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Dioxygen Reduction by a Pd(0)–Hydroquinone Diphosphine Complex

Horak, Kyle T. and Agapie, Theodor (2016) Dioxygen Reduction by a Pd(0)–Hydroquinone Diphosphine Complex. Journal of the American Chemical Society, 138 (10). pp. 3443-3452. ISSN 0002-7863. doi:10.1021/jacs.5b12928. https://resolver.caltech.edu/CaltechAUTHORS:20160315-101431160

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Abstract

A novel p-terphenyl diphosphine ligand was synthesized with a noninnocent hydroquinone moiety as the central arene (1-H). Pseudo-tetrahedral 4-coordinate Ni^0 and Pd^0–quinone (2 and 3, respectively) complexes proved accessible by metalating 1-H with the corresponding M(OAc)_2 precursors. O_2 does not react with the Pd^0–quinone species (3) and protonation occurs at the quinone moiety indicating that the coordinated oxidized quinonoid moiety prevents reactivity at the metal. A 2-coordinate Pd^0–hydroquinone complex (4-H) was prepared using a one-pot metalation with Pd^(II) followed by reduction. The reduced quinonoid moiety in 4-H shows metal-coupled reactivity with small molecules. 4-H was capable of reducing a variety of substrates including dioxygen, nitric oxide, nitrous oxide, 1-azido adamantane, trimethylamine n-oxide, and 1,4-benzoquinone quantitatively producing 3 as the Pd-containing reaction product. Mechanistic investigations of dioxygen reduction revealed that the reaction proceeds through a η^2-peroxo intermediate (Int1) at low temperatures followed by subsequent ligand oxidation at higher temperatures in a reaction that consumed half an equivalent of O_2 and produced water as a final oxygenic byproduct. Control compounds with methyl protected phenolic moieties (4-Me), displaying a Ag^I center incapable of O_2 binding (7-H) or a cationic Pd–H motif (6-H) allowed for the independent examination of potential reaction pathways. The reaction of 4-Me with dioxygen at low temperature produces a species (8-Me) analogous to Int1 demonstrating that initial dioxygen activation is an inner sphere Pd-based process where the hydroquinone moiety only subsequently participates in the reduction of O_2, at higher temperatures, by H^+/e^– transfers.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1021/jacs.5b12928DOIArticle
http://pubs.acs.org/doi/abs/10.1021/jacs.5b12928PublisherArticle
http://pubs.acs.org/doi/abs/10.1021/jacs.5b12928PublisherSupporting Information
ORCID:
AuthorORCID
Agapie, Theodor0000-0002-9692-7614
Additional Information:© 2016 American Chemical Society. Received: December 10, 2015; Publication Date (Web): March 7, 2016. We thank Lawrence M. Henling and Mike Takase for crystallographic assistance. We thank Caltech and NSF (CHE-1151918) for funding. T.A. is grateful for Sloan, Cottrell, and Dreyfus fellowships. The Bruker KAPPA APEXII X-ray diffractometer was purchased via an NSF CRIF:MU award to Caltech, CHE0639094. The authors declare no competing financial interest.
Funders:
Funding AgencyGrant Number
CaltechUNSPECIFIED
NSFCHE-1151918
Alfred P. Sloan FoundationUNSPECIFIED
Cottrell Scholar of Research CorporationUNSPECIFIED
Camille and Henry Dreyfus FoundationUNSPECIFIED
NSFCHE-0639094
Issue or Number:10
DOI:10.1021/jacs.5b12928
Record Number:CaltechAUTHORS:20160315-101431160
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20160315-101431160
Official Citation:Dioxygen Reduction by a Pd(0)–Hydroquinone Diphosphine Complex Kyle T. Horak and Theodor Agapie Journal of the American Chemical Society 2016 138 (10), 3443-3452 DOI: 10.1021/jacs.5b12928
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:65357
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:15 Mar 2016 19:02
Last Modified:10 Nov 2021 23:44

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