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Molecules (Basel, Switzerland) Apr 2020In an effort to explain the experimentally observed variation of the photocatalytic activity of t Bu 3 P, n Bu 3 P and (MeO) 3 P in the blue-light regime [Helmecke et...
In an effort to explain the experimentally observed variation of the photocatalytic activity of t Bu 3 P, n Bu 3 P and (MeO) 3 P in the blue-light regime [Helmecke et al., Org. Lett. 21 (2019) 7823], we have explored the absorption characteristics of several phosphine- and phosphite-IC 4 F 9 adducts by means of relativistic density functional theory and multireference configuration interaction methods. Based on the results of these computational and complementary experimental studies, we offer an explanation for the broad tailing of the absorption of t Bu 3 P-IC 4 F 9 and (MeO) 3 P-IC 4 F 9 into the visible-light region. Larger coordinate displacements of the ground and excited singlet potential energy wells in n Bu 3 P-IC 4 F 9 , in particular with regard to the P-I-C bending angle, reduce the Franck-Condon factors and thus the absorption probability compared to t Bu 3 P-IC 4 F 9 . Spectroscopic and computational evaluation of conformationally flexible and locked phosphites suggests that the reactivity of (MeO) 3 P may be the result of oxygen lone-pair participation and concomitant broadening of absorption. The proposed mechanism for the phosphine-catalyzed homolytic C-I cleavage of perfluorobutane iodide involves S ← S absorption of the adduct followed by intersystem crossing to the photochemically active T 1 state.
Topics: Algorithms; Iodides; Light; Models, Theoretical; Molecular Conformation; Phosphines; Photochemical Processes; Quantum Theory; Spectrum Analysis
PubMed: 32244568
DOI: 10.3390/molecules25071606 -
Organic Letters Jun 2021Decarbonylative Sonogashira cross-coupling of carboxylic acids by palladium catalysis is presented. The carboxylic acid is activated in situ by the formation of a mixed...
Decarbonylative Sonogashira cross-coupling of carboxylic acids by palladium catalysis is presented. The carboxylic acid is activated in situ by the formation of a mixed anhydride and further decarbonylates using the Pd(OAc)/Xantphos system to provide an aryl-Pd intermediate, which is intercepted by alkynes to access the traditional Pd(0)/(II) cycle using carboxylic acids as ubiquitous and orthogonal electrophilic cross-coupling partners. The methodology efficiently constructs new C(sp)-C(sp) bonds and can be applied to the derivatization of pharmaceuticals. Mechanistic studies give support to decarbonylation preceding transmetalation in this process.
Topics: Alkynes; Anhydrides; Carboxylic Acids; Catalysis; Molecular Structure; Palladium; Phosphines; Xanthenes
PubMed: 34096312
DOI: 10.1021/acs.orglett.1c01445 -
Chemistry (Weinheim An Der Bergstrasse,... Sep 2022The fine-tuning of metal-phosphine-catalyzed reactions relies largely on accessing ever more precisely tuned phosphine ligands by de-novo synthesis. Late-stage C-H...
The fine-tuning of metal-phosphine-catalyzed reactions relies largely on accessing ever more precisely tuned phosphine ligands by de-novo synthesis. Late-stage C-H functionalization and diversification of commercial phosphines offers rapid access to entire libraries of derivatives based on privileged scaffolds. But existing routes, relying on phosphorus-directed transformations, only yield functionalization of C -H bonds in a specific position relative to phosphorus. In contrast to phosphorus-directed strategies, herein we disclose an orthogonal functionalization strategy capable of introducing a range of substituents into previously inaccessible positions on arylphosphines. The strongly coordinating phosphine group acts solely as a bystander in the sterically controlled borylation of bulky phosphines, and the resulting borylated phosphines serve as the supporting ligands for palladium during diversification through phosphine self-assisted Suzuki-Miyaura reactions.
Topics: Catalysis; Ligands; Palladium; Phosphines; Phosphorus
PubMed: 35789048
DOI: 10.1002/chem.202202074 -
Molecules (Basel, Switzerland) Dec 2014The synthesis and structural characterisation of phosphine-substituted alkynylboronates is reported. A P(III)-centred alkynylboronate (2) was prepared that showed little...
The synthesis and structural characterisation of phosphine-substituted alkynylboronates is reported. A P(III)-centred alkynylboronate (2) was prepared that showed little evidence for the conjugation of the P-lone pair to the boron via the alkyne π-system, as judged by X-ray crystallography studies of 2 and a related P(V) compound, 3. In addition, corresponding alkynyltrifluoroborate salts were prepared that showed improved stability by comparison to their boronic ester counterparts. These salts undergo Pd-catalysed cross-coupling reactions with aryl halides.
