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We present the synthesis of colloidal anisotropic Cu2–xSe nanocrystals (NCs) with excellent size and shape control, using the unexplored phosphine-free selenium precursor 1-dodecaneselenol (DDSe). This precursor forms lamellar complexes with Cu(I) that enable tailoring the NC morphology from 0D polyhedral to highly anisotropic 2D shapes. The Cu2–xSe NCs are subsequently used as templates in postsynthetic cation exchange reactions, through which they are successfully converted to CdSe and CuInSe2 quantum dots, nanoplatelets, and ultrathin nanosheets. The shape of the template hexagonal nanoplatelets is preserved during the cation exchange reaction, despite a substantial reorganization of the anionic sublattice, which leads to conversion of the tetragonal umangite crystal structure of the parent Cu2–xSe NCs into hexagonal wurtzite CdSe and CuInSe2, accompanied by a change of both the thickness and the lateral dimensions of the nanoplatelets. The crystallographic transformation and reconstruction of the product NCs are attributed to a combination of the unit cell dimensionalities of the parent and product crystal phases and an internal ripening process. This work provides novel tools for the rational design of shape-controlled colloidal anisotropic Cu2–xSe NCs, which, besides their promising optoelectronic properties, also constitute a new family of cation exchange templates for the synthesis of shape-controlled NCs of wurtzite CdSe, CuInSe2, and other metal selenides that cannot be attained through direct synthesis approaches. Moreover, the insights provided here are likely applicable also to the direct synthesis of shape-controlled NCs of other metal selenides, since DDSe may be able to form lamellar complexes with several other metals. [ABSTRACT FROM AUTHOR]

Dissolved air flotation (DAF) is broadly applied in wastewater treatment, especially for the recovery of organic pollution with low concentration. However, the mechanism of interaction between nanoscale gas bubbles and nanoparticles in the process of DAF remains unclear. Here, we investigated the role of nanobubbles in the precipitation of styryl phosphoric acid (SPA)-Pb particles and recovering organic phosphine containined in beneficiation wastewater by UV-vis (ultraviolet-visible) spectra, microflotation tests, nanoparticle tracking analysis, dynamic light scattering, and atomic force microscopy measurements. As suggested from the results, nanobubbles can inhibit the crystallization of SPA-Pb precipitation, which makes the sediment flotation recovery below 20%. After the precipitation crystallization is completed, nanobubbles can flocculate precipitated particles, which can promote the flotation recovery of precipitated particles to 90%. On the basis of the results, we proposed a model to explain the different roles of nanobubbles in the process of precipitation and flotation of SPA-Pb particles. This study will be helpful to understand the interaction between nanobubbles and nanoparticles in the application of flotation. [ABSTRACT FROM AUTHOR]

Inspired by the addition-elimination catalytic mechanism of natural pyrroloquinoline quinone (PQQ) containing proteins, PQQ-modified hybrid nanomaterials have been increasingly developed recently as biomimetic heterogeneous electrocatalysts. However, up until now, no existing electrochemical approach was able to assess the intrinsic catalytic activity of PQQ sites, impeding the design of efficient PQQ-based electrocatalysts. Herein, in this work, we introduced a new method to calculate the turnover frequency (TOF) of any individual PQQ functional group for electrocatalytic oxidation of tris(2-carboxyethyl)phosphine (TCEP), through the study of single PQQ-decorated carbon nanotube (CNT) collisions at a carbon fiber ultramicroelectrode by chronoamperometry. The core advantage of this approach is being able to resolve the number of PQQ catalytic sites grafted on each individual CNT, so that the charge of any CNT collision event can be accurately translated into the intrinsic activity of the respective PQQ functional groups. The resulting collision-induced current responses clearly showed that the functionalization of CNTs with PQQ could indeed enhance its catalytic performance by 3 times, reaching a TOF value of 133 s-1 at 1.0 V vs Ag/AgCl. Such a single CNT collision technique, which is proposed for the first time in this work, can open up a new avenue for studying the intrinsic (electro)catalytic performance at a molecular level. [ABSTRACT FROM AUTHOR]

