Pál Hencsei

The molecular structure of 1-fluorosilatrane

Abstract The crystal structure of 1-fluorosilatrane has been determined by X-ray diffraction. The N → Si dative bond length is 2.042(1) A, somewhat longer than that in the 1-chloro derivative (2.023 A). 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 effect of the C-methyl substitution on the molecular geometry of the silatrane skeleton: The crystal structures of 1-(4′-tolyl)-silatrane and 1-(4′-tolyl)-3,7,10-trimethylsilatrane

Abstract Unsubstituted (1) and 3,7,10-trimethyl substituted (2) 1-(4′-tolyl)-silatranes were synthesized. 1H, 13C, 15N and 29Si NMR spectra were recorded and assigned. The conformation of the 2 stereoisomers in solution were characterized by the NMR spectra. 1 is monoclinic, P21/c, with a = 13.454(2), b = 13.888(2), c = 14.345(2) A, β = 99.10(2)°. The major stereoisomer fraction of 2 is orthorhombic, Pbca, with a = 12.168(2), b = 13.754(4), c = 20.260(3) A. The structures were solved by direct methods and were refined by least squares to R values of 0.039 and 0.066 for 3523 and 2158 reflexions. The N→Si distances are 1: 2.169(2) (mean) and 2: 2.236(3) A. The solid state conformation of the 2 major stereoisomer fraction is different from that in solution and this is the first example of a silatrane crystal structure where the silatrane moiety lacks C3 symmetry.

The effect of ring substitution on the geometry of the silatrane skeleton: the crystal structures of 1-phenyl-3,7,10-trimethylsilatrane and 1-p-tolyl-carbasilatrane

The crystal structures of 1-phenyl-3,7,10-trimethylsilatrane (I) and 1-p-tolyl-carbasilatrane (II) were determined by X-ray diffraction. Both compounds crystallize with two independent molecules in the asymmetric unit. I (d(Si ← N) = 2.175(6) A) is the minor stereoisomer fraction of the diastereomer mixture possessing approximate C3 symmetry. The conformation of the silatrane moiety is different from that observed in the major (asymmetric) structure of p-tolyl-trimethylsilatrane. The mean Si ← N distance in II (2.29(2) A) is identical with the bond length observed for the phenyl derivative. The dative bond lengths in various silatranes and silatrane analogs are compared.

1-[N-(2-Aminoethyl)aminoalkyl]silatranes and their complexes with CuCl2

Abstract 1-[ N -(2-aminoethyl)aminoalkyl]silatranes, NH 2 (CH 2 ) 2 NH(CH 2 ) n Si(OCH 2 -CH 2 ) 3 N (I, n = 1; III, n = 3) and their paramagnetic complexes with CuCl 2 (2 : 1) (III) and IV) have ben synthesized. Relevant 1 H and 13 C NMR data reveal, that the molecule I in the series of silatranes has the weakest transannular Si ← N bond. The pattern of the signals and the value of the g -factor in the ESR spectra of complexes III and IV in the crystaline state and in MeOH or DMSO solution points to distortion of the chelate planes and to conformational inhomogeneity. The fragmentation of complexes III and IV in Xe 0 fast atom bombardment (FAB) mass spectra indicates that the Si ← N bond in their molecules is stronger than those in the initial silatranes I and II.

The molecular structure of 1-(γ-hydroxypropyl)silatrane

Abstract The molecular structure of 1-(γ-hydroxypropyl)silatrane [HO(CH 2 ) 3 S i(OCH 2 -CH 2 ) 3 N was determined by X-ray diffraction and investigated by IR spectroscopy. The Si ← N dative bond length is 2.173(2) A, similar to those observed in other γ-organopropylsilatranes and in methylsilatrane. Two molecules form a dimer about an inversion center in the crystal lattice, linked by an OH…O hydrogen bond.

The crystal structure of 1-(γ-mercaptopropyl)silatrane

The crystal structure of 1-(γ-mercaptopropyl)silatrane HS(CH2)3Si(OCH2CH2)3N has been determined by X-ray diffraction. The Si←N dative bond length is 2.177(4) A, similar to those observed in other γ-organopropylsilatranes and in methylsilatrane. In contrast to the corresponding hydroxypropyl compound, no hydrogen-bonded dimers are formed in the lattice.

The crystal structure of 1-phenylcarbasilatrane

Abstract The crystal structure of 1-phenylcarbasilatrane, [Ph Si(OCH 2 CH 2 ) 2 (CH 2 CH 2 CH 2 )N ], has been determined by X-ray diffraction. The Si ← N dative bond length is 2.291(1) A, which is 0.13 A longer than the mean value found in the phenylsilatrane modifications. The conformation and the geometry of the carbasilatrane group is fairly similar to those of the silatrane moiety observed in normal silatranes.

Conformational study of tetramethyl-N,N′-bis-arylcyclodisilazanes by 13C NMR and X-ray diffraction methods II. The conformation of tetramethyl-N,N′-bis(o-chlorophenyl)cyclodisilazane

Abstract The conformation of tetramethyl- N,N′ -bis( o -methoxyphenyl)cyclodisilazane was investigated by 13 C NMR in solution and by X-ray diffraction in the solid state. The conformation in solution compares to that of o -methoxyaniline. The phenyl and the cyclodisilazane ring forms a dihedral angle of 7.4° and there is a non-bonded Si ⋯ O distance of 2.73 A in the crystal. The molecular geometry suggests an analogy to S ⋯ O non-bonded interactions often observed in organosulphur chemistry.

Investigations on the bond structure of alkylphenoxysilanes using ultraviolet spectrophotometric methods

Abstract 1. Substances of formula (CH 3 ) n Si(OC 6 H 5 ) 4- n where n = 0–3 have been investigated by an ultraviolet spectrophotometric method. The compounds were prepared partly as described in the literature and partly by our own method. 2. It has been found that the phenoxy—silicon bond of phenoxysilanes shows a small bathochromic effect as compared with the phenoxy group of the phenyl ethers. The position of the absorption maximum is independent of the number of phenoxy groups. 3. The spectra observed indicate that besides the − I and + M effects of oxygen, silicon has + I and − M effects. These four effects together cause the bathochromic shift which is of a lower degree than would be expected from the order of electronegativity. 4. The π « π* transitions of the phenoxy groups in the phenyl ethers and of the phenoxysilicon groups in the phenoxysilanes have been calculated (1.8274 β and 1.8071 β) by the LCAO-MO one-electron method. The results are in accordance with the absorption maxima (271 nm and 273 nm) observed.

The crystal structure of 1-m-chlorophenoxysilatrane

Summary The pentavalent silicon in the title compound is coordinated by four oxygen atoms. The N→Si dative bond is rather short (2.079(2) A). 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 bipyra-mid around silicon for the various compounds may represent stages along the pathway of the SN2-type reaction ≡Si−X + HN≡ → ≡Si−N≡.