29 research outputs found
Synthesis of Heteroaryl Compounds through Cross-Coupling Reaction of Aryl Bromides or Benzyl Halides with Thienyl and Pyridyl Aluminum Reagents
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
PdÂ(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
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 [(Me<sub>3</sub>Si)<sub>2</sub>N]<sub>3</sub>REÂ(μ-Cl)ÂLiÂ(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)Âindole with [(Me<sub>3</sub>Si)<sub>2</sub>N]<sub>3</sub>REÂ(μ-Cl)ÂLiÂ(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>BuNî—»CH)ÂC<sub>8</sub>H<sub>4</sub>N]ÂRE<sub>2</sub>Â(μ<sub>2</sub>-Cl)<sub>2</sub>(THF)Â[NÂ(SiMe<sub>3</sub>)<sub>2</sub>]Â(η<sup>1</sup>:η<sup>1</sup>-[μ-η<sup>5</sup>:η<sup>2</sup><i>-</i>3-(<i>t</i>BuNî—»CH)ÂC<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)Âindole with [(Me<sub>3</sub>Si)<sub>2</sub>N]<sub>3</sub>REÂ(μ-Cl)ÂLiÂ(THF)<sub>3</sub> afforded novel binuclear complexes formulated as {3-[PhNCHÂ(CH<sub>2</sub>SiMe<sub>2</sub>)ÂNÂ(SiMe<sub>3</sub>)]ÂC<sub>8</sub>H<sub>5</sub>NREÂ(THF)Â(μ<sub>2</sub>-Cl)ÂLiÂ(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)Âindole
or 3-(4-methylphenylimino)Âindole with [(Me<sub>3</sub>Si)<sub>2</sub>N]<sub>3</sub>ÂYbÂ(μ-Cl)ÂLiÂ(THF)<sub>3</sub> generated
the corresponding dinuclear rare-earth-metal amido complexes {3-[(2-MePh)ÂNCHÂ(CH<sub>2</sub>SiMe<sub>2</sub>)ÂNÂ(SiMe<sub>3</sub>)]ÂC<sub>8</sub>H<sub>5</sub>NYbÂ(THF)Â(μ<sub>2</sub>-Cl)ÂLiÂ(THF)<sub>2</sub>}<sub>2</sub> (<b>3</b>) and {3-[(4-MePh)ÂNCHÂ(CH<sub>2</sub>SiMe<sub>2</sub>)ÂNÂ(SiMe<sub>3</sub>)]ÂC<sub>8</sub>H<sub>5</sub>NYbÂ(THF)Â(μ<sub>2</sub>-Cl)ÂLiÂ(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)Âindole with [(Me<sub>3</sub>Si)<sub>2</sub>N]<sub>3</sub>REÂ(μ-Cl)ÂLiÂ(THF)<sub>3</sub> afforded new hexanuclear rare-earth-metal complexes {3-[(4-<sup><i>t</i></sup>Bu-Ph)ÂNHCHÂ(CH<sub>2</sub>SiMe<sub>2</sub>)ÂNÂ(SiMe<sub>3</sub>)]ÂC<sub>8</sub>H<sub>5</sub>NRENÂ(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)ÂNCHÂ(CH<sub>2</sub>SiMe<sub>2</sub>)ÂNÂ(SiMe<sub>3</sub>)]ÂC<sub>8</sub>H<sub>5</sub>NYNÂ(SiMe<sub>3</sub>)<sub>2</sub>ÂLiÂ(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
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 bisÂ[2-(3-benzylÂimidazolium)-4-methylÂphenyl]Âamine
dichlorides (H<sub>3</sub><b>L</b>Cl<sub>2</sub>) with [(Me<sub>3</sub>Si)<sub>2</sub>ÂN]<sub>3</sub>ÂREÂ(μ-Cl)ÂLiÂ(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>-benzoÂ[4,5]ÂimidazoÂ[2′,1′:2,3]ÂimidazoÂ[1,2-<i>a</i>]ÂimidazoÂ[2,1-<i>c</i>]Âquinoxaline
(<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>ÂN]<sub>3</sub>ÂErÂ(μ-Cl)ÂLiÂ(THF)<sub>3</sub> in toluene afforded the CNC-pincer erbium amido complex incorporating
a diarylamido linked biscarbene ligand <b>L</b>ErÂ[NÂ(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>ÂN]<sub>3</sub>ÂREÂ(μ-Cl)ÂLiÂ(THF)<sub>3</sub>, generated zwitterion complexes [<b>L</b><sub>2</sub>RE]Â[REClÂ{NÂ(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>-[NÂ(CH)<sub>2</sub>ÂCN]}ÂC<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 NaNÂ(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]Â[{NaÂ(μ-NÂ(SiMe<sub>3</sub>)<sub>2</sub>)}<sub>5</sub>Â(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>ÂN]<sub>3</sub>ÂREÂ(μ-Cl)ÂLiÂ(THF)<sub>3</sub> in THF at −78 °C, generated the CNC-pincer lanthanide
bisamido complexes <b>L</b>REÂ[NÂ(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 bisÂ(imidazolium) salt (H<sub>3</sub><b>L</b>Cl<sub>2</sub>) with 5 equiv of NaNÂ(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
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>Nî—»CH)ÂC<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>)ÂC<sub>4</sub>H<sub>2</sub>N]ÂAlR}<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>)ÂC<sub>4</sub>H<sub>3</sub>NAlRÂ(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
The reaction of 2-(2,6-DippNHCH<sub>2</sub>)ÂC<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>YbÂ(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>)ÂIndÂ(μ-η<sup>6</sup>:η<sup>1</sup>:η<sup>1</sup>)-2-(2,6-DippNCH<sub>2</sub>)ÂInd]Â[GdÂ(CH<sub>2</sub>SiMe<sub>3</sub>)Â(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>)ÂC<sub>8</sub>H<sub>5</sub>NH with 1.25 equiv of (Me<sub>3</sub>SiCH<sub>2</sub>)<sub>3</sub>GdÂ(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>)ÂIndÂ(μ-η<sup>2</sup>:η<sup>1</sup>:η<sup>1</sup>)-2-(2,6-DippNCH<sub>2</sub>)ÂInd<i>-</i>(η<sup>1</sup>:η<sup>1</sup>)-2-(2,6-DippNCH<sub>2</sub>)ÂInd]-Gd<sub>3</sub>[(μ<sub>3</sub><i>-</i>OÂ(CH<sub>2</sub>)<sub>5</sub>SiMe<sub>3</sub>)Â(μ<sub>2</sub>-OÂ(CH<sub>2</sub>)<sub>5</sub>SiMe<sub>3</sub>)Â(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 OÂ(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>)ÂC<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>SmÂ(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>)ÂInd]<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]Â[BÂ(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]Â[BÂ(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
The asymmetric addition
of pyridyl aluminum reagents to aldehydes
has been successfully developed by employing a titaniumÂ(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