(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 2 SiMe 2 OH · HHal ( 2a , b and 5b ), and their precursors, (C,O)-chelate chlorosilanes RC(O)NHCH 2 SiMe 2 Cl ( 6a , b ) and disiloxanes [RC(O)NHCH 2 SiMe 2 ] 2 O ( 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 2 SiMe 2 OH · HX ( 2b and 5b ) in the crystal exist in the form of cation–anion pairs [PhC(O)NHCH 2 SiMe 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 A while the exocyclic Si–O bonds are 1.979 and 2.009 A, for Hal = Cl and Br, respectively. Quantum chemical calculations have shown that the cation [PhC(O)NHCH 2 SiMe 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 2 O molecules rather than a silyloxonium ion.