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Mechanistic Studies of Styrene Production from Benzene and Ethylene Using [(η²-C₂H₄)₂Rh(μ-OAc)]₂ as Catalyst Precursor: Identification of a Bis-Rh^I Mono-Cu^(II) Complex As the Catalyst

Musgrave, Charles B., III and Zhu, Weihao and Coutard, Nathan and Ellena, Jeffrey F. and Dickie, Diane A. and Gunnoe, T. Brent and Goddard, William A., III (2021) Mechanistic Studies of Styrene Production from Benzene and Ethylene Using [(η²-C₂H₄)₂Rh(μ-OAc)]₂ as Catalyst Precursor: Identification of a Bis-Rh^I Mono-Cu^(II) Complex As the Catalyst. ACS Catalysis, 11 (9). pp. 5688-5702. ISSN 2155-5435. doi:10.1021/acscatal.1c01203. https://resolver.caltech.edu/CaltechAUTHORS:20210503-115704194

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Abstract

We report a combined experimental and computational study focused on the mechanism of oxidative conversion of benzene and ethylene to styrene using [(η²-C₂H₄)₂Rh(μ-OAc)]₂ as the catalyst precursor in the presence of Cu(OPiv)₂ (OPiv = pivalate). Using [(η²-C₂H₄)₂Rh(μ-OAc)]₂ as the catalyst precursor, ∼411 turnovers of styrene are observed after 1 h, giving an apparent turnover frequency of ∼0.11 s⁻¹ (calculated assuming the binuclear structure is maintained in the active catalyst). We identify the catalyst resting state to be [(η²-C₂H₄)₂Rh^I(μ-OPiv)₂]₂(μ-Cu), which is a heterotrinuclear molecular complex in which a central Cu^(II) atom bridges two Rh moieties. At high Rh concentration in the presence of Cu(OPiv)₂ and pivalic acid (HOPiv), the trinuclear complex [(η²-C₂H₄)₂Rh^I(μ-OPiv)₂]₂(μ-Cu) converts to the binuclear Rh(II) complex [(HOPiv)Rh^(II)(μ-OPiv)₂]₂, which has been identified by ¹H NMR spectroscopy and single crystal X-ray diffraction. The binuclear Rh(II) [(HOPiv)Rh^(II)(μ-OPiv)₂]₂ is not a catalyst for styrene production, but under catalytic conditions [(HOPiv)Rh^(II)(μ-OPiv)₂]₂ can be partially converted to the active catalyst, the Rh–Cu–Rh complex [(η²-C₂H₄)₂Rh^I(μ-OPiv)₂]₂(μ-Cu), following an induction period of ∼6 h. Using quantum chemical calculations, we sampled possible mononuclear and binuclear Rh species, finding that the binuclear Rh(II) [(HOPiv)Rh^(II)(μ-OPiv)₂]₂ paddle-wheel is a low energy global minimum, which is consistent with experimental observations that [(HOPiv)Rh^(II)(μ-OPiv)₂]₂ is not a catalyst for styrene formation. Further, we investigated the mechanism of styrene production starting from [(η²-C₂H₄)₂Rh^I(μ-OAc)₂]₂(μ-Cu), [(η²-C₂H₄)₂Rh(μ-OAc)]₂, and (η²-C₂H₄)₂Rh(κ²-OAc). For all reaction pathways studied, the predicted activation barriers for styrene formation from [(η²-C₂H₄)₂Rh(μ-OAc)]₂ and (η²-C₂H₄)₂Rh(κ²-OAc) are too high compared to experimental kinetics. In contrast, the overall activation barrier for styrene formation predicted by DFT from the Rh–Cu–Rh complex [(η²-C₂H₄)₂Rh^I(μ-OPiv)₂]₂(μ-Cu) is in agreement with experimentally determined rates of catalysis. Based on these results, we conclude that incorporation of Cu(II) into the active Rh–Cu–Rh catalyst reduces the activation barrier for benzene C–H activation, O–H reductive elimination, and ethylene insertion into the Rh–Ph bond.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1021/acscatal.1c01203DOIArticle
ORCID:
AuthorORCID
Musgrave, Charles B., III0000-0002-3432-0817
Dickie, Diane A.0000-0003-0939-3309
Gunnoe, T. Brent0000-0001-5714-3887
Goddard, William A., III0000-0003-0097-5716
Alternate Title:Mechanistic Studies of Styrene Production from Benzene and Ethylene Using [(η2-C2H4)2Rh(μ-OAc)]2 as Catalyst Precursor: Identification of a Bis-RhI Mono-CuII Complex As the Catalyst
Additional Information:© 2021 American Chemical Society. Received: March 15, 2021; Revised: April 13, 2021. Experimental studies were supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division (DE-SC0000776). Author Contributions: C.B.M. and W.Z. contributed equally. The authors declare no competing financial interest.
Funders:
Funding AgencyGrant Number
Department of Energy (DOE)DE-SC0000776
Subject Keywords:C−H activation, rhodium, arene, alkenylation styrene
Other Numbering System:
Other Numbering System NameOther Numbering System ID
WAG1428
Issue or Number:9
DOI:10.1021/acscatal.1c01203
Record Number:CaltechAUTHORS:20210503-115704194
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20210503-115704194
Official Citation:Mechanistic Studies of Styrene Production from Benzene and Ethylene Using [(η2-C2H4)2Rh(μ-OAc)]2 as Catalyst Precursor: Identification of a Bis-RhI Mono-CuII Complex As the Catalyst. Charles B. Musgrave, Weihao Zhu, Nathan Coutard, Jeffrey F. Ellena, Diane A. Dickie, T. Brent Gunnoe, and William A. Goddard. ACS Catalysis 2021 11 (9), 5688-5702; DOI: 10.1021/acscatal.1c01203
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:108932
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:05 May 2021 17:53
Last Modified:06 Jun 2021 04:35

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