43 research outputs found

    Interaction of Ferrocene Moieties Across a Square Pt<sub>4</sub> Unit: Synthesis, Characterization, and Electrochemical Properties of Carboxylate-Bridged Bimetallic Pt<sub>4</sub>Fe<sub><i>n</i></sub> (<i>n</i> = 2, 3, and 4) Complexes

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    Four types of square Pt<sub>4</sub> complexes bearing two or more ferrocenecarboxylate ligands[Pt<sub>4</sub>(μ-OCOCH<sub>3</sub>)<sub>4</sub>(μ-OCOC<sub>5</sub>H<sub>4</sub>FeCp)<sub>4</sub>] (<b>6</b>); [Pt<sub>4</sub>(μ-OCOCH<sub>3</sub>)<sub>4</sub>(μ-OCOC<sub>5</sub>H<sub>4</sub>FeCp)<sub>3</sub>(μ-ArNCHNAr)], where ArNCHNAr = <i>N</i>,<i>N′</i>-diarylformamidinate) (<b>7</b>); <i>trans</i>-[Pt<sub>4</sub>(μ-OCOCH<sub>3</sub>)<sub>4</sub>(μ-OCOC<sub>5</sub>H<sub>4</sub>FeCp)<sub>2</sub>(μ-ArNCHNAr)<sub>2</sub>] (<b>8</b>); and <i>cis</i>-[Pt<sub>4</sub>(μ-OCOCH<sub>3</sub>)<sub>4</sub>(μ-OCOC<sub>5</sub>H<sub>4</sub>FeCp)<sub>2</sub>(κ<sup>4</sup>-<i>N</i><sub>4</sub>-DArBp)<sub>2</sub>], where DArBp = 1,3-bis(benzamidinato)propane (<b>9</b>)were successfully prepared via reactions of [FeCp(η<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>COOH)] (<b>5</b>) with the corresponding square Pt<sub>4</sub> complexes, which have labile <i>in-plane</i> acetate ligands. The newly prepared Pt<sub>4</sub> complexes (<b>6</b>–<b>9</b>) with ferrocene moieties as pendants were characterized by nuclear magnetic resonance (NMR) spectroscopy, mass spectroscopy (MS), combustion analyses, and single-crystal X-ray analysis for <b>6</b>, some of the <i>trans</i>-Pt<sub>4</sub>Fe<sub>2</sub> <b>8</b>, and the <i>cis</i>-Pt<sub>4</sub>Fe<sub>2</sub> complexes <b>9</b>. Weak interactions between two ferrocene moieties across the Pt<sub>4</sub> core, providing Δ<i>E</i><sub>1/2</sub> values and <i>K</i><sub>c</sub> constants, were revealed electrochemically, using cyclic and differential-pulse voltammetry in dichloromethane containing [<sup><i>n</i></sup>Bu<sub>4</sub>N][BAr<sup>F</sup><sub>4</sub>] (where Ar<sup>F</sup> = C<sub>6</sub>H<sub>3</sub>(CF<sub>3</sub>)<sub>2</sub>-3,5), which was a better supporting electrolyte for such an interaction than [<sup><i>n</i></sup>Bu<sub>4</sub>N][PF<sub>6</sub>]

    Interaction of Ferrocene Moieties Across a Square Pt<sub>4</sub> Unit: Synthesis, Characterization, and Electrochemical Properties of Carboxylate-Bridged Bimetallic Pt<sub>4</sub>Fe<sub><i>n</i></sub> (<i>n</i> = 2, 3, and 4) Complexes

