Synthesis, properties and reactivity of intramolecular hypercoordinate silicon complexes

Analysis of the Hypersensitivity of the29Si NMR Chemical Shift of the Pentacoordinate Silicon Compounds to the Temperature Effect.N-(Silylmethyl)acetamides

“…The geometrical interpretation − ,− , of the dependence δ = f ( T ) is based on the results of quantum-chemical and spectral (IR, multinuclear NMR) studies of I having different coordination centers, − ,,,− and, in the case of tricyclic silatranes XSi­(OCH 2 CH 2 ) 3 N, also on the direct structural data. ,,− They suggest the ease of deformation of the silicon polyhedron (especially of the length of the dative Si ← D contact) under the influence of environment. An increase of the solvent polarity induced by the lowering of the temperature of solution − should be accompanied for ISC I possessing the Si ← D coordination by the dominating shortening of the Si···D distance, ,, i.e., by increasing the degree of Si pentacoordination, and, therefore, in full agreement with the experiment, by the upfield shift of the 29 Si signal.…”

“…The geometrical interpretation [1][2][3][4][5][6][7][8][22][23][24][25]32 of the dependence δ = f (T) is based on the results of quantum-chemical and spectral (IR, multinuclear NMR) studies of I having different coordination centers, 1−8,46,47,49−54 and, in the case of tricyclic silatranes XSi(OCH 2 CH 2 ) 3 N, also on the direct structural data. 2,5,55−58 They suggest the ease of deformation of the silicon polyhedron (especially of the length of the dative Si ← D contact) under the influence of environment.…”

“…NMR 29 Si chemical shift (δ) is anomalously sensitive to the temperature effect in a series of the trigonal-bipyramidal (TBP) intramolecular silicon complexes, ISC, I (Scheme ). − The temperature drift of δ (gradient Δδ/Δ T ) of the hypercoordinate silicon compounds exceeds by more than an order of magnitude that of the tetracoordinate silicon compounds (Si IV ). − In the general case, the value and sign of Δδ/Δ T depend on the structural, energetic, and electronic characteristics of ISC I and the properties of their external environment. − An interest to the study of such an unusual dependence δ = f ( T ) being characteristic of I is unabated, because this certainly contributes to our understanding of chemical reactions of the important organic derivatives of pentacoordinate silicon (Si V ). − …”

Tetrel Bonding along the Pathways of Transsilylation and Alkylation ofN-Trimethylsilyl-N-methylacetamide with Bifunctional (Chloromethyl)fluorosilanes

“…The chemistry of organosilicon hypervalent compounds was intensively developed over last several decades. The methods of synthesis were designed and the data on the structure and reactivity were obtained for organosilicon compounds with intramolecular coordination bond D → Si (D = O, N), which led to their use as synthons and catalysts in synthetic and medicinal chemistry as well as in the chemistry of materials. − The nature of hypervalent D → Si bonding has also been explored. ,− However, some problems still remain to be solved. Thus, for (O–Si)-monochelate N -[(halogeno)­silylmethyl]­carboxamides and their analogues, which are classical representatives of pentacoordinate organosilicon compounds, the synthetic approach, structure, and reactivity are well known ,− but still there is no clear understanding of the process of formation of these structures, which would allow us to direct the reaction toward the selective formation of the desired products.…”

“…The methods of synthesis were designed and the data on the structure and reactivity were obtained for organosilicon compounds with intramolecular coordination bond D → Si (D = O, N), which led to their use as synthons and catalysts in synthetic and medicinal chemistry as well as in the chemistry of materials. − The nature of hypervalent D → Si bonding has also been explored. ,− However, some problems still remain to be solved. Thus, for (O–Si)-monochelate N -[(halogeno)­silylmethyl]­carboxamides and their analogues, which are classical representatives of pentacoordinate organosilicon compounds, the synthetic approach, structure, and reactivity are well known ,− but still there is no clear understanding of the process of formation of these structures, which would allow us to direct the reaction toward the selective formation of the desired products. Recently, we have studied the reaction of N -trimethylsilyl- N -methylacetamide 1 , an ambident nucleophile existing as a tautomeric mixture of amide 1a and imidate 1b forms, with bifunctional silane ClCH 2 SiF 3 2 and showed the occurrence of two independent parallel processes, transsilylation and alkylation (Schemes – ).…”