Understanding the formation of benzosiloles by the intramolecular palladium-catalyzed annulation of alkynyl(aryl)silanes is crucial for achieving synthetic diversity toward the enhancement of the chemistry of siloles. By a combination of density functional theory calculations and experiments, we describe not only the whole mechanism of reaction but also the drawbacks that block this type of reaction. We also unravel the role of the phosphine ligand, without which the reactions could not go forward. Moreover, in silico predictive catalysis is presented here since the substitution of the phosphine ligand by an N-heterocyclic carbene (NHC) promises milder experimental conditions. A screening of substrates with different electronic properties was carried out to further understand the two fundamental steps of the reaction: stereoisomerization and concerted metalation-deprotonation. [ABSTRACT FROM AUTHOR]

We explore the growth of InxGa1-xP nanocrystals (x = 1, InP; x = 0, GaP; and 1 > x > 0, alloys) in a nonthermal plasma. By tuning the reactor conditions, we gain control over the morphology of the final product, producing either 10 nm diameter hollow nanocrystals or smaller 3 nm solid nanocrystals. We observe the gas-phase chemistry in the plasma reactor using plasma emission spectroscopy to understand the growth mechanism of the hollow versus solid morphology. We also connect this plasma chemistry to the subsequent native surface chemistry of the nanocrystals, which is dominated by the presence of both dative- and lattice-bound phosphine species. The dative phosphines react readily with oleylamine in an L-type ligand exchange reaction, evolving phosphines and allowing the particles to be dispersed in nonpolar solvents. Subsequent treatment by HF causes the solid InP1.5 and In0.5Ga0.5P1.3 to become photoluminescent, whereas the hollow particles remain nonemissive. [ABSTRACT FROM AUTHOR]

Second-generation ruthenium olefin metathesis catalysts bearing aminophosphine ligands were investigated with systematic variation of the ligand structure. The rates of phosphine dissociation (k1; initiation rate) and relative phosphine reassociation (k-1) were determined for two series of catalysts bearing cyclohexyl(morpholino)phosphine and cyclohexyl(piperidino)phosphine ligands. In both cases, incorporating P-N bonds into the architecture of the dissociating phosphine accelerates catalyst initiation relative to the parent [Ru]-PCy3 complex; however, this effect is muted for the tris(amino)phosphine-ligated complexes, which exhibit higher ligand binding constants in comparison to those with phosphines containing one or two cyclohexyl substituents. These results, along with X-ray crystallographic data and DFT calculations, were used to understand the influence of ligand structure on catalyst activity. Especially noteworthy is the application of phosphines containing incongruent substituents (PR1R'2); detailed analyses of factors affecting ligand dissociation, including steric effects, inductive effects, and ligand conformation, are presented. Computational studies of the reaction coordinate for ligand dissociation reveal that ligand conformational changes contribute to the rapid dissociation for the fastest-initiating catalyst of these series, which bears a cyclohexyl-bis(morpholino)phosphine ligand. Furthermore, the effect of amine incorporation was examined in the context of ring-opening metathesis polymerization, and reaction rates were found to correlate well with catalyst initiation rates. The combined experimental and computational studies presented in this report reveal important considerations for designing efficient ruthenium olefin metathesis catalysts. [ABSTRACT FROM AUTHOR]

As the [2Fe]H subsite models of [FeFe]-hydrogenases, a series of PNP-chelated and -bridged diiron dithiolate complexes 1a-f and 2a-f together with the three related monophosphine complexes 3a-c were prepared by the selective substitutions of the all-carbonyl complex Fe2(μ-pdt)(CO)6 (A, pdt = SCH2CH2CH2S) with aminodiphosphines (Ph2P)2NR (denoted as PNP) under different reaction conditions. The first UV irradiation of the toluene solutions of A with different PNP ligands (PNP = (Ph2P)2NR; R = (CH2)3Me, (CH2)3NMe2, (CH2)3Si(OEt)3, C6H5, C6H4OMe-p, C6H4CO2Me-p) readily afforded the target PNP-chelated complexes Fe2(μ-pdt)(CO)4{(κ²-Ph2P)2NR} (1a-f), while the reflux of xylene solutions of A with the aforementioned PNP ligands produced the PNP-bridged complexes Fe2(μ-pdt)(CO)4{(μ-Ph2P)2NR} (2a-f). Comparatively, treatments of A and one type of PNP ligand with N-aryl substituents R (R = C6H5, C6H4OMe-p, C6H4CO2Me-p) in MeCN at room temperature in the presence of the decarbonylating agent Me3NO·2H2O formed the unexpected monophosphine complexes Fe2(μ-pdt)(CO)5{κ¹-Ph2P(NHR)} (3a-c) and the minor chelated complexes 1d-f. All of the complexes 1a-f, 2a-f, and 3a-c have been characterized by elemental analysis, FT-IR, NMR spectroscopy, and particularly for 1a,b,d-f, 2b,d-f, and 3b by X-ray crystallography. Additionally, the electrochemical and electrocatalytic properties of complexes 1a and 2a as a pair of representative isomers have been evaluated and compared by cyclic voltammetry in MeCN as solvent in the absence and presence of HOAc as a proton source. [ABSTRACT FROM AUTHOR]

