Homocatenated Ga4 Complexes with Unsaturated Ga-Ga=Ga-Ga Chains: Synthesis, Structural Characterization, and Diverse Reactivity

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 linear unsaturated Ga-Ga = Ga-Ga chains with trans -bent geometries. These compounds were synthesized through salt-metathesis reactions using Cp*Ga, (L ¹ )K ₂ /(L ² )Li ₂ , and 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (I i Pr). 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 analogue [(L ¹ )GaK]. Additionally, the reactivity of compound 1a with I ₂ , PhS-SPh, Ph ₃ P = S, and Ph ₂ C = O was explored, leading to the formation of tetra-gallium subhalides ( 4 ), disulfide addition product ( 5 ), an unprecedented gallium thiirane analogue ( 6 ), and a [2 + 2] cycloaddition product ( 7 ), respectively.