Synthesis, structural characterization, and reactivity of homocatenated Ga₄ complexes with unsaturated Ga–Ga=Ga–Ga chains

The homocatenation of electron-deficient Group 13 metals to form metal-metal multiple bonds through covalent self-assembly remains extremely challenging. Herein we demonstrate the synthesis and characterizations of N-heterocyclic carbene (NHC)-stabilized digallyl digallenes (1a and 1b), which exhibit unsaturated Ga-Ga=Ga-Ga chains with trans-bent geometries. These compounds were synthesized through salt-metathesis reactions using Cp*Ga, (L¹)K₂/(L²)Li₂, and 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (IiPr). Employing both experimental and computational techniques, our investigation reveals that the chain elongation of 1a was initiated by the in-situ generation of a gallium(I) carbene analog [(L¹)GaK]. Additionally, the reactivity of compound 1a with I₂, PhS-SPh, Ph₃P = S, and Ph₂C = O was explored, leading to the formation of tetra-gallium subhalides (4), disulfide addition product (5), a gallium thiirane analog (6), and a [2 + 2] cycloaddition product (7), respectively.