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    Four types of square Pt<sub>4</sub> complexes bearing two or more ferrocenecarboxylate ligands[Pt<sub>4</sub>(μ-OCOCH<sub>3</sub>)<sub>4</sub>(μ-OCOC<sub>5</sub>H<sub>4</sub>FeCp)<sub>4</sub>] (<b>6</b>); [Pt<sub>4</sub>(μ-OCOCH<sub>3</sub>)<sub>4</sub>(μ-OCOC<sub>5</sub>H<sub>4</sub>FeCp)<sub>3</sub>(μ-ArNCHNAr)], where ArNCHNAr = <i>N</i>,<i>N′</i>-diarylformamidinate) (<b>7</b>); <i>trans</i>-[Pt<sub>4</sub>(μ-OCOCH<sub>3</sub>)<sub>4</sub>(μ-OCOC<sub>5</sub>H<sub>4</sub>FeCp)<sub>2</sub>(μ-ArNCHNAr)<sub>2</sub>] (<b>8</b>); and <i>cis</i>-[Pt<sub>4</sub>(μ-OCOCH<sub>3</sub>)<sub>4</sub>(μ-OCOC<sub>5</sub>H<sub>4</sub>FeCp)<sub>2</sub>(κ<sup>4</sup>-<i>N</i><sub>4</sub>-DArBp)<sub>2</sub>], where DArBp = 1,3-bis(benzamidinato)propane (<b>9</b>)were successfully prepared via reactions of [FeCp(η<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>COOH)] (<b>5</b>) with the corresponding square Pt<sub>4</sub> complexes, which have labile <i>in-plane</i> acetate ligands. The newly prepared Pt<sub>4</sub> complexes (<b>6</b>–<b>9</b>) with ferrocene moieties as pendants were characterized by nuclear magnetic resonance (NMR) spectroscopy, mass spectroscopy (MS), combustion analyses, and single-crystal X-ray analysis for <b>6</b>, some of the <i>trans</i>-Pt<sub>4</sub>Fe<sub>2</sub> <b>8</b>, and the <i>cis</i>-Pt<sub>4</sub>Fe<sub>2</sub> complexes <b>9</b>. Weak interactions between two ferrocene moieties across the Pt<sub>4</sub> core, providing Δ<i>E</i><sub>1/2</sub> values and <i>K</i><sub>c</sub> constants, were revealed electrochemically, using cyclic and differential-pulse voltammetry in dichloromethane containing [<sup><i>n</i></sup>Bu<sub>4</sub>N][BAr<sup>F</sup><sub>4</sub>] (where Ar<sup>F</sup> = C<sub>6</sub>H<sub>3</sub>(CF<sub>3</sub>)<sub>2</sub>-3,5), which was a better supporting electrolyte for such an interaction than [<sup><i>n</i></sup>Bu<sub>4</sub>N][PF<sub>6</sub>]

    Alkyne-Induced Facile C–C Bond Formation of Two η<sup>2</sup>‑Alkynes on Dinuclear Tantalum Bis(alkyne) Complexes To Give Dinuclear Tantalacyclopentadienes

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    The dinuclear tantalum–alkyne complexes [(η<sup>2</sup>-RCCR)­TaCl<sub>2</sub>]<sub>2</sub>(μ-OMe)<sub>2</sub>(μ-thf) (<b>2a</b>, R = Et; <b>2b</b>, R = <sup><i>n</i></sup>Pr) were synthesized by treating the mononuclear tantalum–alkyne complexes (η<sup>2</sup>-RCCR)­TaCl<sub>3</sub>(dme) (<b>1a</b>, R = Et; <b>1b</b>, R = <sup><i>n</i></sup>Pr) with 1 equiv of NaOMe in THF. We found that adding a catalytic amount (20 mol %) of 3-hexyne to <b>2a</b> induced the spontaneous formation of Ta<sub>2</sub>Cl<sub>4</sub>(OMe)<sub>2</sub>(μ-C<sub>4</sub>Et<sub>4</sub>)­(thf) (<b>4a</b>). Similarly, Ta<sub>2</sub>Cl<sub>4</sub>(OMe)<sub>2</sub>(μ-C<sub>4</sub><sup><i>n</i></sup>Pr<sub>4</sub>)­(thf) (<b>4b</b>) was obtained by treatment of <b>2b</b> with a catalytic amount (20 mol %) of 4-octyne. Reaction of <b>4a</b>,<b>b</b> with 4-dimethylaminopyridine gave 4-dimethylaminopyridine-coordinated complexes <b>6a</b>,<b>b</b>, whose structures were elucidated by the X-ray structure of <b>6a</b>. We conducted a control experiment in which 10 equiv of 4-octyne was added to <b>2a</b> to give Ta<sub>2</sub>Cl<sub>4</sub>(OMe)<sub>2</sub>(μ-C<sub>4</sub>-2,3-<sup><i>n</i></sup>Pr<sub>2</sub>-4,5-Et<sub>2</sub>)­(thf) (<b>7</b>) in 90% yield, indicating that free 4-octyne reacted with the tantalacyclopropene moiety of <b>2a</b> to form a dissymmetric tantalacyclopentadiene, followed by the release of 3-hexyne. The catalytic activity of <b>4a</b>–<b>6a</b> for [2 + 2 + 2] cyclotrimerization of 3-hexyne was examined, and we found that their activities were in the order <b>5a</b> > <b>4a</b> ≫ <b>6a</b>

