A Synthetic Equivalent of a Germanone Derivative

Reaction of two molar equivalents of 2,6-bis(diisopropyl-aminomethyl)phenyllithium (ArLi) with tetramethoxygermane afforded the colourless crystalline dimethoxy bis[2,6-bis(diisopropylaminomethyl)phenyl]germane Ar2Ge(OMe)(2) (1) in good yield. Treatment of 1 with AgF/H2O led to the fluorohydroxy derivative Ar2Ge(F)OH (2), which was characterized, among other techniques, by single-crystal structure analysis. The corresponding lithio compound Ar2Ge(F)OLi (3) obtained from 2 by reaction with tBuLi behaves as a synthetic equivalent of the heavier analogue of ketone [Ar2Ge=O, 5]. Germanone 5 could not be isolated even at low temperature due to the impossibility of dissociating it from LiF. Treatment of 3 with various reactants on the basis of the known reactivity of ketones led to the expected products. The reaction of 3 with H2O led, as expected, quantitatively to the germanium gem-diol Ar2Ge(OH)(2) (6) as colourless crystals. Such gem-diols are scarce compounds and only a few are structurally known; in our case, 6 is stabilized by a hydrogen linkage between the hydrogen atoms of the alcohol functionalities and the nitrogen atoms. Other trapping reactions of 3 were investigated with tBuLi and methanol, and the corresponding germanols Ar2Ge(tBu)OH (7) and Ar2Ge(OMe)OH (8) were isolated after hydrolysis in good yields. Attempts to eliminate LiF from 3 by using the chelating agent 1,4,7,10-tetraoxacyclododecane (12-crown-4) allowed us to isolate lithio complex 9. Generation of germanones from fluorohydroxygermanes and their lithio derivatives appears to be a new promising method. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)