Dinuclear Palladium(III) Complexes with a Single Unsupported Bridging Halide Ligand: Reversible Formation from Mononuclear Palladium(II) or Palladium(IV) Precursors

Khusnutdinova, Julia R.; Rath, Nigam P.; Mirica, Liviu M.

doi:10.1002/ange.201100928

Cited by 6 publications

(7 citation statements)

References 46 publications

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“…This is exactly a similar observation reported by Mirica et al on dinuclear Pd III complexes with a single unsupported bridging halide ligand. 14 Reaction of this species has not been considered further here as elimination of Cl 2 in this reaction has not been observed. 4c show that bonds form and break almost 40−50% and TS is "middle" TS, middle in the sense that it is neither "reactant" nor "product" like.…”

Section: Inorganic Chemistrymentioning

confidence: 99%

“…13 Further, it has been reported that the tridentate ligand N′,N″-trimethyltriazacyclononane (Me 3 tacn) could also stabilize the halogen-bridged dinuclear Pd III complex. 14 These high-valent Pd III and Pd IV centers are stabilized with a multidentate flexible ligand such as R N4 = N,N′-di-alkyl-2,11-diaza- [3,3](2,6)pyridinophane, 15 and these complexes undergo thermal or photo-induced reductive elimination forming ethane and methyl chloride. 16 The aerobic oxidations of organometallic Pd II complexes also directly yield ethane via an elimination reaction.…”

Section: ■ Introductionmentioning

confidence: 97%

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Structure and Reactivity of Pd Complexes in Various Oxidation States in Identical Ligand Environments with Reference to C–C and C–Cl Coupling Reactions: Insights from Density Functional Theory

Jagadeesan

Sabapathi

Jaccob³

et al. 2018

Inorg. Chem.

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Bonding and reactivity of [(N4)Pd CHX] complexes have been investigated at the M06/BS2//B3LYP/BS1 level. Feasible mechanisms for the unselective formation of ethane and methyl chloride from mono-methyl Pd complexes and selective formation of ethane or methyl chloride from Pd complexes are reported here. Density functional theory (DFT) results indicate that Pd is more reactive than Pd and Pd in different oxidation states that follow different mechanisms. Pd complexes react in three steps: (i) conformational change, (ii) transmetalation, and (iii) reductive elimination. In the first step a five-coordinate Pd intermediate is formed by the cleavage of one Pd-N bond, and in the second step one methyl group is transferred from the Pd complex to the above intermediate via transmetalation, and subsequently a six-coordinate Pd intermediate is formed by disproportion. In this step, transmetalation can occur on both singlet and triplet surfaces, and the singlet surface is lying lower. Transmetalation can also occur between the above intermediate and [(N4)Pd(CH)(CHCN) ], but this not a feasible path. In the third step this Pd intermediate undergoes reductive elimination of ethane and methyl chloride unselectively, and there are three possible routes for this step. Here axial-equatorial elimination is more facile than equatorial-equatorial elimination. Pd complexes react in two steps, a conformational change followed by reductive elimination, selectively forming ethane or methyl chloride. Thus, Pd complex reacts through a six-coordinate Pd intermediate that has competing C-C and C-Cl bond formation, and Pd complex reacts through a five-coordinate Pd intermediate that has selective C-C and C-Cl bond formation. Free energy barriers indicate that iPr, in comparison to the methyl substituent in the N4 ligand, activates the cleaving of the Pd-N bond through electronic and steric interactions. Overall, reductive elimination leading to C-C bond formation is easier than the formation of a C-Cl bond.

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Section: Inorganic Chemistrymentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 97%

Structure and Reactivity of Pd Complexes in Various Oxidation States in Identical Ligand Environments with Reference to C–C and C–Cl Coupling Reactions: Insights from Density Functional Theory

Jagadeesan

Sabapathi

Jaccob³

et al. 2018

Inorg. Chem.

