H(2)SiCl(2) and substituted pyridines (Rpy) form adducts of the type all-trans-SiH(2*)Cl(2)2 Rpy. Pyridines with substituents in the 4- (CH(3), C(2)H(5), H(2)C=CH, (CH(3))(3)C, (CH(3))(2)N) and 3-positions (Br) give the colourless solids 1 a-f. The reaction with pyrazine results in the first 1:2 adduct (2) of H(2)SiCl(2) with an electron-deficient heteroaromatic compound. Treatment of 1 d and 1 e with CHCl(3) yields the ionic complexes [SiH(2)(Rpy)(4)]Cl(2*)6 CHCl(3) (Rpy=4-methylpyridine (3 d) and 4-ethylpyridine (3 e)). All products are investigated by single-crystal X-ray diffraction and (29)Si CP/MAS NMR spectroscopy. The Si atoms are found to be situated on centres of symmetry (inversion, rotation), and the Si-N distances vary between 193.3 pm for 1 c (4-(dimethylamino)pyridine complex) and 197.3 pm for 2. Interestingly, the pyridine moieties are coplanar and nearly in an eclipsed position with respect to the SiH(2) units, except for the ethyl-substituted derivative 1 e, which shows a more staggered conformation in the solid state. Calculation of the energy profile for the rotation of one pyridine ring indicates two minima that are separated by only 1.2 kJ mol(-1) and a maximum barrier of 12.5 kJ mol(-1). The (29)Si NMR chemical shifts (delta(iso)) range from -145.2 to -152.2 ppm and correlate with the electron density at the Si atoms, in other words with the +I and +M effects of the substituents. Again, compound 1 e is an exception and shows the highest shielding. The bonding situation at the Si atoms and the (29)Si NMR tensor components are analysed by quantum chemical methods at the density functional theory level. The natural bond orbital analysis indicates polar covalent Si-H bonds and very polar Si-Cl bonds, with the highest bond polarisation being observed for the Si-N interaction, which must be considered a donor-acceptor interaction. An analysis of the topological properties of the electron distribution (AIM) suggests a Lewis structure, thereby supporting this bonding situation.

Stable solid adducts of substituted pyridines (Rpy) with HSiCl(3) and HSiCl(2)Me were prepared in high yields under aprotic and anaerobic conditions at room temperature. The octahedral complexes of HSiCl(3) underwent dismutation reactions in polar solvents. In contrast, the HSiCl(2)Me(Rpy)(2) adducts were not susceptible to dismutation under comparable conditions, but they tended to dissociate more easily because of the reduced Lewis acidity of HSiCl(2)Me relative to HSiCl(3). The bonding between silicon and its surrounding ligands is highly ionic, as can be seen from QTAIM and charge distribution analyses. (29)Si CP/MAS spectra in combination with quantum-chemical calculations show that the lowest shielding is along the Cl-Si-Cl axis. The other two components of the shielding tensor are oriented along the N-Si-N and H-Si-Cl/Me axes. It is known that many reactions of (hydrido)chlorosilanes are catalyzed by pyridine bases. Therefore, the results presented here provide a basis for better control of these reactions, especially chlorine substitution and hydrosilylation.

Stable in the solid state and isolable in high yields are adducts of H(2)SiCl(2), HSiCl(3), and RSiCl(3) (R = Me, Ph) with the N,N'-chelating ligands 1,10-phenanthroline (phen; 1c), 2,2'-bipyridine (bipy; 1b), and (to a limited extent) N,N,N',N'-tetramethylethylenediamine (tmeda; 1a). The products were comprehensively characterized via multinuclear solution and solid-state NMR spectroscopy, including analysis of the (29)Si NMR chemical shift anisotropy tensors, Raman spectroscopy, elemental analyses, and, for SiCl(4)(phen) (2c), HSiCl(3)(bipy) (3b), H(2)SiCl(2)(bipy) (4b), MeSiCl(3)(phen) (5c), and PhSiCl(3)(phen) (6c), single-crystal X-ray structure analyses. The latter revealed that the nonchlorine substituents (i.e., H, Me, and Ph) are exclusively trans-disposed to the N-donor atoms of the chelating ligands. A dismutation of the complexes HXSiCl(2)(bipy) and HXSiCl(2)(tmeda) (X = H or Cl) was observed in polar solvents at elevated temperatures. This reaction is more pronounced when phen is used instead of bipy or tmeda. For MeHSiCl(2)(phen), in addition to undergoing H-Cl redistribution accompanied by the formation of 5c, an unexpected 1,4-hydrosilylation was observed. The latter was proven NMR-spectroscopically and by a single-crystal X-ray structure analysis of the product MeSiCl(2)(4H-phen) (7), a pentacoordinated silicon compound with a trigonal-bipyramidal arrangement of the subsituents and the methyl group located in an equatorial position.

The prepapration, and first comprehensive spectroscopic and structural characterization of octahedral trichlorosilane adducts HSiCl3(Rpy)2 with R = H, 4‐CH3, 4‐C6H5, 3‐Br, 4‐CHCH2, 4‐C2H5, 4‐C(CH3)3 and 4‐N(CH3)2 is reported. The products are surprisingly stable in the solid state and easily obtained in high yield. Single‐crystal X‐ray diffraction analysis of HSiCl3(3‐Brpy)2 revealed relatively short Si–Cl bonds (218–223 pm) while the Si–N bonds (ca. 198 pm) are only slightly longer than in the corresponding H2SiCl2(Rpy)2adducts. Dismutation reactions were observed only in polar solvents at elevated temperatures.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

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