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A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Organic Chemistry".

Deadline for manuscript submissions: closed (15 July 2016) | Viewed by 70940

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Prof. Dr. Mitsuo Kira

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Department of Chemistry, Graduate School of Science, Tohoku University, Sendai, Japan
Interests: silicon chemistry; organometallic chemistry; physical organic chemistry; theoretical organometallic chemistry
Special Issues, Collections and Topics in MDPI journals

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Dear Colleagues,

Today, in addition to tetravalent and hypercoordinate silicon compounds, various silicon unsaturated compounds, such as silylenes, silaethenes, disilenes, disilynes, and silicon-heteroatom doubly bonded compounds, are in our hands as isolable compounds thanks to the recent efforts of many researchers. They have revealed rather unusual features of bonding and structure of these silicon compounds, asking for restructuring of a widely applicable theory of bonding and structure of heavy main group elements including silicon. As single element chemistry, silicon chemistry is going to compare favorably with relatively well-established organic chemistry. To overview which directions studies in this research field are heading, this Special Issue is aimed to provide a forum for every aspect of molecular silicon compounds, including synthesis, properties, and new reactions of various molecular silicon compounds, their theoretical, spectroscopic, optoelectronic, and mechanistic studies, and their application towards the material science.

Prof. Dr. Mitsuo Kira
Guest Editor

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Keywords

low-coordinate and multiply-bonded silicon compounds
silicon compounds with unusual structures
hypercoordinate silicon compounds
silicon transition-metal complexes
bonding and structure
reactions and mechanisms
silicon-based materials

Related Special Issues

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Progress in Silicon and Organosilicon Chemistry in Molecules (4 articles)
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Published Papers (13 papers)

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171 KiB

Open AccessEditorial

Strait Gate: Special Issue on Advances in Silicon Chemistry

by Mitsuo Kira

Molecules 2017, 22(9), 1497; https://doi.org/10.3390/molecules22091497 - 07 Sep 2017

Viewed by 2958

Abstract

Manufacturing high-purity element silicon and organic polysilicones are two major silicon industries, supporting the basis of the modern electronic industry and our daily lives [...]
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2498 KiB

Open AccessCommunication

Discovery of an Octahedral Silicon Complex as a Potent Antifungal Agent

by Chen Fu, Bin Fu, Xixi Peng and Guojian Liao

Molecules 2017, 22(4), 637; https://doi.org/10.3390/molecules22040637 - 15 Apr 2017

Cited by 1 | Viewed by 4577

Abstract

Octahedral transition metal complexes have been shown to have tremendous applications in chemical biology and medicinal chemistry. Meanwhile, structural transition metals can be replaced by inert octahedral silicon in a proof-of-principle study. We here introduce the first example of octahedral silicon complexes, which can very well serve as an efficient antimicrobial agent. The typical silicon arenediolate complex 1 {[(phen)₂Si(OO)](PF₆)₂, with phen = 1,10-phenanthroline, OO = 9,10-phenanthrenediolate} exhibited significant inhibition towards the growth of Cryptococcus neoformans with MIC and MFC values of 4.5 and 11.3 μM, respectively. Moreover, it was fungicidal against both proliferative and quiescent Cryptococcus cells. This work may set the stage for the development of novel antifungal drugs based upon hexacoodinate silicon scaffolds. Full article

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3351 KiB

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A Computational Investigation of the Substituent Effects on Geometric, Electronic, and Optical Properties of Siloles and 1,4-Disilacyclohexa-2,5-dienes

by Aleksandra V. Denisova, Julius Tibbelin, Rikard Emanuelsson and Henrik Ottosson

Molecules 2017, 22(3), 370; https://doi.org/10.3390/molecules22030370 - 28 Feb 2017

