Conformation Control of Oligosilanes Based on Configurationally Constrained Bicyclic Disilane Units

Tamao, Kohei; Tsuji, Hayato; Terada, Masayoshi; Asahara, Masahiro; Yamaguchi, Shigehiro; Toshimitsu, Akio

doi:10.1002/1521-3773(20000915)39:18<3287::aid-anie3287>3.0.co;2-q

Cited by 107 publications

(75 citation statements)

References 14 publications

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“…It was shown theoretically and experimentally that the σ-σ* absorption peak shifts dramatically to the red as the SiSiSiSi dihedral angle, ω, is increased from 0° to 180° [99][100][101][102][103][104]. This effect was explained by 1,4-orbital interactions (β vic ), being most effective (maximum orbital overlap) in the HOMO (σ-type orbital) of a syn-conformer, while not present in an anti-conformer.…”

Section: Conformational Effectsmentioning

confidence: 95%

“…Perhaps, the most striking example provides a series of conformationally constrained hexasilanes 59-62 (composed of three dihedral angles) that have been structurally characterized by X-ray studies [100,101] (Figure 22). These findings clearly revealed that σ-conjugation in polysilanes is effectively extended by anti or deviant conformations, while conformations with small dihedral angles such as syn, cis or gauche do not contribute to the extent of σ-conjugation [102].…”

Section: Conformational Effectsmentioning

confidence: 99%

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Polysilane Dendrimers

Krempner

2012

Polymers

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Abstract:The synthesis, structure and electronic properties of polysilane dendrimers, a relatively new class of highly branched and silicon-rich molecular architectures is reviewed. After a detailed discussion of main synthetic strategies to well-defined single-core and double-core polysilane dendrimers, important structural and conformational features determined by single crystal X-ray crystallography and 29 Si-NMR spectroscopy are presented. The last part highlights the most interesting photochemical properties of polysilane dendrimers such as UV absorption and emission behavior, which are compared with those of linear and branched polysilanes.

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Section: Conformational Effectsmentioning

confidence: 95%

Section: Conformational Effectsmentioning

confidence: 99%

Polysilane Dendrimers

Krempner

2012

Polymers

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“…Furthermore, homocatenated silicon oligomers with conformations (trans, cis, etc.) controlled by introducing bulky substituents have also been synthesized to examine the change in electronic and optical properties caused by σ-conjugation [4].Nanotechnology that can manipulate molecules or polymers has encouraged the development of single molecular conduction using scanning tunneling microscope (STM) analysis [5,6]. The STM-controlled break junction method can measure step-like conductance in molecular samples affixed to the cantilever of the STM system.…”

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confidence: 99%

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confidence: 99%

Electronic transport properties of linear homocatenated indium chains

Matsuura

2015

Theor Chem Acc

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examine the electrical and optical properties arising from σ-conjugation in the silicon main chain. Furthermore, homocatenated silicon oligomers with conformations (trans, cis, etc.) controlled by introducing bulky substituents have also been synthesized to examine the change in electronic and optical properties caused by σ-conjugation [4].Nanotechnology that can manipulate molecules or polymers has encouraged the development of single molecular conduction using scanning tunneling microscope (STM) analysis [5,6]. The STM-controlled break junction method can measure step-like conductance in molecular samples affixed to the cantilever of the STM system. The step-like conductance was thought to be due to the quantized conduction of electrons, which were transported by a ballistic tunneling process. Furthermore, theoretical studies have been carried out using the non-equilibrium Green's function (NEGF) method to gain an insight into the ballistic tunneling transport in molecular samples sandwiched between metal electrodes [7][8][9][10][11]. Homocatenated silicon oligomers with terminals modified by the 4-(methylthio) phenyl group were used for measuring molecular conduction using the STM method [12]. The NEGF calculations, along with the experimental results, clarified the similarity between the electrical conduction caused by σ-conjugation and organic π-conjugation. Although molecular conduction in homocatenated germanium oligomers has not been measured yet, NEGF calculations explicitly showed molecular conduction through σ-conjugation, similar to the homocatenated silicon oligomers [13].Linear homocatenated oligomers of group 13 elements are rare. For example, a hexa-indium chain synthesized using N-xylyl β-diketiminate as the support showed UV absorption due to σ-conjugation in the indium main chain [14]. Gallium species with genuine Ga-Ga bonds were Abstract The electronic transport properties of linear homocatenated indium chain were estimated through firstprinciple calculations. Long chains comprising four or five indium atoms exhibited a large transmission peak at the Fermi level, which enhanced their conductance. This peak was caused by enhanced σ-conjugation in the indium main chain. Due to σ-conjugation, the conductance did not monotonously attenuate under tunneling upon extension of molecular length. Therefore, homocatenation in indium chains is a promising candidate for molecular conduction.