    Hemilabile <i>N</i>‑Xylyl‑<i>N</i>′‑methylperimidine Carbene Iridium Complexes as Catalysts for C–H Activation and Dehydrogenative Silylation: Dual Role of <i>N</i>‑Xylyl Moiety for ortho-C–H Bond Activation and Reductive Bond Cleavage

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    Direct dehydrogenative silylation of pyridyl and iminyl substrates with triethylsilane was achieved using (L)­Ir­(cod)­(X) (<b>1</b>) (L = a perimidine-based carbene ligand, X = OAc and OCOPh) complexes as catalysts under toluene refluxing conditions in the presence of norbornene as a hydrogen scavenger, and the silylated products were obtained in good yields. The isolated bis­(cyclometalated)iridium complexes, (C<sup>∧</sup>C:)­(C<sup>∧</sup>N)­IrOAc (<b>2</b>) (C<sup>∧</sup>C: = a cyclometalated perimidine-carbene ligand and C<sup>∧</sup>N = a cyclometalated pyridyl- and iminyl-ligated aromatic substrate), were key intermediates, where cyclometalated five-membered metallacycles of substrates such as phenylpyridine were selectively formed before yielding mono-ortho-silylation products. The bis­(cyclometalated)­iridium complex (<sup>Xy</sup>C<sup>∧</sup>C:)­(C<sup>∧</sup>N)­IrOAc (<b>2d</b>) (<sup>Xy</sup>C<sup>∧</sup>C: = a cyclometalated <i>N</i>-xylyl-<i>N</i>′-methylperimidine-carbene ligand and C<sup>∧</sup>N = a 2-pyridylphenyl ligand), reacted with 2 equiv of Et<sub>3</sub>SiH to give an iridium hydride complex, (L<sup>4</sup>)­(C<sup>∧</sup>N)­Ir­(H)­(SiEt<sub>3</sub>) (<b>8d</b>) (L<sup>4</sup> = <i>N</i>-CH<sub>3</sub>, <i>N</i>-3,5-(CH<sub>3</sub>)<sub>2</sub>C<sub>6</sub>H<sub>3</sub> perimidine), via demetalation of a <i>N</i>-3,5-xylyl ring of the carbene ligand of <b>2d</b>. The formation of <b>8d</b> was confirmed by isolating the corresponding chloro complex (L<sup>4</sup>)­(C<sup>∧</sup>N)­Ir­(Cl)­(SiEt<sub>3</sub>) (<b>8d-Cl</b>) by treatment with CCl<sub>4</sub>. The <i>N</i>-methyl moiety of the carbene ligand coordinated to <b>8d</b> was cyclometalated in the presence of norbornene at room temperature to afford (<sup>Me</sup>C<sup>∧</sup>C:)­(C<sup>∧</sup>N)­Ir­(SiEt<sub>3</sub>) (1<b>0d</b>) (<sup>Me</sup>C<sup>∧</sup>C: = a cyclometalated <i>N</i>-xylyl-<i>N</i>′-methylperimidine-carbene), while at high temperature <b>8d</b> reacted with norbornene and Et<sub>3</sub>SiH to afford the silylated product, 2-(2-triethylsilyl)­phenylpyridine (<b>3a</b>) and norbornane. A deuterium labeling experiment using <b>2d</b> and Et<sub>3</sub>SiD (excess) revealed the incorporation of deuterium atoms at two ortho-positions of the <i>N</i>-xylyl group (>90%) and at the 3-position of 2-pyridylphenyl ligand (ca. 40%) within 3 h at room temperature, indicating that the cyclometalation/demetalation of the <i>N</i>-xylylperimidine carbene and 2-phenylpyridine ligands were reversible processes. Isolation of these cyclometalated iridium complexes under controlled conditions and D-labeling experiments thus revealed a dual function of the <i>N</i>-aryl group bound to the perimidine-carbene ligand, which acted as both a neutral carbene ligand and a monoanionic ortho-metalated aryl-carbene ligand through reversible C–H bond activation and Ir–C bond cleavage of the <i>N</i>-aryl group during the catalytic cycle

