Dynamic Conformational Behavior in Stable Pentaorganosilicates

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.