Copper-Catalyzed Difunctionalization of Propargylic Carbonates through Tandem Nucleophilic Substitution/Boroprotonation.

Highly functionalized organic molecules are in high demand, but their preparation is challenging. Copper-catalyzed transformation of alkynyl- and allenyl-containing substrates has emerged as a powerful tool to achieve this objective. Herein, an efficient copper-catalyzed difunctionalization of propargylic carbonates through tandem nucleophilic substitution/boroprotonation has been developed, affording the formation of thiol-, selenium-, and boron-functionalized alkenes with high yield and stereoselectivity. Two distinct catalytic mechanisms involving a single reaction without any requirement of catalyst change were successfully demonstrated.

Palladium/Lewis Acid Co-catalyzed Cyclocarbonylation of (2-Aminoaryl)(aryl)methanols: An Access to 3-Aryl-indolin-2-ones.

A benign approach to valuable 3-aryl-indolin-2-ones was developed based on palladium(II)/Lewis acid-cocatalyzed cyclocarbonylation of readily available (2-aminoaryl)(aryl)methanols. The protocol features producing water as the only byproduct, mild reaction conditions, and good efficiency, constituting an array of 3-arylindolin-2-ones in yields of 35 to 90%. The reaction can be easily scaled up to the gram scale in good yields.

Copper-Catalyzed Asymmetric Boroprotonation of Phosphinylallenes.

Synthesis of chiral phosphorus compounds from readily available substrates by a facile method is an attractive strategy. In this study, an efficient route for copper-catalyzed asymmetric boroprotonation of phosphinylallenes with bis(pinacolato)diboron with high regioselectivity was developed, affording chiral allylphosphine oxides in high yields with high enantioselectivities of up to 98% ee. The synthetic utility was further demonstrated by the facile transformation of the chiral allylphosphine oxides to several stereospecific products.

Covalent Metalloporphyrin Polymer Coated on Carbon Nanotubes as Bifunctional Electrocatalysts for Water Splitting.

Metalloporphyrins have exhibited excellent electrocatalytic activities for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). In order to improve the efficiency and conductivity, these molecular catalysts need to be immobilized on conductive electrode materials. Herein, a facile "one-pot" strategy was developed to coat a covalent metalloporphyrin polymer on a carbon nanotube (CNT) as bifunctional catalysts [denoted as MTIPP@CNTs, H2TIPP = 5,10,15,20-tetra(4-(imidazole-1-yl)phenyl)porphyrin)] for water splitting in alkaline solution. MTIPP@CNTs have shown excellent electrocatalytic activities for both the HER and OER when metalloporphyrin's central metal is optimized as well as the amount of catalysts that is loaded on the CNT. The overpotential (η10) of NiTIPP@CNT-2 for the OER is only 320 mV at a current density of 10 mA cm-2 in 1.0 M KOH, and CoTIPP@CNT-1 exhibited an excellent electrocatalytic activity for the HER (η10 = 450 mV for 10 mA cm-2). Furthermore, the remarkable bifunctional electrocatalytic performance (a cell voltage of 2.04 V with a current density of 10 mA cm-2) was also explored in the overall water splitting test.

An α-diiminato germylene family: syntheses, structures, and reactivity towards C-C coupled digermylene and digermylene oxide.

The synthesis and reactivity of a rigid α-diiminate ligand supported chlorogermylene 2 were demonstrated. The reaction of 2 with hydride donor K[BH(sBu)3] yielded a hydride addition product, a five-membered 6π-aromatic germylene 3. A nonaromatic germylene 4 was produced by dehydrochlorination of 2 with KN(SitBuMe2)2. Halide abstraction with AlCl3 from 2 afforded a cationic germylene 5, and the reduction of 2 with potassium led to a C-C coupled digermylene 6via a radical coupling pathway. Hydrolysis of 2 in the presence of NHC ((tBu-NCH)2C:) gave digermylene oxide 7. DFT investigations of central GeII-rings in molecules 3-5 provided the details of frontier molecular orbitals. The energy level of the lone pair on the Ge atom in 3 is slightly higher than that in 4, indicating that 3 is the stronger σ-donor than 4. Digermylene 6 and its diastereoisomer 6a feature trans-bent and gauche-bent configurations along their axially chiral C-C bonds, respectively. The conformational and cis-trans isomerism was observed by the isolation of crystal structures 7 and 7a because of intramolecular steric hindrance.

Anionic oxoborane and thioxoborane molecules supported by a 1,2-bis(imino)acenaphthene ligand.