    Hemilabile <i>N</i>‑Xylyl‑<i>N</i>′‑methylperimidine Carbene Iridium Complexes as Catalysts for C–H Activation and Dehydrogenative Silylation: Dual Role of <i>N</i>‑Xylyl Moiety for ortho-C–H Bond Activation and Reductive Bond Cleavage

    No full text
    Direct dehydrogenative silylation of pyridyl and iminyl substrates with triethylsilane was achieved using (L)­Ir­(cod)­(X) (<b>1</b>) (L = a perimidine-based carbene ligand, X = OAc and OCOPh) complexes as catalysts under toluene refluxing conditions in the presence of norbornene as a hydrogen scavenger, and the silylated products were obtained in good yields. The isolated bis­(cyclometalated)iridium complexes, (C<sup>∧</sup>C:)­(C<sup>∧</sup>N)­IrOAc (<b>2</b>) (C<sup>∧</sup>C: = a cyclometalated perimidine-carbene ligand and C<sup>∧</sup>N = a cyclometalated pyridyl- and iminyl-ligated aromatic substrate), were key intermediates, where cyclometalated five-membered metallacycles of substrates such as phenylpyridine were selectively formed before yielding mono-ortho-silylation products. The bis­(cyclometalated)­iridium complex (<sup>Xy</sup>C<sup>∧</sup>C:)­(C<sup>∧</sup>N)­IrOAc (<b>2d</b>) (<sup>Xy</sup>C<sup>∧</sup>C: = a cyclometalated <i>N</i>-xylyl-<i>N</i>′-methylperimidine-carbene ligand and C<sup>∧</sup>N = a 2-pyridylphenyl ligand), reacted with 2 equiv of Et<sub>3</sub>SiH to give an iridium hydride complex, (L<sup>4</sup>)­(C<sup>∧</sup>N)­Ir­(H)­(SiEt<sub>3</sub>) (<b>8d</b>) (L<sup>4</sup> = <i>N</i>-CH<sub>3</sub>, <i>N</i>-3,5-(CH<sub>3</sub>)<sub>2</sub>C<sub>6</sub>H<sub>3</sub> perimidine), via demetalation of a <i>N</i>-3,5-xylyl ring of the carbene ligand of <b>2d</b>. The formation of <b>8d</b> was confirmed by isolating the corresponding chloro complex (L<sup>4</sup>)­(C<sup>∧</sup>N)­Ir­(Cl)­(SiEt<sub>3</sub>) (<b>8d-Cl</b>) by treatment with CCl<sub>4</sub>. The <i>N</i>-methyl moiety of the carbene ligand coordinated to <b>8d</b> was cyclometalated in the presence of norbornene at room temperature to afford (<sup>Me</sup>C<sup>∧</sup>C:)­(C<sup>∧</sup>N)­Ir­(SiEt<sub>3</sub>) (1<b>0d</b>) (<sup>Me</sup>C<sup>∧</sup>C: = a cyclometalated <i>N</i>-xylyl-<i>N</i>′-methylperimidine-carbene), while at high temperature <b>8d</b> reacted with norbornene and Et<sub>3</sub>SiH to afford the silylated product, 2-(2-triethylsilyl)­phenylpyridine (<b>3a</b>) and norbornane. A deuterium labeling experiment using <b>2d</b> and Et<sub>3</sub>SiD (excess) revealed the incorporation of deuterium atoms at two ortho-positions of the <i>N</i>-xylyl group (>90%) and at the 3-position of 2-pyridylphenyl ligand (ca. 40%) within 3 h at room temperature, indicating that the cyclometalation/demetalation of the <i>N</i>-xylylperimidine carbene and 2-phenylpyridine ligands were reversible processes. Isolation of these cyclometalated iridium complexes under controlled conditions and D-labeling experiments thus revealed a dual function of the <i>N</i>-aryl group bound to the perimidine-carbene ligand, which acted as both a neutral carbene ligand and a monoanionic ortho-metalated aryl-carbene ligand through reversible C–H bond activation and Ir–C bond cleavage of the <i>N</i>-aryl group during the catalytic cycle