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“…The UV-Vis spectrum of 1 + shows a strong absorption peak at 625 nm, which is tentatively assigned to a ligand to metal charge transfer (LMCT). 39,40,49 The UV-Vis spectrum of complex 2 + reveals a red shift in the LMCT relative to 1 + , with an absorption peak at 675 nm. A similar red shift going from an organometallic ligand plus a halide ligand to two organometallic ligands has been observed previously in the UV-Vis spectra of [( Me N4)Pd III MeCl] + and [( Me N4)Pd III Me2] + .…”

Section: Resultsmentioning

confidence: 99%

C-H Bond Activation via Concerted Metalation-Deprotonation at a Palladium(III) Center

Bouley

Tang

Bae

et al. 2022

Preprint

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Herein we report the direct observation of C-H bond activation at an isolated mononuclear Pd(III) center. The oxidation of the Pd(II) complex (MeN4)PdII(neophyl)Cl (neophyl = -CH2C(CH3)2Ph; MeN4 = N,N′-di-tert-butyl-2,11-diaza[3.3](2,6)pyridinophane) using the mild oxidant ferrocenium hexafluorophosphate (FcPF6) yields the stable Pd(III) complex [(MeN4)PdIII(neophyl)Cl]PF6. Upon the addition of an acetate source, [(MeN4)PdIII(neophyl)Cl]PF6 undergoes Csp2-H bond activation to yield the cyclometalated product [(MeN4)PdIII(cycloneophyl)]PF6. This metallacycle can be independently prepared, allowing for a complete characterization of both the starting and final Pd(III) complexes. The C-H activation step can be monitored directly by EPR and UV-Vis spectroscopies, and kinetic isotope effect (KIE) studies suggest the C-H activation likely occurs after the rate determining step. Density functional theory calculations support that molecular isomerization/ligand rearrangement is rate limiting and proceeds through a κ3 ligand geometry. Overall, this study represents the first example of discrete C-H bond activation occurring at a Pd(III) center through a concerted metalation-deprotonation mechanism, akin to that observed for Pd(II) and Pd(IV) centers.

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“…However, during the catalytic process, the C ipso −H bond activation is likely to occur at Pd III (or Pd IV ), and the resulting organometallic complex is further stabilized by binding a second bromide ligand to generate 4a/4b. 51 We further probed the chemistry of 4b with TlPF 6 , a wellknown halide abstraction reagent. Reaction of 4b with 1 equiv of TlPF 6 resulted in the isolation of a purple complex identified as [ pMe N3CPd III (MeCN) 2 ](PF 6 ) 2 , 6.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Mononuclear Organometallic Pd(II), Pd(III), and Pd(IV) Complexes Stabilized by a Pyridinophane Ligand with a C-Donor Group

et al. 2019

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A series of Pd complexes bearing modified tetradentate pyridinophane ligands R N3CH, containing a Cdonor phenyl group, were isolated and characterized. The ( R N3CH)Pd II (OAc) 2 complexes contain a C ipso −H bond that remains unactivated at the Pd II stage, even upon heating or addition of excess acetate. These Pd II (OAc) 2 complexes exhibit catalytic reactivity in the Kharasch radical addition of bromotrichloromethane to methyl methacrylate. Interestingly, novel Pd III complexes ( R N3C)Pd III Br 2 were isolated from the Kharasch reaction mixture and have been characterized by EPR, UV−vis spectroscopy, and X-ray crystallography, suggesting that activation of the C ipso −H bond has occurred during the oxidative conditions of the Kharasch radical addition. Inspired by this observation, several ( pMe N3C)Pd III complexes were synthesized upon oxidation of the Pd II precursors with PhICl 2 and subsequent halide abstraction with thallium salts. Furthermore, additional one-electron oxidation generates detectable Pd IV species, including an uncommon tricationic [( pMe N3C)Pd IV (MeCN) 3 ] 3+ complex. Overall, these initial results show that the R N3C(H) ligand system is capable of stabilizing high-valent Pd species that can undergo uncommon oxidative and catalytic reactivity, including C−H bond activation.

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Dinuclear Palladium(III) Complexes with a Single Unsupported Bridging Halide Ligand: Reversible Formation from Mononuclear Palladium(II) or Palladium(IV) Precursors

Cited by 6 publications

References 46 publications

Structure and Reactivity of Pd Complexes in Various Oxidation States in Identical Ligand Environments with Reference to C–C and C–Cl Coupling Reactions: Insights from Density Functional Theory

Structure and Reactivity of Pd Complexes in Various Oxidation States in Identical Ligand Environments with Reference to C–C and C–Cl Coupling Reactions: Insights from Density Functional Theory

C-H Bond Activation via Concerted Metalation-Deprotonation at a Palladium(III) Center

Mononuclear Organometallic Pd(II), Pd(III), and Pd(IV) Complexes Stabilized by a Pyridinophane Ligand with a C-Donor Group

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