Acyclic Dialkylstannylene and -Plumbylene Compounds That Are Monomeric in the Solid State

The new phosphine-borane adduct (Me2PhSi)CH2P(BH3)Me2 is prepared by the reaction between Me2PhSiCl and in situ-generated Me2P(BH3)CH2Li; the adduct undergoes clean deprotonation on treatment with n-BuLi to give the phosphine-borane-stabilized carbanion complex [(Me2PhSi){Me2P(BH3)}CH]Li. The reaction between 2 equiv of [(Me2PhSi){Me2P(BH3)}CH]Li and either Cp2Sn or Cp2Pb gives the acyclic dialkylstannylene and -plumbylene compounds rac-[(Me2PhSi){Me2P(BH3)}CH]2E [E = Sn (13), Pb (14)]. Similarly, the reaction between 2 equiv of [(Me3Si){Me2P(BH3)}CH]Li and either Cp2Sn or Cp2Pb yields rac-[(Me3Si){Me2P(BH3)}CH]2E [E = Sn (15), Pb (16)]. X-ray crystallography reveals that compounds 13−16 crystallize as discrete monomers that are stabilized by two agostic-type B−H···E contacts in each case; multielement NMR spectroscopy and UV/visible spectroscopy indicate that these agostic-type contacts are preserved in solution. DFT calculations reveal that these B−H···E contacts stabilize compounds 13−16 by between 38.0 and 43.7 kcal mol−1. Calculations suggest that the dimerization of 15, which is isoelectronic with the archetypal dialkylstannylene {(Me3Si)2CH}2Sn, to the corresponding distannene [(Me3Si){Me2P(BH3)}CH]2SnSn[CH{P(BH3)Me2}(SiMe3)]2 (152) is disfavored by some 30.5 kcal mol−1.