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Published in final edited form as: ACS Catal. 2021 May 13;11:6363–6370. doi: 10.1021/acscatal.1c01074

Benzoquinone Cocatalyst Contributions to DAF/Pd(OAc)2-Catalyzed Aerobic Allylic Acetoxylation in the Absence and Presence of a Co(salophen) Cocatalyst

Caitlin V Kozack 1, Stephen J Tereniak 1, Jonathan N Jaworski 1, Bao Li 1, David L Bruns 1, Spring M M Knapp 1, Clark R Landis 1, Shannon S Stahl 1,*
PMCID: PMC8373043  NIHMSID: NIHMS1724085  PMID: 34422447

Abstract

Palladium(II)-catalyzed allylic acetoxylation has been the focus of extensive development and investigation. Methods that use molecular oxygen (O2) as the terminal oxidant typically benefit from the use of benzoquinone (BQ) and a transition-metal (TM) cocatalyst, such as Co(salophen), to support oxidation of Pd0 during catalytic turnover. We previously showed that Pd(OAc)2 and 4,5-diazafluoren-9-one (DAF) as an ancillary ligand catalyze allylic oxidation with O2 in the absence of cocatalysts. Herein, we show that BQ enhances DAF/Pd(OAc)2 catalytic activity, nearly matching the performance of reactions that include both BQ and Co(salophen). These observations are complemented by mechanistic studies of DAF/Pd(OAc)2 catalyst systems under three different oxidation conditions: (1) O2 alone, (2) O2 with cocatalytic BQ, and (3) O2 with cocatalytic BQ and Co(salophen). The beneficial effect of BQ in the absence of Co(salophen) is traced to synergistic roles of O2 and BQ, both of which are capable of oxidizing Pd0 to PdII The reaction of O2 generates H2O2 as a byproduct, which can oxidize hydroquinone to quinone in the presence of PdII NMR spectroscopic studies, however, show that hydroquinone is the predominant redox state of the quinone cocatalyst in the absence of Co(salophen), while inclusion of Co(salophen) maintains oxidized quinone throughout the reaction, resulting in better reaction performance.

Keywords: allylic acetoxylation, catalysis, palladium, oxidation, benzoquinone

Graphical Abstract

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Introduction

Palladium(II)-mediated allylic C–H acetoxylation was first reported nearly 60 years ago.1 Since then, many other catalytic applications of this method have been reported that employ various stoichiometric oxidants, including benzoquinone derivatives,1,2–10 peroxides,11–14 copper salts,15,16 and hypervalent iodine reagents17,18 (Scheme 1). Benzoquinone (BQ) is commonly used in cocatalytic quantities with a stoichiometric oxidant, such as MnO219–21 or a peroxide.11,14,22 Molecular oxygen (O2) has been used effectively, typically in combination with BQ and a transition-metal (TM) complex, such as iron phthalocyanine or Co(salophen), as a cocatalyst to support catalytic turnover (Scheme 2).20,21,23–30 In rare cases, O2 is an effective oxidant for Pd-catalyzed allylic acetoxylation without any cocatalysts.31,32

Scheme 1.

Scheme 1.

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Pd-catalyzed allylic acetoxylation with various oxidants

Scheme 2.

Scheme 2.

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Proposed mechanism for aerobic allylic acetoxylation with multicomponent catalyst systems (ETM = electron-transfer mediator)

Our initial studies of Pd-catalyzed allylic acetoxylation were motivated by an interest in developing a ligand-based strategy to support the use of O2 as an oxidant and led to the discovery of 4,5-diazafluoren-9-one (DAF) as an effective ancillary ligand for these reactions.30,32–35 Subsequent mechanistic studies revealed that these reactions exhibit a kinetic “burst” of product formation at the start of the reaction, coinciding with the formation of a PdI dimer,36 followed by steady-state catalytic turnover in which the catalyst resting state consists of an allyl-PdII species (Scheme 3).37 The catalytic rate exhibits a dependence on pO2 during steady-state turnover, implicating catalyst reoxidation by O2 as the turnover-limiting step. Recognizing that BQ is capable of promoting both C–O bond-formation (formally, reductive elimination) from allyl-PdII species and reoxidation of Pd0,38 we evaluated BQ derivatives as additives in a recent study of allylic acyloxylation with diverse carboxylic acids.30 In the course of this work, we found that use of 5 mol% 2,6-dimethylbenzoquinone (Me2BQ) in the absence of a TM cocatalyst more than doubled the yield relative to a reaction with O2 in the absence of quinone. This result is not readily understood from prior studies, which suggest that the cocatalyst is needed to reoxidize hydroquinone (H2Q).23–30,39

Scheme 3.