Cited by 13 | Viewed by 5101

Abstract

Thirty two differently substituted siloles 1a–1p and 1,4-disilacyclohexa-2,5-dienes 2a–2p were investigated by quantum chemical calculations using the PBE0 hybrid density functional theory (DFT) method. The substituents included σ-electron donating and withdrawing, as well as π-electron donating and withdrawing groups, and their effects when placed at the Si atom(s) or at the C atoms were examined. Focus was placed on geometries, frontier orbital energies and the energies of the first allowed electronic excitations. We analyzed the variation in energies between the orbitals which correspond to HOMO and LUMO for the two parent species, here represented as Δε_HL, motivated by the fact that the first allowed transitions involve excitation between these orbitals. Even though Δε_HL and the excitation energies are lower for siloles than for 1,4-disilacyclohexa-2,5-dienes the latter display significantly larger variations with substitution. The Δε_HL of the siloles vary within 4.57–5.35 eV (ΔΔε_HL = 0.78 eV) while for the 1,4-disilacyclohexa-2,5-dienes the range is 5.49–7.15 eV (ΔΔε_HL = 1.66 eV). The excitation energy of the first allowed transitions display a moderate variation for siloles (3.60–4.41 eV) whereas the variation for 1,4-disilacyclohexa-2,5-dienes is nearly doubled (4.69–6.21 eV). Cyclobutadisiloles combine the characteristics of siloles and 1,4-disilacyclohexa-2,5-diene by having even lower excitation energies than siloles yet also extensive variation in excitation energies to substitution of 1,4-disilacyclohexa-2,5-dienes (3.47–4.77 eV, variation of 1.30 eV). Full article

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1649 KiB

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Theoretical Study on the Second Hyperpolarizailities of Oligomeric Systems Composed of Carbon and Silicon π-Structures

by Hiroshi Matsui, Takanori Nagami, Shota Takamuku, Soichi Ito, Yasutaka Kitagawa and Masayoshi Nakano

Molecules 2016, 21(11), 1540; https://doi.org/10.3390/molecules21111540 - 15 Nov 2016

Cited by 2 | Viewed by 4359

Abstract

To explore the prospect of molecules involving silicon-silicon multiple bonds as nonlinear optical molecular systems, the relationship between the structure and the second hyperpolarizabilities γ of the oligomeric systems composed of carbon and silicon π-structures is investigated using the density functional theory method. It is found that these compounds indicate intramolecular charge transfer (ICT) from the silicon units to the carbon units together with nonzero diradical characters. The γ values of these compounds are shown to be 2–13 times as large as those of the carbon analogs. Although asymmetric carbon and silicon π-systems exhibit comparable enhancement to the corresponding symmetric systems, donor-π-donor structures exhibit remarkable enhancement of γ despite of their both-end short silicon π-chain moieties (donor units). Further analysis using the odd electron and γ densities clarifies that the intermediate diradical character also contributes to the enhancement of γ. These results predict that even short π-conjugated silicone moieties can cause remarkable enhancement of γ by introducing them into π-conjugated hydrocarbon structures. Full article

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3796 KiB

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Reactions of an Isolable Dialkylsilylene with Aroyl Chlorides. A New Route to Aroylsilanes

by Xu-Qiong Xiao, Xupeng Liu, Qiong Lu, Zhifang Li, Guoqiao Lai and Mitsuo Kira

Molecules 2016, 21(10), 1376; https://doi.org/10.3390/molecules21101376 - 15 Oct 2016

Cited by 8 | Viewed by 4510

Abstract

The reactions of isolable dialkylsilylene 1 with aromatic acyl chlorides afforded aroylsilanes 3a–3c exclusively. Aroylsilanes 3a–3c were characterized by ¹H-, ¹³C-, and ²⁹Si-NMR spectroscopy, high-resolution mass spectrometry (HRMS), and single-crystal molecular structure analysis. The reaction mechanisms [...] Read more.

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3761 KiB

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Synthesis of Thioethers by InI₃-Catalyzed Substitution of Siloxy Group Using Thiosilanes

by Yoshihiro Nishimoto, Aya Okita, Akio Baba and Makoto Yasuda

Molecules 2016, 21(10), 1330; https://doi.org/10.3390/molecules21101330 - 06 Oct 2016

Cited by 4 | Viewed by 5760

Abstract

The substitution of a siloxy group using thiosilanes smoothly occurred in the presence of InI₃ catalyst to yield the corresponding thioethers. InI₃ was a specifically effective catalyst in this reaction system, while other typical Lewis acids such as BF₃⋅OEt₂, AlCl₃, and TiCl₄were ineffective. Various silyl ethers such as primary alkyl, secondary alkyl, tertiary alkyl, allylic, benzylic, and propargylic types were applicable. In addition, bulky OSitBuMe₂ and OSiiPr₃ groups, other than the OSiMe₃ group, were successfully substituted. The substitution reaction of enantiopure secondary benzylic silyl ether yielded the corresponding racemic thioether product, which suggested that the reaction of tertiary alkyl, secondary alkyl, benzylic, and propargylic silyl ethers would proceed via a S_N1 mechanism. Full article