Topics: Boronic Acids; Crystallography, X-Ray; Phosphines; Salts
PubMed: 25529019
DOI: 10.3390/molecules191221324 -
Chemical Science Feb 2021A novel and efficient desymmetrizing asymmetric -selective mono-bromination of bisphenol phosphine oxides under chiral squaramide catalysis was reported. Using this...
A novel and efficient desymmetrizing asymmetric -selective mono-bromination of bisphenol phosphine oxides under chiral squaramide catalysis was reported. Using this asymmetric -bromination strategy, a wide range of chiral bisphenol phosphine oxides and bisphenol phosphinates were obtained with good to excellent yields (up to 92%) and enantioselectivities (up to 98.5 : 1.5 e.r.). The reaction could be scaled up, and the synthetic utility of the desired -stereogenic compounds was proved by transformations and application in an asymmetric reaction.
PubMed: 34163723
DOI: 10.1039/d0sc07008d -
Langmuir : the ACS Journal of Surfaces... Nov 2018This study advances the chemical research community toward the goal of replacing toxic cadmium-containing quantum dots (QDs) with environmentally benign InP QDs. The InP...
This study advances the chemical research community toward the goal of replacing toxic cadmium-containing quantum dots (QDs) with environmentally benign InP QDs. The InP QD synthesis uniquely combines the previously reported use of InP magic-sized clusters (MSCs) as a single-source precursor for indium and phosphorus to form InP QDs, with zinc incorporation and subsequent ZnS shelling, to form InPZn/ZnS QDs with luminescence properties comparable to those of commonly used cadmium-containing luminescent QDs. The resulting InPZn/ZnS QDs have an emission quantum yield of about 50% across a broad range of emission peak wavelengths and emission peaks averaging 50 nm fwhm. The emission peak wavelength can be easily tuned by varying the Zn/In ratio in the reaction mixture. The strategy of using zinc stearate to tune the emission properties is advantageous as it does not lead to a loss of emission quantum yield or emission peak broadening. Although the initial optical properties of InP and InPZn/ZnS QDs are promising, thermal stability measurements of InPZn QDs show significant degradation in the absence of a shell compared to the CdSe QDs particularly at increased temperature in the presence of oxygen, which is indicative of thermal oxidation. There is no significant difference in the degradation rate of InP QDs made from molecular precursors and from MSCs. Additionally, the emission intensity and quantum yield of InPZn/ZnS QDs when purified and diluted in organic solvents under ambient conditions decrease significantly compared to those of CdSe/ZnS QDs. This indicates instability of the ZnS shell when prepared by common literature methods. This must be improved to realize high-quality, robust Cd-free QDs with the capability of replacing CdSe QDs in QD technologies.
Topics: Cadmium; Chemistry Techniques, Synthetic; Indium; Luminescence; Models, Molecular; Molecular Conformation; Nanotechnology; Phosphines; Quantum Dots; Solutions; Stearic Acids; Sulfides; Zinc Compounds
PubMed: 30351964
DOI: 10.1021/acs.langmuir.8b02402 -
Chimia 2016The secondary phosphine oxides are known to exist in equilibrium between the pentavalent phosphine oxides (SPO) and the trivalent phosphinous acids (PA). This... (Review)
Review
The secondary phosphine oxides are known to exist in equilibrium between the pentavalent phosphine oxides (SPO) and the trivalent phosphinous acids (PA). This equilibrium can be displaced in favour of the trivalent tautomeric form upon coordination to late transition metals. This tutorial review provides the state of the art of the use of secondary phosphine oxides as pre-ligands in transition metal-catalysed reactions. Using a combination of SPOs and several metals such as Pd, Pt, Ru, Rh and Au, a series of effective and original transformations have been obtained and will be discussed here.
Topics: Catalysis; Ligands; Metals; Models, Molecular; Oxides; Phosphines
PubMed: 26931212
DOI: 10.2533/chimia.2016.8 -
PloS One 2018The red palm weevil Rhynchophorus ferrugineus (Olivier) is an important pest of date palms in many regions of the world. This paper reports the first survey of...
