Cumulative 2c-2e vs 3c-2e π-Back Donations: Conformation Preferences in Germylene Gold(I) Complexes

Abstract

The first homoleptic and heteroleptic cationic germylene-gold(I) complexes 3, 4, and 7 have been synthesized and structurally characterized, accompanied by the discovery of novel types of π-back donations. These complexes exhibit distinct conformation preferences (vertical vs quasi-planar) modulated by the π-acidity of germylene and NHC ligands. Our bonding analyses further indicated that the homoleptic complex 3 exhibits marvelous cumulative two-center-two-electron (2c-2e) π-back donations, whereas the heteroleptic complexes 4 and 7 demonstrate extraordinary three-center-two-electron (3c-2e) π-back donations. These findings offer a comprehensive explanation for the atypical disruption of extensive π-systems, along with the transition from quasi-planar to vertical conformations.