Submitted by John Lee / University of Tennessee Chattanooga on Wed, 03/02/2022 - 10:26
My Notes

The literature discussion is based on a manuscript by Gunnoe and coworkers (ACS Catal. 2021, 11, 5688-5702. DOI: 10.1021/acscatal.1c01203). The paper presents mechanistic studies of catalytic oxidative conversion of arenes and olefins to alkenyl arenes with a focus on styrene production. Alkyl and alkenyl arenes are produced on a scale of multi-billions of pounds per annum using acid-catalyzed processes. The acid-catalyzed process provides an opportunity to refresh students on the details of Friedel-Crafts catalysis and electrophilic aromatic substitution. The use of transition metal catalysts mediates the same overall reaction, but the mechanism is distinct and offers potential advantages. The paper presents detailed mechanistic studies including kinetics, isolation of potential catalyst intermediates, isotope effects, in situ NMR studies, and DFT-based computational modeling. The primary conclusion is that Cu(II) is embedded into the active catalyst, which is proposed to be a bis-Rh{m-Cu(OPv)2} complex. The proposed mechanism involves benzene C–H activation by an oxidative addition, followed by O–H reductive coupling and then elimination of carboxylic acid. A subsequent beta-hydride elimination and olefin dissociation completes the steps for styrene formation.

This LO is part of a special VIPEr collection honoring the 2022 ACS National Award recipients in the field of inorganic chemistry. T. Brent Gunnoe was the recipient of the Olah Award in Hydrocarbon or Petroleum Chemistry presented for the development of transition metal-catalyzed arene-alkenylation and -alkylation reactions.

Learning Goals

1. Describe the importance of alkyl and alkenyl arenes as well as commercial methods to prepare alkyl/alkenyl arenes and drawbacks that are based on the mechanism of acid-catalyzed arene alkylation.

2. Compare Friedel-Crafts acid-catalyzed alkylation/alkenylation for C–C coupling to transition metal-mediated alkylation/alkenylation. Describe drawbacks of these processes that are based on acid-based commercial catalytic alkyl arene synthesis.

3. Define the terms pre-catalyst/active catalyst, catalyst resting state, induction period, rate determining step, turnover number and turnover frequency as they are applied to a catalytic cycle.

4.   Interpret experimental data, including data from in situ NMR spectroscopy, kinetic data, and single crystal X-ray diffraction, in the determination of a likely mechanism.

5.  Interpret computational data in the determination of a likely mechanism.

6.  Classify C–H activation using oxidative addition and concerted metalation deprotonation mechanisms; define reductive coupling and reductive elimination; define 1,2-insertion of olefins and beta-hydride elimination.

7. Use CBC to count electrons in the Rh complexes in this paper.

8. Define the terms endergonic and exergonic and how do they relate to endothermic and exothermic

9. Describe computational results used to identify the catalyst resting state

10. Interpret a reaction coordinate and use it to identify a rate-determining step.

Implementation Notes

A copy of this paper (and guided questions) should be made available to students at least one week prior to the scheduled literature discussion. During class, allow students to break into small groups and compare and discuss answers to questions. The instructor can assist by addressing questions by each group as well as opening questions for discussion by the entire class.

Time Required
One 50 to 75 minute lecture
Evaluation Methods

The guided questions can be collected and graded. In addition, (or alternatively) a grade can be given based on class participation.

Evaluation Results

This LO has not yet been implemented so there are no evaluation results to share.

Creative Commons License
Attribution, Non-Commercial, Share Alike CC BY-NC-SA