From stable Sb- and Bi-centered radicals to a compound with a Ga=Sb double bond

Abstract

Neutral stibinyl and bismuthinyl radicals are typically short-lived, reactive species. Here we show the synthesis and solid-state structures of two stable stibinyl [L(Cl)Ga]2Sb· 1 and bismuthinyl radicals [L(I)Ga]2Bi· 4, which are stabilized by electropositive metal centers. Their description as predominantly metal-centered radicals is consistent with the results of NMR, EPR, SQUID, and DFT studies. The Lewis-acidic character of the Ga ligands allow for significant electron delocalization of the Sb- and Bi- unpaired radical onto the ligand. Single-electron reduction of [L(Cl)Ga]2Sb· gave LGaSbGa(Cl)L 5, the first compound containing a Ga=Sb double bond. The π-bonding contribution is estimated to 9.56 kcal mol-1 by NMR spectroscopy. The bonding situation and electronic structure is analyzed by quantum mechanical computations, revealing significant π backdonation from the Sb to the Ga atom. The formation of 5 illustrates the high-synthetic potential of 1 for the formation of new compounds with unusual electronic structures.