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Investigation on Molecular Catalysts for Activation and Effective Fixation of CO2
https://ir.soken.ac.jp/records/166
https://ir.soken.ac.jp/records/1666a0513b8-831c-4450-849c-4c4165ff8b95
| 名前 / ファイル | ライセンス | アクション |
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要旨・審査要旨 / Abstract, Screening Result (367.1 kB)
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本文 / Thesis (11.3 MB)
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| Item type | 学位論文 / Thesis or Dissertation(1) | |||||
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| 公開日 | 2010-02-22 | |||||
| タイトル | ||||||
| タイトル | Investigation on Molecular Catalysts for Activation and Effective Fixation of CO2 | |||||
| タイトル | ||||||
| タイトル | Investigation on Molecular Catalysts for Activation and Effective Fixation of CO2 | |||||
| 言語 | en | |||||
| 言語 | ||||||
| 言語 | eng | |||||
| 資源タイプ | ||||||
| 資源タイプ識別子 | http://purl.org/coar/resource_type/c_46ec | |||||
| 資源タイプ | thesis | |||||
| 著者名 |
中島, 洋
× 中島, 洋 |
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| フリガナ |
ナカジマ, ヒロシ
× ナカジマ, ヒロシ |
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| 著者 |
NAKAJIMA, Hiroshi
× NAKAJIMA, Hiroshi |
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| 学位授与機関 | ||||||
| 学位授与機関名 | 総合研究大学院大学 | |||||
| 学位名 | ||||||
| 学位名 | 博士（理学） | |||||
| 学位記番号 | ||||||
| 内容記述タイプ | Other | |||||
| 内容記述 | 総研大甲第186号 | |||||
| 研究科 | ||||||
| 値 | 数物科学研究科 | |||||
| 専攻 | ||||||
| 値 | 07 構造分子科学専攻 | |||||
| 学位授与年月日 | ||||||
| 学位授与年月日 | 1996-03-21 | |||||
| 学位授与年度 | ||||||
| 値 | 1995 | |||||
| 要旨 | ||||||
| 内容記述タイプ | Other | |||||
| 内容記述 | Utilization of CO2 is the subject of continuing importance in the view of predictable energy shortage in near future and the increase of a green house effect. Photo- and electro-chemical CO2 fixation catalyzed by metal complexes has a significant advantage for elucidation of the reaction mechanism because of facile physical measurements for tracing reaction intermediates. The design of the molecular catalysts based on the knowledge concerning the reaction intermediates would largely contribute for improving the efficient utilization of CO2. Recent progress in the reduction of CO2 using metal complexes as catalyst precursors has disclosed for the formation of CO and/or HCOO- in some detail. It is generally accepted that metal-carbonyl complexes ([M-CO](n+2)+) formed through an acid - base equilibrium with [M-COOH] (n+1)+ and [M-η1-CO2]n+ in protic media play a role in CO evolution (eq 1). While the reductive disproportionation between [M(CO2)]n+ and CO2 or another [M(CO2)]n+ becomes predominant pathways for the [M-CO](n+2)+ formation in aprotic media (eq 2). The mechanism of an oxide transfer reaction of the terminal oxygen atom from η1-coordinated CO2 to another CO2 (eq 3), however, has not been fully explored due to a limited number of a well-characterized metal-η1 -CO2 complexes. In chapter 2, to obtain a definitive evidence for the reductive disproportionation the author discusses the oxide transfer reaction from CO32-to [Ru(bpy)2(CO)2]2+ to afford [Ru(bpy)2(CO)(η1 -CO2)] which is well-known as a stable η1 -CO2 complex. The reaction proceeds through two steps: a nucleophilic attack of CO32- to the carbonyl ligand of [Ru(bpy)2(CO)2]2+, and the subsequent dissociation of CO2 to afford [Ru(bpy)2(CO)(η1-CO2)] (Scheme 1 ). The observed rate constant of the first step (k1obs) is followed by the first-order with respect to the concentrations of both the complex and CO3 2-, and that of the second one (k2obs) was essentially independent on the concentration of CO32- under the pseudo-first order reaction conditions. The similarities of 13C-NMR spectrum and the MLCT band of the intermediate (σ = 201.7 and 205.2 ppm, and λmax = 390 nm ) to those of [Ru(bpy)2(CO)(COOH)]+ (σ = 201.5 and 204.3, and λmax = 390 nm) also support the adduct formation between [Ru(bpy)2(CO)2]2+ with CO3 2- prior to the oxide transfer from CO3 2- to [Ru(bpy)2(CO)2]2+. The finding of the reverse reaction of eq 3 via the proposed intermediate in eq 3 demonstrates the validity of eq 3 for the reductive disproportionation of CO2 under aprotic conditions. The smooth conversion from [Ru(bpy)(trpy)(η1-CO2)] to [Ru(bpy)(trpy)(CO)]2+ (trpy= 2, 2':6', 2"-terpyridine) in EtOH/H2O (eq 1), and the subsequent reduction to[Ru(bpy)(trpy)(CHO)]+ and [Ru(bpy)(trpy)(CH2OH)]+ in the same solvent has been applied to the first catalytic generation of HCHO, CH3OH, HOOCCHO, and HOOCCH2OH in electro chemical reduction of CO2. Multi-electron reduction of CO2 using organic electrophiles instead of protons would provide more versatile routes for the catalytic carbon-carbon bond formation in the viewpoint of CO2 as potential C1 sources for organic compounds. The smooth conversion from CO2 to CO under aprotic conditions, therefore, may be a promising gateway to the multi-electron reduction of CO2 in the presence of organic electrophiles. In contrast to the conversion from [M-η1-CO2]n+ to [M-CO2](n+2)+ assisted by proton (eq 1), strong basicity of [M-η1 -CO2]n+ would be required for the facile