Halogenaustausch an Siliciumtetrahalogeniden. XIII. Zur Struktur und Reaktivität von Siliciumtetrahalogenid‐Pyridin‐Komplexen

Bechstein, O.; Ziemer, Burkhard; Hass, Dieter; Trojanov, S.; Рыбаков, В. Б.; Maso, G. N.

doi:10.1002/zaac.19905820125

Cited by 41 publications

(27 citation statements)

References 7 publications

(3 reference statements)

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“…Thus, substitution of Si À H for Si À X moieties leads to significant out-of-plane positions of all four substituents, as can easily be seen in the structures of the pyridine adducts of SiCl 4 . [11,12] Contrasting the conformational behaviour of the compounds discussed above, the Si atom of complex 1 e is not situated on a centre of inversion and its H-Si-H axis is located on a twofold axis of rotation, which means that the pyridine ring systems are not coplanar (Figure 3, right, Figure 4). Despite this conformational difference, the coordination behaviour of the pyridine ligand (Si À N separation) is similar to those in complexes 1 a, 1 b, 1 d and 1 f.…”

Section: Resultsmentioning

confidence: 72%

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

Fester

Wagler

Brendler

et al. 2008

Chemistry A European J

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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.

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Section: Resultsmentioning

confidence: 72%

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

Fester

Wagler

Brendler

et al. 2008

Chemistry A European J

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“…Some of the molecules investigated exist in the solid state, i.e. SiH 3 Cl(OMe 2 ), [10] SiH 2 Cl 2 (py) 2 , [1f,9] SiH 2 Br 2 (py) 2 , [1f] SiF 4 (py) 2 , [11] SiCl 4 (py) 2 , [12] SiF 4 (NH 3 ) 2 , [13] , SiF 4 (NH 3 ), [6] SiF 5 Ϫ , [14] and SiF 6 2Ϫ , [15] the others are model compounds, i.e.…”

Section: Introductionmentioning

confidence: 99%

Molecular “Floppyness” and the Lewis Acidity of Silanes: A Density Functional Theory Study

Fleischer

2001

Eur. J. Inorg. Chem.

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A comprehensive set of Lewis acid‐base adducts of silanes was investigated by means of the density functional theory geometry optimization [B3LYP/6−31G(d)], and thermochemical calculations, [B3LYP/6−311+G(2d,p)//B3LYP/6−31G(d)]. Complex formation was found to weaken Si−Cl and Si−Br bonds more than Si−F or Si−H bonds. Comparable distances between Si and a Lewis base L (L = NH3, OH2, F−) are shorter in hexa‐ than in pentacoordinated complexes. The molecular structures of the pentacoordinated Si complexes allowed for a mapping of an SN2 reaction pathway by correlating the lengths of the Si−X and Si−L bonds. Complex formation was found to be exothermic for most of the coordination compounds, and the analysis of the natural atomic charges revealed a high ionic character of the dative bonds. Formation of the anionic complexes and of SiH2X2(py)2 is most exothermic with X = Cl or Br and otherwise most exothermic with X = F. Only small enthalpy differences were found between the trans and cis configurations of SiF4(py)2. The standard free enthalpy of complex formation is negative only for complexes between halosilanes and F−, i.e. all other silane Lewis base adducts are thermodynamically unstable under standard conditions with respect to dissociation. It is inferred that the existence of some of the silicon complexes in the solid state or in solution is caused by stabilizing intermolecular forces, and silanes are classified as very weak Lewis acids. The thermochemistry of complex formation was analyzed in terms of molecular “floppyness” of the silanes and the energy of interaction between the deformed silane and the Lewis base. The enhanced complex stability of SiCl4(py)2 compared to SiH4(py)2 and of GeF4(NH3), [GeF5]− and [GeF6]2− compared to the analogues silane adducts does not result from a stronger Lewis acid base interaction but from an increased “floppyness” of SiCl4 and GeF4 compared to SiH4 and SiF4, respectively.

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“…The four chlorine atoms are displayed about the equatorial plane, with the two phosphoramides trans to each other. [17] The complex shows a lengthened P À O bond (Dd = 0.048 ) as well as shorter P À N bond lengths (Dd = À0.035 for P1ÀN3 and À0.012 for P1ÀN2 and P1ÀN1) than in the free phosphoramide (Table 1), [18] while the SiÀCl bonds are lengthened (Dd = + + 0.19 and + 0.26 ) when compared with SiCl 4 (measured by electron diffraction, Si À Cl 2.02 ). [19] Interestingly, this complex can be isolated in excellent yield and is a stable colorless powder if stored in an anhydrous environment.…”

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confidence: 97%

Neutral and Cationic Phosphoramide Adducts of Silicon Tetrachloride: Synthesis and Characterization of Their Solution and Solid‐State Structures

Denmark

Eklov

2007

Chemistry A European J

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The solution and solid-state structures of hexamethylphosphoramide (HMPA) adducts of tetrachlorosilane (SiCl4) are discussed. In solution, the meridional and facial isomers of the hexa-coordinate cationic complex 3 HMPASiCl3 + Cl(-) (2) predominate at all HMPA concentrations, and are in equilibrium with the hexa-coordinate neutral trans- and cis-2 HMPASiCl4 complexes (1), as well as the penta-coordinate cationic cis-2 HMPASiCl3 + Cl(-) (3). Single crystal X-ray analyses are reported for the ionized mer-3 HMPASiCl3 + HCl2 (-) and the neutral trans-2 HMPASiCl4 complexes.

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Halogenaustausch an Siliciumtetrahalogeniden. XIII. Zur Struktur und Reaktivität von Siliciumtetrahalogenid‐Pyridin‐Komplexen

Cited by 41 publications

References 7 publications

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

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

Molecular “Floppyness” and the Lewis Acidity of Silanes: A Density Functional Theory Study

Neutral and Cationic Phosphoramide Adducts of Silicon Tetrachloride: Synthesis and Characterization of Their Solution and Solid‐State Structures

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Halogenaustausch an Siliciumtetrahalogeniden. XIII. Zur Struktur und Reaktivität von Siliciumtetrahalogenid‐Pyridin‐Komplexen

Cited by 41 publications

References 7 publications

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

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

Molecular “Floppyness” and the Lewis Acidity of Silanes: A Density Functional Theory Study

Neutral and Cationic Phosphoramide Adducts of Silicon Tetrachloride: Synthesis and Characterization of Their Solution and Solid‐State Structures

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Product

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

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