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Synthesis of a 1-Aryl-2,2-chlorosilyl(phospha)silene Coordinated by an N-Heterocyclic Carbene

by Andreas Wolfgang Kyri, Paresh Kumar Majhi, Takahiro Sasamori, Tomohiro Agou, Vitaly Nesterov, Jing-Dong Guo, Shigeru Nagase, Norihiro Tokitoh and Rainer Streubel

Molecules 2016, 21(10), 1309; https://doi.org/10.3390/molecules21101309 - 30 Sep 2016

Cited by 11 | Viewed by 5663

Abstract

Phosphasilenes, P=Si doubly bonded compounds, have received considerable attention due to their unique physical and chemical properties. We report on the synthesis and structure of a chlorophosphasilene coordinated by an N-heterocyclic carbene (NHC), which has the potential of functionalization at the Si–Cl moiety. Treatment of a silylphosphine, ArPH–SiCl₂R_Si (Ar = bulky aryl group, R_Si = Si(SiMe₃)₃) with two equivalents of Im-Me₄ (1,3,4,5-tetramethylimidazol-2-ylidene) afforded the corresponding NHC-coordinated phosphasilene, ArP=SiClR_Si(Im-Me₄) as a stable compound. Bonding properties of the P=Si bond coordinated to an NHC will be discussed on the basis of theoretical calculations. Full article

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1109 KiB

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Effects of Substitution on Solid-State Fluorescence in 9-Aryl-9-methyl-9H-9-silafluorenes

by Yoshinori Yamanoi, Takayuki Nakashima, Masaki Shimada, Hiroaki Maeda and Hiroshi Nishihara

Molecules 2016, 21(9), 1173; https://doi.org/10.3390/molecules21091173 - 03 Sep 2016

Cited by 4 | Viewed by 5791

Abstract

Aromatic groups were incorporated into 9H-9-silafluorene units at the 9-position (mono-9H-silafluorenes) and 9,9′-positions (di-9H-9-silafluorenes). The aryl substituents showed weak conjugation to the 9H-9-silafluorene for 9-aryl substituted ones 1–7 and a 9,9′-phenylene substituted one (compound 8) and they exhibited similar absorption and emission spectra. The 9H-9-silafluorene 10 containing a 5,5′-(2,2′-bithiophenyl) group showed a significantly red-shifted absorption and fluorescence maxima in the solid-state. Single-crystal X-ray diffraction studies found J-type aggregated structures formed by intermolecular CH–π interactions (ca. 2.6–2.7 Å). Density functional theory (DFT), time-dependent DFT (TD-DFT), and configuration interaction single (CIS) calculations were conducted to explain the observed optical properties. Full article

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2665 KiB

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Facile Access to Stable Silylium Ions Stabilized by N-Heterocyclic Imines

by Tatsumi Ochiai, Tibor Szilvási and Shigeyoshi Inoue

Molecules 2016, 21(9), 1155; https://doi.org/10.3390/molecules21091155 - 30 Aug 2016

Cited by 12 | Viewed by 6636

Abstract

Novel silylium ions with N-heterocyclic imines were successfully synthesized. The reaction of trimethylsilyl imidazolin-2-imine Me₃SiNIPr (NIPr = bis(2,6-diisopropylphenyl)-imidazolin-2-imino) with B(C₆F₅)₃ leads to dimeric imino-substituted silylium ions through a methyl group abstraction on the silicon atom. Meanwhile, the intermolecular imino-coordinated silylium ion is formed by using the less sterically crowded imine Me₃SiNItBu (NItBu = bis(tert-butyl)-imidazolin-2-imino). Furthermore, the treatment of dimethylchlorosilane Me₂(Cl)SiNIPr with AgOTf affords the contact ion pair Me₂(OTf)SiNIPr by substitution of the chloride. A novel complex with the formula [Me₂(DMAP)SiNIPr][OTf] was prepared by coordination with 4-dimethylamino-pyridine (DMAP). In the solid state, the DMAP adduct [Me₂(DMAP)SiNIPr][OTf] contains a distinct [Me₂(DMAP)SiNIPr]⁺ moiety. Full article

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8225 KiB

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σ-Bond Electron Delocalization in Oligosilanes as Function of Substitution Pattern, Chain Length, and Spatial Orientation

by Johann Hlina, Filippo Stella, Mohammad Aghazadeh Meshgi, Christoph Marschner and Judith Baumgartner

