Phosphasilaallenes >Si = C = P- and phosphagermaallenes >Ge = C = P-Phosphasilaallenes >Si=C=P- et phosphagermaallenes >Ge=C=P

摘要

Phosphasilaallene Tip(Ph)Si = C = PMes* (Tip = 2,4,6-triisopropylphenyl, Mes* = 2,4,6-tri-tert-butylphenyl) and phosphagermaallene Mes2Ge = C = PMes* (Mes = 2,4,6-trimethyl-phenyl) have been obtained by dehalogenation of their corresponding dihalopho-sphametallaprqpenes >E(X)-C(X') - P-by tert-butyllithium. They dimerize above -40 °C by a cycloaddition involving two E = C double bonds or the E = C and the P = C double bonds but can be characterized at low temperature by trapping reactions and by low field shifts in ~(31)P,~(29)Si and particularly ~(13)C NMR for the sp carbon atom. Owing to a small increase in the steric hindrance, phosphagermaallene Tip(t-Bu)Ge = C = PMes* can be stabilized and isolated. The Ge = C double bond undergoes nearly quantitative [2 +1 ] cycloadditions with chalcogens and [2 + 2] cycloadditions with aldehydes or ketones. The surprisingly stable lithiochlorosilane R(Cl2)Si-C(Li) = PMes* (R = 9-methylfluorenyl) behaves as a synthetic equivalent of the phosphasilaallene R(Cl)Si = C = PMes*. With two alkyl groups (t-Bu) on the germanium atom, the phosphagermaallene t-Bu2Ge = C = PMes* is not obtained but its formal dimers 1,3-digermacyclobutanes have been isolated.