Alkyl-GeMe3 : Neutral Metalloid Radical Precursors upon Visible-Light Photocatalysis

Abstract

Single-electron transfer (SET) oxidation of ionic hypervalent complexes, in particular alkyltrifluoroborates (Alkyl-BF₃ ^- ) and alkylbis(catecholato)silicates (Alkyl-Si(cat)₂ ^- ), have contributed substantially to alkyl radical generation compared to alkali or alkaline earth organometallics because of their excellent activity-stability balance. Herein, another proposal is reported by using neutral metalloid compounds, Alkyl-GeMe₃ , as radical precursors. Alkyl-GeMe₃ shows comparable activity to that of Alkyl-BF₃ ^- and Alkyl-Si(cat)₂ ^- in radical addition reactions. Moreover, Alkyl-GeMe₃ is the first successful group 14 tetraalkyl nucleophile in nickel-catalyzed cross-coupling. Meanwhile, the neutral nature of these organogermanes offset the limitation of ionic precursors in purification and derivatization. A preliminary mechanism study suggests that an alkyl radical is generated from a tetraalkylgermane radical cation with the assistance of a nucleophile, which may also result in the development of more non-ionic alkyl radical precursors with a metalloid center.

Keywords: Cross-Coupling; Germanium; Photoredox; Radicals.