Due to the low intrinsic acidity of amines, palladium-catalyzed C-N cross-coupling has been plagued continuously by the necessity to employ strong, inorganic, or insoluble bases. To surmount the many practical obstacles associated with these reagents, we utilized a commercially available dialkyl triarylmonophosphine-supported palladium catalyst that facilitates a broad range of C-N coupling reactions in the presence of weak, soluble bases. The mild and general reaction conditions show extraordinary tolerance for even highly base-sensitive functional groups. Additionally, insightful heteronuclear NMR studies using [sup 15]N-labeled amine complexes provide evidence for the key acidifying effect of the cationic palladium center. [ABSTRACT FROM AUTHOR]

Trialkylphosphine organocatalysts have enabled regioselective anti-hydroboration of internal alkynes with pinacolborane reagents to provide (E)-disubstituted alkenylboronate compounds. The alkenylboronate can be used for derivatizations, such as protodeborylation, Suzuki–Miyaura coupling, conjugate reduction, and Diels–Alder reactions. [ABSTRACT FROM AUTHOR]

A novel protocol for effective rhodium(I)-catalyzed C–H arylation of tertiary phosphines has been devised. It is amenable to a wide range of substrates and gives the products in moderate to high yields. This strategy provides a simple and efficient route to peri-substituted (naphthalen-1-yl)phosphines. [ABSTRACT FROM AUTHOR]

Herein, 2-vinylpyridines as a new type of electron-poor system for the asymmetric cross Rauhut-Currier reaction are reported. 2-Vinylpyridines are chemo- and enantioselectively activated by a newly designed chiral phosphine catalyst. The new reaction provides a powerful synthetic tool for accessing structurally diverse, highly valued chiral pyridine building blocks in good yields and with high enantioselectivities. Preliminary mechanistic studies reveal that two NH protons in the catalyst are critical for the synergistic activation of the substrates and governing the stereoselectivity of this reaction. [ABSTRACT FROM AUTHOR]

Emergency response to chemical suicides has become more common place in recent years. In order to address the operational implications of these events, it is first important to understand the methodologies which are commonly used, the locations where the events often occur, the concentrations of material generated, and how those concentration relates to exposure standards and flammability. Using hydrogen sulfide, carbon monoxide, hydrogen cyanide, and phosphine as examples, guidance is offered about risk control measures including personal protective equipment and decontamination strategies to effectively and safely mitigate the incidents. [ABSTRACT FROM AUTHOR]

Attractive metallophilic (aurophilic, argentophilic, cuprophilic, etc.) interactions play an important role in arrangement and stabilization of oligonuclear metal ion complexes. We report a combined experimental and theoretical assessment of aurophilic interactions in closed-shell gold(I) dimers. The experimental binding energies were obtained for charged [(LH)AuCl]+…[(L')AuCl] dimers (L is either a phosphine or an N-heterocyclic carbene ligand) in the gas phase. These energies served for benchmarking of correlated quantum chemical calculations (CCSD(T)-calibrated SCS-MP2/CBS method) that were then applied to neutral [(L)AuCl]…[(L')AuCl] dimers. The overall attractive interactions between monomeric units are in the order of 100- 165 kJ mol[sup -1] in the charged dimers and of 70-105 kJ mol[sup -1] in the corresponding neutral dimers. In the neutral dimers, pure aurophilic interactions account for 25-30 kJ mol-1, the dipole-dipole interactions for 30-45 kJ mol-1, and the L…;L' "inter-ligand" dispersion interactions for 5-25 kJ mol-1. Energy of the aurophilic interactions is thus comparable or even larger than that of strong hydrogen bonds. [ABSTRACT FROM AUTHOR]

