CATALYTIC ALKYLATION AND ALKENYLATION OF ARENES
Aromatic hydrocarbons (e.g benzene, naphthalene, anthracene etc.) and heterocyclic aromatic compounds (e.g quinoline) are present in many biologically active compounds. Structural modifications to these substrates are frequently done in the pharmaceutical industry to synthesize high value precursors to commodity pharmaceuticals. These modifications can be expensive or require harsh conditions. Our group is currently applying our alkenylation chemistry to functionalize these aromatic hydrocarbon substrates. Functionalized polycyclic aromatic substrates can be used further as a precursor to commodity pharmaceuticals. These substrates are typically synthesized through Friedel-Crafts alkylation and related processes catalyzed by Brønstead and/or Lewis acids. These processes operate through carbocation intermediates which dictate the regioselectivity.
We have developed transition metal catalysts based on Ru, Pt, Rh, Ir and Pd which operate through olefin insertion into metal–aryl bonds formed by arene C–H activation. Depending on catalyst steric and electronic properties, the resulting metal–alkyl arene complex can either (1) activate the C–H bond of a second arene and release alkyl arene product or (2) undergo β–hydride elimination to form alkenyl arene product. In the presence of an oxidant (Cu(II) carboxylate or dioxygen), the starting catalyst is regenerated by reaction of oxidant with the metal–H intermediate. While selectivity for Friedel-Crafts alkylation and related processes is controlled by carbocations, selectivity for these transition metal catalysts is catalyst controlled. This facilitates selectivity for anti-Markovnikov products and complementary ortho/meta/para selectivity to Friedel-Crafts and related processes.
Relevant Publications
1. "The Reaction Mechanism Underlying Pd(II)-Catalyzed Oxidative Coupling of Ethylene and Benzene to Form Styrene: Identification of a Cyclic Mono-PdII Bis-CuII Complex as the Active Catalyst" Musgrave III, C. B., Bennett, M. T., Ellena, J. F., Dickie, D. A. Gunnoe, T. B.*, Goddard III, W. A.*Organometallics 2022, 41, 1988–2000 DOI: 10.1021/acs.organomet.2c00183
2. "Advances in Group 10 Transition Metal-Catalyzed Arene Alkylation and Alkenylation" Zhu, W., Gunnoe, T. B.* J. Am. Chem. Soc. 2021, 143, ASAP. DOI: 10.1021/jacs.1c01810
3. "Mechanistic Studies of Styrene Production from Benzene and Ethylene using [Rh(μ-OAc)(η2-C2H4)2]2 as Catalyst Precursor: Identification of a Bis-RhI Mono-CuII Complex as Catalyst" Musgrave III, C. B., Zhu, W., Coutard, N., Ellena, J. F., Dickie, D. A., Gunnoe, T. B.*, Goddard III*, W. A. ACS Catal. 2021, 11, 5688-5702. DOI: 10.1021/acscatal.1c01203
4. "Transition Metal-Catalyzed Arene Alkylation and Alkenylation: Catalytic Processes for the Generation of Chemical Intermediates" Gunnoe, T. B.*, Schinski, W. L.*, Jia, X. ACS Catal. 2020, 10, 14080-14092. DOI: 10.1021/acscatal.0c03494
5. "Rhodium-Catalyzed Arene Alkenylation Using Only Dioxygen as Oxidant" Zhu, W., Gunnoe, T. B.* ACS Catal. 2020, 10, 11519-11531. DOI: 10.1021/acscatal.0c03439
6. "Synthesis of Stilbenes by Rhodium-Catalyzed Aerobic Alkenylation of Arenes via C–H Activation" Jia, X., Frye, L. I., Zhu, W., Gu S., Gunnoe, T. B.* J. Am. Chem. Soc. 2020, 142, 10534-10543. DOI: 10.1021/jacs.0c03935
7. "Advances in Rhodium Catalyzed Oxidative Arene Alkenylation" Zhu, W., Gunnoe, T. B.* Acc. Chem. Res. 2020, 53, 920-936. DOI: 10.1021/acs.accounts.0c00036
8. "Catalytic Synthesis of Super Linear Alkenyl Arenes Using a Rh(I) Catalyst Supported by a "Capping Arene" Ligand: Access to Aerobic Catalysis" Chen, J., Nielsen, R. J.*, Goddard III, W. A., McKeown, B. A., Dickie, D. A., Gunnoe, T. B.* J. Am. Chem. Soc. 2018, 140, 17007-17018. DOI: 10.1021/jacs.8b07728
9. "A Rhodium Catalyst for Single-Step Styrene Production" Vaughan, B. A., Webster-Gardiner, M. S., Cundari, T. R.*, Gunnoe, T. B.* Science 2015, 348, 421-424. This manuscript was highlighted in Chemical and Engineering News 2015, 93 (17), 26 and Phys.org. DOI.org/10.1126/science.aaa2260