Dynamic Conformational Behavior in Stable Pentaorganosilicates

Abstract

Silicates with five organic groups are conformationally dynamic even with two bidentate ligands. Symmetry breaking by incorporating a single nitrogen or phosphorus atom provides insight into their dynamic behavior. N‐containing silicates with bidentate 2‐phenylpyridine, biphenyl, and a Me (8), Et (9) or Ph (10) ligand were studied comprehensively by NMR spectroscopy and DFT theory to reveal two isoenergetic conformers with a barrier of ca. 10 kcal mol–1. P‐containing silicate 14 with bidentate triphenylphosphane, biphenyl, and Me ligands is subject to multiple Berry pseudorotations, turnstile rotations, and conformational flexibility of the P‐center. The stability increased by masking the P‐center with a BH3 group (16). DFT and NMR modeling reveal two isoenergetic conformers for 16 with a barrier of ca. 19 kcal‧mol–1 for a complex interconversion pathway. This barrier bodes well for the design of configurationally stable chiral‐at‐metal transition metal catalysts.