容易かつ選択的なコバルト誘発B-H活性化による,前例のないボロン機能化されたカルボラン誘導体
Zhaojin Wang1, Hongde Ye, Yuguang Li
1State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing, Jiangsu 210093, China.
Journal of the American Chemical Society
|July 10, 2013
まとめ
この研究は,多用途の中間物質として機能する新しい17電子コバルト複合体を明らかにしています. これらの複合体は,コバルト媒介のB-H活性化により,独特のボロン機能化されたカルボラン誘導体の効率的な合成を可能にします.
科学分野:
- 有機金属化学 有機金属化学
- ボロン化学 ボロン化学
- カーボラン合成
背景:
- 16電子コバルト複合体は,有機金属合成における前駆体として機能する.
- カーボランの誘導体は,独特の構造的および電子的特性を有しています.
- 機能化されたカルボランのための新しい合成経路の開発は進行中です.
研究 の 目的:
- 新しい17電子コバルト複合体を合成し,特徴づけること.
- これらのパラマグネティック複合体の反応性と合成有用性を調査する.
- ボロン機能化されたカルボラン誘導体のための効率的なコバルト媒介経路を開発する.
主な方法:
- CpCoS2C2B10H10が様々なアルキンと反応する.
- 17電子コバルト複合体とその誘導体の特徴.
- 反応機構を解明するための密度関数理論 (DFT) 計算.
- 異なる条件 (空気,湿度,シリカ,AlCl3,加熱) の下で反応性の探求.
主要な成果:
- 2種類の17電子コバルト複合体 (2a-dと3a-d) をノルボニルカルボラン部分で形成する.
- コバルトフリーカルボラン誘導体 (4a-d, 5a-d) につながるC-S結合割れの実証.
- Co-S結合にアルキンを挿入すると,ビニル硫化カルボラン (7a-d, 8a-d) が生成されます.
- Retro-Diels-Alder製品 (9a-d) と[1,2]-Hシフト製品 (10b,c) は,特定の条件下で観察されました.
結論:
- 17電子コバルト複合体は,貴重な合成中間物質である.
- コバルト媒介のB-H活性化により,さまざまなボロン機能化されたカルボランに効率的にアクセスできます.
- 従来の方法では入手できないカルボラン誘導体の新しい合成経路が確立されています.
関連する概念動画
03:08Hydroboration-Oxidation of Alkenes
In addition to the oxymercuration–demercuration method, which converts the alkenes to alcohols with Markovnikov orientation, a complementary hydroboration-oxidation method yields the anti-Markovnikov product. The hydroboration reaction, discovered in 1959 by H.C. Brown, involves the addition of a B–H bond of borane to an alkene giving an organoborane intermediate. The oxidation of this intermediate with basic hydrogen peroxide forms an alcohol.
02:36Regioselectivity and Stereochemistry of Hydroboration
A significant aspect of hydroboration–oxidation is the regio- and stereochemical outcome of the reaction.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
02:47Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation
Introduction
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
02:15Preparation of Alcohols via Addition Reactions
Overview
The acid-catalyzed addition of water to the double bond of alkenes is a large-scale industrial method used to synthesize low-molecular-weight alcohols. An acidic atmosphere is required to allow the hydrogen in the water molecule to act as an electrophile and attack the double bond in an alkene. The addition of a proton to the double bond creates a carbocation intermediate. The proton preferentially bonds to the less substituted end of the double bond to create a more stable carbocation...
The acid-catalyzed addition of water to the double bond of alkenes is a large-scale industrial method used to synthesize low-molecular-weight alcohols. An acidic atmosphere is required to allow the hydrogen in the water molecule to act as an electrophile and attack the double bond in an alkene. The addition of a proton to the double bond creates a carbocation intermediate. The proton preferentially bonds to the less substituted end of the double bond to create a more stable carbocation...
01:15α-Bromination of Carboxylic Acids: Hell–Volhard–Zelinski Reaction
The method to achieve α-brominated carboxylic acids using a mixture of phosphorus tribromide and bromine is known as the Hell–Volhard–Zelinski reaction. The reaction is catalyzed by phosphorus tribromide, which can be used directly or produced in situ from red phosphorus and bromine. The mechanism comprises PBr3 catalyzed conversion of acid to acid bromide and hydrogen bromide. The acid bromide enolizes to its enol form in the presence of HBr. The nucleophilic enol attacks the bromine molecule...
02:10Carbocations
Carbocations are one of the reaction intermediates formed during several nucleophilic substitutions or elimination reactions. A carbocation is an electron-deficient species with the central carbon atom having six electrons and three bonded atoms. The central carbon in a carbocation is sp2 hybridized with trigonal planar geometry. It has an empty p orbital perpendicular to the plane of the structure that can accept electrons. Thus, carbocations act as strong electrophiles and may react with any...