Dichlorosilane–dimethyl ether aggregation: a new motif in halosilane adduct formation

Abstract

The crystal structures of (H(3)C)(2)O, H(2)SiCl(2) and an adduct of these were determined by low-temperature X-ray crystallography on crystals grown in situ at low temperatures on a diffractometer. The adduct of (H(3)C)(2)O and H(2)SiCl(2) has the composition [(H(3)C)(2)O.H(2)SiCl(2)](2) and contains a four-membered Si(2)O(2) ring, with the Cl atoms pointing to the outside and the Si-H functions pointing to the inner side of the ring. The Si(2)O(2) ring has two longer and two shorter SiO bonds and thus deviates from a square. Quantum chemical calculations give a geometry for [(H(3)C)(2)O.H(2)SiCl(2)](2) which has D(2h) symmetry and allow to obtain an estimate for the adduct formation energies, which are -13.4 kJ mol(-1) for the formation of the mono adduct [(H(3)C)(2)O + H(2)SiCl(2)-->(H(3)C)(2)O.H(2)SiCl(2)], -14.4 kJ mol(-1) for the dimerization of two mono adducts [(H(3)C)(2)O.H(2)SiCl(2)-->[(H(3)C)(2)O.H(2)SiCl(2)](2)] and -41.2 kJ mol(-1) for the reaction 2 (H(3)C)(2)O + 2 H(2)SiCl(2)-->[(H(3)C)(2)O.H(2)SiCl(2)](2). The results are used to rationalize the strongly reduced reactivity of H(2)SiCl(2) towards nucleophilic substitution reactions in (H(3)C)(2)O at low temperatures.

Chirality transfer through sulfur or selenium to chiral propellers

“…Conf 1 0.00 56 À80, À36, À45 Conf 2 0.14 44 À5, 51, 67 Table 1 Lengths of the C-X bonds (in A) in dimethyl and ditrityl monoand dichalcogenides based on X-ray diffraction data [8][9][10][11] Me-X-Me Me-X-X-Me Ph 3 C-X-X-CPh 3 Such behaviour can be explained by the electronic effect of sulfur and selenium atom. Calculated CD spectrum of triphenylmethane having the same conformation as in conformer 1 of 1a showed different pattern and lower intensity of the Cotton effects (dotted line in Fig.…”

“…Lengths of the C-X bonds (in A) in dimethyl and ditrityl monoand dichalcogenides based on X-ray diffraction data[8][9][10][11] …”

How Many Molecules Can Fit in a Zeolite Pore? Implications for the Hydrocarbon Pool Mechanism of the Methanol-to-Hydrocarbons Process

“…We used three different methods to determine the molecular volume (see Section 4 as this is not a well-defined parameter. It can be seen that the Molinspiration [12] values (which are calculated as a sum of group contributions) are consistently smaller than those based on experimental values (crystal structure [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] and density [33]). However, while the absolute values differ between the methods, in all three cases the trends are similar and they match chemical intuition, e.g., phenanthrene is larger than toluene.…”

“…This is seen as a sum of group contributions. The data in column 3 of Table 1 (labelled 'Structure') was generated from the crystal structures [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32], which were obtained from the Cambridge Structural Database (CSD) [62]. We define the molecular volume as the unit cell volume divided by the number of molecules in the unit cell.…”

5 Carbon, silicon, germanium, tin and lead

“…The dimethyl ether adduct of dichlorosilane has been prepared and crystallised at low temperature in situ on the diffractometer, 40. 97 The [Si-O-Si-O] ring is not square because there are two long (2.960 A ˚) and two short silicon-oxygen bonds (2.699 A ˚). The Si-Cl contacts are in the range 2.05-2.07 A ˚.…”