18 research outputs found
Imine-palladacycles as phosphine-free precatalysts for low temperature Suzuki-Miyaura synthesis of nucleoside analogues in aqueous media
The synthesis and characterization of new water-soluble dinuclear palladacycles of the general formula [{Pd(R-C^N-SO3Na)(μ-AcO)}2] (R = H (1), OMe (2), Cl (3)) incorporating an ortho-metalated sodium 4-(N-benzylideneamino)benzenesulfonate moiety is reported. These complexes have been revealed to be excellent phosphine-free catalysts for the synthesis of functionalized nucleoside analogues involving a low-temperature Suzuki–Miyaura coupling of 5-iodo-2′-deoxyuridine with different arylboronic acids in neat water. The potential of 1–3 as synthetic precursors was also tested, and bridging acetates were cleaved by reaction with neutral PPh3, yielding the corresponding mononuclear derivatives [Pd(R-C^N-SO3Na)(AcO)(PPh3)] (R = H (4), MeO (5), Cl (6)). Analytical and spectroscopic techniques confirmed the proposed formulas and reactivities reported for complexes 1–6. Structural characterization by X-ray diffraction of single crystals grown from samples of 4 and 6 produced the unexpected but valuable crystallization-mediated compounds 4cm and 6cm that also supported the results presented here.This work has been partially supported by RTI2018-098233-B-C21 (MICINN) and
20790/PI/18 (Fundación SENECA CARM) grants. A.R.K would like to acknowledge
SERB for EMR grant (EMR/2016/005439). Professor Gregorio Sánchez, who recently
passed away, is gratefully acknowledged for his contribution to this work and his wise
and continuous advise and suppor
Recyclable Supramolecular Ruthenium Catalyst for the Selective Aerobic Oxidation of Alcohols on Water: Application to Total Synthesis of Brittonin A
A supramolecule-based
ruthenium catalyst has been developed for
on-water aerobic oxidation of alcohols. The catalyst is synthesized
by supporting ruthenium nanoparticles on cyclodextrin-modified graphene
oxides (rGO@Ru-RMβ-CD) via a simultaneous one-pot reduction
of ruthenium precursor and graphite oxide in water. The rGO@Ru-RMβ-CD
was completely characterized by various techniques such as X-ray diffraction,
thermogravimetric analysis, Fourier transform infrared, scanning electron
microscopy, transmission electron microscopy, and X-ray photoelectron
spectroscopy to understand its morphology and structure. The catalyst
showed promising efficiency with good selectivity for benzylic, propargylic,
and aromatic alcohols under aqueous conditions. Sensitive functional
groups such as −NH<sub>2</sub> and phenolic −OH were
well tolerated under the reaction conditions and exclusively afforded
the aldehydes in good to excellent yields with no side products. Moreover,
the used catalyst was found to be easily recoverable and recyclable
up to five times. Additionally, the developed oxidation methodology
has been used as a key step for the total synthesis of natural product
Brittonin A, including other functional group transformations such
as Wittig olefination and reduction exclusively in water. Notably,
these oxidation and reduction transformations could be carried out
using the developed catalyst under aqueous conditions. This unique
ability of the catalyst to switch between oxidation and reduction
reactions simply by changing O<sub>2</sub> and H<sub>2</sub> atmospheres
with a balloon assembly exemplifies its versatility. To the best of
our knowledge this is a first report showing the total synthesis of
a molecule completely on water
Phenothiazine-Based Cu(II)-Selective Fluorescent Sensor: GHK-Cu Sensing Applications
Sensing important metals in different environments is
an important
area and involves the development of a wide variety of metal-sensing
materials. The employment of fluorescent sensors in metal sensing
has been one of the most widely applied methodologies, and the identification
of selective metal sensors is important. We herein report a phenothiazine-based
Cu(II) fluorescent sensor that is highly selective to Cu(II) ions
compared with other transition metal salts. The Lewis acidity of the
Cu(II) salt certainly was found to be a factor for obtaining an enhanced
sensing response in MeOH as the solvent, while a ratio of 1:1 was
calculated to be the most optimum for getting the desired response
Cobalt(II)/<i>N</i>‑Hydroxyphthalimide-Catalyzed Cross-Dehydrogenative Coupling Reaction at Room Temperature under Aerobic Condition
This work reports a cobaltÂ(II)/<i>N</i>-hydroxyphthalimide
(NHPI)-catalyzed cross-dehydrogenative oxidative coupling of <i>N</i>-aryl tetrahydroisoquinolines with various pro-nucleophiles,
such as indoles, nitroalkanes, and trialkylphosphites, active methylene
compounds, and other nucleophiles, such as cyanide (ethyl cyanoformate),
at room temperature under aerobic conditions. The present protocol
is operationally simple and can be carried out without photoirradiation
and under peroxide-free conditions, even on a gram scale, to afford
the products in good to excellent yields. On the basis of mass spectrometry
and control experiments, a catalytic reaction pathway has been proposed
Active Palladium Colloids via Palladacycle Degradation as Efficient Catalysts for Oxidative Homocoupling and Cross-Coupling of Aryl Boronic Acids
Active palladium colloids formed
upon degradation of a palladacyclic
complex (Herrmann–Beller <b>1</b>) have been isolated
for the first time and thoroughly characterized with techniques such
as transmission electron microscopy (TEM), high-resolution TEM, X-ray
photoelectron spectroscopy (XPS), and extended X-ray absorption fine
structure spectroscopy. The synthesized palladium colloids have been
utilized as efficient catalysts for the oxidative homocoupling of
aryl boronic acids. Cross-coupling of two different aryl boronic acids
has also been made possible using these active palladium colloids.
