Crystalline Silagermenides: Unraveling π-Bonding and Lone Pair Effects in the Multiple Bonds of Heavier Vinyl Anion Analogs

Compared to vinyl anions, their heavier heteronuclear analogs silagermenides in the form of [R ₂ Si═GeR]ˉ remain exceedingly rare. Herein, we present a systematic investigation of silagermenides, synthesized via a straightforward desilylation route. We delve into the bonding characteristics, revealing a weak, polarized Si–Ge π bond with a significant nonbonded lone pair character at the β-Si position. This β-Si exhibits predominantly nucleophilic behavior, while the α-Ge position demonstrates subtly electrophilic tendencies, despite the presence of a vinylic, formally anionic Ge atom. This behavior leads to the formation of silagermenide complexes in an unprecedented η ² coordination mode, as well as various silagermenes and a germylene with unconventional substituents. Cleavage of the Si═Ge double bond was also revealed. Our findings expand the understanding of heavier vinyl anion analogs, with important implications for their synthesis and reactivity.