The Rivalry between Intramolecular Tetrel Bonds and Intermolecular Hydrogen Bonds in (O-Si) Chelates of N-Silylmethylamides and -ureas. A Theoretical Study

The comparison of the results of theoretical calculations of (O-Si) chelates of N-silylmethylated amides and ureas with the axial chlorine or fluorine atom at silicon to the data of X-ray analysis of related compounds revealed the formation of covalent O-Si tetrel bonds (TB) or noncovalent O & sdot;& sdot;& sdot;Si tetrel bonds (NTB). The nature of the formed tetrel bond depends on the substituents at silicon and the polarity of the medium. The competition between the intramolecular TB and intermolecular hydrogen bonds (HB) with proton donors depends on the center of basicity involved in the formation of HB, which could be either oxygen or halogen. The hydrogen bonding can result in changing the nature of the tetrel bonds from covalent to noncovalent and vice versa by varying their lengths and energies. The O-Si bond energies estimated by QTAIM analysis of N-[(chlorodimethylsilyl)methyl]-N-methylacetamide and its H-complexes vary within the range of 7.2 and 12 kcal/mol in gas and solution, respectively, and correlate with the O-Si bond lengths.