화학공학소재연구정보센터
Inorganic Chemistry, Vol.59, No.5, 2621-2625, 2020
Why Diorganyl Zinc Lewis Acidity Dramatically Increases with Narrowing C-Zn-C Bond Angle
The Lewis acidity of a metal center is influenced not only by the electronic properties of the bonded ligands but also by the bond angles, which we suggest to be important for zinc diorganyls. Molecular orbital correlation predicts that a narrower C- Zn-C bond angle of the R2Zn fragment lowers its lowest unoccupied molecular orbital (LUMO) and increases its Lewis acidity, such that it binds added ligands more strongly. Computations on Me2Zn(bipy) (bipy = 2,2'-bipyridine) yield that, for every 10 degrees of C-Zn-C narrowing close to tetrahedral geometry, the Zn-N distance shortens by 0.027 angstrom (0.048 angstrom per 10 degrees for the range 180-90 degrees) and that the LUMO of the Me2Zn fragment drops by 0.24 eV. A total of 10 dialkyl zinc complexes of bipy or 4,4'-di-tert-butyl-2,2'-bipyridine are crystallographically characterized here. Structure correlations (published and new data) confirm the link between the C-Zn-C angle and Zn-N distance. Principal component analysis provides a detailed picture of the correlated distortions. Relevance for zinc fingers/zinc enzymes is discussed.