Si Dative Bond Research Articles

1-Styrylsilatrane

The structure of (E)-1-(2-phenylethenyl)-2,8,9-trioxa-5-aza-1-silabicyclo[3.3.3]undecane, C14H19NO3Si, has been determined by X-ray analysis. The N—Si dative bond length of 2.127 (4) Å is in agreement with structural trends found for such systems. The C atoms linked to the N atom are disordered, an effect which has been observed in other silatrane structures.

The molecular structure of 1-fluorosilatrane

The crystal structure of 1-fluorosilatrane has been determined by X-ray diffraction. The N → Si dative bond length is 2.042(1) Å, somewhat longer than that in the 1-chloro derivative (2.023 Å). The carbon atoms linked to nitrogen are disordered. The atoms in the close-packed crystal structure are well fixed and have low thermal motion. Deformation electron density calculations show considerable density in the region between the silicon and nitrogen atoms. A mass spectrometric study indicates a strong SiF bond.

The crystal structure of 1- m-chlorophenoxysilatrane

The pentavalent silicon in the title compound is coordinated by four oxygen atoms. The N→Si dative bond is rather short (2.079(2) Å). The crystal structure is partially disordered: carbon atoms attached to nitrogen appear on both sides of the SiO(eq)C, N plane with a population of 0.8 and 0.2, respectively. The change of the configuration around silicon and nitrogen, as a function of the N→Si dative bond length, is reviewed for several silatrane structures. Structural data suggest that different extents of the distortion of the trigonal bipyramid around silicon for the various compounds may represent stages along the pathway of the S N2-type reaction SiX + HN → SiN.

The crystal structures of m-trifluoromethylphenylsilatranone and p-fluorophenylsilatranone

The crystal structures of two silatranone derivatives are reported. The close N → Si approach (2.106(3) Å in m-trifluoromethylphenyl-, and 2.129(3) Å in p-fluorophenyl-silatranone) indicates strong dative acceptor bonds. For various silatrane derivatives and inverse relation has been revealed between the mean group electronegativity of the substituent R attached to silicon and the N → Si dative bond distance. In both structures there are long (1.72 Å) SiO bonds in the SiOCO moiety. The m-trifluoromethylphenyl derivative contains a disordered CF 3 group.