N-heterocyclic carbene complexes of Zn(II): synthesis, X-ray structures and reactivity

The synthesis of six novel zinc (II) mono(N-heterocyclic carbene) complexes is described. 1,3-Bis(mesityl)-imidazol-2-ylidene was reacted with the zinc salts ZnX2 (X=Cl, CH3COO, PhCOO, and PhCH2COO) to yield the corresponding monomeric Zn–NHC complex ZnCl2(NHC)(THF) (1) and dimeric [Zn(OOCCH3)2(NHC)]2 (2), [Zn(OOCPh)2(NHC)]2 (3), [Zn(OOCCH2Ph)2(NHC)]2 (4) (NHC=1,3-bis(mesityl)-imidazol-2-ylidene). Reaction of 1 with 2 equivalents of silver trifluoromethanesulfonate yielded monomeric Zn(O3SCF3)2(NHC)(THF) (5), reaction of 1 with sodium {[R(+)-α-2-(1-phenyl-ethylimino)-methyl]-phenolate} yielded monomeric ZnCl(OC6H4-2-CHN(CHPhCH3)(NHC) (6). Compounds 1, 4–6 were structurally characterized by X-ray analysis. Selected compounds were investigated for their activity in the copolymerization of carbon dioxide with cyclohexene oxide as well as in the ring-opening polymerization of cyclohexene oxide and ε-caprolactone.