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

Chen, Junqi and Nielsen, Robert J. and Goddard, William A., III and McKeown, Bradley A. and Dickie, Diane A. and Gunnoe, T. Brent (2018) Catalytic Synthesis of Superlinear Alkenyl Arenes Using a Rh(I) Catalyst Supported by a “Capping Arene” Ligand: Access to Aerobic Catalysis. Journal of the American Chemical Society, 140 (49). pp. 17007-17018. ISSN 0002-7863. doi:10.1021/jacs.8b07728.

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Alkyl and alkenyl arenes are used in a wide range of products. However, 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 provides 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.

Item Type:Article
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URLURL TypeDescription Information
Nielsen, Robert J.0000-0002-7962-0186
Goddard, William A., III0000-0003-0097-5716
Dickie, Diane A.0000-0003-0939-3309
Gunnoe, T. Brent0000-0001-5714-3887
Additional Information:© 2018 American Chemical Society. Received: July 21, 2018; Published: November 29, 2018. T.B.G. was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division (DE-SC0000776). R.J.N. and W.A.G. were supported by NSF CBET-15127509. The quantum mechanic calculations used the resources of the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant number ACI-1053575. The authors declare no competing financial interest.
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Department of Energy (DOE)DE-SC0000776
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Issue or Number:49
Record Number:CaltechAUTHORS:20181129-110052381
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Official Citation:Catalytic Synthesis of Superlinear Alkenyl Arenes Using a Rh(I) Catalyst Supported by a “Capping Arene” Ligand: Access to Aerobic Catalysis. Junqi Chen, Robert J. Nielsen, William A. Goddard, III, Bradley A. McKeown, Diane A. Dickie, and T. Brent Gunnoe. Journal of the American Chemical Society 2018 140 (49), 17007-17018. DOI: 10.1021/jacs.8b07728
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:91328
Deposited By: George Porter
Deposited On:29 Nov 2018 20:57
Last Modified:16 Nov 2021 03:40

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