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Title: Catalytic Synthesis of Superlinear Alkenyl Arenes Using a Rh(I) Catalyst Supported by a “Capping Arene” Ligand: Access to Aerobic Catalysis

Abstract

Alkyl and alkenyl arenes are used in a wide range of products. Yet, the synthesis of 1-phenylalkanes or their alkenyl variants from arenes and alkenes is not accessible with current commercial acid-based catalytic processes. Here, it is reported that an air-stable Rh(I) complex, (5-FP)Rh(TFA)(η 2-C 2H 4) (5-FP = 1,2-bis( N-7-azaindolyl)benzene; TFA = trifluoroacetate), serves as a catalyst precursor for the oxidative conversion of arenes and alkenes to alkenyl arenes that are precursors to 1-phenylalkanes upon hydrogenation. It has been demonstrated that coordination of the 5-FP ligand enhances catalyst longevity compared to unligated Rh(I) catalyst precursors, and the 5-FP-ligated catalyst permits in situ recycling of the Cu(II) oxidant using air. The 5-FP ligand offers a Rh catalyst that can maintain activity for arene alkenylation over at least 2 weeks in reactions at 150 °C that involve multiple Cu(II) regeneration steps using air. Conditions to achieve >13 000 catalytic turnovers with an 8:1 linear:branched (L:B) ratio have been demonstrated. In addition, the catalyst is active under aerobic conditions using air as the sole oxidant. At 80 °C, an 18:1 L:B ratio of alkenyl arenes has been observed, but the reaction rate is substantially reduced compared to 150 °C. Quantum mechanics (QM)more » calculations compare two predicted reaction pathways with the experimental data, showing that an oxidative addition/reductive elimination pathway is energetically favored over a pathway that involves C–H activation by concerted metalation–deprotonation. In addition, our QM computations are consistent with the observed selectivity (11:1) for linear alkenyl arene products.« less

Authors:
 [1]; ORCiD logo [2]; ORCiD logo [2];  [1]; ORCiD logo [1]; ORCiD logo [1]
  1. Univ. of Virginia, Charlottesville, VA (United States)
  2. California Inst. of Technology (CalTech), Pasadena, CA (United States)
Publication Date:
Research Org.:
Univ. of Virginia, Charlottesville, VA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Chemical Sciences, Geosciences & Biosciences Division; National Science Foundation (NSF)
OSTI Identifier:
1596588
Grant/Contract Number:  
[SC0000776; CBET-15127509; ACI-1053575]
Resource Type:
Accepted Manuscript
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
[ Journal Volume: 140; Journal Issue: 49]; Journal ID: ISSN 0002-7863
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Catalysts; Atmospheric chemistry; Hydrocarbons; Aromatic compounds; Alkyls

Citation Formats

Chen, Junqi, Nielsen, Robert J., Goddard, William A., McKeown, Bradley A., Dickie, Diane A., and Gunnoe, T. Brent. Catalytic Synthesis of Superlinear Alkenyl Arenes Using a Rh(I) Catalyst Supported by a “Capping Arene” Ligand: Access to Aerobic Catalysis. United States: N. p., 2018. Web. doi:10.1021/jacs.8b07728.
Chen, Junqi, Nielsen, Robert J., Goddard, William A., McKeown, Bradley A., Dickie, Diane A., & Gunnoe, T. Brent. Catalytic Synthesis of Superlinear Alkenyl Arenes Using a Rh(I) Catalyst Supported by a “Capping Arene” Ligand: Access to Aerobic Catalysis. United States. doi:10.1021/jacs.8b07728.
Chen, Junqi, Nielsen, Robert J., Goddard, William A., McKeown, Bradley A., Dickie, Diane A., and Gunnoe, T. Brent. Thu . "Catalytic Synthesis of Superlinear Alkenyl Arenes Using a Rh(I) Catalyst Supported by a “Capping Arene” Ligand: Access to Aerobic Catalysis". United States. doi:10.1021/jacs.8b07728. https://www.osti.gov/servlets/purl/1596588.
@article{osti_1596588,
title = {Catalytic Synthesis of Superlinear Alkenyl Arenes Using a Rh(I) Catalyst Supported by a “Capping Arene” Ligand: Access to Aerobic Catalysis},
author = {Chen, Junqi and Nielsen, Robert J. and Goddard, William A. and McKeown, Bradley A. and Dickie, Diane A. and Gunnoe, T. Brent},
abstractNote = {Alkyl and alkenyl arenes are used in a wide range of products. Yet, the synthesis of 1-phenylalkanes or their alkenyl variants from arenes and alkenes is not accessible with current commercial acid-based catalytic processes. Here, it is reported that an air-stable Rh(I) complex, (5-FP)Rh(TFA)(η2-C2H4) (5-FP = 1,2-bis(N-7-azaindolyl)benzene; TFA = trifluoroacetate), serves as a catalyst precursor for the oxidative conversion of arenes and alkenes to alkenyl arenes that are precursors to 1-phenylalkanes upon hydrogenation. It has been demonstrated that coordination of the 5-FP ligand enhances catalyst longevity compared to unligated Rh(I) catalyst precursors, and the 5-FP-ligated catalyst permits in situ recycling of the Cu(II) oxidant using air. The 5-FP ligand offers a Rh catalyst that can maintain activity for arene alkenylation over at least 2 weeks in reactions at 150 °C that involve multiple Cu(II) regeneration steps using air. Conditions to achieve >13 000 catalytic turnovers with an 8:1 linear:branched (L:B) ratio have been demonstrated. In addition, the catalyst is active under aerobic conditions using air as the sole oxidant. At 80 °C, an 18:1 L:B ratio of alkenyl arenes has been observed, but the reaction rate is substantially reduced compared to 150 °C. Quantum mechanics (QM) calculations compare two predicted reaction pathways with the experimental data, showing that an oxidative addition/reductive elimination pathway is energetically favored over a pathway that involves C–H activation by concerted metalation–deprotonation. In addition, our QM computations are consistent with the observed selectivity (11:1) for linear alkenyl arene products.},
doi = {10.1021/jacs.8b07728},
journal = {Journal of the American Chemical Society},
number = [49],
volume = [140],
place = {United States},
year = {2018},
month = {11}
}

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