Six‐Membered NHC Stabilized Monomeric Zinc Complexes

The use of 6-SIDipp is shown to stabilize various monomeric zinc adducts without the use of any solvent. Unsymmetrical zinc adduct (ZnEtBr) is also realized. The treatment of 6-SIDipp→ZnEt₂ with five membered NHC led to unprecedented base exchange to give 5-SIDipp→ZnEt₂ and 5-SIDipp→ZnEt₂.

Abstract

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).

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