Pentacoordinated Organo and Hydrido Cyclic Silanes via Sulfur Donor Action¹

Abstract

The new cyclic organosilanes S(C10H6O)2SiMe2 (1) and S(C10H6O)2SiPh2 (2) were obtained by the reaction of R2Si(NMe2)2 (R = Me, Ph) with thiobis(2,2‘-naphthol), while S[Me2C6H2O]2SiH(Me) (3) and S[(t-Bu)MeC6H2O]2SiH(Me) (4) were formed by reaction of Cl2SiH(Me) with the appropriate diol in the presence of Et3N. Characterization was achieved by 29Si and 1H solution NMR, 29Si solid-state NMR, and X-ray structural studies. As a result of sulfur donor interaction, pentacoordinate geometries were obtained where 3 and 4 were displaced further toward a trigonal bipyramid (TBP) compared to 1 and 2. Variable-temperature NMR spectra showed 1 to be fluxional with an activation energy of 9.4 kcal/mol. An exchange mechanism involving rupture of the Si−S donor interaction accompanying a ring pseudorotation is postulated. The less symmetric silanes 3 and 4 do not exchange, as indicated by the 1H NMR data. Comparison of the degree of Si−S donor interaction of 1−4 with that of related cyclic organosilanes possessing Si−O and Si−N donor action allows a correlation of the degree of geometrical displacement toward a TBP, which increases as ring substituents enhance the Lewis basicity of the donor group and the electrophilicity at the silicon center is enhanced by its ligand attachments.

Synthesis, solid-state and solution structures of tris[(2-methoxymethyl)phenyl]germanes with a substituent on germanium

“…The purity of the compound thus obtained was rather poor, so we chose to prepare 3 from pure 1. The fluoride, fluorotris[(2-methoxymethyl)phenyl]germane (2), was prepared from chlorotris[(2-methoxymethyl)phenyl]germane (3) via the hydroxide, tris[(2-methoxymethyl)phenyl]germyl hydroxide (7).…”

“…The compound was prepared by the method described in the previous paper. 4 The reaction between the Grignard reagent (7). The benzene solution (30 ml) of 3 (0.1 g, 0.21 mmol) was added to aq.…”

“…In this case, the measure of structural feature is to calculate the extent to which the Ge -O donor distance has changed from the van der Waals sum of 3.62 Å compared to the sum of the covalent radius of Ge and O, 1.96 Å . This method has successfully been used for cyclic silanes by Holmes et al7 Values of the percent trigonal bipyramidal character (% TBP) obtained in this manner are listed inTable 1.In the case of cyclic silanes investigated by Holmes et al, many compounds have % TBP values similar with those of 2 -4. However, if the central atom (Si) is substituted by halogens, the % TBP tends to be larger.…”

X-ray crystallographic study of some pentacoordinated organogermanium compounds

“…This method has successfully been used for cyclic silanes by Holmes et al [12]. Values of the percent trigonal bipyramidal character (% TBP) obtained in this manner are listed in Table 1 for 1 Á/5.…”

Pentacoordinate hydrochlorosilanes with lactamomethyl ligand

“…According to X-ray and 29 Si NMR data, replacing two equatorial methyl groups by two electron-donating trimethylsilyl groups in pentacoordinate chelate derived from N-methylacetamide does not affect the strength of the O-Si bond [16]. Although a broad range of pentacoordinate silicon hydrides were described [2,[17][18][19][20][21][22], the amide-containing complexes having a Si-H bond are unknown until now. Meanwhile an additional Si-H bond provides further potential site for ligand substitutions that might lead to novel hypervalent silicon compounds.…”