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

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

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

The reactivities of different 3-imino-functionalized indoles with rare-earth-metal amides [(Me₃Si)₂N]₃RE­(μ-Cl)­Li­(THF)₃ 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 [(Me₃Si)₂N]₃RE­(μ-Cl)­Li­(THF)₃ produced tetranuclear rare-earth-metal complexes {[η¹:(μ₂-η¹:η¹):η¹-3-(<i>t</i>BuNCH)­C₈H₄N]­RE₂­(μ₂-Cl)₂(THF)­[N­(SiMe₃)₂]­(η¹:η¹-[μ-η⁵:η²<i>-</i>3-(<i>t</i>BuNCH)­C₈H₅N]₂Li)}₂ (RE = Ho (<b>1a</b>), Er (<b>1b</b>)), incorporating a unique indolyl-1,2-dianion through sp² C–H activation bonded with the central metal in η¹:(μ₂-η¹:η¹) mode. The reactions of 3-(phenylimino)­indole with [(Me₃Si)₂N]₃RE­(μ-Cl)­Li­(THF)₃ afforded novel binuclear complexes formulated as {3-[PhNCH­(CH₂SiMe₂)­N­(SiMe₃)]­C₈H₅NRE­(THF)­(μ₂-Cl)­Li­(THF)₂}₂ (RE = Y (<b>2a</b>), Sm (<b>2b</b>), Dy (<b>2c</b>), Yb (<b>2d</b>)) through an unexpected sp³ C–H bond activation with subsequent C–C bond coupling reactions. Treatment of 3-(2-methylphenylimino)­indole or 3-(4-methylphenylimino)­indole with [(Me₃Si)₂N]₃­Yb­(μ-Cl)­Li­(THF)₃ generated the corresponding dinuclear rare-earth-metal amido complexes {3-[(2-MePh)­NCH­(CH₂SiMe₂)­N­(SiMe₃)]­C₈H₅NYb­(THF)­(μ₂-Cl)­Li­(THF)₂}₂ (<b>3</b>) and {3-[(4-MePh)­NCH­(CH₂SiMe₂)­N­(SiMe₃)]­C₈H₅NYb­(THF)­(μ₂-Cl)­Li­(THF)₂}₂ (<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 [(Me₃Si)₂N]₃RE­(μ-Cl)­Li­(THF)₃ afforded new hexanuclear rare-earth-metal complexes {3-[(4-^<i>t</i>Bu-Ph)­NHCH­(CH₂SiMe₂)­N­(SiMe₃)]­C₈H₅NREN­(SiMe₃)₂}₆ (RE = Dy (<b>5a</b>), Ho (<b>5b</b>), Er (<b>5c</b>)) via sp³ 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(CH₂SiMe₂)­N­(SiMe₃)]­C₈H₅NYN­(SiMe₃)₂­Li­(THF)}₆ (<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

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 (H₃<b>L</b>Cl₂) with [(Me₃Si)₂­N]₃­RE­(μ-Cl)­Li­(THF)₃ (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 H₃<b>L</b>Cl₂ with [(Me₃Si)₂­N]₃­Er­(μ-Cl)­Li­(THF)₃ in toluene afforded the CNC-pincer erbium amido complex incorporating a diarylamido linked biscarbene ligand <b>L</b>Er­[N­(SiMe₃)₂]₂ (<b>2</b>) in low yield and the above fused-heterocyclic compound <b>1</b>. The stepwise reaction of H₃<b>L</b>Cl₂ with strong bases (<i>n</i>-BuLi or LiCH₂SiMe₃) in THF for 4 h, followed by treatment with [(Me₃Si)₂­N]₃­RE­(μ-Cl)­Li­(THF)₃, generated zwitterion complexes [<b>L</b>₂RE]­[RECl­{N­(SiMe₃)₂}₃] (<b>L</b> = [4-CH₃-2-{(C₆H₄CH₂-[N­(CH)₂­CN]}­C₆H₃]₂N; 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 H₃<b>L</b>Cl₂ with 6 equiv of NaN­(SiMe₃)₂ in THF for 4 h, followed by treatment with YbCl₃, generated a novel discrete complex [<b>L</b>₂Yb]­[{Na­(μ-N­(SiMe₃)₂)}₅­(μ₅-Cl)] (<b>6</b>). The one-pot reaction of H₃<b>L</b>Cl₂ with <i>n</i>-BuLi, followed by reaction with [(Me₃Si)₂­N]₃­RE­(μ-Cl)­Li­(THF)₃ in THF at −78 °C, generated the CNC-pincer lanthanide bisamido complexes <b>L</b>RE­[N­(SiMe₃)₂]₂ (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 (H₃<b>L</b>Cl₂) with 5 equiv of NaN­(SiMe₃)₂, followed by treatment with RECl₃, 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

