Organogermanium compounds have been gaining more attention for their unique properties compared to silicon or tin. Among which, tetraalkylgermanes, especially alkyltrimethylgermanes that have been confirmed to be active in photoredox radical reactions, are still lack of efficient and simple synthesis methods. Herein, we report a new protocol using commercially available trimethylgermanium bromide and alkyl bromides as substrates and cheap copper(II) sulfate as catalyst. When using magnesium powder as the reductant, a series of alkyltrimethylgermanes could be generated in moderate to good yield. Mechanism studies suggested a probable in-situ Grignard reaction pathway. The copper salt added could significantly accelerate the reaction between organohalogermanes and Grignard reagents so that the formation of Ge-Ge byproduct from the reduction of organohalogermanes by magnesium could be inhibited. Compared to the traditional method using Grignard reagent and organohalogermanes, this new protocol has better compatibility towards functional groups like esters and amides. The protocol could also be expanded to the synthesis of various tetraalkylgermanes or germacycloalkanes using dichlorodimethylgermane and alkyl bromides. General procedure for the synthesis of alkyltrimethylgermane is: To an oven-dried 25 mL screw-capped tube equipped with a stir bar was charge with 48 mg (2 mmol) magnesium powder and 8.0 mg (0.05 mmol) CuSO₄. The tube was vacuumed and backfilled with argon for three cycles. 6 mL freshly distilled THF was added followed by the addition of 128 μL (1 mmol) trimethylgermanium bromide and 1.5 mmol alkyl bromide. The mixture was sealed with a Teflon stopper, warmed to 60 ℃ and stirred for 10 h. After cooled to room temperature, the resulted mixture was quenched with saturated NH₄Cl solution, extracted with diethyl ether and washed with brine. Combined organic layer was dried over Na₂SO₄ and concentrated under reduced pressure. The residue was purified by flash column chromatography on silica gel or distillation to give the desired alkyltrimethylgermane.

Key words: organogermanium, tetraalkylgermane, in-situ Grignard reagent, copper catalysis, cross-coupling