Scheme 3.

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Mechanistic steps in DAF/Pd(OAc)2-catalyzed aerobic allylic acetoxylation

The mechanistic model commonly invoked for multicomponent catalyst systems of this type features a redox cascade in which O2 oxidizes the TM cocatalyst, the TM cocatalyst oxidizes H2Q, BQ oxidizes Pd0, and PdII oxidizes the organic substrate (Scheme 2).23,24,40 This cascade sequence is widely invoked, but few studies have interrogated mechanistic features of the cocatalyst system40,41 and prior studies do not provide a rationale for the beneficial role of BQ in the absence of a TM cocatalyst. Two recent studies seemed to offer possible insights. DAF/Pd(OAc)2 was found to undergo redox equilibration with H2Q, generating BQ and reduced Pd species;39 however, this reactivity doesn’t provide a clear basis for improved catalyst performance. A separate study showed that PdII salts catalyze oxidation of H2Q to BQ derivatives using tBuOOH as the oxidant.42 This reactivity contributes to the Pd/BQ-cocatalyzed 1,4-diacyloxylation of cyclohexadiene with tBuOOH, complementing other Pd/BQ cocatalyst systems that use peroxides as the stoichiometric oxidant,11 including one case using DAF/Pd(OAc)2 as the Pd catalyst.14 The relevance of these insights is apparent upon recognizing that oxidation of Pd0 by O2 in the presence of AcOH generates H2O2 (Scheme 4),35,43–45 and we postulated that this in situ-generated H2O2 could promote oxidation of H2Q to BQ, thereby accounting for the beneficial effect of BQ on Pd-catalyzed aerobic allylic oxidation, even in the absence of a TM cocatalyst.

Scheme 4.

Scheme 4.

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Reaction of Pd0 with O2 resulting in the formation of H2O2

The present study surveys the influence of various quinones on Pd-catalyzed aerobic allylic acetoxylation in the absence and presence of Co(salophen) as a cocatalyst. We then investigate the relative rates of H2Q oxidation by O2 in the presence of different components of the catalyst system and employ NMR spectroscopy to probe the quinone speciation in the absence and presence of cocatalytic Co(salophen). Collectively, the results provide unique mechanistic insights into commonly used multicomponent catalyst systems in Pd-catalyzed oxidation reactions.

Results and Discussion

Influence of quinones on Pd-catalyzed allylic oxidation.

We initiated our study by investigating Pd-catalyzed acetoxylation of allylbenzene (1) with 5 mol% loading of quinones 3a-3m, which have different steric properties and redox potentials (Figure 1A). Reactions carried out in the absence and presence of 0.5 mol% Co(salophen) show a “volcano”-like dependence of the cinnamyl acetate (2) yield on the quinone 2e−/2H+ redox potential (Figure 1B).46 Reaction times were shortened from 14 to 7 h when using Co(salophen) in order to enhance the contrast among different quinones. The variations in yields among the best quinones probably reflect the superposition of steric and electronic contributions to the outcome. But, optimal yields of 2 were generally obtained with BQs with redox potentials ranging from ~ 550-635 mV (3d–3h) in the absence of Co(salophen). The range of optimal quinone redox potentials expands for reactions conducted in the presence of Co(salophen), accommodating quinones with potentials of ~ 550-700 mV (3d–3k).

Figure 1.

Figure 1.

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Allylic acetoxylation of allylbenzene with different benzoquinone derivatives. (A) Benzoquinone additives and their redox potentials. (B) Observed yields relative to the 2H+/2e− redox potential of the quinone for conditions without Co(salophen) (14 h) and with Co(salophen) (7h).

The poor performance of low and high potential quinones in both cases is rationalized by offsetting electronic effects on the redox processes involving quinones: (a) BQ promotion of Pd-catalyzed substrate oxidation, including C–O bond formation from allyl-PdII species and reoxidation of Pd0, is expected to benefit from high-potential quinones, while (b) reoxidation of H2Q will be more facile for low-potential quinones. The positive shift in quinone redox potentials for reactions with Co(salophen) is consistent with the ability of this cocatalyst to promote H2Q oxidation (see below).

