One-electron oxidation of L 2 Pd II (CH 3 ) 2 complexes: Ligand effects on production of ethane vs. Pd–C bond homolysis

Lanci, Michael P.; McKeown, Bradley A.; Lao, David; Spettel, Karen E.; Mayer, James M.

doi:10.1016/j.poly.2014.06.008

Cited by 3 publications

(5 citation statements)

References 52 publications

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“…These results show that, despite the endergonic oxidation of [ 9a ](OTf) 2 by AgOTf, the overall process became feasible due to the use of an excess of oxidant and the shift of the electron-transfer equilibrium to the products: namely, the precipitation of Ag(0), this being a typical feature of irreversible oxidants . It is worth noting that the one-electron oxidation of d 8 Pd(II) dialkyl complexes was reported to induce the homolytic cleavage of a Pd–alkyl bond, forming an alkyl radical and the corresponding cationic Pd(II) monoalkyl complexes . It is therefore reasonable to propose that a similar redox transformation can occur in the case of the electron-rich pincer palladate complex [ 9a ](OTf).…”

Section: Resultsmentioning

confidence: 91%

Diverse C-Coordination Modes of NHC-Tricyclohexylphosphonium Ylide Ligands in Palladium(II) Complexes

et al. 2022

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Thanks to the + PCy3 substituents unlikely to undergo intramolecular C−H activation, a Pd(II) complex [(C,C,C)PdCl](OTf) exhibiting the neutral LX2-type NHC, diphosphonium bis(ylide) pincer ligand was selectively prepared by a double deprotonation of the [(NHC)PdCl2(Py)] precursor with tBuOK. The influence on the + PCy3 substituents on the overall electronic properties of this pincer scaffold was evaluated by IR spectroscopy data of the corresponding Pd−CO adduct revealing its stronger electron-donating character compared to the structurally related NHC core pincer bearing + PPh3 extremities. Treatment of the electron-rich pincer complex [(C,C,C)PdCl](OTf) with AgOTf led to the C,C-chelating NHC-phosphonium ylide Pd(II) complex [(C,C)Pd(OTf)Cl](OTf) via the oxidatively induced homolytic cleavage of a Pd−ylide bond. In the presence of stronger base (KHMDS or LDA) cyclometalation of a + P−Cy substituent was observed affording a constraint Pd(II) complex featuring the unique anionic LX3-type C,C,C,C-NHC, diphosphonium tris(ylide) ligand.

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Section: Resultsmentioning

confidence: 91%

Diverse C-Coordination Modes of NHC-Tricyclohexylphosphonium Ylide Ligands in Palladium(II) Complexes

et al. 2022

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“…Bimolecular methyl transfer reactions have been invoked for oxidatively induced reductive elimination from related LPdMe 2 and LPtMe 2 complexes. While these reactions are typically proposed to involve the transfer of methyl cations between an electrophilic LPd(III)Me 2 center and LPd(II)-Me 2 , [10][11][12]17,19,38,39,50,54 recent experimental 13−16 and computational studies 18 have suggested that methyl radical exchange, as proposed here, is also a viable pathway for the interchange of Pd methyl groups.…”

Section: ■ Results and Discussionmentioning

confidence: 94%

“…For multidentate chelating phosphorus or nitrogen ligands (bipy, phen) the reductive elimination of sp 3 –sp 3 bonds typically requires promotion of Pd(II) dialkyls to higher oxidation states to facilitate reductive elimination. Mechanistic − and computation studies ,, suggest that initial oxidation of Pd(II)MeX (X = halide or Me) to Pd(III) is followed by bimolecular methyl transfer to generate Pd(IV)Me 2 species, which are the key intermediates leading to ethane.…”