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

The reaction of 2-(2,6-DippNHCH₂)­C₈H₅NH (Dipp = 2,6-^<i>i</i>PrC₆H₃, C₈H₅NH = indolyl) with 1 equiv of (Me₃SiCH₂)₃Yb­(THF)₂ at room temperature generated mononuclear ytterbium complex <b>1</b> having the indolyl ligands in η¹:η¹ mode with reduction of Yb³⁺ to Yb²⁺ 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-η²:η²:η¹ 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-η⁵:η¹:η¹ and μ-η⁶:η¹:η¹ modes with Dy, and its isomer <b>4b</b> having the indolyl ligands only in μ-η⁵:η¹:η¹ modes with Dy. However, when the rare-earth metal is Gd, the reaction only produced the mixed ligated dinuclear gadolinium complex [(μ-η⁵:η¹:η¹)-2-(2,6-DippNCH₂)­Ind­(μ-η⁶:η¹:η¹)-2-(2,6-DippNCH₂)­Ind]­[Gd­(CH₂SiMe₃)­(thf)]₂ (<b>5</b>), having indolyl ligands in μ-η⁵:η¹:η¹ and μ-η⁶:η¹:η¹ modes with Gd. In addition, treatment of 2-(2,6-DippNHCH₂)­C₈H₅NH with 1.25 equiv of (Me₃SiCH₂)₃Gd­(THF)₂ produced the alkoxido-bridged trinuclear gadolinium complex [(μ-η³:η²:η¹:η¹)-2-(2,6-DippNCH₂)­Ind­(μ-η²:η¹:η¹)-2-(2,6-DippNCH₂)­Ind<i>-</i>(η¹:η¹)-2-(2,6-DippNCH₂)­Ind]-Gd₃[(μ₃<i>-</i>O­(CH₂)₅SiMe₃)­(μ₂-O­(CH₂)₅SiMe₃)­(thf)₃] (<b>6</b>) having indolyl ligands in η¹:η¹, μ-η²:η¹:η¹, and μ-η³:η²:η¹:η ¹ modes with metals, respectively. In complex <b>6</b>, sp² C–H activation is observed at the 7-indolyl position producing unique 2-amido substituted indolyl-1,7-dianions having a μ-η³:η²:η¹:η¹ bonding modes with three metals. The O­(CH₂)₅SiMe₃ arises from the ring-opening of THF by attack of CH₂SiMe₃. Moreover, when 2-(2,6-DippNHCH₂)­C₈H₅NH was treated with 1 equiv of (Me₃SiCH₂)₃Sm­(THF)₂, a dinuclear samarium complex [μ-η³:η¹:η¹-2-(2,6-DippNCH₂)­Ind]₃Sm₂(thf)₃ (<b>7</b>) having a bridged indolyl ligand in μ-η³:η¹:η¹ 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^<i>i</i>Bu₃ and [Ph₃C]­[B­(C₆F₅)₄]. 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^<i>i</i>Bu₃ and [Ph₃C]­[B­(C₆F₅)₄]

Indolyl-based Copper(I) Complex-Catalyzed Intermolecular Trifluoromethylazolation of Alkenes via Radical Process

Herein, we synthesized and characterized a binuclear copper(I) complex supported by the indolyl-based ligand. Employing this complex as catalyst, we have developed a three-component intermolecular trifluoromethylazolation of alkenes to deliver various trifluoromethylated azole derivatives. The method features exclusive chemo- and regioselectivity, a broad scope of alkenes and oxazoles, thiazoles, and good tolerance of functional groups under mild conditions. Preliminary mechanistic studies support a radical process for the transformation

