The effect of substituents on the structure and reactivity of organogermanium anions

The replacement of the ethyl group in Et₃GeH by a phenyl group was shown by equilibrium metallation to halve the pK_a value compared with analogous CH acids. NMR showed that the decreased acceptor effect of the phenyl group in the PhEt₂Ge^- anion is caused by a considerably reduced contribution of the mesomeric effect to anion stabilization compared with what happens in the corresponding carbanions. At the same time, the stabilization of the organogermanium anion increases the role of π-polarization of the aromatic substituent and this contribution is comparable with the mesomeric effect value. A stabilizing effect of organosilicon and organogermanium substituents due to a high degree of polarizability has been shown by concurrent methanolysis of Et₃GeLi and REt₂GeLi (R = Me₃Si, Et₃Si, Me₃Ge, Et₃Ge, t-Bu, Ph). An unexpected reaction of the trimethylsilyl anion with the Me₃SiGeEt^-2 anion leading to diethylgermane dianion, Et₂Ge^2- has been revealed. The existence of this process supports the suggested absence of (d-p)π interaction in germanium anions with organo-silicon and -germanium substituents.