    Synthesis of Alkyl and Alkylidene Complexes of Tungsten Bearing Imido and Redox-Active α‑Diimine or <i>o</i>‑Iminoquinone Ligands and Their Application as Catalysts for Ring-Opening Metathesis Polymerization of Norbornene

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    We report a new strategy to synthesize tungsten imido complexes bearing bidentate redox-active ligands through reduction of high-valent tungsten imido complexes by 1-methyl-3,6-bis­(trimethylsilyl)-1,4-cyclohexadiene (abbreviated MBTCD) without forming any metal salt waste. Reaction of W­(NC<sub>6</sub>H<sub>3</sub>-2,6-<sup><i>i</i></sup>Pr<sub>2</sub>)­Cl<sub>4</sub> and MBTCD in the presence of redox-active ligands, such as α-diimine and <i>o</i>-iminoquinone, produced tungsten imido complexes with the corresponding redox-active ligands, (α-diimine)­W­(NC<sub>6</sub>H<sub>3</sub>-2,6-<sup><i>i</i></sup>Pr<sub>2</sub>)­Cl<sub>2</sub> (<b>1</b>), [(<i>o</i>-iminoquinone)­W­(NC<sub>6</sub>H<sub>3</sub>-2,6-<sup><i>i</i></sup>Pr<sub>2</sub>)­Cl]<sub>2</sub>(μ-Cl)<sub>2</sub> (<b>3</b>), and (<i>o</i>-iminoquinone)­W­(NC<sub>6</sub>H<sub>3</sub>-2,6-<sup><i>i</i></sup>Pr<sub>2</sub>)­Cl<sub>2</sub>(THF) (<b>4</b>), along with Me<sub>3</sub>SiCl and toluene as whole byproducts. Reaction of the brown complex <b>1</b> with [<sup><i>n</i></sup>Bu<sub>4</sub>N]­[Cl] afforded intensely green single crystals of [<sup><i>n</i></sup>Bu<sub>4</sub>N]­[(α-diimine)­W­(NC<sub>6</sub>H<sub>3</sub>-2,6-<sup><i>i</i></sup>Pr<sub>2</sub>)­Cl<sub>3</sub>] (<b>2</b>). The versatile coordination modes of the α-diimine and <i>o</i>-iminoquinone ligands were clarified by spectroscopic methods and X-ray diffraction studies. Treatment of complex <b>1</b> with 1 equiv of Mg­(CH<sub>2</sub>Ph)<sub>2</sub>·Et<sub>2</sub>O resulted in the formation of (α-diimine)­W­(NC<sub>6</sub>H<sub>3</sub>-2,6-<sup><i>i</i></sup>Pr<sub>2</sub>)­(CH<sub>2</sub>Ph)<sub>2</sub> (<b>5</b>), and thermolysis of <b>5</b> in the presence of PMe<sub>2</sub>Ph at 80 °C afforded the alkylidene complex (α-diimine)­W­(NC<sub>6</sub>H<sub>3</sub>-2,6-<sup><i>i</i></sup>Pr<sub>2</sub>)­(CHPh)­(PMe<sub>2</sub>Ph) (<b>6</b>). On the other hand, thermolysis of <b>5</b> in the presence of CCl<sub>4</sub> afforded the dissymmetric benzylidene complex (Cl<sub>3</sub>C-amido-imino)­W­(NC<sub>6</sub>H<sub>3</sub>-2,6-<sup><i>i</i></sup>Pr<sub>2</sub>)­(CHPh)Cl (<b>7</b>) via reductive cleavage of the C–Cl bond of CCl<sub>4</sub>. Isolated alkylidene complexes <b>6</b> and <b>7</b> served as catalysts for ring-opening metathesis polymerization of norbornene with 1 mol% of catalyst loading in toluene at 80 °C. Treatment of <i>o</i>-iminoquinone complex <b>4</b> with 2 equiv of LiCH<sub>2</sub>CMe<sub>2</sub>Ph afforded the dialkyl complex (<i>o</i>-iminoquinone)­W­(NC<sub>6</sub>H<sub>3</sub>-2,6-<sup><i>i</i></sup>Pr<sub>2</sub>)­(CH<sub>2</sub>CMe<sub>2</sub>Ph)<sub>2</sub> (<b>8</b>). Dialkyl complexes <b>5</b> and <b>8</b> at 80 °C served as catalysts to give poly­(norbornene) with rather broad polydispersity

