Natural abundance studies of silicon-29 to nitrogen-15 coupling constants

Abstract

One-bond 29Si 15N and 29Si 14N coupling constants ( 1 J SiN) were measured at natural isotope abundance in 50 compounds containing covalently bonded N and Si atoms. The strategy and experimental details of 1J( 29 Si 15 N) measurements were considered. Routine measurement of 1J( 29 Si 15 N) is possible in 29Si NMR spectra using polarization transfer methods (INEPT, DEPT, etc.). The central line in 29Si NMR spectra was suppressed by the INEPT + Hahn spin-echo pulse sequence. The values of 29Si 15N coupling constants ranged from +6 to 47.6 Hz. 'JsiN show marked dependence on the nature of the SiN bond, specifically, on the extent of d π - p π bonding, nitrogen hybridization, and SiN bond length and polarity. A quantitative relationship between 1 J SiN and hybridization is derived. It is suggested that 1 J SiN may be considered as a measure of SiN bond reactivity in nitrogen-containing organosilicon compounds. In parallel, the 29Si and 15N chemical shifts, 29Si 13C and 15N 1H coupling constants, and 1Δ 29 Si( 15 N 14 N) and 1Δ 15 N( 29 Si 28 Si) isotope shifts were measured. These 29Si 14N coupling constants and isotope shifts were measured for the first time.