(Amidomethyl)dimethylsilanol hydrohalides: Synthesis, NMR and IR studies. Characteristic features of the electronic structure from high-resolution X-ray study and quantum chemical calculation

(C,O)-chelate silanol hydrohalides RC(O)NHCH2SiMe2OH · HHal (2a,b and 5b), and their precursors, (C,O)-chelate chlorosilanes RC(O)NHCH2SiMe2Cl (6a,b) and disiloxanes [RC(O)NHCH2SiMe2]2O (8a,b) (R = Me (a), Ph (b); Hal = Cl (2), Br (5)), were obtained by several routes. The original scheme of hydrolysis of the above chlorides was discussed in detail. X-ray analysis has shown that the silanol hydrohalogenides PhC(O)NHCH2SiMe2OH · HX (2b and 5b) in the crystal exist in the form of cation–anion pairs [PhC(O)NHCH2SiMe2(OH2)]+ · X− (14b · Cl− and 14b · Br−) assembled by H-bonds in a 3D framework. The Si atom in the cation has a trigonal bipyramidal configuration with the oxygen atom of the carbonyl group and protonated hydroxyl exo-substituent in axial positions. The endocyclic Si–O bonds are equal with an average of 1.905 Å while the exocyclic Si–O bonds are 1.979 and 2.009 Å, for Hal = Cl and Br, respectively. Quantum chemical calculations have shown that the cation [PhC(O)NHCH2SiMe2(OH2)]+ (14b) is stable only in the crystal. Based on a high-resolution X-ray study and a quantum chemical calculation, it was found that the chemical bonding pattern in the OSiO axial fragment of the cation 14b corresponds to a three-centred four electron interaction. The cation 14b should be considered as a silylium cation stabilized by coordinated H2O molecules rather than a silyloxonium ion.