Have you ever wondered how ligand substituents affect the efficiency of an iron catalyst during oxidation/reduction reactions? We do!
Synthetic chemistry is a large part of everyday life, whether you know it or not! Synthetic chemists are responsible for creating everyday objects like pharmaceuticals, plastics, and batteries. A common synthetic step required to make these things are oxidation and reduction reactions. Below are simplified examples of a ketone reduction and an alcohol oxidation.
However, many oxidation and reduction reactions can be costly, inefficient, and an environmental burden. In some cases large amounts of toxic and/or expensive reagents are needed. In other cases highly efficient catalysts are used, but they may be made from rare metals or use reactive terminal oxidants or reductants. Our research is continuing the ongoing investigation of a class of (cyclopentadienone)iron tricarbonyl compounds that catalyze these reactions, with a focus on low cost, efficiency, and sustainability. Iron is the second most abundant metal in the earth’s crust, and we are using simple, relatively unreactive oxidants and reductants in our processes.
We have two main projects this summer: 1) synthesizing and exploring the reactivity of iron catalysts with different substituents (collections of atoms) to determine how electron distribution impacts catalyst activity; and 2) exploring the reactivity of (cyclopentadienone)iron tricarbonyl compounds in transfer oxidations. Amelia and Evan are working on project #1, and Tracy and Melanie are tackling project #2.
Amelia spent the first couple weeks synthesizing a catalyst and purifying it, but now she is testing out the reactivity of five different catalysts. She spends her days oxidizing 4-phenyl-2-butanol and reducing acetophenone and comparing the relative rates and conversions of those reactions to gain insight into whether electron-rich or electron-poor catalysts are more reactive. Considering each reaction takes 48-72 hours, it takes her a lot of time to get data points! The goal of all her waiting is to find which catalyst is the best at each reaction. We will eventually use what we have learned to design new, more active catalysts.
Evan has been synthesizing cyclopentadienones and their corresponding iron carbonyl compounds for most of his time in the lab. Isolating and purifying those catalysts has produced a love-hate relationship between Evan and flash column chromatography. After he isolated said catalysts, he began testing one of them for its catalytic ability over 24 hours and running it through a kinetic gauntlet to determine how the initial rate of his catalyst in redox reaction compares to the other catalysts. He is currently performing cyclic voltammetry on the catalysts to gain insight into their electrochemical behavior.
Tracy is testing three different catalysts on an abundance of different diols (compounds with two alcohols) to try to form lactones (cyclic esters) through sequential oxidations. Lactones are found in everything from natural flavors to antibiotics. She is collecting mountains of data on these reactions to collect as much information on the reactivities of these catalysts as possible. Not only does she have to test each diol with each catalyst, but she often has to make the diol as well!
Melanie is working with one catalyst/oxidant system that has shown itself to be efficient in alcohol oxidation reactions. Conveniently, the terminal oxidant is readily available from agricultural waste, and because she is also using an iron-based catalyst, her process is sustainable. She has spent the summer first finding the best conditions for the catalyst (solvent, temperature, length of reaction, concentration of substrate, etc) and is now testing these conditions on multiple alcohols to determine how well it works with different structures and functional groups. The objective of these studies is to determine how general her synthetic method is. She is also working on getting isolated yields of carbonyl products to see how much of the product from the reaction can actually be obtained.