Positional and stereochemical selectivity in the isomerization of terminal alkenes to internal alkenes is observed using the cis-Mo(CO)4(PPh3)2 precatalyst. A p-toluenesulfonic acid (TsOH) cocatalyst is essential for catalyst activity. Various functionalized terminal alkenes have been converted to the corresponding 2-alkenes, generally favoring the Z isomer with selectivity as high as 8:1 Z:E at high conversion. Interrogation of the catalyst initiation mechanism by 31P NMR reveals that cis-Mo(CO)4(PPh3)2 reacts with TsOH at elevated temperatures to yield a phosphine-ligated Mo hydride (MoH) species. Catalysis may proceed via 2,1-insertion of a terminal alkene into a MoH group and stereoselective β-hydride elimination to yield the (Z)-2-alkene. [ABSTRACT FROM AUTHOR]

In the presence of a catalytic amount of heavier tetrylene dichlorides, an allenic diborene 1 undergoes a 1,3-hydrogen shift to afford a terminal diborene 2, which can be deemed a boron analogue of vinylidene dication stabilized by Lewis bases. X-ray diffraction analysis and computational studies revealed that 2 involves a conjugative interaction between the C= C and B=B π-orbitals. The reaction of 2 with ZnBr[sub 2]afforded the corresponding isolable complex 3, in which two boon centers coordinate to the Zn atom asymmetrically. [ABSTRACT FROM AUTHOR]

A method for the coupling of aryl chlorides and thiophenols using an air-stable nickel(0) catalyst is described. This thioetherification procedure can be effectively applied to a range of electronically diverse aryl/heteroaryl chlorides without more expensive metal catalysts such as palladium, iridium, or ruthenium. This investigation also illustrates both, a variety of thiol coupling partners and, in certain cases, the use of Cs2CO3. [ABSTRACT FROM AUTHOR]

Remote binding of B(C6F5)3 to (PPO)PdMeL (L = pyridine or lutidine) or {(PPO)PdMe}2 ethylene polymerization catalysts that contain phosphine-arenephosphinate or phosphine-arenephosphonate ligands (PPO- = [1-PAr2-2-PR'O2-Ph]-: Ar = R' = Ph (1a); Ar = Ph, R' = OEt (1b); Ar = Ph, R' = OiPr (1c); Ar = 2-OMe-Ph, R' = OiPr (1d)) significantly increases the catalyst activity and the molecular weight of the polyethylene (PE) product. In the most favorable case, in situ conversion of (1d)PdMe(py) to the base-free adduct {1d•B(C6F5)3}PdMe increases the ethylene polymerization activity from 9.8 to 5700 kg mol-1 h-1 and the Mn of the PE product from 9030 to 99 200 Da (80 °C, 410 psi). X-ray structural data, trends in ligand lability, and comparative studies of BF3 activation suggest that these allosteric effects are primarily electronic in origin. The B(C6F5)3 binding enhances the chain growth rate (Rgrowth) by increasing the degree of positive charge on the Pd center. This effect does not result in the large increase in the chain transfer rate (Rtransfer) and concomitant reduction in PE molecular weight seen in previous studies of analogous (PO)PdRL catalysts that contain phosphine-arenesulfonate ligands, because of the operation of a dissociative chain transfer process, which is inhibited by the increased charge at Pd. [ABSTRACT FROM AUTHOR]

A series of well-defined phosphine-ligated diarylgold(III) complexes cis-[Au(L)(ArF)(Ar')(Cl)] were prepared, and detailed kinetics of the C(sp²)-C(sp²) reductive elimination from these complexes were studied. The mechanism of the reductive elimination from the complexes cis-[Au(L)(ArF)(Ar')(Cl)] was further studied by theoretical calculations. The combination of experimental and theoretical results suggests that the biaryl reductive elimination from organogold(III) complexes cis-[Au(L)(ArF)(Ar')(Cl)] proceeds through a concerted biaryl-forming pathway from the four-coordinated Au(III) metal center. These studies also disclose that the steric hindrance of the phosphine ligands plays a major role in promoting the biaryl-forming reductive elimination from diarylgold(III) complexes cis-[Au(L)(ArF)(Ar')(Cl)], while electronic properties of these ligands have a much smaller effect. Futhermore, it was found that the complexes with more weakly electron withdrawing aryl ligands undergo reductive elimination more quickly and the elimination rate is not sensitive to the polarity of the solvents. [ABSTRACT FROM AUTHOR]

