Metal-Stabilized Phenoxonium Cation

Vigalok, Arkadi; Rybtchinski, Boris; Gozin, Yael; Koblenz, Tehila S.; Ben‐David, Yehoshoa; Rozenberg, Haim; Milstein, David

doi:10.1021/ja0385639

Cited by 46 publications

(51 citation statements)

References 33 publications

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“…Figure 1 shows its molecular structure along with selected metrical parameters. Formulation of 3 as an iridaepoxide is one extreme of a continuum between this Ir(III) structure and an iridium η 2 -carbonyl representation similar to that found for an Ir stabilized phenoxonium cation by Milstein et al, 12 in which the Ir center is formally in the +1 oxidation state (Scheme 1). The 13 C chemical shift for the iridaepoxide carbon is moderately upfield at 65.0 ppm, but is not particularly diagnostic.…”

supporting

confidence: 59%

Ligand Cooperation in the Formal Hydrogenation of N₂O Using a PC_sp2P Iridium Pincer Complex

2015

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A new PC(carbene)P pincer ligand with 2,3-benzo[b]thiophene linkers connecting the flanking dialkyl phosphine donors to the central carbene can be attached to Ir(I). The chloro derivative reacts with N2O with loss of N2 to form an iridaepoxide species by addition of an oxygen atom to the Ir═C linkage. This compound reacts with H2 to afford the oxidative addition product, in which the hydride ligands are trans to the Ir-O bond. Heating this dihydride results in slow release of H2O; kinetic and spectroscopic studies show that conversion of the dihydride to its isomer, in which the hydrides are cis to the Ir-O bond, is required for H2O elimination to take place. Together, these reactions constitute the stoichiometric conversion of N2O and H2 to N2 and H2O; further mechanistic studies suggest ways to make the system catalytic.

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confidence: 59%

Ligand Cooperation in the Formal Hydrogenation of N₂O Using a PC_sp2P Iridium Pincer Complex

2015

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“…The mechanism is illustrated in Scheme . Vigalok et al38 isolated the stabilized phenoxonium cation, which supports the ionic pathway for the C O coupling.…”

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confidence: 82%

The effect of ligand molecular weight on copper salt catalyzed oxidative coupling polymerization of 2,6‐dimethylphenol

Zhao

et al. 2010

J of Applied Polymer Sci

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Polyphenylene oxide (PPO) was prepared via oxidative coupling polymerization of 2,6-dimethylphenol (DMP) catalyzed by copper salt. The ligand was a novel series of random copolymers (PSVP) of styrene and 4-vinylpyridine prepared by reversible addition-fragmentation chain transfer (RAFT) copolymerization. The copolymers with well-controlled molecular weight (MW) were used to study the effects of ligand molecular weight on the catalytic activity and selectivity. It was found that the catalytic activity increased with the molecular weight but there existed an upper MW limit above which no further increase in activity could be achieved. With PSVP of F vPy ¼ 0.39, the critical MW was about 5000 g/mol. The mechanism involved in the successive complexation of copper ions and PSVP was elucidated and the equilibrium constants were estimated by pH titration. It was found that the macromolecular ligand was in favor of bridging Cu II ions that formed catalytically active dinuclear copperamine complexes. However, the catalytic selectivity was almost independent of the ligand MW.

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“…[8] Other coordination modes in quinonoid systems are much more common. [9][10][11][12] Complex 5 shows very similar spectroscopic properties to an analogous complex lacking the p-methyl group on the aromatic ring.…”

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confidence: 99%

“…[7] The CÀO, RhÀO, and RhÀC bonds of 1.325(3), 2.0562 (16), and 2.186(2) , respec-tively, compare well with those observed for a monomeric Ir I phenoxonium cation. [8] Other coordination modes in quinonoid systems are much more common. [9][10][11][12] 1 H, 31 P{ 1 H}, and 13 C{ 1 H} NMR spectroscopy measurements of a sample of the reaction mixture before addition of the oxidation reagent indicated the initial formation of the unstable Rh III hydride complex 3 as the only detectable phosphorus-containing product [Eq.…”