Molecules 2016, 21(8), 1079; https://doi.org/10.3390/molecules21081079 - 18 Aug 2016

Cited by 11 | Viewed by 5484

Abstract

Polysilanes are known to exhibit the interesting property of σ-bond electron delocalization. By employing optical spectroscopy (UV-vis), it is possible to judge the degree of delocalization and also differentiate parts of the molecules which are conjugated or not. The current study compares oligosilanes of similar chain length but different substitution pattern. The size of the substituents determines the spatial orientation of the main chain and also controls the conformational flexibility. The chemical nature of the substituents affects the orbital energies of the molecules and thus the positions of the absorption bands. Full article

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921 KiB

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Intramolecular Chain Hydrosilylation of Alkynylphenylsilanes Using a Silyl Cation as a Chain Carrier

by Hidekazu Arii, Kenichi Nakabayashi, Kunio Mochida and Takayuki Kawashima

Molecules 2016, 21(8), 999; https://doi.org/10.3390/molecules21080999 - 01 Aug 2016

Cited by 24 | Viewed by 4781

Abstract

Diorganyl[2-(trimethylsilylethynyl)phenyl]silanes 1a–c and methyl-substituted phenylsilanes 1d and 1e were treated with a small amount of trityl tetrakis(pentafluorophenyl)borate (TPFPB) as an initiator in benzene to afford the corresponding benzosiloles (2a–e) in moderate to good yields. However, no reaction was observed for the reaction using [2-(1-hexynyl)phenyl]diisopropylsilane lf. The methyl substituent was tolerated under the reaction conditions and increased the yield of the corresponding benzosilole depending on the substitution position. From the result using 1f, the current reaction was found to require the trimethylsilyl group, which can stabilize intermediary alkenyl carbocations by the β-silyl effect. The current reaction can be considered an intramolecular chain hydrosilylation of alkynylarylsilanes involving silyl cations as chain carriers. Therefore, the silyl cations generated by hydride abstraction from hydrosilanes 1 with the trityl cation causes intramolecular electrophilic addition to the C-C triple bond to form ethenyl cations, which abstract a hydride from 1 to afford benzosiloles 2 with the regeneration of the silyl cations. Full article

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2904 KiB

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Isolation of a Cyclic (Alkyl)(amino)germylene

by Liliang Wang, Yi Shan Lim, Yongxin Li, Rakesh Ganguly and Rei Kinjo

Molecules 2016, 21(8), 990; https://doi.org/10.3390/molecules21080990 - 29 Jul 2016

Cited by 26 | Viewed by 9121

Abstract

A 1,4-addition of a dichlorogermylene dioxane complex with α,β-unsaturated imine 1 gave a dichlorogermane derivative 2 bearing a GeC₃N five-membered ring skeleton. By reducing 2 with KC₈, cyclic (alkyl)(amino)germylene 3 was synthesized and fully characterized. Germylene 3 readily reacted [...] Read more.

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1528 KiB

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Synthesis of a Conjugated D-A Polymer with Bi(disilanobithiophene) as a New Donor Component

by Makoto Nakashima, Yousuke Ooyama, Takuya Sugiyama, Hiroyoshi Naito and Joji Ohshita

Molecules 2016, 21(6), 789; https://doi.org/10.3390/molecules21060789 - 17 Jun 2016

Cited by 5 | Viewed by 4818

Abstract

A new conjugated donor-acceptor (D-A) polymer pDSBT2-BT containing bi(disilano-bisthiophene) and benzothiadiazole as donor and acceptor units, respectively, was prepared. The polymer showed a broad UV-vis absorption band at λ_max = 599 nm in chlorobenzene. The absorption band was shifted to λ_max = 629 nm when the polymer was measured as a film, indicating enhanced interchain interactions of the polymer. Bulk hetero-junction polymer solar cells (BHJ-PSCs) were fabricated using pDSBT2-BT and PC₇₁BM as host and guest materials, respectively. Optimization of cell fabrication conditions provided a maximal power conversion efficiency of 3.3% and the following cell parameters: V_oc = 0.86 V, J_sc = 7.56 mA/cm², and FF = 0.51. Although the efficiency still leaves much to be desired, these data underscore the potential of pDSBT2-BT as a high-voltage polymer solar cell material. Full article

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