Ligand‐Promoted Reactivity of Alkenes in Dehydrogenative Heck Reactions of Furans and Thiophenes

Vasseur, Alexandre; Laugel, Caroline; Harakat, Dominique; Мuzart, Jacques; Bras, Jean Le

doi:10.1002/ejoc.201403475

Cited by 35 publications

(30 citation statements)

References 30 publications

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“…DAF/Pd(OAc) 2 proved to be an effective catalyst for aerobic allylic C–H acetoxylation of allyl benzene and numerous other terminal alkene substrates. Subsequent studies have shown that DAF is uniquely effective in a number of other Pd-catalyzed aerobic oxidation reactions, including oxidative C–C and C–O coupling reactions with arenes, 18 α,β-dehydrogenation of cyclic ketones, 19 oxidative Heck reactions, 20 and also various non-aerobic oxidation reactions. 21 …”

Section: Introductionmentioning

confidence: 99%

Diazafluorenone-Promoted Oxidation Catalysis: Insights into the Role of Bidentate Ligands in Pd-Catalyzed Aerobic Aza-Wacker Reactions

et al. 2016

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2,2'-Bipyridine (bpy), 1,10-phenanthroline (phen) and related bidentate ligands often inhibit homogeneous Pd-catalyzed aerobic oxidation reactions; however, certain derivatives, such as 4,5-diazafluoren-9-one (DAF), can promote catalysis. In order to gain insight into this divergent ligand behavior, eight different bpy- and phen-derived chelating ligands have been evaluated in Pd(OAc)2-catalyzed oxidative cyclization of (E)-4-hexenyltosylamide. Two of the ligands, DAF and 6,6'-dimethyl-2,2'-bipyridine (6,6'-Me2bpy), support efficient catalytic turnover, while the others strongly inhibit the reaction. DAF is especially effective and is the only ligand that exhibits “ligand-accelerated catalysis”. Evidence suggests that the utility of DAF and 6,6'-Me2bpy originates from the ability of these ligands to access κ1-coordination modes via dissociation of one of the pyridyl rings. This hemilabile character is directly observed by NMR spectroscopy upon adding one equivalent of pyridine to solutions of 1:1 L/Pd(OAc)2 (L = DAF and 6,6'-Me2bpy), and is further supported by an X-ray crystal structure of Pd(py)(κ1-DAF)OAc2. DFT computational studies illuminate the influence of three different chelating ligands [DAF, 6,6'-Me2bpy, and 2,9-dimethyl-1,10-phenanthroline (2,9-Me2phen)] on the energetics of the aza-Wacker reaction pathway. The results show that DAF and 6,6'-Me2bpy destabilize the corresponding ground-state Pd(N~N)(OAc)2 complexes, while stabilizing the rate-limiting transition state for alkene insertion into a Pd–N bond. Interconversion between κ2- and κ1-coordination modes facilitate access to open coordination sites at the PdII center. The insights from these studies introduce new ligand concepts that could promote numerous other classes of Pd-catalyzed aerobic oxidation reaction.

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Section: Introductionmentioning

confidence: 99%

Diazafluorenone-Promoted Oxidation Catalysis: Insights into the Role of Bidentate Ligands in Pd-Catalyzed Aerobic Aza-Wacker Reactions

et al. 2016

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“…[2] Prominent examples include the Wacker process, [3] alcohol oxidation, [4] Wacker-type cyclization [5] and the Fujiwara-Moritani (dehydrogenative/oxidative Heck) reaction. [ 6] The majority of Pd-catalyzed aerobic oxidations proceed through a catalytic cycle wherein Pd II mediates substrate oxidation and Pd 0 is reoxidized by O 2 (Scheme 1). [7] The Pd 0 intermediate in this cycle is metastable and susceptible to decomposition via aggregation into Pd nanoparticles and/or bulk metallic Pd.…”

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confidence: 99%

Detection of Palladium(I) in Aerobic Oxidation Catalysis

et al. 2017

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PdII-catalyzed oxidation reactions exhibit broad utility in organic synthesis; however, they often feature high catalyst loading and low turnover numbers relative to non-oxidative cross-coupling reactions. Insights into the fate of the Pd catalyst during turnover could help to address this limitation. Here, we report the identification and characterization of a dimeric PdI species in two prototypical Pd-catalyzed aerobic oxidation reactions: allylic C–H acetoxylation of terminal alkenes and intramolecular aza-Wacker cyclization. Both reactions employ 4,5-diazafluoren-9-one (DAF) as an ancillary ligand. The dimeric PdI complex, [PdI(μ-DAF)(OAc)]2, which features two bridging DAF ligands and two terminal acetate ligands, has been characterized by several spectroscopic methods, as well as single-crystal X-ray crystallography. The origin of this PdI complex and its implications for catalytic reactivity are discussed.

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“…First, L should sufficiently provide electron density towards the metal but still maintain moderate steric hindrance . Second, it should not promote intramolecular deprotonation of the Pd−H bond, which thus rules out a good number of bidentate nitrogen ligands . Third, it should operate under neutral conditions to preserve the chemical integrity of both the Pd−H species and the substrate.…”

Section: Methodsmentioning

confidence: 99%

Secondary Phosphine Oxides as Multitalented Preligands En Route to the Chemoselective Palladium‐Catalyzed Oxidation of Alcohols

et al. 2017

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Secondary phosphine oxides O=PHR2 (SPOs) were identified as multitalented preligands for the chemoselective Pd‐catalyzed oxidation of alcohols by a hydrogen‐abstracting methodology. SPOs were found to promote the hydrogen‐abstraction step as well as hydrogen transfer to a Michael acceptor by generating a putative active H−Pd species. The catalytic system operates under neutral conditions and was proven to be compatible with various electrophilic and nucleophilic functionalities within the substrates as well as water‐ and air‐sensitive functional groups.

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Ligand‐Promoted Reactivity of Alkenes in Dehydrogenative Heck Reactions of Furans and Thiophenes

Cited by 35 publications

References 30 publications

Diazafluorenone-Promoted Oxidation Catalysis: Insights into the Role of Bidentate Ligands in Pd-Catalyzed Aerobic Aza-Wacker Reactions

Diazafluorenone-Promoted Oxidation Catalysis: Insights into the Role of Bidentate Ligands in Pd-Catalyzed Aerobic Aza-Wacker Reactions

Detection of Palladium(I) in Aerobic Oxidation Catalysis

Secondary Phosphine Oxides as Multitalented Preligands En Route to the Chemoselective Palladium‐Catalyzed Oxidation of Alcohols

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