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

Abstract

(C,O)-chelate silanol hydrohalides RC(O)NHCH 2SiMe 2OH · HHal ( 2a, b and 5b), and their precursors, (C,O)-chelate chlorosilanes RC(O)NHCH 2SiMe 2Cl ( 6a, b) and disiloxanes [RC(O)NHCH 2SiMe 2] 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)NHCH 2SiMe 2OH · HX ( 2b and 5b) in the crystal exist in the form of cation–anion pairs [PhC(O)NHCH 2SiMe 2(OH 2)] + · 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)NHCH 2SiMe 2(OH 2)] + ( 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 H 2O molecules rather than a silyloxonium ion.