Mechanistic Dichotomy of Magnesium- and Zinc-Based Germanium Nucleophiles in the C(sp3 )-Ge Cross-Coupling with Alkyl Electrophiles.

Robust procedures for two mechanistically distinct C(sp3 )-Ge bond formations from alkyl electrophiles and germanium nucleophiles are reported. The germanium reagents were made available as bench-stable solutions by lithium-to-magnesium and lithium-to-zinc transmetalation, respectively. The germanium Grignard reagent reacts with various primary and secondary alkyl electrophiles by an ionic nucleophilic displacement. Conversely, the coupling of the corresponding zinc reagent requires a nickel catalyst, which then engages in radical bond formations with primary, secondary, and even tertiary alkyl bromides. Both methods avoid the regioselectivity issue of alkene hydrogermylation and enable the synthesis of a wide range of functionalized alkyl-substituted germanes.