The terminal phosphine groups at the tungsten bisphosphine alkyne complex [Tp*W(CO)(I)(η²-C,C'-Ph2PC2PPh2)] (2) {Tp* = hydridotris(3,4,5-trimethylpyrazolyl)borate} were selectively oxidized by common methods to form the alkyne complexes 2EE (E = O, S) with either two phosphine oxide or two phosphine sulfide substituents. The respective mono-oxidized analogues 2E (E = O, S) were obtained by subjecting the already oxidized intermediates [Tp*W(CO)(I)(η²-C,C'-Ph2P(E)C2H)] 1E (E = O, S) to a late-stage phosphine introduction at the complex template. These modulations of the peripheral alkyne moiety have a clear impact on the redox potential of the metal-based oxidation altering the W(II/III) potential by +0.1 V on average per oxidized phosphine. In contrast to the comparable redox behavior of 2O and 2S, the coordination behavior of these complex ligands differs substantially. XRD studies show that complex 2 and the sulfide 2Sact either as a P,P'- or P,S-chelate ligand leading to the dinuclear complexes [(2)PdCl2], 3, and [(2S)PdCl2], 3S. In contrast, the corresponding PdCl2 complex of the monoxide 2O is connected by the free phosphine group and the W-bonded iodide as a μ²-bridging ligand leaving the phosphine oxide pending. A similar binding mode was found for the trinuclear gold complex [(2)2Au][PF6] (5-PF6). Furthermore, these findings explain the undesired outcome in the reaction of [Pd(NCMe)4][BF4]2 with two equivalents of 2, which resulted in the iodide abstraction product [(2)PdI2] (4). [ABSTRACT FROM AUTHOR]

We report the first isolation of phosphine copper boryl complexes--species pivotal to numerous copper-catalyzed borylation reactions. The reaction of diboron(4) derivatives with copper tert-butoxide complexes of phosphine ligands allows the isolation of the dimeric μ-boryl-bridged Cu(I) complexes [(iPr3P)Cu-Bdmab]2 (4) and [(C6H4(Ph2P)2)Cu-Bpin]2 (6) with Cu•••Cu distances of 2.24-2.27 Å (dmab = (NMe)2C6H4, pin = (OCMe2)2)). A slightly more sterically demanding boryl ligand furnishes the unprecedented multinuclear copper boryl complex [(iPr3P)2Cu8(B(iPrEn))3(OtBu)3] (5), a potential intermediate of the decomposition of an initial Cu(I) boryl complex (iPrEn = (NiPr)2C2H4). All complexes were characterized by single-crystal X-ray diffraction, NMR spectroscopy, and elemental analysis. DFT computations support the nature of these unique complexes and give insight into their electronic structures. [ABSTRACT FROM AUTHOR]

Catalytic enantioselective Cu-B(pin) (pin = pinacolato) addition to N-heteroaryl-substituted alkenes followed by protonation promoted by phosphine-Cu complexes is presented. The resulting alkylboron products that contain a N-heteroaryl moiety are afforded in up to 97% yield and 99:1 enantiomeric ratio. The highly versatile C-B(pin) bond can be converted to a range of useful functional groups, delivering a variety of enantiomerically enriched building blocks that are otherwise difficult to access. The utility of this method is further demonstrated by application to a fragment synthesis of biologically active molecule U-75302. Preliminary mechanistic studies revealed that the adjacent N atom of the heterocycles plays a unique role in high reactivity and enantioselectivity. [ABSTRACT FROM AUTHOR]

A first phosphine-catalyzed enantioselective umpolung γ-addition of ketimines to allenoates has been developed that provides efficient access to optically active γ,δ-unsaturated α-amino esters and δ-amino esters with a chiral tertiary stereocenter under mild conditions. The salient features of this reaction include general substrate scope, mild conditions, good yields, high enantioselectivity, ease of scale-up to gram scale, and further transformations. [ABSTRACT FROM AUTHOR]

Density functional theory was used to study interactions between phosphine and 17 functional groups, revealing that only the functional groups containing metal ions bind phosphine strongly. This led to a detailed examination of the adsorption of the pnictogen hydride gases ammonia, phosphine, and arsine on 33 metal catecholates in order to examine periodic trends in the binding strength for these adsorbates. Phosphine and arsine adsorption is primarily driven by donation of electron density from the adsorbate molecule to the metal atom, while ammonia binding involves both electron donation and a significant Coulomb attraction between the negatively charged N atom and the positive metal atom. This Coulomb effect results in notably different binding behavior for ammonia than for phosphine and arsine, which are quite similar to each other. Generally, for metals on the left side of the periodic table, the Coulomb effect dominates in ammonia adsorption, and metals on the right side of the periodic table have lower positive charge and accept greater amounts of electron density, making the electron-sharing contribution more important to the binding strength. We find that more electronegative metals, particularly Pd, Ir, Pt, and Au, which accept more electron density from the adsorbate, yield the best selectivity for the target molecules over water because water adsorption is mostly due to Coulomb attraction. We also analyze changes in the d orbital occupancy upon ammonia and phosphine adsorption. [ABSTRACT FROM AUTHOR]

