29 research outputs found

    Synthesis of Heteroaryl Compounds through Cross-Coupling Reaction of Aryl Bromides or Benzyl Halides with Thienyl and Pyridyl Aluminum Reagents

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    An efficient method for synthesis of useful biaryl building blocks containing 2-thienyl, 3-thienyl, 2-pyridyl, and 3-pyridyl moieties was provided through cross-coupling reactions of aryl bromides or benzyl halides with heteroaryl aluminum reagents in the presence of Pd­(OAc)<sub>2</sub> and (<i>o</i>-tolyl)<sub>3</sub>P. The coupling reaction also worked efficiently with heteroaryl bromides affording series of heterobiaryl compounds. The reaction of phenylbromide with in situ prepared 3-pyridyl aluminum was demonstrated to afford the product <b>8a</b> in high yield. Additionally, the catalytic system was also suited well for the coupling reaction of benzyl halides with pyridyl aluminum reagents to afford series of pyridyl-arylmethane

    Lewis Acid Catalyzed Cascade Reaction to Carbazoles and Naphthalenes via Dehydrative [3 + 3]-Annulation

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    A novel Lewis acid catalyzed dehydrative [3 + 3]-annulation of readily available benzylic alcohols and propargylic alcohols was developed to give polysubstituted carbazoles and naphthalenes in moderate to good yields with water as the only byproduct. The reaction was presumed to proceed via a cascade process involving Friedel–Crafts-type allenylation, 1,5-hydride shift, 6π-eletrocyclization, and Wagner–Meerwein rearrangement

    A Novel Lewis Acid Catalyzed [3 + 3]-Annulation Strategy for the Syntheses of Tetrahydro-β-Carbolines and Tetrahydroisoquinolines

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    A novel Lewis acid catalyzed [3 + 3]-annulation process for the efficient syntheses of both tetrahydro-β-carbolines and tetrahydroisoquinolines from readily available benzylic alcohols and aziridines was developed, which would be a highly valuable complement to the widely used Pictet–Spengler reaction. A probable mechanism was proposed based on the isolation and characterization of two key intermediates. This strategy enables facile access to important alkaloid frameworks not easily available with other known methods

    Reactivity of 3‑Imino-Functionalized Indoles with Rare-Earth-Metal Amides: Unexpected Substituent Effects on C–H Activation Pathways and Assembly of Rare-Earth-Metal Complexes

