二次アルキルニオビウム複合体のアルファおよびベータアゴスティック安定化ロタマー間の均衡
J Jaffart1, M Etienne, F Maseras
1Laboratoire de Chimie de Coordination du CNRS, UPR 8241, 205 Route de Narbonne, 31077 Toulouse Cedex 4, France.
Journal of the American Chemical Society
|June 21, 2001
まとめ
この研究では,ニオビウムの二次アルキル複合体は,異なるベータ-アゴスティックとアルファ-アゴスティック構造を示し,その均衡は電子的およびステリック的要因の影響を受けることを明らかにしています. これらの複合体は,線形アルキル複合体へと熱的再編成される.
科学分野:
- 有機金属化学 有機金属化学
- 協調化化学について
- ボロン化学 ボロン化学
背景:
- この研究では,ヒドロトリス (3,5-ジメチルピラゾリル) ボラート (TpMe2) リガンドを含む二次アルキル複合体の構造動態を調査しています.
- アゴスティック相互作用の理解は,有機金属化合物の反応性と安定性を予測するために重要である.
研究 の 目的:
- 二次アルキルニオビウム複合体の構造的好みと動的均衡を解明する.
- これらのシステムにおけるアゴスティック相互作用に対する電子的およびステリック的要因の影響を調査する.
- Rotamericの均衡と再配置を制御する熱力学および運動学的パラメータを特徴付ける.
主な方法:
- 固体構造を特定するためのX線結晶学.
- 溶液核磁気共鳴 (NMR) スペクトロスコーピーは,動的均衡と運動学を研究する.
- 理論的な分析のための混合量子力学/分子力学 (QM/MM) 計算.
主要な成果:
- イソプロピルクロロ複合体Tp(Me2) NbCl(i-Pr) ((PhCCMe) は,結晶においてβ-アゴスティックな構造を示し,溶液中のβ-アゴスティックとα-アゴスティックなロタマーの間の均衡を保っている.
- セック-ブチル複合体のダイアステロエーマーには,固体状態と溶液状態で明確なアゴスティック相互作用があり,一つのダイアステロエーマーには観察可能な均衡がある.
- NMR研究は,Nb-C結合のバランスと回転に関する熱力学および運動学的パラメータを提供した.
- イソトープ効果と計算による研究は,アゴスティックな好みにステリックと電子的要因の影響を確認した.
結論:
- 二次アルキルニオビウム複合体は,電子効果とステリック効果のバランスによって引き起こされる複雑なアゴスティック行動を示します.
- Tp(Me2) リガンドのステリック塊は,アルキルグループの構成を指示する上で重要な役割を果たします.
- 研究されたすべての二次アルキル複合体は,第一次流程による線形アルキル複合体への熱的再配置を受けます.
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.
01:202° Amines to N-Nitrosamines: Reaction with NaNO2
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01:19Types of Enols and Enolates
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01:09Complexation Equilibria: Factors Influencing Stability of Complexes
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