Theoretical study on the structure and electronic properties of mono- and bimetallic methylzinc complexes containing bidentate ligands

The reactions of 1 and 2 equiv of dimethylzinc with 10 different model liga nds, each containing two heteroatoms, were investigated at the HF and B3LYP level of theory. As the heteroatom combination is varied, the stability of the A.ZnMe (formed from acidic ligands) and B.ZnMe2 (formed from nonacidic ligands) species will decrease as follows: A-type ligands, NS > SS > NO > NN > OO; B-type ligands, NN > NO > NS > OO > SS. Formation of the A.ZnMe co mplex is exothermic by ca. -20 kcal/mol when the ligand contains N and/or O and ca. -30 kcal/mol when S is present, DeltaE(f) is a magnitude of order larger (-2 to -9 kcal/mol) for the formation of B.ZnMe2 complexes. Only mon ometallic A.ZnMe species are capable of complexing with a second equivalent of dimethylzinc to form a bimetallic A.Zn2Me3 species. NBO analyses provid e no indication for a bonding Zn-Zn interaction. The 3d orbitals on zinc ar e not involved in bonding or hyperconjugative interactions in either the mo no- or the bimetallic organozinc species. Zinc-carbon and zinc-ligand bonds to O, N, and S have a nearly pure s character at zinc.