The effect of quinone on DAF/Pd(OAc)2-catalyzed acetoxylation of 1 was evaluated further by monitoring the reaction time course under three different aerobic oxidation conditions: (1) with 1 atm O2 in the absence of cocatalysts, (2) with 1 atm O2 and 5 mol% 2-tert-butyl-1,4-benzoquinone (tBuBQ) as a cocatalyst, and (3) with 1 atm O2, 5 mol% tBuBQ, and 0.5 mol% Co(salophen) as cocatalysts (Figure 2). The reaction conducted under O2 in the absence of cocatalysts exhibits a rapid burst of product formation during the first ~10 min followed by slower steady state turnover, consistent with previous reports.36,37 Both reactions with tBuBQ exhibit higher rates and lead to high yields of 2 after 15 h, at which time the O2-alone reaction has reached only ~40% yield. The presence of both tBuBQ and Co(salophen) leads to the best performance, as expected,23 but the good results observed with tBuBQ in the absence of Co(salophen) is noteworthy. Similar results were obtained with a series of other substrates, including electronically differentiated allylbenzene derivatives (1a-1c) and aliphatic substrates (1d, 1e). In each case, addition of tBuBQ to the reaction substantially improves the yield, and further improvements are evident when both tBuBQ and Co(salophen) are included as cocatalysts in the reaction mixture (Figure 3).

Figure 2.

Figure 2.

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Time course of cinnamyl acetate formation during the aerobic allylic acetoxylation of allylbenzene without additives, with 5 mol% tBuBQ, and with 5 mol% tBuBQ and 0.5 mol% Co(salophen). Trendlines reflect empirical fits to guide the eye (see Supporting Information for details).

Figure 3.

Figure 3.

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1H NMR yields of allylic acetates 2a-2e obtained from substrates 1a-1e under three different aerobic reaction conditions: without cocatalysts (black), with 5 mol% tBuBQ (red), and with 5 mol% tBuBQ and 0.5 mol% Co(salophen) (blue).

Analysis of H2Q oxidation and quinone speciation under catalytic conditions.

BQ cocatalysts can play at least two roles in these reactions: (a) promote C–O bond formation/reductive elimination from allyl-PdII species5,38,47–49 and (b) promote reoxidation of Pd0 to PdII.50 The first role does not alter the redox state of the BQ,51 while the second will generate H2Q, which must be reoxidized to BQ in order to continue serving as a cocatalyst. The latter process is typically thought to require Co(salophen) or a related cocatalyst,23,24 raising questions about the beneficial effect of BQ in the absence of a TM cocatalyst.

Experiments were undertaken to probe methods for oxidation of tBuH2Q to tBuBQ that could be operative under the Pd-catalyzed oxidation conditions (Figure 4). The reaction temperature for these studies was lowered to 40 °C to facilitate data collection at early time points for some of the rapid reactions. O2 alone does not promote oxidation of tBuH2Q to tBuBQ (Figure 4a) and only minor oxidation was observed with H2O2 in the absence of metal (co)catalysts (4% yield after 6 h, Figures 4b). Similar moderate rates of tBuH2Q oxidation were observed with Co(salophen) under O2 and DAF/Pd(OAc)2 under O2 (52% and 55% yields after 6 h, Figure 4c and 4d, respectively). The DAF/Pd(OAc)2/O2 outcome is somewhat unexpected considering BQ derivatives are typically used to oxidize Pd0; however, it aligns with the recent observation of redox equilibria between DAF/Pd(OAc)2 and H2Q derivatives39 and indicates that net O2 reduction to H2O drives tBuH2Q oxidation under these conditions. In this context, DAF/Pd(OAc)2 mediates rapid oxidation of tBuH2Q by H2O2 under anaerobic conditions (75% yield after 6 h, Figure 4e). Oxidation of tBuH2Q is most rapid when both DAF/Pd(OAc)2 and Co(salophen) are used as cocatalysts under an O2 atmosphere (Figure 4f).

Figure 4.

Figure 4.

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Time course plots obtained from the oxidation of tBuH2Q to tBuBQ under a series of different conditions.

The redox state of the quinone cocatalyst during the catalytic acetoxylation reaction was then interrogated for reactions conducted in the absence and presence of the Co(salophen) cocatalyst. The quinone speciation was determined by analyzing aliquots of the reaction mixture throughout the reaction time course by 1H NMR spectroscopy (samples were quenched with pyridine and diluted in CDCl3 for analysis; see Supporting Information for details). In the absence of Co(salophen), tBuBQ is completely consumed during the first 30 min with concomitant formation of tBuH2Q. Then, tBuH2Q is slowly oxidized to tBuBQ as the allylic oxidation reaction proceeds to completion over the next 15-20 h (Figure 5A). The reaction conducted in the presence of Co(salophen) also shows an initial reduction of tBuBQ to tBuH2Q; however, this progression is reversed after 25-30% conversion to tBuH2Q, and tBuBQ is present in a high steady-state concentration throughout most of the reaction (Figure 5B).

Figure 5.

Figure 5.