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

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 AlMe₃ produced only imino-coordinated aluminum complex 1-Bn-2-(2,6-^<i>i</i>Pr₂C₆H₃NCH)­C₄H₃NAlMe₃ (<b>1</b>), while reactions of N-protected 2-amino-functionalized pyrroles with aluminum alkyls produced the aluminum alkyl complexes {[η¹-μ-η¹:η¹-1-R₁-2-(2,6-^<i>i</i>Pr₂C₆H₃NCH₂)­C₄H₂N]­AlR}₂ (R₁ = Bn, R = Me (<b>2</b>); R₁ = Bn, R = Et (<b>3</b>); R₁ = R = Me (<b>4</b>); R₁ = 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 (^<i>i</i>PrOH) afforded the corresponding aluminum alkoxide complexes [1-R₁-2-(2,6-^<i>i</i>Pr₂C₆H₃NCH₂)­C₄H₃NAlR­(μ-O^<i>i</i>Pr)]₂ (R₁ = Bn, R = Me (<b>6</b>); R₁ = Bn, R = Et (<b>7</b>); R₁ = R = Me (<b>8</b>); R₁ = 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

Novel Lanthanide Amides Incorporating Neutral Pyrrole Ligand in a Constrained Geometry Architecture: Synthesis, Characterization, Reaction, and Catalytic Activity

The first series of lanthanide amido complexes incorporating a neutral pyrrole ligand in a constrained geometry architecture were synthesized, and their bonding, reactions, and catalytic activities were studied. Treatment of [(Me₃Si)₂N]₃Ln­(μ-Cl)­Li­(THF)₃ with 1 equiv of (<i>N</i>-C₆H₅NHCH₂CH₂)­(2,5-Me₂C₄H₂N) (<b>1</b>) afforded the first example of bisamido lanthanide complexes having the neutral pyrrole η⁵-bonded to the metal formulated as [η⁵:η¹-(<i>N</i>-C₆H₅NCH₂CH₂)­(2,5-Me₂C₄H₂N)]­Ln­[N­(SiMe₃)₂]₂ (Ln = La (<b>2</b>) and Nd (<b>3</b>)). Reaction of [(Me₃Si)₂N]₃Sm­(μ-Cl)­Li­(THF)₃ with 2 equiv of <b>1</b> produced the complex [η⁵:η¹-(<i>N</i>-C₆H₅NCH₂CH₂)­(2,5-Me₂C₄H₂N)]­[η¹-(<i>N</i>-C₆H₅NCH₂CH₂)­(2,5-Me₂C₄H₂N)]]­SmN­(SiMe₃)₂ (<b>4</b>). Treatment of <b>3</b> with 2 equiv of <b>1</b> gave the sandwich neodymium complex [η⁵:η¹-(<i>N</i>-C₆H₅NCH₂CH₂)­(2,5-Me₂C₄H₂N)]₂Nd­[η¹-(<i>N</i>-C₆H₅NCH₂CH₂)­(2,5-Me₂C₄H₂N)] (<b>5</b>), in which two neutral pyrroles bonded with metal in an η⁵ mode. Complex <b>5</b> could also be prepared by reaction of [(Me₃Si)₂N]₃Nd­(μ-Cl)­Li­(THF)₃ with 3 equiv of <b>1</b>. Reactivities of the lanthanide bisamido complexes were further investigated. Reaction of complex <b>2</b> with pyrrolyl-functionalized imine [2-(2,6-^<i>i</i>Pr₂C₆H₃NCH)­C₄H₃NH] afforded a mixed η⁵-bonded neutral pyrrole and η¹-bonded anionic pyrrolyl lanthanum complex [η⁵:η¹-(<i>N</i>-C₆H₅NCH₂CH₂)­(2,5-Me₂C₄H₂N)]­{η¹-2-[(2,6-^<i>i</i>Pr₂C₆H₃)­NCH]­C₄H₃N}­La­[N­(SiMe₃)₂] (<b>6</b>). Reactions of complexes <b>2</b> and <b>3</b> with pyrrolyl-functionalized secondary amine afforded the mixed η⁵-bonded neutral pyrrole and the η¹-bonded anionic pyrrolyl lanthanide complexes [η⁵:η¹-(<i>N</i>-C₆H₅NCH₂CH₂)­(2,5-Me₂C₄H₂N)]­[(η¹-2-^<i>t</i>BuNCH)­C₄H₃N]₂Ln (Ln = La (<b>7</b>), Nd (<b>8</b>)) with dehydrogenation of the secondary amine. Investigation of the catalytic properties of complexes <b>2</b>–<b>8</b> indicated that all complexes exhibited a high activity with a high chemo- and regioselectivity on the addition of dialkyl phosphite to α,β-unsaturated carbonyl derivatives. An interesting result was found that 1,2-hydrophosphonylation substrates could be catalytically converted to 1,4-hydrophosphinylation products when the substrates are the substituted benzylideneacetones by controlling the reaction conditions