Studies Towards the Acceleration of Diels-Alder Reactions using η6-metal Arene Complex Substituents

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Authors
Lohar, Noah
Advisor
Hitt, David
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Date of Issue
2024
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Title
Studies Towards the Acceleration of Diels-Alder Reactions using η6-metal Arene Complex Substituents
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Abstract
The Diels-Alder (DA) reaction is a cycloaddition reaction between a conjugated diene and a two-atom π system (dienophile) that forms an unsaturated six-membered ring. DA reactions under normal electron demand conditions (diene is electron rich) are limited by the dienophile requiring an electron-withdrawing group (EWG) to proceed at a reasonable rate. These EWGs, in short, are functional groups conjugated with the π system that can act as a π acceptor, most commonly nitriles, carbonyl functional groups (e.g. ketones,esters, etc.), and nitro groups. The complexation of a monocationic (𝜂5-cyclopentadienyl)metal fragment (CpM+) to the π system of a benzenoid compound in an 𝜂6 configuration results in significant electron withdrawal from substituents attached to the aryl ring. This functionality, therefore, may expand the applicability of the Diels-Alder reaction to progress by utilizing the CpM(𝜂6-aryl) substituent to serve as an activating dienophile substituent. The formation of a DA adduct between CpRu(η6-ethyl trans-cinnamate)PF6 and 2,3-dimethyl-1,3-butadiene was successful as observed by 1H NMR. Characterization of the adduct has been assigned on the basis of 13C NMR, 1H NMR, and IR spectra. This research also explored the synthesis of an analogous iron complex, CpFe(η6-ethyl trans-cinnamate)PF6, to accelerate DA reactions. Compared to ruthenium, iron offers many advantages primarily due to its abundance compared to ruthenium. Herein we report our progress in synthesizing CpFe(η6-ethyl trans-cinnamate)PF6.
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Chemistry and Physics