The red palm weevil Rhynchophorus ferrugineus (Olivier) is an important pest of date palms in many regions of the world. This paper reports the first survey of insecticide resistance in field populations of R. ferrugineus in Pakistan which were collected from seven date palm growing areas across Punjab and Khyber Pakhtunkhwa (KPK) provinces, Pakistan. The resistance was assessed by the diet incorporation method against the formulated commonly used chemical insecticides profenophos, imidacloprid, chlorpyrifos, cypermethrin, deltamethrin, spinosad, lambda-cyhalothrin and a fumigant phosphine. Elevated levels of resistance were recorded for cypermethrin, deltamethrin and phosphine after a long history of insecticide use in Pakistan. Resistance Ratios (RRs) were 63- to 79-fold for phosphine, 16- to 74-fold for cypermethrin, 13- to 58-fold for deltamethrin, 2.6- to 44-fold for profenophos, 3- to 24-fold for chlorpyrifos, 2- to 12-fold for lambda-cyhalothrin and 1- to 10-fold for spinosad compared to a susceptible control line. Resistant R. ferrugineus populations were mainly found in southern Punjab and to some extent in KPK. The populations from Bahawalpur, Vehari, Layyah and Dera Ghazi Khan were most resistant to chemical insecticides, while all populations exhibited high levels of resistance to phosphine. Of the eight agents tested, lower LC50 and LC90 values were recorded for spinosad and lambda-cyhalothrin. These results suggest that spinosad and lambda-cyhalothrin exhibit unique modes of action and given their better environmental profile, these two insecticides could be used in insecticide rotation or assist in phasing out the use of older insecticides. A changed pattern of both insecticides can be used sensibly be recommended without evidence of dose rates and frequencies used.
Topics: Animals; Chlorpyrifos; Drug Combinations; Inhibitory Concentration 50; Insecticide Resistance; Insecticides; Macrolides; Neonicotinoids; Nitriles; Nitro Compounds; Organothiophosphates; Pakistan; Phoeniceae; Phosphines; Plant Diseases; Pyrethrins; Weevils
PubMed: 30024882
DOI: 10.1371/journal.pone.0192628 -
Nature Mar 2019Carbon-hydrogen (C-H) and carbon-carbon (C-C) bonds are the main constituents of organic matter. Recent advances in C-H functionalization technology have vastly expanded...
Carbon-hydrogen (C-H) and carbon-carbon (C-C) bonds are the main constituents of organic matter. Recent advances in C-H functionalization technology have vastly expanded our toolbox for organic synthesis. By contrast, C-C activation methods that enable editing of the molecular skeleton remain limited. Several methods have been proposed for catalytic C-C activation, particularly with ketone substrates, that are typically promoted by using either ring-strain release as a thermodynamic driving force or directing groups to control the reaction outcome. Although effective, these strategies require substrates that contain highly strained ketones or a preinstalled directing group, or are limited to more specialist substrate classes. Here we report a general C-C activation mode driven by aromatization of a pre-aromatic intermediate formed in situ. This reaction is suitable for various ketone substrates, is catalysed by an iridium/phosphine combination and is promoted by a hydrazine reagent and 1,3-dienes. Specifically, the acyl group is removed from the ketone and transformed to a pyrazole, and the resulting alkyl fragment undergoes various transformations. These include the deacetylation of methyl ketones, carbenoid-free formal homologation of aliphatic linear ketones and deconstructive pyrazole synthesis from cyclic ketones. Given that ketones are prevalent in feedstock chemicals, natural products and pharmaceuticals, these transformations could offer strategic bond disconnections in the synthesis of complex bioactive molecules.
Topics: Acylation; Carbon; Hydrazines; Iridium; Ketones; Phosphines; Pyrazoles
PubMed: 30758326
DOI: 10.1038/s41586-019-0926-8 -
Molecules (Basel, Switzerland) Oct 2022The Mitsunobu reaction plays a vital part in organic chemistry due to its wide synthetic applications. It is considered as a significant reaction for the interconversion... (Review)
Review
The Mitsunobu reaction plays a vital part in organic chemistry due to its wide synthetic applications. It is considered as a significant reaction for the interconversion of one functional group (alcohol) to another (ester) in the presence of oxidizing agents (azodicarboxylates) and reducing agents (phosphines). It is a renowned stereoselective reaction which inverts the stereochemical configuration of end products. One of the most important applications of the Mitsunobu reaction is its role in the synthesis of natural products. This review article will focus on the contribution of the Mitsunobu reaction towards the total synthesis of natural products, highlighting their biological potential during recent years.
Topics: Biological Products; Phosphines; Reducing Agents; Esters; Oxidants
PubMed: 36296545
DOI: 10.3390/molecules27206953