Organogermanium compounds : XII. The stereochemistry of the reactions between optically active ethyl(1-naphthyl)phenylgermyllithium and alkyl halides

The interaction of optically active ethyl(1-naphthyl)phenylgermyllithium, R′₃-Ge*Li, with alkyl halides, RX, to give optically active R′₃Ge*R compounds, occurs with predominant retention of configuration at germanium in the case of MeBr, i-PrCl, i-PrBr, n-BuCl, n-BuBr, t-BuCl, t-BuBr, CH₂CHCH₂Cl, CH₂CHCH₂Br and PhCH₂Cl, but with predominant inversion in the case of MeI, i-PrI, CH₂CHCH₂I, PhCH₂I, and PhCH₂Br. It is suggested that the retention reactions involve direct coupling between R′₃Ge*Li and RX, in a four-centre process, while the inversion reactions involve halogen—lithium exchange, to give R′₃GeX and RLi, also in a four-centre retentive process, followed by coupling between R′₃GeX and RLi in an invertive process.