structurally characterized as having a distorted octahedral environment around the ytterbium(III) centre. Compounds were used to polymerize epsilon-caprolactone at room temperature in toluene, with only compounds and exhibiting significant catalytic activities. The polycaprolactone formed in these reactions was generally of high molecular weight and polydispersities<1.90 in all but one case.