Apicophilicity versus Hydrogen Bonding. Intramolecular Coordination and Hydrogen Bonds in N-[(Hydroxydimethylsilyl)methyl]-N,N′-propyleneurea and Its Hydrochloride. DFT and FT-IR Study and QTAIM and NBO Analysis

Abstract

Conformers of N-[(hydroxydimethylsilyl)methyl]-N,N′-propyleneurea (1) and their hydrochlorides (2) with HCl coordinated to different basic sites have been studied experimentally by FT-IR and theoretically using the density functional theory (DFT) method at the B3LYP/6-311+G(d,p) and M06/6-311+G(d,p) levels of theory. The structures of silanols 1 and 2 are determined by the balance of two competing effects: namely, intramolecular C═O→Si coordination and intramolecular C═O···H–O or intermolecular X···H–Cl hydrogen bonding. The preferred conformation of silanol 1 is that with an equatorial hydroxyl group, in apparent contradiction with the apicophilicity rule. In the crystal, silanol 1 exists as a conformer with a bifurcated bond composed of a weak C═O→Si coordinated bond and a substantially more strong C═O···H–O hydrogen bond. From the NBO analysis, the energies of the nO → σ*Si–X and nO → σ*H–O orbital interactions responsible for the formation of the coordination and hydrogen bonds, as well as the lengths...