Six-Membered NHC Stabilized Monomeric Zinc Complexes

This paper describes the rare use of a 6-membered saturated N-heterocyclic carbene (NHC) known as 1,3-di(2,6-diisopropylphenyl) tetrahydropyrimidine-2-ylidene (abbreviated as 6-SIDipp) as a ligand in zinc chemistry. We report on the investigation of the reactions between 6-SIDipp and ZnX₂, which resulted in a range of new monomeric 6-SIDipp⋅ZnX₂ complexes (X=Et ( 1 ), Cl ( 2 ), Br ( 3 ), and I ( 4 )). We also prepared a new NHC zinc complex where the two substituents of the zinc atom are different, 6-SIDipp⋅Zn(Et)Br ( 7 ) through the reaction of the proligand 6-SIDippH]Br with ZnEt₂. We have observed that the reactions of complex 1 with sulfur and HBpin led to the removal of the ZnEt₂ moiety, resulting in the formation of a C=S double bond and a B−H activation product, respectively. Lastly, the reaction of 1 with five-membered NHCs led to the exchange of carbene and the formation of either 5-IDipp⋅ZnEt₂ ( 8 ) or 5-SIDipp⋅ZnEt₂ ( 9 ).