Section: Introductionmentioning

confidence: 99%

Ligand-Induced Reductive Elimination of Ethane from Azopyridine Palladium Dimethyl Complexes

et al. 2018

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Reductive elimination (RE) is a critical step in many catalytic processes. The reductive elimination of unsaturated groups (aryl, vinyl and ethynyl) from Pd(II) species is considerably faster than RE of saturated alkyl groups. Pd(II) dimethyl complexes ligated by chelating diimine ligands are stable toward RE unless subjected to a thermal or redox stimulus. Herein, we report the spontaneous RE of ethane from (azpy)PdMe complexes and the unique role of the redox-active azopyridine (azpy) ligands in facilitating this reaction. The (azpy)PdMe complexes are air- and moisture-stable in the solid form, but they readily produce ethane upon dissolution in polar solvents at temperatures from 10 °C to room temperature without the need for an external oxidant or elevated temperatures. Experimental and computational studies indicate that a bimolecular methyl transfer precedes the reductive elimination step, where both steps are facilitated by the redox-active azopyridine ligand.

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“…36,37 However, later studies indicate that this highvalent pathway is only operating when diamine ligands are employed and that bis-phosphine ligands instead lead to oxidation-induced Pd−C bond homolysis, producing methane along with a substantial amount of ethane. 38 Photodecomposition of a bis-phosphine-ligated complex, (dppe)PdMe 2 , has also been studied briefly. 39 Interestingly, while photolysis of (dppe)PdMeCl was found to proceed through radical pathways, a nonradical pathway was indicated for photodecomposition of (dppe)PdMe 2 , although the presence of several simultaneously operating mechanisms complicated the conclusions.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…Sanford et al reported on the mechanism for the formation of ethane from ( t -Bu 2 bpy)PdMe 2 in the presence of the one-electron oxidant [Cp 2 Fe]PF 6 . It was discovered that following the initial formation of Pd(III), a disproportion to Pd(II)/Pd(IV) takes place followed by reductive elimination of ethane from the Pd(IV) species to form Pd(II). , However, later studies indicate that this high-valent pathway is only operating when diamine ligands are employed and that bis-phosphine ligands instead lead to oxidation-induced Pd–C bond homolysis, producing methane along with a substantial amount of ethane . Photodecomposition of a bis-phosphine-ligated complex, (dppe)PdMe 2 , has also been studied briefly .…”

Section: Resultsmentioning

confidence: 99%

Evidence for Single-Electron Pathways in the Reaction between Palladium(II) Dialkyl Complexes and Alkyl Bromides under Thermal and Photoinduced Conditions

et al. 2017

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Palladium(II) dialkyl complexes have previously been studied for their formation of alkanes through reductive elimination. More recently, these complexes, especially L2Pd(CH2TMS)2 derived from Pd(COD)(CH2TMS)2, have found general use as palladium(0) precursors for stoichiometric formation of oxidative addition complexes through a two-electron reductive elimination/oxidative addition sequence. Herein, we report evidence for an alternative pathway, proceeding through single-electron elementary steps, when DPEPhosPd(CH2TMS)2 is treated with an α-bromo-α,α-difluoroacetamide. This new pathway does not take place through a palladium(0) intermediate, neither does it afford the expected oxidative addition complexes. Instead, stoichiometric amounts of carbon-centered alkyl radicals are formed, which can be trapped in high yields either by TEMPO or by an arene, leading to α-aryl-α,α-difluoroacetamides. The same overall transformation takes place under both thermal conditions (70 °C) and irradiation with a household light bulb (at 30 °C). It is also demonstrated that DPEPhosPdMe2, made in situ from Pd(TMEDA)Me2, displays a similar initial reactivity. Finally, electronically and structurally different alkyl bromides were evaluated as reaction partners.

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One-electron oxidation of L 2 Pd II (CH 3 ) 2 complexes: Ligand effects on production of ethane vs. Pd–C bond homolysis

Cited by 3 publications

References 52 publications

Diverse C-Coordination Modes of NHC-Tricyclohexylphosphonium Ylide Ligands in Palladium(II) Complexes

Diverse C-Coordination Modes of NHC-Tricyclohexylphosphonium Ylide Ligands in Palladium(II) Complexes

Ligand-Induced Reductive Elimination of Ethane from Azopyridine Palladium Dimethyl Complexes

Evidence for Single-Electron Pathways in the Reaction between Palladium(II) Dialkyl Complexes and Alkyl Bromides under Thermal and Photoinduced Conditions

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