reductive disproportionation of CO2 under mild conditions (eq 2). The basicity of η1 -CO2, species is estimated from the pKa values of the hydroxycarbonyl complexes ([M-COOH](n+1)+) in eq 1. On the basis of the pKa of [Ru(bpy)2(CO)(COOH)]+ (9.6), and the wide range of pKa values from over 14 to 2.5 of hydroxycarbonyl complexes reported so far, the replacement of the carbonyl ligand in [Ru(bpy)2(CO)(η1 -CO2)] with an electron donating group would greatly enhance the basicity of the η1 -CO2 moiety to enable the smooth oxide transfer from η1 -CO2 to CO2. In chapter 3, the author discusses the first catalytic formation of acetone and acetoacetic acid in electrochemical CO2 reduction by [Ru(bpy)2 (qu)(CO)]2+ (qu = quinoline) under aprotic conditions, which is composed of two key reactions. The first is the double methylation of the two electron form of [Ru-CO]2+ to afford CH3C(O)CH3 where [Ru-CO]2+ is regenerated through the oxide transfer from Ru-η1 -CO2]0 to CO2 (eq 3). The second is the subtraction of the proton from resulting CH3C(O)CH3 by [Ru-η1 -CO2] to give [Ru-COOH]+ and CHO3C(O)CH2-, the latter of which further undergoes carboxylation to produce CH3C(O)CH2COO-. Tetramethyl ammonium as an electrolyte was proved to function as the methyl source for the methylation of [Ru-CO]0. Current efficiencies of CO, HCOO-, CH3C(O)CH3, and CH3C(O)CH2COO- were 42, 7, 16, and 6%, respectively, after 60 C passed. The first catalytic formation of ketones and ketoacids by double alkylation of metal-carbonyl species resulting from reductive disproportionation of CO2 demonstrates the feasibility of CO2 as a building block in organic synthesis, although the main products of the CO2 reduction is still CO. As mentioned above, one of the advantage of homogeneous reactions using molecular catalysts is facile physical measurements for tracing reaction intermediates. Another advantage is the capability of the modification of the reaction sites to suit to the reaction by choosing appropriate ligands. In homogeneous catalytic reactions, site opening of catalysts only when reactions take place would be preferable for stabilization of the catalysts, inhibition of side reactions, and promotion of eliminating the products from a reaction center. Metal complexes with the ligands which can vary their coordination modes reversibly with a little configurational barrier would serve to construct such a reaction system. Taking into account that some metal- 1, 8- naphthyridine (napy) complexes undergo fast isomerization reactions between η1 - and η2 -modes in solutions, napy is expected to be a suitable ligand for the design of homogeneous catalysts provided with the function of site-opening and -closing in catalytic cycles. In chapter 4, a dynamic behavior of [Ru(bpy)2(η1 -napy)(solvent)]n+ and [Ru(bpy)2(η2 -napy)]n+ (n = 1 and 2) is discussed in connection with the efficient catalytic activity of the analogous [Ru(bpy)2 (qu)(CO)]2+ for electro-chemical reduction of CO2 as described in chapter 3. The detailed study revealed that relative stability between rutherjum η1 - and η2 - napy complexes is largely dependent on the charges of the complexes and temperatures, which gives fundamental knowledge of controlling η1 - and η2- modes of napy directed toward effective site-opening and -closing system in homogeneous electrochemical catalysts. Based on the achievements of the smooth oxide transfer from [Ru(bpy)2(qu)(η1 -CO2)] to CO2 (chapter 3) and the control of the coordination modes of the napy ligand in [Ru(bpy)2(η1 -napy)(solvent)]n+ and [Ru(bpy)2(η2 -napy)]n+ (n = 1, 2) (chapter 4), the activation of the carbonyl moiety of [Ru(bpy)2 (η1 -napy)(CO)]2+ resulting from the reductive disproportionation of the CO2 ligand of [Ru(bpy)2(η1 -napy)(η1 -CO2)] was conducted by taking advantage of the smooth inter conversion of the coordination modes of the napy ligand. In chapter 5, the author discussed the reversible conversion from the carbonyl moiety to the metallacyclo ring driven by the [Ru(bpy)2(η1 -napy)(CO)]2+/+ redox reaction. One-electron reduction of [Ru(bpy)2(η1 -napy)(CO)]2+ takes place on a molecular orbital localized in the napy ligand. The increase in the electron density in the napy ligand results in the intramolecular nucleophilic attack of the free nitrogen atom of the ligand against the carbonyl group to afford a five-membered carbamoyl ring ( Ru - C(O) - N - C - N), which can be opened to regenerate [Ru(bpy)2(η1 -napy)(CO)]2+ quantitatively upon the reoxidation. Thus, the participation of a well designed ligand in the activation of the carbonyl group is expected to afford new methodology for the smooth conversion from CO2 to organic carbonyl groups without accompanying an unfavorable CO dissociation due to an M-CO bond cleavage in the reduction of CO2. |
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| 値 | 有 | |||||
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| 内容記述タイプ | Other | |||||
| 内容記述 | application/pdf | |||||
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| 出版タイプ | AM | |||||
| 出版タイプResource | http://purl.org/coar/version/c_ab4af688f83e57aa | |||||