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    The reactivities of different 3-imino-functionalized indoles with rare-earth-metal amides [(Me<sub>3</sub>Si)<sub>2</sub>N]<sub>3</sub>RE­(μ-Cl)­Li­(THF)<sub>3</sub> were studied to reveal unexpected substituent effects on C–H bond activation pathways, leading to the formation of unusual rare-earth-metal complexes. The reactions of 3-(<i>tert-</i>butylimino)­indole with [(Me<sub>3</sub>Si)<sub>2</sub>N]<sub>3</sub>RE­(μ-Cl)­Li­(THF)<sub>3</sub> produced tetranuclear rare-earth-metal complexes {[η<sup>1</sup>:(μ<sub>2</sub>-η<sup>1</sup>:η<sup>1</sup>):η<sup>1</sup>-3-(<i>t</i>BuNCH)­C<sub>8</sub>H<sub>4</sub>N]­RE<sub>2</sub>­(μ<sub>2</sub>-Cl)<sub>2</sub>(THF)­[N­(SiMe<sub>3</sub>)<sub>2</sub>]­(η<sup>1</sup>:η<sup>1</sup>-[μ-η<sup>5</sup>:η<sup>2</sup><i>-</i>3-(<i>t</i>BuNCH)­C<sub>8</sub>H<sub>5</sub>N]<sub>2</sub>Li)}<sub>2</sub> (RE = Ho (<b>1a</b>), Er (<b>1b</b>)), incorporating a unique indolyl-1,2-dianion through sp<sup>2</sup> C–H activation bonded with the central metal in η<sup>1</sup>:(μ<sub>2</sub>-η<sup>1</sup>:η<sup>1</sup>) mode. The reactions of 3-(phenylimino)­indole with [(Me<sub>3</sub>Si)<sub>2</sub>N]<sub>3</sub>RE­(μ-Cl)­Li­(THF)<sub>3</sub> afforded novel binuclear complexes formulated as {3-[PhNCH­(CH<sub>2</sub>SiMe<sub>2</sub>)­N­(SiMe<sub>3</sub>)]­C<sub>8</sub>H<sub>5</sub>NRE­(THF)­(μ<sub>2</sub>-Cl)­Li­(THF)<sub>2</sub>}<sub>2</sub> (RE = Y (<b>2a</b>), Sm (<b>2b</b>), Dy (<b>2c</b>), Yb (<b>2d</b>)) through an unexpected sp<sup>3</sup> C–H bond activation with subsequent C–C bond coupling reactions. Treatment of 3-(2-methylphenylimino)­indole or 3-(4-methylphenylimino)­indole with [(Me<sub>3</sub>Si)<sub>2</sub>N]<sub>3</sub>­Yb­(μ-Cl)­Li­(THF)<sub>3</sub> generated the corresponding dinuclear rare-earth-metal amido complexes {3-[(2-MePh)­NCH­(CH<sub>2</sub>SiMe<sub>2</sub>)­N­(SiMe<sub>3</sub>)]­C<sub>8</sub>H<sub>5</sub>NYb­(THF)­(μ<sub>2</sub>-Cl)­Li­(THF)<sub>2</sub>}<sub>2</sub> (<b>3</b>) and {3-[(4-MePh)­NCH­(CH<sub>2</sub>SiMe<sub>2</sub>)­N­(SiMe<sub>3</sub>)]­C<sub>8</sub>H<sub>5</sub>NYb­(THF)­(μ<sub>2</sub>-Cl)­Li­(THF)<sub>2</sub>}<sub>2</sub> (<b>4</b>), following the same pathway for the formation of complexes <b>2a</b>–<b>d</b>. Treatment of 3-(4-<i>tert</i>-butylphenylimino)­indole with [(Me<sub>3</sub>Si)<sub>2</sub>N]<sub>3</sub>RE­(μ-Cl)­Li­(THF)<sub>3</sub> afforded new hexanuclear rare-earth-metal complexes {3-[(4-<sup><i>t</i></sup>Bu-Ph)­NHCH­(CH<sub>2</sub>SiMe<sub>2</sub>)­N­(SiMe<sub>3</sub>)]­C<sub>8</sub>H<sub>5</sub>NREN­(SiMe<sub>3</sub>)<sub>2</sub>}<sub>6</sub> (RE = Dy (<b>5a</b>), Ho (<b>5b</b>), Er (<b>5c</b>)) via sp<sup>3</sup> C–H bond activation followed by C–C bond coupling reactions. In contrast, under the same conditions as those for the preparation of <b>5</b>, the reaction with the corresponding yttrium complex provided the new heterohexayttrium complex {3-[(4-<i>t</i>Bu-Ph)­NCH­(CH<sub>2</sub>SiMe<sub>2</sub>)­N­(SiMe<sub>3</sub>)]­C<sub>8</sub>H<sub>5</sub>NYN­(SiMe<sub>3</sub>)<sub>2</sub>­Li­(THF)}<sub>6</sub> (<b>6</b>), having a 4-<i>t</i>Bu-anilido moiety. All of these complexes were fully characterized by elemental analysis, spectroscopic methods, and X-ray structure analysis. Plausible pathways for the formation of these different rare-earth-metal complexes were proposed

    CNC-Pincer Rare-Earth Metal Amido Complexes with a Diarylamido Linked Biscarbene Ligand: Synthesis, Characterization, and Catalytic Activity