The isolable anionic oxoborane 3 and thioxoborane 4 have been assembled using a 1,2-bis(imino)acenaphthene ligand (Dip-BIAN). Structural characterization and DFT calculations confirmed that two compounds contain terminal doubly bonded B[double bond, length as m-dash]E (E = O, S) groups, respectively, in which only the B[double bond, length as m-dash]O group is associated with imidazolium via a hydrogen bond.

Palladium(II)/Lewis Acid Cocatalyzed Oxidative Annulation of 2-Alkenylanilines and Propargylic Esters: An Access to Benzo[b]azepines.

An attractive approach to valuable yet synthetically challenging benzo[b]azepines was established via palladium(II)/Lewis acid cocatalyzed oxidative [5 + 2] annulation of readily available 2-alkenylanilines and propargylic esters. The protocol features mild reaction conditions and good functional group tolerance, constituting an array of benzo[b]azepines in yields of 30-75%.

Giant Anisotropy of Gilbert Damping in Epitaxial CoFe Films.

Tailoring Gilbert damping of metallic ferromagnetic thin films is one of the central interests in spintronics applications. Here we report a giant Gilbert damping anisotropy in epitaxial Co_{50}Fe_{50} thin films with a maximum-minimum damping ratio of 400%, determined by broadband spin-torque ferromagnetic resonance as well as inductive ferromagnetic resonance. We conclude that the origin of this damping anisotropy is the variation of the spin orbit coupling for different magnetization orientations in the cubic lattice, which is further corroborated from the magnitude of the anisotropic magnetoresistance in Co_{50}Fe_{50}.

Ultrastable Luminescent Organic-Inorganic Perovskite Quantum Dots via Surface Engineering: Coordination of Methylammonium Bromide and Covalent Silica Encapsulation.

Encapsulation of luminescent perovskite quantum dots (QDs) into a solid matrix has been approved to be an efficient way to improve their stability. In this work, we reported a green encapsulation method to produce ultrastable CH3NH3PbBr3 QDs incorporated into the SiO2 matrix. Specifically, fresh-prepared CH3NH3PbBr3 QDs were covalently embedded into silica by an aqueous sol-gel method assisted with CH3NH3Br, which not only effectively inhibited the water-driven degradation of QDs through surface coordination, but also strongly stabilized the QDs in solid powder via concentration gradient. As far as we know, this silica encapsulation of perovskite QDs in aqueous environments is reported for the first time. Luminescent properties of perovskite QDs during the course of gelation as well as in resulting composite powder were investigated using steady-state and time-resolved spectroscopies, and a 2 wt % QD-doped sample treated with 11.5 mM of CH3NH3Br was demonstrated to be the optimal phosphor. The green-emissive phosphor had a PLQY of 60.3% and a full width at half maxima of ∼25 nm, exhibiting ultrahigh stability tested by cycle heating (120 °C), continuous heating (80 °C, 60 h), and light irradiation (450 nm light, 350 h). The phosphor was readily blended with polymers and applied as a color-converting layer on blue light-emitting diodes.

In situ silica coating-directed synthesis of orthorhombic methylammonium lead bromide perovskite quantum dots with high stability.

Luminescent perovskite quantum dots (QDs) had attracted great attention by virtue of the merits of color-tunable and narrow-band emissions. However, sofar reported perovskite QDs suffered from instability more or less. In this work, a type of silica-coated orthorhombic CH3NH3PbBr3 QDs (SiO2-QDs) with greatly improved stability was reported. The SiO2-QDs were one-pot synthesized using a reprecipitation-encapsulation method assisted with an amine functional silane, which not conly controlled the crystallization of QDs, but also encapsulated QDs with a silica layer simultaneously. More interestingly, the in situ encapsulation of silica shell induced the presence of orthorhombic perovskite that was thought to be unstable at room temperature. This is the first report of orthorhombic CH3NH3PbBr3 QDs, as far as we are concerned. The orthorhombic SiO2-QDs exhibited narrow-band green luminescence with a quantum yield of 78%, and a high production yield of ∼70wt%. Moreover, stability of SiO2-QDs was considerably improved due to silica-coating. White-LEDs were also successfully fabricated with the green SiO2-QDs and a red commercial phosphors using a noncontact configuration. These results demonstrated that the orthorhombic SiO2-QDs held great promise for high-performance display or lighting technology.

Palladium-Catalyzed Sequential Vinylic C-H Arylation/Amination of 2-Vinylanilines with Aryl boronic Acids: Access to 2-Arylindoles.

A palladium-catalyzed selective and successive vinylic C-H arylation/amination of 2-vinylanilines with arylboronic acids to generate indoles has been developed. This procedure represents a straightforward and practical approach to valuable multifunctionalized indoles.