    Oxidation of Alcohols to Carbonyl Compounds Catalyzed by Oxo-Bridged Dinuclear Cerium Complexes with Pentadentate Schiff-Base Ligands under a Dioxygen Atmosphere

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    Ionic mononuclear and neutral dinuclear complexes of cerium­(III) <b>3-L</b><sup><b>1</b></sup><b>–3-L</b><sup><b>9</b></sup> bearing a series of dianionic pentadentate Schiff-base ligands were synthesized, characterized, and used as catalysts for <i>N</i>-oxyl radical-free aerobic alcohol oxidation. Reactions of Ce­(NO<sub>3</sub>)<sub>3</sub>·6H<sub>2</sub>O with <i>o</i>-<i>tert</i>-butyl-substituted sterically hindered ligands NH­(CH<sub>2</sub>CH<sub>2</sub>NCHC<sub>6</sub>H<sub>2</sub>-3-(<sup><i>t</i></sup>Bu)-5-R<sup>2</sup>-2-OH)<sub>2</sub> (for <b>L</b><sup><b>1</b></sup>H<sub>2</sub>, R<sup>2</sup> = <sup><i>t</i></sup>Bu; for <b>L</b><sup><b>2</b></sup>H<sub>2</sub>, R<sup>2</sup> = OMe; and for <b>L</b><sup><b>3</b></sup>H<sub>2</sub>, R<sup>2</sup> = H) in the presence of triethylamine afforded the corresponding anionic cerium complexes [HNEt<sub>3</sub>]­[Ce­(<b>L</b><sup><b>1–3</b></sup>)­(NO<sub>3</sub>)<sub>2</sub>] (<b>3-L</b><sup><b>1</b></sup>–<b>3-L</b><sup><b>3</b></sup>), whereas complexation with sterically less hindered ligands, such as NH­(CH<sub>2</sub>CH<sub>2</sub>NCHC<sub>6</sub>H<sub>2</sub>-3-R<sup>1</sup>-5-R<sup>2</sup>-2-OH)<sub>2</sub> (for <b>L</b><sup><b>4</b></sup>H<sub>2</sub>, R<sup>1</sup> = OMe and R<sup>2</sup> = H; for <b>L</b><sup><b>5</b></sup>H<sub>2</sub>, R<sup>1</sup> = H and R<sup>2</sup> = <sup><i>t</i></sup>Bu; for <b>L</b><sup><b>6</b></sup>H<sub>2</sub>, R<sup>1</sup> = H and R<sup>2</sup> = OMe; for <b>L</b><sup><b>7</b></sup>H<sub>2</sub>, R<sup>1</sup> = H and R<sup>2</sup> = H; for <b>L</b><sup><b>8</b></sup>H<sub>2</sub>, R<sup>1</sup> = H and R<sup>2</sup> = NO<sub>2</sub>; and for <b>L</b><sup><b>9</b></sup>H<sub>2</sub>, R<sup>1</sup> = <sup><i>t</i></sup>Bu and R<sup>2</sup> = NO<sub>2</sub>), afforded neutral dinuclear complexes [Ce­(<b>L</b><sup><b>4–9</b></sup>)­(NO<sub>3</sub>)]<sub>2</sub> (<b>3-L</b><sup><b>4</b></sup><b>–3-L</b><sup><b>9</b></sup>). Among these newly prepared complexes, complex <b>3-L</b><sup><b>1</b></sup> was selected as the best catalyst for oxidizing primary and secondary alcohols under a dioxygen atmosphere without any <i>N</i>-oxyl radicals such as TEMPO to produce the corresponding carbonyl compounds, where the oxo-bridged dinuclear complex worked as a catalyst while maintaining its dinuclear skeleton during the catalytic cycle. In addition, an intramolecular redox process between the two cerium centers through the bridging oxygen atom played a key role in forming the ligand phenoxide radical-mediated TEMPO-free alcohol oxidation reaction

