A comparative study of sparteine, α-isosparteine and 2-methylsparteine monoperchlorate salts and zinc (II) complexes by NMR chemical shifts

Structural Studies on (–)‐Sparteine‐Coordinated Lithiosilanes

“…The chemical shift of the lithium atom has a value of 1.61 ppm at room temperature and 1.16 ppm at -50°C. A quartet with four equal peaks is expected for 29 Si, 7 Li coupling; yet, the observed signal form is not symmetric. This can be caused by an overlap of the 29 Si, 6 Li coupling of the second NMR-active isotope of lithium (natural abundance 7 Li/ 6 Li ≈ 92.5:7.5).…”

“…A quartet with four equal peaks is expected for 29 Si, 7 Li coupling; yet, the observed signal form is not symmetric. This can be caused by an overlap of the 29 Si, 6 Li coupling of the second NMR-active isotope of lithium (natural abundance 7 Li/ 6 Li ≈ 92.5:7.5). To rationalise the shape, a simulated 29 Si,Li coupling of 2·(-)-sparteine was performed (see Figure 7).…”

“…In accordance with this, we observed only one signal for each atom in the NMR spectra. At both temperatures (r.t. and -50°C), a coupling between the silicon and the lithium atoms was detected in the 29 Si NMR spectrum (see Figure 6). This coupling supports the strong Si-Li contact of 2.600(5) Å, already found in the crystal.…”

“…This can be caused by an overlap of the 29 Si, 6 Li coupling of the second NMR-active isotope of lithium (natural abundance 7 Li/ 6 Li ≈ 92.5:7.5). To rationalise the shape, a simulated 29 Si,Li coupling of 2·(-)-sparteine was performed (see Figure 7). Spectrum A in Figure 7 shows the superimposed simulated spectra of the 29 Si, 7 Li-and 29 Si, 6 Li coupling, whereas B shows the same for the 29 Si, 7 Li coupling and C shows the 29 Si, 6 Li coupling.…”

“…To rationalise the shape, a simulated 29 Si,Li coupling of 2·(-)-sparteine was performed (see Figure 7). Spectrum A in Figure 7 shows the superimposed simulated spectra of the 29 Si, 7 Li-and 29 Si, 6 Li coupling, whereas B shows the same for the 29 Si, 7 Li coupling and C shows the 29 Si, 6 Li coupling. In all three cases the magenta line refers to the simulated spectrum and the black line to the experimental spectrum.…”