This is the first report of this kind of coupling between aryl boronic
acids
Palladacycle-Catalyzed Triple Suzuki Coupling Strategy for the Synthesis of Anthracene-Based OLED Emitters
The
development of the site-selective Suzuki–Miyaura cross-coupling
of dibromoanthracene as an efficient strategy toward organic light
emitting diodes (OLEDs) is disclosed in this article. An unprecedented
step-economic palladacycle-promoted triple Suzuki coupling protocol
allowed the synthesis of three new OLED emitters and could prove to
be a useful general strategy for researchers working in this field.
Characterization of the synthesized molecules by UV–vis spectroscopy
and thermogravimetric analysis–differential scanning calorimetry
followed by density functional theory studies of the different properties
strongly confirms the derivatives possess more significant hole mobility
character than electron transfer capability
Phosphine Ligands Based on the Ferrocenyl Platform: Advances in Catalytic Cross-Couplings
International audienceFerrocenyl skeletons tagged with a variety of donor atoms (metalloligands) have become popular in modern metal-catalyzed organic transformations, broadening the applications. Ferrocenylphosphines, such as 1′-bis(diphenylphosphino)ferrocene (dppf), have been widely used as metalloligands in academic and industrial research, motivating further investigation into novel ferrocenylphosphine ligands. The current review concentrated non-exhaustively on emblematic applications of different ferrocenylphosphine ligands in transition metal-catalyzed cross-coupling strategies. Initially, the stereochemical aspects of the ferrocenyl skeleton, nomenclature, and applications of chiral ferrocenyl phosphines in asymmetric synthesis are evoked. We simply classified ferrocenyl phosphine ligands, eventually further functionalized at cyclopentadienyl (Cp) ring, into three types based on the number of phosphine donors on the ferrocenyl backbone: monophosphine, bisphosphine, and polyphosphine ferrocenyl ligands. Furthermore, the use of hybrid monophosphinoferrocene type scaffolds (P, N)–, (P, O)–, (P, S–), (P, NHC)–, and (P, X)– (X is polar/hydrophilic like guanidium) in cross-coupling is evoked. The latest advances in the chemistry of symmetric achiral di- and polyphosphine ferrocene-based ligands related to metal-catalyzed bond-forming reactions (C–C, C–N, and C–O bonds) are discussed, with a special emphasis on consolidating all important work in this area. A cumulative table is provided in the end, with a focus on compiling significant work in this field. The general structure and electronic features and effects of ferrocenylphosphine ligands on the selectivity and activity in catalysis is also briefly evoked. The literature cut-off date was in general ending of 2020
Pd/PTABS: An Efficient Catalytic System for the Aminocarbonylation of a Sugar-Protected Nucleoside
Heteroatom-Assisted Regio- and Stereoselective Palladium-Catalyzed Carboxylation of 9‑Allyl Adenine
Strategy for the synthesis of acyclic
nucleoside analogs of biological
relevance via highly regio- and stereoselective C–H functionalization
employing heteroatom-assisted palladium-catalyzed carboxylation of
9-allyl adenine is disclosed. Substrate scope with different carboxylic
acids was performed giving decent to good yields of the desired products.
The method also allowed for the synthesis of deuterated analogs