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Time courses of product formation and starting material depletion (top plot) and tBuBQ speciation (bottom plot) during the aerobic allylic acetoxylation of allylbenzene (A) without Co(salophen) and (B) with 0.5% Co(salophen). Trendlines reflect empirical fits to guide the eye based on functions described in the Supporting Information.

We then used the Wisconsin High-Pressure NMR Reactor (WiHP-NMRR)52 to conduct operando analysis of the reactions. This apparatus enables reactions to be run under a continuous supply of a gaseous reagent while recording NMR spectra,37,53–55 and it enabled us to probe the Pd catalyst under three different reaction conditions: (1) O2 alone, (2) O2 + 5 mol% tBuBQ, and (3) O2 + 5 mol% tBuBQ + 0.5 mol% Co(salophen) (Figure 6). These experiments exhibit relatively low signal-to-noise, but still provide valuable insights into the Pd speciation.

Figure 6.

Figure 6.

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Palladium speciation monitored by operando WiHP-NMRR during the acetoxylation of 4-fluoroallylbenzene 1f to the allyl acetate 2f. (A) Formation/decay of [PdI dimer 5] analyzed by 1H NMR spectroscopy, and (B) appearance of [π-cinnamyl-PdII 6] (or lack thereof) determined by 19F NMR analysis. Trendlines reflect empirical fits to guide the eye (see Supporting Information for details).

Previous investigation of DAF/Pd(OAc)2-catalyzed allylic oxidation under aerobic conditions (i.e., in the absence of cocatalysts) revealed formation of the dimeric PdI species 5 at early stages of the reaction, arising from comproportionation of Pd0 and PdII species present in the reaction mixture (cf. Scheme 3).37 These observations were reproduced under the O2-alone conditions (black data, Figure 6A). Inclusion of tBuBQ leads to reduced build-up of the PdI dimer intermediate early in the reaction (red data, Figure 6A) and even less formation of PdI when both tBuBQ and Co(salophen) are included in the reaction (blue data, Figure 6A). As the reaction progresses, π-cinnamyl-PdII species (6) become evident in the reaction mixture lacking cocatalysts (Figure 6B, black data), implicating an allyl-PdII resting state during steady-state turnover. This species is not evident, however, in both reaction mixtures containing cocatalysts (Figure 6B, red and blue data, respectively).

The reduced formation of the PdI dimer in the presence of tBuBQ (Figure 6A) is rationalized by the ability of tBuBQ to coordinate to Pd0 and reoxidize it to PdII,50 thereby minimizing Pd0/PdII comproportionation to form the PdI dimer. The lack of allyl-PdII species when cocatalysts are present (Figure 6B) is consistent with the ability of BQ cocatalysts to promote C–O bond formation from allyl-PdII.5,38,47–49 These data provide direct operando evidence for the two commonly invoked roles of quinones in Pd-catalyzed allylic oxidation reactions.

Summary and catalytic mechanism.

The data presented herein illuminate a number of features that have not been characterized previously for multicomponent Pd/cocatalyst systems for aerobic oxidation. The results show a synergistic role of O2 and BQ, in which the H2O2 byproduct of Pd0 aerobic oxidation supports oxidation of the H2Q species. This feature allows BQ to be an effective cocatalyst, even in the absence of a Co(salophen) cocatalyst (cf. Figure 2). Nonetheless, the catalytic reaction is more effective when both quinone and Co(salophen) are included in the reaction. This mutual benefit reflects improved rates of H2Q oxidation when Co(salophen) is present (cf. Figure 4), resulting in oxidized BQ species being available throughout the catalytic reaction (cf. Figure 5) to support C–O bond formation and reoxidation of the Pd catalyst.

The catalytic mechanism in Scheme 5 accounts for many of the observations described herein. In the absence of cocatalysts, DAF/Pd(OAc)2 activates the allylic C–H bond of the olefin substrate, leading to the formation of an allyl-PdII intermediate that can undergo (reversible32) C–O bond formation to afford a DAF/Pd0 species that can be reoxidized by O2 via a peroxo-PdII intermediate (right catalytic cycle, Figure 5). The presence of BQ promotes C–O bond formation from the allyl-PdII species and provides an alternative pathway for reoxidation of Pd0 via a DAF/Pd0-BQ adduct. The latter step will generate H2Q, which can undergo reoxidation to BQ, using H2O2 from the aerobic pathway or a cocatalytic process involving DAF/Pd/Co(salophen)/O2 (cf. Figure 4).

Scheme 5.

Scheme 5.

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Proposed catalytic mechanism for Pd-catalyzed aerobic allylic acetoxylation.