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“…In our recent study on the photophysical properties of conformationally controlled oligosilanes using disilane units configurationally constrained into syn or anti by two pentamethylene tethers ( Figure), 1 we reported the synthesis of the tetrasilane compound anti,anti-dimer 2 (shown in Scheme) by the reaction of syn,syn-1,4-dichlorotetrasilane 1 with methyllithium with inversion of configuration at both silicon centers. 2 Since the yield of this reaction was not satisfactory (30%), we have been trying to optimize the reaction conditions and found the following unprecedented effect by metal cyanides: (1) the yield and the selectivity for 2 are dramatically increased by the addition of potassium cyanide to the reaction mixture, and (2) the stereoselectivity is completely changed from inversion to retention by the change in the countercation of the cyanide salt added, namely from potassium to copper(I).…”

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Stereochemical Control of the Reaction of Chlorosilane with Methyllithium by the Addition of Metal Cyanide: Inversion by Potassium Cyanide and Retention by Copper(I) Cyanide

Tamao¹,

Tsuji²,

Toshimitsu³

2001

Synlett

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Abstract:In the 1,4-dichlorotetrasilane derivative composed of disilane units bearing two pentamethylene tethers, the substitution of a chlorine atom on the silicon atom by the methyl group during the reaction with methyllithium mainly proceeds with inversion of configuration of the silicon atoms, (1) the yield being dramatically improved by the addition of potassium cyanide, and (2) the stereochemistry being changed to retention of configuration by the addition of copper(I) cyanide.Key words: bicyclic compounds, copper(I) cyanide, organosilicon compounds, potassium cyanide, stereoselectivityIn our recent study on the photophysical properties of conformationally controlled oligosilanes using disilane units configurationally constrained into syn or anti by two pentamethylene tethers (Figure), 1 we reported the synthesis of the tetrasilane compound anti,anti-dimer 2 (shown in Scheme) by the reaction of syn,syn-1,4-dichlorotetrasilane 1 with methyllithium with inversion of configuration at both silicon centers.2 Since the yield of this reaction was not satisfactory (30%), we have been trying to optimize the reaction conditions and found the following unprecedented effect by metal cyanides: (1) the yield and the selectivity for 2 are dramatically increased by the addition of potassium cyanide to the reaction mixture, and (2) the stereoselectivity is completely changed from inversion to retention by the change in the countercation of the cyanide salt added, namely from potassium to copper(I). These results are reported in this paper. 6:1, 0°C -r.t., 12 h) revealed that, in addition to the anti,anti-dimer 2 in 30% yield, the anti,syn-dimer 3 arising from the substitution reaction with retention of configuration at one silicon center was also formed in 15% yield (Scheme and Table, entry 1). With the addition of potassium cyanide to this reaction mixture, the yields of 2 were dramatically increased (entries 2 and 3) accompanied by the formation of a small amount of syn,syn-dimer 4, the yields of the anti,syn-dimer 3 remaining nearly the same. Thus, the total number of reactions with inversion of configuration N(inv) and that with retention N(ret) at each silicon center 3 were only slightly changed, keeping the N(inv)/N(ret) at 4.8: 1 ~ 6.8: 1 (Figure 1, none and KCN). Table Yields In contrast, in the presence of a catalytic amount of copper(I) cyanide (0.4 molar amount), the syn,syn-dimer 4 was found to be the major product (50% yield) accompanied by the formation of the anti,syn-dimer 3 (18% yield) (entry 4). The structure of 4 was unambiguously confirmed by X-ray crystallographic analysis as shown in Si Si Cl Si Si Cl Si Si Me Si Si Me Si Me Si SiMe Si Si SchemeThis document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.

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Conformation Control of Oligosilanes Based on Configurationally Constrained Bicyclic Disilane Units

Cited by 107 publications

References 14 publications

Polysilane Dendrimers

Polysilane Dendrimers

Electronic transport properties of linear homocatenated indium chains

Stereochemical Control of the Reaction of Chlorosilane with Methyllithium by the Addition of Metal Cyanide: Inversion by Potassium Cyanide and Retention by Copper(I) Cyanide

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