Studies Towards the Acceleration of Diels-Alder Reactions using η6-metal Arene Complex Substituents
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Authors
Lohar, Noah
Date of Issue
2024
Type
Thesis
Language
en_US
Subject Keywords
Other Titles
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 π acceptors, 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 as activating dienophile substituents. Towards this goal, we have isolated the DA adduct between CpRu(η6-ethyl trans-cinnamate)PF6 and 2,3-dimethyl-1,3-butadiene. Characterization of the adduct has been assigned on the basis of 1H NMR, 13C 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.