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    In preparation of CNC-pincer rare-earth metal amido complexes with a diarylamido linked biscarbene ligand, it is found that conditions have a key influence on final products. Reaction of a THF suspension of bis­[2-(3-benzyl­imidazolium)-4-methyl­phenyl]­amine dichlorides (H<sub>3</sub><b>L</b>Cl<sub>2</sub>) with [(Me<sub>3</sub>Si)<sub>2</sub>­N]<sub>3</sub>­RE­(μ-Cl)­Li­(THF)<sub>3</sub> (RE = Yb, Eu, Sm) in THF at room temperature afforded the only unexpected fused-heterocyclic compound 8,9-dibenzyl-3,14-dimethyl-8<i>a</i>,9-dihydro-8<i>H</i>-benzo­[4,5]­imidazo­[2′,1′:2,3]­imidazo­[1,2-<i>a</i>]­imidazo­[2,1-<i>c</i>]­quinoxaline (<b>1</b>) containing an imidazolyl ring and a piperidyl ring, which formed through carbene C–C and C–N coupling. However, the reaction of H<sub>3</sub><b>L</b>Cl<sub>2</sub> with [(Me<sub>3</sub>Si)<sub>2</sub>­N]<sub>3</sub>­Er­(μ-Cl)­Li­(THF)<sub>3</sub> in toluene afforded the CNC-pincer erbium amido complex incorporating a diarylamido linked biscarbene ligand <b>L</b>Er­[N­(SiMe<sub>3</sub>)<sub>2</sub>]<sub>2</sub> (<b>2</b>) in low yield and the above fused-heterocyclic compound <b>1</b>. The stepwise reaction of H<sub>3</sub><b>L</b>Cl<sub>2</sub> with strong bases (<i>n</i>-BuLi or LiCH<sub>2</sub>SiMe<sub>3</sub>) in THF for 4 h, followed by treatment with [(Me<sub>3</sub>Si)<sub>2</sub>­N]<sub>3</sub>­RE­(μ-Cl)­Li­(THF)<sub>3</sub>, generated zwitterion complexes [<b>L</b><sub>2</sub>RE]­[RECl­{N­(SiMe<sub>3</sub>)<sub>2</sub>}<sub>3</sub>] (<b>L</b> = [4-CH<sub>3</sub>-2-{(C<sub>6</sub>H<sub>4</sub>CH<sub>2</sub>-[N­(CH)<sub>2</sub>­CN]}­C<sub>6</sub>H<sub>3</sub>]<sub>2</sub>N; RE = Y (<b>3</b>), Er (<b>4</b>), Yb (<b>5</b>)) in less than 20% yields together with fused-heterocyclic compound <b>1</b>. Additionally, the reaction of H<sub>3</sub><b>L</b>Cl<sub>2</sub> with 6 equiv of NaN­(SiMe<sub>3</sub>)<sub>2</sub> in THF for 4 h, followed by treatment with YbCl<sub>3</sub>, generated a novel discrete complex [<b>L</b><sub>2</sub>Yb]­[{Na­(μ-N­(SiMe<sub>3</sub>)<sub>2</sub>)}<sub>5</sub>­(μ<sub>5</sub>-Cl)] (<b>6</b>). The one-pot reaction of H<sub>3</sub><b>L</b>Cl<sub>2</sub> with <i>n</i>-BuLi, followed by reaction with [(Me<sub>3</sub>Si)<sub>2</sub>­N]<sub>3</sub>­RE­(μ-Cl)­Li­(THF)<sub>3</sub> in THF at −78 °C, generated the CNC-pincer lanthanide bisamido complexes <b>L</b>RE­[N­(SiMe<sub>3</sub>)<sub>2</sub>]<sub>2</sub> (RE = Er (<b>2</b>), Y (<b>7</b>), Sm (<b>8</b>), Eu (<b>9</b>)) in moderate yields. These kinds of biscarbene supported pincer bisamido complexes could also be prepared by a one-pot reaction of bis­(imidazolium) salt (H<sub>3</sub><b>L</b>Cl<sub>2</sub>) with 5 equiv of NaN­(SiMe<sub>3</sub>)<sub>2</sub>, followed by treatment with RECl<sub>3</sub>, in good yields at −78 °C. Investigation of the catalytic activity of complexes <b>2</b> and <b>7</b>–<b>9</b> indicated that all complexes showed a high activity toward the addition of terminal alkynes to carbodiimides producing propiolimidines, which represents the first example of rare-earth metal CNC-pincer-type catalysts applied for catalytic C–H bond addition of terminal alkynes to carbodiimides at room temperature

    Aluminum Complexes Bearing N‑Protected 2‑Amino- or 2‑Imino-Functionalized Pyrrolyl Ligands: Synthesis, Structure, and Catalysis for Preparation of Pyrrolyl-End-Functionalized Polyesters

