Hydrogermylation initiated by trialkylborohydrides: a living anionic mechanism

Sodium trialkylborohydrides were found to be initiators of selective hydrogermylation of aromatic alkenes. Addition of phenylgermane and diphenylgermane in the presence of 10 mol% of NaHB(-Bu) proceeded in a highly selective manner to give - in contrast to the analogous hydrosilylation process - β-germylated products. The nature of this process was explained with the aid of DFT calculations and it was proposed that the mechanism proceeds a trisubstituted germanide anion whose attack on the terminal vinyl carbon is the source of selectivity.