Experimental Investigations andabInitioStudies on Hexacoordinated Complexes of Dichlorosilane

Abstract

Dichlorosilane, SiH2Cl2, forms two different kinds of coordination compounds with pyridine and 3-picoline: the simple adduct trans-SiH2Cl2(L)2 and the ionic complex [SiH2(L)4]Cl2·4CHCl3 (L = pyridine, 3-picoline). The adducts trans-SiH2Cl2(py)2, 1, and trans-SiH2Cl2(3pic)2, 2, form directly from the reaction of bis(dichlorosilyl)methylamine, NMe(SiHCl2)2 with pyridine (py), and 3-picoline (3pic). Reaction of 1 with an excess of pyridine in chloroform yielded [SiH2(py)4]Cl2·4CHCl3, 3. The molecular and crystal structures of 1−3 were investigated by single-crystal X-ray diffraction. The Si atoms of all three compounds are hexacoordinated and lie on centers of inversion. The basic structural parameters are the following: 1 (monoclinic, C2/c): Si−N 196.9(1) pm, Si−Cl 228.8(1) pm; N−Si−Cl 90.0(1)°, C−N−C 119.0(2)o; Cl−Si−N−C 102.4(1)°. 2 (triclinic, P1̄): Si−N 197.5(1) pm, Si−Cl 229.2(1) pm; N−Si−Cl 90.3(1)°, C−N−C 118.8(1)°; Cl−Si−N−C 101.2(1)°. 3 (monoclinic, C2/m): Si−N 196.2(4) and 197.0(4) pm, Si···Cl 419.9 pm; N−Si−N 90.0°. All three complexes, neutral and cationic, exhibit very similar lengths of the dative Si−N bond. Hartree−Fock calculations with 3-21G(d) and 6-31G(d) basis sets and density functional calculations with the B3LYP functional and a 6-31G(d) basis set were employed for geometry optimizations of trans-SiH2Cl2(py)2 and [SiH2(py)4]2+. The optimized structures revealed similar Si−N bond lengths and geometric parameters of the pyridine moieties for both types of complexes as well. Single point energy calculations [B3LYP/6-311+G(2d,p)//B3LYP/6-31G(d)], including corrections for the basis set superposition error, showed that the formation of 1 from SiH2Cl2 and pyridine in the gas phase is slightly endothermic (ΔH 298 = 17.2 kJ mol-1) and endergonic (ΔG 298 = 113.6 kJ mol-1). The significance of the Lewis acidity of SiH2Cl2 is thus questioned and intermolecular interactions (e.g. hydrogen bonds) are held responsible for the existence of 1 in the solid state.

On the Mechanism of the Disproportionation of Chlorinated Silanes under the Influence of Lewis Bases

“…Consequently, our calculations do not support the assumption that the disproportionation is faciliated or initiated by the formation of Si 2 Cl 4 Me 2 -donor complex. These results are in accordance with the data from Hensen et al [38]. They showed that complexes consisting of SiH 2 Cl 2 and two pyridine molecules are computed to be instable, if the BSSE is taken into account.…”

Octahedral Adducts of Dichlorosilane with Substituted Pyridines: Synthesis, Reactivity and a Comparison of Their Structures and 29Si NMR Chemical Shifts

“…204.8(8) 2200 [8] H À145.1 196.9(1) [5] 228 for the Br substituent and intermediate for the alkyl-substituted pyridines.…”

“…The molecular structures of 1 a, 1 b, 1 d and 1 f are depicted in Figure 1. The pyridine Natoms, silane H-atoms and Cl atoms in these adducts are situated trans to each other in a pattern that makes these complexes structurally related to the adducts (pyridine) 2 SiH 2 Cl 2 , [5] (3-methylpyridine) 2 SiH 2 Cl 2 [5] and (2,4-dimethylpyridine) 2 SiH 2 Cl 2 . [6] Complex 1 c crystallises as the chloroform solvate 1 c·2 CHCl 3 ( Figure 2) and the chloroform molecules may play a role in achieving a dense molecular packing due to the modified steric demands of the substituent at the pyridine system.…”

“…[1][2][3][4] Most of these chlorosilane-amine adducts are only stable in the solid state and dissociate quantitatively on melting, dissolution, or evaporation, [5] which explains why only limited information about their molecular structure is available. The adducts described in the literature mainly involve those with unsubstituted or methyl-substituted pyridines as donor molecules.…”

“…Another route to hexacoordinate SiH 2 Cl 2 derivatives is based on the decomposition of NMeA C H T U N G T R E N N U N G (SiHCl 2 ) 2 into the dichlorosilane pyridine complex and a mixture of by-products by the action of tertiary amines [5] [Eq. (2) …”