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confidence: 99%

“…Orange crystals of 4 were obtained from a benzene solution by slow evaporation of the solvent under N 2 at room temperature ( Figure 2). [17] The CÀO, IrÀO, Ir···C separations of 1.334(9), 2.083(5), and 2.363 (8) are in agreement with a phenoxy type structure. [16] In sharp contrast to the aforementioned reactivity of the analogous Rh III hydride complex 3, no formation of bimetallic compounds or other iridium complexes was detected even after three days of heating at 60 8C in THF in a sealed pressure tube.…”

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confidence: 99%

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Self‐Oxidation of a Phenolate Complex to a Bimetallic Stilbene Quinone

Boom¹,

Zubkov²,

Shukla³

et al. 2004

Angew Chem Int Ed

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Oxidation chemistry of phenol derivatives is of interest, [1][2][3][4] mainly since it affords convenient routes to a variety of basic chemicals.[1] Widely used phenolic food antioxidants, such as 4-methyl-2,6-di-tert-butylphenol (butylated hydroxy toluene, BHT) are known to form a diversity of compounds upon oxidation, including colored stilbenequinone systems.[2] Selective oxidative CÀC coupling of alkylated phenols to stilbenequinones is rare [3] and this process often requires strong oxidants.[4] To our knowledge, self-oxidation of phenols or phenol derivatives, in the absence of external oxidant, has not been reported. Herein we report an unprecedented oxidativecoupling process in which a phenolate oxygen atom serves as the oxidant, which results in cleavage of the aryl-oxygen bond. This process involves a phenolate metal complex and results in the synthesis and crystallographic characterization of a new bimetallic stilbenequinone complex having two quinonoid C = O bonds h 2 -coordinated to the metal centers.[5]The metal oxidation state in the CÀO cleaved product is retained. Oxidative coupling of the metal complex, can also be affected by an external oxidant, and, significantly, it is metal selective. Treatment of the 4-methylphenol bisphosphine ligand 1 [6] with 0. 1 J Rh,P = 117.7 Hz), which indicates that the phosphorus atoms are chemically equivalent and coordinated to a metal center. FAB-MS measurements showed the signal for the molecular ion (m/z 1118.307) and a correct isotope pattern. The UV/Vis spectrum of 2 exhibited one broad charge-transfer band at l max = 576 nm (w1 = 2 = 77 nm, e = 29 10 3 in acetone). Dark blue crystals of complex 2 were obtained upon slow evaporation of a CH 2 Cl 2 solution under a nitrogen atmosphere at room temperature. The X-ray structure of 2 reveals the formation of the bimetallic stilbenequinone structure and the rare h 2 coordination mode of the metal centers to the quinonoid C=O double bonds (Figure 1). [17] The fourteen carbon atoms of the stilbenequinone backbone are located in the same plane with the two metalcoordinated oxygen atoms out of the plane by about 0.3 . The relatively short C(14)-C(14A) bond length of 1.404(5) may indicate a contribution of other resonance structures. [3] The phosphine groups are mutually trans with a significantly distorted P-Rh-P angle of 167.84(2)8. Distorted P-M-P angles are common for pincer complexes.[7] The CÀO, RhÀO, and RhÀC bonds of 1.325(3), 2.0562(16), and 2.186(2) , respec-

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Metal-Stabilized Phenoxonium Cation

Cited by 46 publications

References 33 publications

Ligand Cooperation in the Formal Hydrogenation of N₂O Using a PC_sp2P Iridium Pincer Complex

Ligand Cooperation in the Formal Hydrogenation of N₂O Using a PC_sp2P Iridium Pincer Complex

The effect of ligand molecular weight on copper salt catalyzed oxidative coupling polymerization of 2,6‐dimethylphenol

Self‐Oxidation of a Phenolate Complex to a Bimetallic Stilbene Quinone

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Metal-Stabilized Phenoxonium Cation

Cited by 46 publications

References 33 publications

Ligand Cooperation in the Formal Hydrogenation of N2O Using a PCsp2P Iridium Pincer Complex

Ligand Cooperation in the Formal Hydrogenation of N2O Using a PCsp2P Iridium Pincer Complex

The effect of ligand molecular weight on copper salt catalyzed oxidative coupling polymerization of 2,6‐dimethylphenol

Self‐Oxidation of a Phenolate Complex to a Bimetallic Stilbene Quinone

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Ligand Cooperation in the Formal Hydrogenation of N₂O Using a PC_sp2P Iridium Pincer Complex

Ligand Cooperation in the Formal Hydrogenation of N₂O Using a PC_sp2P Iridium Pincer Complex