Silatranes, 29Si chemical shifts

FIGURE 45. 29Si chemical shift powder patterns collected under cross-polarization conditions at 39.8 MHz on X-substituted silatranes 63 with X indicated. The fluorosilatrane chemical shift powder pattern was collected under high-power H and 19F decoupling conditions at 200 MHz. Reprinted with permission from Reference 150. Copyright 1993 American Chemical Society... 

TABLE 2. H, 15N and 29Si NMR chemical shifts of silatranes (1) in CDCI3 solutions (sol) and in... 

Pronounced shifts to lower frequency occur in the 29Si resonance when silicon compounds with coordination numbers higher than four are obtained. Several studies have now been conducted in which intramolecular coordination of nitrogen to silicon to form a pentacoordinate bond has been shown to produce a strong shielding effect of the silicon chemical shift. Specifically, the silatranes (15) are compounds in which a transan-... 

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