Phosphine-catalyzed (3+2) annulations of δ-acetoxy allenoates with 2-naphthols are reported, wherein the δC of allentoate reacts with the αC of 2-naphthol to form the C-C bond while a C-O bond is formed between the γC of allenoate and the hydroxyl group of 2-naphthol. When (R)-SITCP is used as the catalyst, 1,2-dihydronaphtho[2,1-b]furans are obtained in moderate to good yields and with high enantioselectivity. This method is useful for the construction of enantiomerically enriched atropoisomeric furans via a central to axial chirality conversion strategy. [ABSTRACT FROM AUTHOR]

A phosphine-catalyzed [4 + 2] cycloaddition of cyclic α-substituted allenoates with sulfamate-derived cyclic imines has been reported. Using dibenzylphenylphosphine as the nucleophilic catalyst, the reaction worked efficiently to yield various fused multicyclic heterocyclic compounds in high yields with excellent diastereoselectivities. It undergoes a new reaction mode involving γ'-carbon of α-substituted allenoate. [ABSTRACT FROM AUTHOR]

Despite the considerable synthetic challenge, polymers that incorporate phosphorus atoms within or adjacent to a π-conjugated backbone framework are of interest due to the ability to modulate the photophysical properties of the polymer based on the chemical environment at phosphorus. We report the synthesis and characterization of poly(p-phenylenediethlynylene phosphine)s, 1a-1e, a new class of σ-π conjugated polymer. Polymers 1a-1e were prepared by a Ni-catalyzed coupling of dialkynes with phenyldichlorophosphine in the presence of excess triethylamine and have molecular weights (Mw) up to 12,000 g mol-1 (vs. polystyrene). While the polymers 1b-1e are nonfluorescent, blue fluorescence is observed upon oxidation of the phosphorus centers (Φsoln = 0.12-0.28). Polymers 1b·O-1e·O also exhibit yellow/green fluorescence in the solid state (Φsolid = 0.04-0.08). These results introduce a fascinating new class of main group-containing macromolecule and lay the groundwork for their utilization in sensory applications and/or their incorporation into optoelectrical devices. [ABSTRACT FROM AUTHOR]

Methyl tert-butyl ether is found to undergo C-O bond cleavage in the formation of an iridium(III) methallyl at a cationic bis(phosphine) iridium complex. An exploration of this transformation has revealed a cyclometalated complex which was previously postulated to form reversibly in the first example of alkane dehydrogenation by a homogeneous transition-metal complex. The competence of this cyclometalated species in alkane dehydrogenation is demonstrated in a stoichiometric example, giving an isolable olefin dihydride. Detection and assignment of this elusive species confirms a previous hypothesis that reversible intramolecular phosphine cyclometalation can precede intermolecular alkane dehydrogenation. [ABSTRACT FROM AUTHOR]

The direct electrophilic, nucleophilic, and amphiphilic allylations of allylic alcohol by use of a palladium catalyst and organometallic reagents such as organoborane and organozinc has been developed. The phosphine-borane compound works as the effective ligand for palladium-catalyzed direct allylic amination of allylic alcohol. Thus, with secondary amines, the reaction was completed in only 1 h, even at room temperature. [ABSTRACT FROM AUTHOR]

The first enantioenriched synthesis of 1,1,3-trisubstituted (trifluoromethyl)indene derivatives, bearing a quaternary stereogenic carbon center, is reported using a simple chiral sulfinamide phosphine-catalyzed asymmetric allylic alkylation of a mixture of indenes with Morita-Baylis-Hillman carbonates. The resulting derivatives can serve as a valuable synthetic building block for some drugs and natural products. Broad substrate scope and high regio- and enantioselectivity of this reaction were particularly remarkable. [ABSTRACT FROM AUTHOR]