Conclusion.

This study provides new insights into the cooperative contributions of O2, BQ, and Co(salophen) in promoting Pd catalyst reoxidation in allylic acetoxylation reactions. O2 can reoxidize the Pd catalyst directly when a suitable ancillary ligand, such as DAF, is present to ensure catalyst stability and promote the reaction with O2. The beneficial effect of BQ reflects its ability to promote both C–O bond formation in the substrate oxidation half-reaction and its ability to oxidize Pd0 under acidic reaction conditions. But, a method is needed to ensure reoxidation of H2Q after each catalytic cycle. Hydroquinone does not react readily with O2, but we show that O2/BQ are effective together in the Pd-catalyzed conditions. Under these conditions, O2 reduction generates H2O2, which then supports efficient oxidation of H2Q in the presence of the Pd catalyst. The best conditions feature a combination of quinone and Co(salophen) cocatalysts, reflecting the ability of the Co(salophen) to promote rapid oxidation of the H2Q species, maximizing the steady-state quantity of quinone available to support substrate and catalyst oxidation steps. The results described herein provide new insights and direct evidence for previous mechanistic proposals.

Supplementary Material

Supplementary Material

ACKNOWLEDGMENT

This work was funded by the NSF (CHE-1665120 and CHE-1953926). NMR instrumentation was supported by NSF CHE-1048642, NIH S10 OD012245 and a generous gift from Paul J. and Margaret M. Bender. The WiHP-NMRR was supported by the Dow Chemical Company. C.V.K. was supported in part by the National Science Foundation Graduate Research Fellowship Program under Grant No. DGE-1256259. S.J.T. was funded by the NIH (NRSA Fellowship Award F32GM119214). Support was also provided by the Graduate School and the Office of the Vice Chancellor for Research and Graduate Education at the University of Wisconsin-Madison with funding from the Wisconsin Alumni Research Foundation.

Footnotes

The authors declare no competing financial interests.

Supporting Information. The Supporting Information is available free of charge on the ACS Publications website. Experimental details and NMR data.

References.

