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-acceptor capacity of germylene and NHC ligands. Our bonding analyses further indicated that the homoleptic complex 3 exhibits marvellous 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.