    End-Functionalized Polymerization of 2-Vinylpyridine through Initial C–H Bond Activation of <i>N</i>-Heteroaromatics and Internal Alkynes by Yttrium Ene–Diamido Complexes

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    We successfully introduced end-capping functional groups to poly(2-vinylpyridine)s by initial introduction of the functional groups on yttrium catalysts through C–H bond activation of heteroaromatics and internal alkynes to the Y center via alkylyttrium-mediated σ-bond metathesis

    Aminomethylation Reaction of <i>ortho</i>-Pyridyl C–H Bonds Catalyzed by Group 3 Metal Triamido Complexes

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    Tris­[<i>N</i>,<i>N</i>-bis­(trimethylsilyl)­amido] complexes of group 3 metals, especially yttrium and gadolinium, served as catalysts for <i>ortho</i>-C–H bond addition of pyridine derivatives and N-heteroaromatics into the CN double bond of nonactivated imines to afford the corresponding aminomethylated products. Addition of catalytic amounts of secondary amines, such as dibenzylamine, dramatically improved the catalytic activity through the formation of a mixed ligated complex such as [(Me<sub>3</sub>Si)<sub>2</sub>N]<sub>2</sub>Y­(NBn<sub>2</sub>)­(THF) (<b>4</b>). Furthermore, kinetic studies using the isolated complex <b>4</b> provided a plausible reaction mechanism by which coordination of two pyridine derivatives afforded a penta-coordinated species as a key step

    Synthesis and Characterization of Paramagnetic Tungsten Imido Complexes Bearing α‑Diimine Ligands

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    Tungsten imido complexes bearing a redox-active ligand, such as <i>N</i>,<i>N</i>′-bis­(2,6-diisopropylphenyl)-1,4-diaza-2,3-dimethyl-1,3-butadiene (L1), <i>N</i>,<i>N</i>′-bis­(2,6-diisopropylphenyl)-1,4-diaza-1,3-butadiene (L2), and 1,2-bis­[(2,6-diisopropylphenyl)­imino]­acenaphthene (L3), were prepared by salt-free reduction of W­(NC<sub>6</sub>H<sub>3</sub>-2,6-<sup><i>i</i></sup>Pr<sub>2</sub>)­Cl<sub>4</sub> (<b>1</b>) using 1-methyl-3,6-bis­(trimethylsilyl)-1,4-cyclohexadiene (MBTCD) followed by addition of the corresponding redox-active ligands. In the initial stage, reaction of W­(NC<sub>6</sub>H<sub>3</sub>-2,6-<sup><i>i</i></sup>Pr<sub>2</sub>)­Cl<sub>4</sub> with MBTCD afforded a tetranuclear W­(V) imido cluster, [W­(NC<sub>6</sub>H<sub>3</sub>-2,6-<sup><i>i</i></sup>Pr<sub>2</sub>)­Cl<sub>3</sub>]<sub>4</sub> (<b>2</b>), which served as a unique precursor for introducing redox-active ligands to the tungsten center to give the corresponding mononuclear complexes with a general formula of W­(NC<sub>6</sub>H<sub>3</sub>-2,6-<sup><i>i</i></sup>Pr<sub>2</sub>)­Cl<sub>3</sub>(L) (<b>3</b>, L = L1; <b>4</b>, L = L2; and <b>6</b>, L = L3). X-ray analyses of complexes <b>3</b> and <b>6</b> revealed a neutral coordination mode of L1 and L3 to the tungsten in solid state, while the electron paramagnetic resonance (EPR) spectra of <b>3</b> and <b>4</b> clarified that a radical was predominantly located on the tungsten center supported by neutral L1 or L2, and the EPR spectra of complex <b>6</b> indicated that a radical was delocalized over both the tungsten center and the monoanionic redox-active ligand L3
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