Syntheses and Crystal Structures of Highly Diastereomerically Enriched Lithiated Benzylsilanes in the Presence of External Donor Molecules: Experiment and Theory

The solid‐state structures of the lithiated (aminomethyl)benzylsilanes Me 2 Si[( R )‐(CHPhLi·0.5TMEDA)](CH 2 SMP) [{( R , S )‐ 2 } 2 ·TMEDA] and Me 2 Si[( R )‐(CHPhLi·DABCO)](CH 2 SMP) [( R , S )‐ 2· DABCO] [CH 2 SMP = ( S )‐2‐(methoxymethyl)pyrrolidinomethyl] and the absolute configurations at the stereogenic metallated carbon centres of these compounds were determined by single‐crystal X‐ray diffraction methods. The crystal structures of the TMEDA‐bridged dimer [( R , S )‐ 2 ] 2 ·TMEDA and monomeric ( R , S )‐ 2· DABCO were compared to that of the parent compound ( R , S )‐ 2 , a coordination polymer. By computational methods [B3LYP/6−31+G(d)], the mechanism of the deprotonation of the starting compound, (aminomethyl)benzylsilane [( S )‐ 1 ], as well as the stability of configuration of the lithiated derivatives of ( R , S )‐ 2 , were examined. For the highly diastereoselective substitution reactions of the derivatives of ( R , S )‐ 2 with iodomethane, inversion of the configuration at the metallated carbon centre was observed and correlated with the results of the quantum‐chemical studies. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)