  • 1.Vargaftik MN; Moiseev II; Syrkin, Ya K Formation of Mixed Allyl Esters During Reaction of Higher Olefins with Palladium Chloride in Anhydrous Carboxylic Acid Solutions. Izv. Akad. Nauk SSSR 1962, 5, 930–931. [Google Scholar]
  • 2.McMurry JE; Kočovsky P A Method for the Palladium-Catalyzed Allylic Oxidation of Olefins. Tet. Lett 1984, 25, 4187–4190. [Google Scholar]
  • 3.Åkermark B; Hansson S; Rein T; Vågberg J; Heumann A; Bäckvall J-E Palladium-Catalyzed Allylic Acetoxylation: an Exploratory Study of the Influence of Added Acids J. Org. Chem 1989, 369, 433–444. [Google Scholar]
  • 4.Chen MS; White MC A Sulfoxide-Promoted, Catalytic Method for the Regioselective Synthesis of Allylic Acetates from Monosubstituted Olefins via C–H Oxidation. J. Am. Chem. Soc 2004, 126, 1346–1347. [DOI] [PubMed] [Google Scholar]
  • 5.Chen MS; Prabagaran N; Labenz NA; White MC Serial Ligand Catalysis: A Highly Selective Allylic C–H Oxidation. J. Am. Chem. Soc 2005, 127, 6970–6971. [DOI] [PubMed] [Google Scholar]
  • 6.Covell DJ; White MC A Chiral Lewis Acid Strategy for Enantioselective Allylic C–H Oxidation. Angew. Chem. Int. Ed 2008, 47, 6448–6451. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 7.Lin B-L; Labinger JA; Bercaw JE Mechanistic Investigations of Bipyrimidine-Promoted Palladium-Catalyzed Allylic Acetoxylation of Olefins. Can. J. Chem 2009, 87, 264–271. [Google Scholar]
  • 8.Thiery E; Aouf C; Belloy J; Harakat D; Le Bras J; Muzart J Palladium-Catalyzed Allylic Acyloxylation of Terminal Alkenes in the Presence of a Base. J. Org. Chem 2009, 75, 1771–1774. [DOI] [PubMed] [Google Scholar]
  • 9.Kondo H; Yu F; Yamaguchi J; Liu G; Itami K Branch-Selective Allylic C–H Carboxylation of Terminal Alkenes by Pd/sox Catalyst. Org. Lett 2014, 16, 4212–4215. [DOI] [PubMed] [Google Scholar]
  • 10.Malik HA; Taylor BLH; Kerrigan JR; Grob JE; Houk KN; Du Bois J; Hamann LG; Patterson AW Non-Directed Allylic C–H Acetoxylation in the Presence of Lewis Basic Heterocycles. Chem. Sci 2014, 5, 2352–2361. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 11.Jia C; Müller P; Mimoun H Palladium-Catalyzed Allylic Acetoxylation of Olefins Using Hydrogen Peroxide as Oxidant. J. Mol. Catal. A: Chem 1995, 101, 127–136. [Google Scholar]
  • 12.Pilarski LT; Janson PG; Szabó KJ Palladium-Catalyzed Selective Acyloxylation Using Sodium Perborate as Oxidant. J. Org. Chem 2011, 76, 1503–1506. [DOI] [PubMed] [Google Scholar]
  • 13.Xing X; O’Connor NR; Stoltz BM Palladium(II)-Catalyzed Allylic C–H Oxidation of Hindered Substrates Featuring Tunable Selectivity Over Extent of Oxidation. Angew. Chem. Int. Ed 2015, 54, 11186–11190. [DOI] [PubMed] [Google Scholar]
  • 14.Litman ZC; Sharma A; Hartwig JF Oxidation of Hindered Allylic C–H Bonds with Applications to the Functionalization of Complex Molecules. ACS Catal. 2017, 7, 1998–2001. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 15.Heumann A; Reglier M; Waegell B Oxidation with Palladium Salts: Stereo- and Regiospecific Acetoxylation of 4-Vinylcyclohexene Derivatives. Angew. Chem. Int. Ed. Engl 1982, 21, 366–367. [Google Scholar]
  • 16.Firdoussi LE; Baqqa A; Allaoud S; Allal BA; Karim A; Catanet Y; Mortreux A Selective Palladium-Catalysed Functionalization of Limonene: Synthetic and Mechanistic Aspects. J. Mol. Catal. A: Chem 1998, 135, 11–22. [Google Scholar]
  • 17.Pilarski LT; Selander N; Bose D; Szabó KJ Catalytic Allylic C–H Acetoxylation and Benzoyloxylation via Suggested (η3-Allyl)palladium(IV) Intermediates. Org. Lett 2009, 11, 5518–5521. [DOI] [PubMed] [Google Scholar]
  • 18.Alam R; Pilarski LT; Pershagen E; Szabó KJ Stereoselective Intermolecular Allylic C–H Trifluoroacetoxylation of Functionalized Alkenes. J. Am. Chem. Soc 2012, 134, 8778–8781. [DOI] [PubMed] [Google Scholar]
  • 19.Heumann A; Åkermark B Oxidation with Palladium Salts: Catalytic Preparation of Allyl Acetates from Monoolefins Using a Three-Component Oxidation System. Angew. Chem. Int. Ed 1984, 23, 453–454. [Google Scholar]
  • 20.Hansson S; Heumann A; Rein T; Åkermark B Preparation of Allylic Acetates from Simple Alkenes by Palladium(II)-Catalyzed Acetoxylation. J. Org. Chem 1990, 55, 975–984. [Google Scholar]
