Novel Aryl Substituted Silanes Part I: Synthesis and Characterization of Diaryl Silicon Dichlorides

Synthesis and Hydrogen-Bond Patterns of Aryl-Group Substituted Silanediols and -triols from Alkoxy- and Chlorosilanes

Organosilanols typically show a high condensation tendency and only exist as stable isolable molecules under very specific steric and electronic conditions at the silicon atom. In the present work, various novel representatives of this class of compounds were synthesized by hydrolysis of alkoxy- or chlorosilanes. Phenyl, 1-naphthyl, and 9-phenanthrenyl substituents at the silicon atom were applied to systematically study the influence of the aromatic substituents on the structure and reactivity of the compounds. Chemical shifts in 29 Si NMR spectroscopy in solution, correlated well with the expected electronic situation induced by the substitution pattern on the Si atom. 1 H NMR studies allowed the detection of strong intermolecular hydrogen bonds. Single-crystal X-ray structures of the alkoxides and the chlorosilanes are dominated by π-π interactions of the aromatic systems, which are substituted by strong hydrogen bonding interactions representing various structural motifs in the respective silanol structures.

Molecular structures of various alkyldichlorosilanes in the solid state

A series of organodichlorosilanes RR'SiCl₂ (R,R' = (CH₂)₃; (CH₂)₄; (CH₂)₅; Me,Me; Me,H; Me,Cl) was studied by single-crystal X-ray diffraction analyses. At ambient temperature liquid chlorosilanes (melting points in the range of 180-220 K) were transferred into glass capillaries and crystallized in situ on a diffractometer. In the solid state structure these chlorosilanes are monomeric, even in the case of the sterically less demanding 1,1-dichlorosilacyclobutane (CH₂)₃SiCl₂. Interestingly, regardless the steric demand of the alkyl substituents, the dialkyldichlorosilanes exhibit essentially the same Cl-Si-Cl angle (for (CH₂)₃SiCl₂, (CH₂)₄SiCl₂, (CH₂)₅SiCl₂, Me₂SiCl₂: 106.08(3)°, 106.07(4)°/105.86(4)°, 106.91(2)° and 105.59(6)°, respectively). Replacement of one alkyl group by hydrogen has only a marginal influence on the Cl-Si-Cl angle (MeHSiCl₂ 106.31(3)°), whereas in MeSiCl₃ slightly wider Cl-Si-Cl angles are found (ranging between 107.04(11)° and 107.86(11)°), in accordance with VSEPR. Computational analyses, i.e., potential energy surface scans of the Cl-Si-Cl angle variation, of (CH₂)₃SiCl₂, Me₂SiCl₂, MeHSiCl₂ and H₂SiCl₂ reveal essentially identical energy profiles for the Cl-Si-Cl deformation in these four dichlorosilanes with basically superimposed curves for (CH₂)₃SiCl₂ and Me₂SiCl₂, whereas with increasing H-substitution the energetic minimum is shifted to a slightly wider Cl-Si-Cl angle. In the crystal packing only MeHSiCl₂ exhibits weak intermolecular SiCl van der Waals contacts, whereas the Si-Cl moieties of the other five chlorosilanes engage in intermolecular ClH and (for (CH₂)₃SiCl₂, (CH₂)₄SiCl₂ and MeSiCl₃) ClCl contacts.