Palladium-Catalyzed Domino Alkenylation/Amination/Pyridination Reactions of 2-Vinylanilines with Alkynes: Access to Cyclopentaquinolines.

A novel domino oxidative annulation of 2-vinylanilines with internal alkynes was developed to constitute a rare class of cyclopentaquinoline derivatives. This transformation encompasses four σ bonds formation, one quaternary carbon center construction, and pyridination steps in one pot under identical conditions, which fascinatingly increases the molecular complexity from easily available starting materials.

Palladium-Catalyzed Oxidative Annulation of ortho-Alkenylanilines and Allenes: An Access to Benzo[b]azepines.

Palladium-catalyzed oxidative annulation of ortho-alkenylanilines and allenes to constitute valuable, but synthetically challenging, benzo[b]azepines has been developed. The procedure, involving the cleavage of the terminal C(sp2)-H bond of the vinyl moiety and the participation of allenes as two-carbon cycloaddition partner, is attractive in terms of assembly efficiency and environmental friendliness. The transformation features mild reaction conditions and good functional group tolerance, resulting in a variety of benzo[b]azepines in good to excellent yields.

Palladium-catalyzed direct coupling of 2-vinylanilines and isocyanides: an efficient synthesis of 2-aminoquinolines.

Palladium-catalyzed oxidative coupling of 2-vinylanilines and isocyanides constitutes a direct, facile, and efficient approach to 2-aminoquinolines. The procedure, employing palladium acetate and silver carbonate, is attractive in terms of assembly efficiency, functional group tolerance, and operational simplicity. A variety of 2-aminoquinolines were prepared in good to excellent yields.

Synthesis of 2(1H)-quinolinones via Pd-catalyzed oxidative cyclocarbonylation of 2-vinylanilines.

Palladium-catalyzed oxidative cyclocarbonylation of N-monosubstituted-2-vinylanilines constitutes a simple, direct, and selective method for the synthesis of 2(1H)-quinolinones. The reaction conditions are attractive in terms of environmental considerations and operational simplicity. 2(1H)-Quinolinones with a variety of functional groups were prepared in up to 97% yield.

Pd-catalyzed direct coupling of indoles with carbon monoxide and alkynes: selective synthesis of linear α,ß-unsaturated ketones.

A new strategy is described for the direct coupling of indoles with CO and alkynes to generate α,ß-unsaturated ketones. This procedure, employing Xantphos and Pd(CH3CN)4(BF4)2, is attractive from both environmental and operational points of view and adds value to the method for the carbonylation of alkynes by using carbon nucleophiles and affording linear regioselectivity.

Synthesis of coumarins via Pd-catalyzed oxidative cyclocarbonylation of 2-vinylphenols.

Palladium-catalyzed oxidative cyclocarbonylation of 2-vinylphenols constitutes a simple, direct method for the synthesis of coumarins. The reaction conditions, employing low pressures of CO, and air or 1,4- benzoquinone as the oxidant, are attractive in terms of environmental considerations and operational simplicity. Coumarins with a variety of functional groups were prepared in yields up to 85%.

Palladium-catalyzed domino C-S coupling/carbonylation reactions: an efficient synthesis of 2-carbonylbenzo[b]thiophene derivatives.

A facile and selective palladium-catalyzed domino procedure has been developed for the preparation of 2-carbonylbenzo[b]thiophene derivatives from 2-gem-dihalovinylthiophenols. This protocol involves intramolecular C-S coupling/intermolecular carbonylation cascade sequences and allows access to various highly functionalized benzo[b]thiophenes in moderate yields.

Palladium-catalyzed domino ring-opening/carboxamidation reactions of N-tosyl aziridines and 2-iodothiophenols: a facile and efficient approach to 1,4-benzothiazepin-5-ones.

A novel and efficient domino procedure has been developed for the synthesis of 1,4-benzothiazepin-5-ones from simple and readily accessible N-tosyl aziridines and o-iodothiophenols. This process involves aziridines ring-opening with o-iodothiophenols, followed by palladium-catalyzed intramolecular carboxamidation. The scope and limitation of this transformation have been investigated in detail by using various aziridines and o-iodothiophenols.

One-step synthesis of quinazolino[3,2-a]quinazolinones via palladium-catalyzed domino addition/carboxamidation reactions.

A highly efficient palladium-catalyzed domino process has been developed for the synthesis of quinazolino[3,2-a]quinazolinones by forming five new bonds in a single step. Despite the high density and variety of functional groups on the substrates, the tetracyclic quinazolinones were obtained in good to excellent yields.