Silicon-29 nuclear magnetic resonance. Chemical shift substituent effects

Performance of DFT for 29Si NMR Chemical Shifts of Silanes

“…In this paper, we present 29 Si NMR calculations on silanes and substituted silane molecules, comparing various methods and showing that, surprisingly, for DFT quite large deviations from experiment can be obtained when the number of hydrogens bonded to silicon is increasing. An empirical correlation scheme is proposed to provide reliable chemical shifts as a function of of the atoms surrounding silicon sites.…”

“…This behavior holds for molecules such as silanes, where the δ values spread over 170 ppm (see, e.g., Marsmann 26 for an overview for Si compounds) and also for solids such as zeolites showing a variation range of around 15 ppm with respect to geometry changes or substitution of a silicon center with another element. 27,28 As a test set of the accuracy that could be expected concerning 29 Si NMR shifts with various environments, we have chosen the silane molecules. The silanes will give us the possibility to study trends by systematic variation of their structures (isomers, substituent effectssreplacing hydrogen by alkyl groups or halogens, etc.…”

“…32 It predicts the 29 Si NMR chemical shifts with an accuracy of ∼2 ppm and considers only structural information of the given site and its next neighbors.…”

Synthesis of aminotri- and aminotetrasilanes by cross-coupling of aminochlorosilanes with chlorotrimethylsilane

“…The one-bond couplings 1 J SiSi and 29 Si resonances present a parabolic dependence on the sum of the electronegativity (R v ) of the substituents [24]. Below R v ‫ס‬ 10.7, the chemical shifts d( 29 Si) increase with R v ; above this value they decrease with increasing R v [25]. For 11a-c, the sum is below the critical value, thus d( 29 …”

“…C NMR: d ‫ס‬ 0.3 (SiCH 3 ), 25.7 (c-CH 2 ), 28.0 (b-CH 2 ), 48.4 (␣-CH 2 ). 29 1,3-Diethyl-2,2-bis(trimethylsilyl )-1,3,2-diazasilolidine (9d).…”