  • 21.Thiery E; Aouf C; Belloy J; Harakat D; Le Bras J; Muzart J Palladium-Catalyzed Allylic Acyloxylation of Terminal Alkenes in the Presence of a Base. J. Org. Chem 2010, 75, 1771–1774. [DOI] [PubMed] [Google Scholar]
  • 22.Åkermark B; Larsson EM; Oslob JD Allylic Carboxylations and Lactonization Using Benzoquinone and Hydrogen Peroxide or tert-Butyl Hydroperoxide as Oxidants. J. Org. Chem 1994, 59, 5729–5733. [Google Scholar]
  • 23.Piera J; Bäckvall J-E Catalytic Oxidation of Organic Substrates by Molecular Oxygen and Hydrogen Peroxide by Multistep Electron Transfer – A Biomimetic Approach. Angew. Chem. Int. Ed 2008, 47, 3506–3523. [DOI] [PubMed] [Google Scholar]
  • 24.Liu J; Guðmundsson A; Bäckvall J-E Efficient Aerobic Oxidation of Organic Molecules by Multistep Electron Transfer. Angew. Chem. Int. Ed 2021, Accepted Article. DOI: 10.1002/anie.202012707 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 25.Bäckvall JE; Hopkins RB; Grennberg H; Mader MM; Awasthi AK Multistep Electron Transfer in Palladium-Catalyzed Aerobic Oxidations via a Metal Macrocycle-Quinone System. J. Am. Chem. Soc 1990, 112, 5160–5166. [Google Scholar]
  • 26.Larsson EM; Åkermark B A Catalytic System for Allylic Acetoxylation Consisting of Palladium(II) and Nitrate and Using Oxygen as Final Oxidant. Tet. Lett 1993, 34, 2523–2526. [Google Scholar]
  • 27.Principato B; Maffei M; Siv C; Buono G; Peiffer B Palladium Catalysed Allylic Acetoxylation of Dialkyl Allyl Phosphonates. Tetrahdron, 1996, 52, 2087–2096. [Google Scholar]
  • 28.Gusevskaya E; Gonsalves JA Palladium(II) Catalyzed Oxidation of Naturally Occurring Terpenes with Dioxygen. J. Mol. Catal. A: Chem 1997, 121, 131–137. [Google Scholar]
  • 29.Henderson WH; Check CT; Proust N; Stambuli JP Allylic Oxidations of Terminal Olefins Using a Palladium Thioether Catalyst. Org. Lett 2010, 12, 824–827. [DOI] [PubMed] [Google Scholar]
  • 30.Kozack CV; Sowin JA; Jaworski JN; Iosub AV; Stahl SS Aerobic Acyloxylation of Allylic C–H Bonds Initiated by a Pd0 Precatalyst with 4,5-Diazafluoren-9-one as an Ancillary Ligand. ChemSusChem, 2019, 3003–3007. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 31.Mitsudome T; Umetani T; Nosaka N; Mori K; Mizugaki T; Ebitani K; Kaneda K Convenient and Efficient Pd-Catalyzed Regioselective Oxyfunctionalization of Terminal Olefins by Using Molecular Oxygen as Sole Reoxidant. Angew. Chem. Int. Ed 2006, 45, 481–485. [DOI] [PubMed] [Google Scholar]
  • 32.Campbell AN; White PB; Guzei IA; Stahl SS Allylic C–H Acetoxylation with a 4,5-Diazafluorenone-Ligated Palladium Catalyst: A Ligand-Based Strategy To Achieve Aerobic Catalytic Turnover. J. Am. Chem. Soc 2010, 132, 15116–15119. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 33.White PB; Jaworski JN; Fry CG; Dolinar BS; Guzei IA; Stahl SS Structurally Diverse Diazafluorene-Ligated Palladium(II) Complexes and Their Implications for Aerobic Oxidation Reactions. J. Am. Chem. Soc 2016, 138, 4869–4880. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 34.White PB; Jaworski JN; Geyunjian HZ; Stahl SS Diazafluorenone-Promoted Oxidation Catalysis: Insights into the Role of Bidentate Ligands in Pd-Catalyzed Aerobic Aza-Wacker Reactions. ACS Catal. 2016, 6, 3340–3348. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 35.Wang D; Weinstein AB; White PB; Stahl SS Ligand-Promoted Palladium-Catalyzed Aerobic Oxidation Reactions. Chem. Rev 2018, 118, 2636–2679. [DOI] [PubMed] [Google Scholar]
  • 36.Jaworski JN; McCann SD; Guzei IA; Stahl SS Detection of Palladium(I) in Aerobic Oxidation Catalysis. Angew. Chem. Int. Ed 2017, 56, 3605–3610. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 37.Jaworski JN; Kozack CV; Tereniak SJ; Knapp SMM; Landis CR; Miller JT; Stahl SS Operando Spectroscopic and Kinetic Characterization of Aerobic Allylic C–H Acetoxylation Catalyzed by Pd(OAc)2/4,5-Diazafluoren-9-one. J. Am. Chem. Soc 2019, 10462–10474. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 38.Diao T; Stahl SS O2-Promoted Allylic Acetoxylation of Alkenes: Assessment of “Push” Versus “Pull” Mechanisms and Comparison Between O2 and Benzoquinone. Polyhedron, 2014, 84, 96–102. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 39.For additional context, see:; Bruns DL; Musaev DG; Stahl SS Can Donor Ligands Make Pd(OAc)2 a Stronger Oxidant? Access to Elusive Palladium(II) Reduction Potentials and Effects of Ancillary Ligands via Palladium(II)/Hydroquinone Redox Equilibria. J. Am. Chem. Soc 2020, 142, 19678–19688. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 40.Anson CW; Ghosh S; Hammes-Schiffer S; Stahl SS Co(salophen)-Catalyzed Aerobic Oxidation of p-Hydroquinone: Mechanism and Implications for Aerobic Oxidation Catalysis. J. Am. Chem. Soc 2016, 138, 4186–4193. [DOI] [PubMed] [Google Scholar]
