Interaction of Trimethylsilyl and Trimethylstannyl Substituants with C-O Bonds at the γ Position. Results from X-ray Structural Studies and Solvolysis Studies

Abstract

Accurate X-ray structural studies have been carried on the γ-Me3M (M = Si, Sn)-substituted cyclohexyl esters 21-Ns, 22-Ns, 23-Ns, 21-PNB, and 24-PNB. Analysis of the structural parameters reveals that the C(alkyl)-O(ester) bond distance is lengthened slightly compared to nonmetal- substituted analogues provided that the C-M, C-O, and intervening C-C bonds are in the W arrangement as is the case for 22-Ns, 23-Ns, and 24-Ns. However, the C-O bond distances for 22-PNB and 22-Ns, which do not have the W geometry, are not significantly lengthened. These structural effects are consistent with the presence of a percaudel interaction between the back lobe of the C-M σ bond and the C-O σ* orbital. Th..