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    Reactivity of N-protected 2-amino- or 2-imino-functionalized pyrroles with aluminum alkyls was investigated, resulting in the isolation of a series of aluminum alkyl complexes. Treatment of 2-imino-functionalized pyrrole with AlMe<sub>3</sub> produced only imino-coordinated aluminum complex 1-Bn-2-(2,6-<sup><i>i</i></sup>Pr<sub>2</sub>C<sub>6</sub>H<sub>3</sub>NCH)­C<sub>4</sub>H<sub>3</sub>NAlMe<sub>3</sub> (<b>1</b>), while reactions of N-protected 2-amino-functionalized pyrroles with aluminum alkyls produced the aluminum alkyl complexes {[η<sup>1</sup>-μ-η<sup>1</sup>:η<sup>1</sup>-1-R<sub>1</sub>-2-(2,6-<sup><i>i</i></sup>Pr<sub>2</sub>C<sub>6</sub>H<sub>3</sub>NCH<sub>2</sub>)­C<sub>4</sub>H<sub>2</sub>N]­AlR}<sub>2</sub> (R<sub>1</sub> = Bn, R = Me (<b>2</b>); R<sub>1</sub> = Bn, R = Et (<b>3</b>); R<sub>1</sub> = R = Me (<b>4</b>); R<sub>1</sub> = Me, R = Et (<b>5</b>)), bearing 3-carbon bonded pyrrolyl ligands via C–H σ-bond metathesis reaction. Further reactions of complexes <b>2</b>–<b>5</b> with a stoichiometric amount of isopropyl alcohol (<sup><i>i</i></sup>PrOH) afforded the corresponding aluminum alkoxide complexes [1-R<sub>1</sub>-2-(2,6-<sup><i>i</i></sup>Pr<sub>2</sub>C<sub>6</sub>H<sub>3</sub>NCH<sub>2</sub>)­C<sub>4</sub>H<sub>3</sub>NAlR­(μ-O<sup><i>i</i></sup>Pr)]<sub>2</sub> (R<sub>1</sub> = Bn, R = Me (<b>6</b>); R<sub>1</sub> = Bn, R = Et (<b>7</b>); R<sub>1</sub> = R = Me (<b>8</b>); R<sub>1</sub> = Me, R = Et (<b>9</b>)) through selective cleavage of the Al–C (Pyr) bonds. The solid-state structures of the aluminum complexes <b>1</b>–<b>6</b> and <b>8</b> were confirmed by an X-ray diffraction study. These aluminum alkyl complexes exhibited notable activity toward the ring-opening polymerization of ε-caprolactone and l-lactide in the absence of alcohol. The end group analysis of the ε-CL oligomer gave strong support that the polymerization proceeded via a coordination–insertion mechanism involving a unique Al–C (Pyr) bond initiation, providing pyrrolyl-end-functionalized polyesters

    Synthesis and Characterization of Rare-Earth Metal Complexes Supported by 2‑Imino or Amino Appended Indolyl Ligands with Diverse Hapticities: Tunable Selective Catalysis for Isoprene Polymerization