  • 41.Anson CW; Stahl SS Cooperative electrocatalytic O2 Reduction Involving Co(salophen) with p-Hydroquinone as an Electron-Proton Transfer Mediator. J. Am. Chem. Soc 2017, 139, 18472–18475. [DOI] [PubMed] [Google Scholar]
  • 42.Zheng B; Schmidt MA; Eastgate MD Synergistic Catalysis: Pd(II) Catalyzed Oxidation of 1,4-Dihydroquinones in the Pd(II) Catalyzed 1,4-Oxidation of 1,3-Dienes. J. Org. Chem 2016, 81, 3112–3118. [DOI] [PubMed] [Google Scholar]
  • 43.Stahl SS; Thorman JL; Nelson RC; Kozee MA Oxygenation of Nitrogen-Coordinated Palladium(0): Synthetic, Structural, and Mechanistic Studies and Implications for Aerobic Oxidation Catalysis. J. Am. Chem. Soc 2001, 123, 7188–7189. [DOI] [PubMed] [Google Scholar]
  • 44.Konnick MM; Guzei IA; Stahl SS Characterization of Peroxo and Hydroperoxo Intermediates in the Aerobic Oxidation of N-Heterocyclic-Carbene-Coordinated Palladium(0). J. Am. Chem. Soc 2004, 126, 10212–10213. [DOI] [PubMed] [Google Scholar]
  • 45.Konnick MM; Gandhi BA; Guzei IA; Stahl SS Reaction of Molecular Oxygen with a PdII–Hydride To Produce a PdII–Hydroperoxide: Acid Catalysis and Implications for Pd-Catalyzed Aerobic Oxidation Reactions. Angew. Chem. Int. Ed 2006, 45, 2904–2907. [DOI] [PubMed] [Google Scholar]
  • 46.Huynh MT; Anson CW; Cavell AC; Stahl SS; Hammes-Schiffer S Quinone 1e− and 2 e−/2 H+ Reduction Potentials: Identification and Analysis of Deviations from Systematic Scaling Relationships. J. Am. Chem. Soc 2016, 138, 15903–15910. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 47.Grennberg H; Gogoll A; Bäckvall J-E Use of Sulfoxides in the Palladium-Quinone-Catalyzed 1,4-Diacetoxylation of 1,3-Dienes. An Example of Ligand-Accelerated Catalysis. J. Org. Chem 1991, 56, 5808–5811. [Google Scholar]
  • 48.Bäckvall J-E; Gogoll A Evidence for (π-allyl)Palladium(II)(quinone) Complexes in the Palladium-Catalyzed 1,4-Diacetoxylation of Conjugated Dienes. Tetrahedron Lett. 1988, 29, 2243–2246. [Google Scholar]
  • 49.Bäckvall J-E; Byström SE; Nordberg RE Stereo- and Regioselective Palladium-Catalyzed 1,4-Diacetoxylation of 1,3-Dienes. J. Org. Chem 1984, 49, 4619–4631. [Google Scholar]
  • 50.Grennberg H; Gogoll A; Bäckvall J-E Acid-Induced Transformation of Palladium(0)-Benzoquinone Complexes to Palladium(II) and Hydroquinone. Organometallics 1993, 12, 1790–1793. [Google Scholar]
  • 51.For an example of the redox-neutral role of BQ in Pd-catalyzed aerobic oxidation reactions, see:; Salazar CA; Flesch KN; Haines BE; Zhou PS; Musaev DG; Stahl SS Tailored Quinones Support High-Turnover Pd Catalysts for Oxidative C–H Arylation with O2. Science 2020, 370, 1454–1460. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 52.Beach NJ; Knapp SMM; Landis CR A Reactor for High-Throughput High-Pressure Nuclear Magnetic Resonance Spectroscopy. Rev. Sci. Instrum 2015, 86, 104101. [DOI] [PubMed] [Google Scholar]
  • 53.Chotchatchawankul S, Mechanistic Studies of Rh(diphosphine)-Catalyzed Methanol Reductive Carbonylation, Dissertation, University of Wisconsin - Madison. Madison, WI, 2015. [Google Scholar]
  • 54.Brezny AC; Landis CR Unexpected CO Dependencies, Catalyst Speciation, and Single Turnover Hydrogenolysis Studies of Hydroformylation via High Pressure NMR Spectroscopy. J. Am. Chem. Soc 2017, 139, 2778–2785. [DOI] [PubMed] [Google Scholar]
  • 55.Tereniak SJ; Landis CR; Stahl SS Are Phosphines Viable Ligands for Pd-Catalyzed Aerobic Oxidation Reactions? Contrasting Insights from a Survey of Six Reactions. ACS Catal. 2018, 8, 3708–3714. [Google Scholar]

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