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    The reaction of 2-(2,6-DippNHCH<sub>2</sub>)­C<sub>8</sub>H<sub>5</sub>NH (Dipp = 2,6-<sup><i>i</i></sup>PrC<sub>6</sub>H<sub>3</sub>, C<sub>8</sub>H<sub>5</sub>NH = indolyl) with 1 equiv of (Me<sub>3</sub>SiCH<sub>2</sub>)<sub>3</sub>Yb­(THF)<sub>2</sub> at room temperature generated mononuclear ytterbium complex <b>1</b> having the indolyl ligands in η<sup>1</sup>:η<sup>1</sup> mode with reduction of Yb<sup>3+</sup> to Yb<sup>2+</sup> and oxidation of the amino to imino group. In the case of Er and Y, the reactions produced dinuclear complexes <b>2</b> and <b>3</b> having the indolyl ligands in μ-η<sup>2</sup>:η<sup>2</sup>:η<sup>1</sup> modes with the central metals. When the rare-earth metal is dysprosium, the reaction afforded mixed ligated dinuclear complex <b>4a</b> having indolyl ligands in μ-η<sup>5</sup>:η<sup>1</sup>:η<sup>1</sup> and μ-η<sup>6</sup>:η<sup>1</sup>:η<sup>1</sup> modes with Dy, and its isomer <b>4b</b> having the indolyl ligands only in μ-η<sup>5</sup>:η<sup>1</sup>:η<sup>1</sup> modes with Dy. However, when the rare-earth metal is Gd, the reaction only produced the mixed ligated dinuclear gadolinium complex [(μ-η<sup>5</sup>:η<sup>1</sup>:η<sup>1</sup>)-2-(2,6-DippNCH<sub>2</sub>)­Ind­(μ-η<sup>6</sup>:η<sup>1</sup>:η<sup>1</sup>)-2-(2,6-DippNCH<sub>2</sub>)­Ind]­[Gd­(CH<sub>2</sub>SiMe<sub>3</sub>)­(thf)]<sub>2</sub> (<b>5</b>), having indolyl ligands in μ-η<sup>5</sup>:η<sup>1</sup>:η<sup>1</sup> and μ-η<sup>6</sup>:η<sup>1</sup>:η<sup>1</sup> modes with Gd. In addition, treatment of 2-(2,6-DippNHCH<sub>2</sub>)­C<sub>8</sub>H<sub>5</sub>NH with 1.25 equiv of (Me<sub>3</sub>SiCH<sub>2</sub>)<sub>3</sub>Gd­(THF)<sub>2</sub> produced the alkoxido-bridged trinuclear gadolinium complex [(μ-η<sup>3</sup>:η<sup>2</sup>:η<sup>1</sup>:η<sup>1</sup>)-2-(2,6-DippNCH<sub>2</sub>)­Ind­(μ-η<sup>2</sup>:η<sup>1</sup>:η<sup>1</sup>)-2-(2,6-DippNCH<sub>2</sub>)­Ind<i>-</i>(η<sup>1</sup>:η<sup>1</sup>)-2-(2,6-DippNCH<sub>2</sub>)­Ind]-Gd<sub>3</sub>[(μ<sub>3</sub><i>-</i>O­(CH<sub>2</sub>)<sub>5</sub>SiMe<sub>3</sub>)­(μ<sub>2</sub>-O­(CH<sub>2</sub>)<sub>5</sub>SiMe<sub>3</sub>)­(thf)<sub>3</sub>] (<b>6</b>) having indolyl ligands in η<sup>1</sup>:η<sup>1</sup>, μ-η<sup>2</sup>:η<sup>1</sup>:η<sup>1</sup>, and μ-η<sup>3</sup>:η<sup>2</sup>:η<sup>1</sup>:η <sup>1</sup> modes with metals, respectively. In complex <b>6</b>, sp<sup>2</sup> C–H activation is observed at the 7-indolyl position producing unique 2-amido substituted indolyl-1,7-dianions having a μ-η<sup>3</sup>:η<sup>2</sup>:η<sup>1</sup>:η<sup>1</sup> bonding modes with three metals. The O­(CH<sub>2</sub>)<sub>5</sub>SiMe<sub>3</sub> arises from the ring-opening of THF by attack of CH<sub>2</sub>SiMe<sub>3</sub>. Moreover, when 2-(2,6-DippNHCH<sub>2</sub>)­C<sub>8</sub>H<sub>5</sub>NH was treated with 1 equiv of (Me<sub>3</sub>SiCH<sub>2</sub>)<sub>3</sub>Sm­(THF)<sub>2</sub>, a dinuclear samarium complex [μ-η<sup>3</sup>:η<sup>1</sup>:η<sup>1</sup>-2-(2,6-DippNCH<sub>2</sub>)­Ind]<sub>3</sub>Sm<sub>2</sub>(thf)<sub>3</sub> (<b>7</b>) having a bridged indolyl ligand in μ-η<sup>3</sup>:η<sup>1</sup>:η<sup>1</sup> hapticities was isolated. All structures of the complexes have been determined by X-ray crystallographic analyses. Dinuclear alkyl complexes <b>2</b>–<b>5</b> have been tested as isoprene polymerization initiators in the presence of Al<sup><i>i</i></sup>Bu<sub>3</sub> and [Ph<sub>3</sub>C]­[B­(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>]. The regioselectivity for isoprene polymerization is tunable from 1,4-<i>cis</i> (up to 93.5%) to 3,4- (up to 86.2%) selectivity by these catalysts simply by adjusting the addition order of Al<sup><i>i</i></sup>Bu<sub>3</sub> and [Ph<sub>3</sub>C]­[B­(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>]

    Asymmetric Addition of Pyridyl Aluminum Reagents to Aldehydes Catalyzed by a Titanium(IV) Catalytic System of (<i>R</i>)‑H<sub>8</sub>‑BINOLate

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    The asymmetric addition of pyridyl aluminum reagents to aldehydes has been successfully developed by employing a titanium­(IV) catalytic system of (<i>R</i>)-H<sub>8</sub>-BINOLate, which affords a series of valuable optically active diarylmethanols containing various pyridyl groups in high yields with excellent enantioselectivities of up to 98% ee
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