Palladium complexes supported with the mixed ligands carbodicarbene (CDC) and different phosphine ligands (PPh3, PTol3, and PCy3) were prepared, and their molecular structures were characterized. Examination of the structures of 2-PPh3 and 2-PTol3 with cis configuration discloses the existence of an unexpected π-π interaction between one phenyl group of the phosphine and the benzimidazole ring of a CDC. The palladium complex 2-PPh3 is an active Suzuki-Miyaura catalyst with a wide scope of substrates containing various functional groups and steric demands. In contrast to electron-withdrawing aryl bromide, the yield of product for electron-rich substrates was improved by adding a catalytic amount of DMSO under aerobic conditions. The solution NMR and structural analysis has revealed that the intramolecular π-π interaction between CDC and phosphine ligands has a positive influence on the activity of the reaction, which is further supported by quantum chemical calculations. [ABSTRACT FROM AUTHOR]

By using designed biphenyl-2-ylphosphines functionalized with a remote basic groups as ligands, N-alkynyl-o-nosylamides are directly converted to (1E,3E)-1-amido-1,3-dienes with excellent diastereoselectivities under gold catalysis. With allenamides as substrates, the gold-catalyzed isomerizations are high yielding and applicable to a broad substrate scope including various nitrogen protecting groups and exhibit unprecedented (3E)-selectivities for the distal C-C double bond and good regioselectivities. Combining this gold catalysis with one-pot Diels-Alder reactions leads to rapid assembly of valuable bicyclic compounds. [ABSTRACT FROM AUTHOR]

The first and asymmetric total synthesis of longeracinphyllin A, a hexacyclic Daphniphyllum alkaloid, has been accomplished. A tetracyclic intermediate was prepared through silver-catalyzed alkyne cyclization and Luche radical cyclization. A phosphine-promoted [3 + 2] cycloaddition reaction was exploited to construct the sterically congested E ring bearing vicinal tertiary and quaternary centers. The cyclopentenone motif was assembled by using intramolecular Horner-Wadsworth-Emmons olefination. Raney Ni reduction delivered the tertiary amine from a thioamide precursor at a late stage. [ABSTRACT FROM AUTHOR]

A facile synthesis routine of β-type strontium hydrogen phosphate (β-SrHPO4) nanosheets was provided by the method of solution growing at temperatures below 80 °C. β-SrHPO4 was utilized for removing lead ions (Pb2+) and adsorbing methyl blue. Within the pH values from 2.0 to 6.0 of lead solutions, the adsorption capacity of β-SrHPO4 could reach above 1000 mg·g-1. The maximum removal capacity was 1409 mg·g-1 for Pb2+ within 15 min at pH = 4.5 and remained stable with the increase of temperatures. Different cations (Zn2+, Cr3+, Cd2+, and Co2+) affected slightly on the adsorption of Pb2+. It is revealed that the adsorption mechanism of Pb2+ was based on dissolution-precipitation theory. The maximum adsorption capacity was 335.68 mg·g-1 for methyl blue. The adsorption data of methyl blue accorded with the Langmuir isotherm model with R2 = 0.994 and the pseudo-second-order kinetic model with R2 = 0.99996, showing that the removal of methyl blue was dominated by a chemical sorption process. The thermodynamic studies demonstrated that the adsorption process toward methyl blue was endothermic and spontaneous. All of the results showed that β-SrHPO4 possessed potential applications in removing Pb2+ and methyl blue. [ABSTRACT FROM AUTHOR]

A novel chiral biamide--phosphine multifunctional catalyst has been developed that mediates the asymmetric intermolecular Michael addition of β-carbonyl esters to β-trifluoromethyl enones and 3-aroyl acrylates in the presence of competing methyl acrylate and the inorganic base. This method provides a facile access to structurally diverse trifluoromethyl and quaternary stereogenic centers with excellent enantioselectivity (up to 99% ee) and good diastereoselectivity (up to 13:1 dr). The addition of the inorganic base (K3PO4) does not cause the background racemic reaction and enhances the reactivity by serving as a co-catalyst. [ABSTRACT FROM AUTHOR]

Asymmetric preparation of all-carbon quaternary stereocenters is an important goal. Despite advances in formation of highly enantioenriched products with quaternary stereocenters proximal to a functional group, methods to install quaternary stereocenters isolated from functional groups are limited. Transition metal catalysis offers a potential solution, but prior cross couplings are limited to allylic substrates or deliver little to no enantiomeric enrichment. We report a stereospecific, nickel-catalyzed Suzuki-Miyaura arylation of tertiary benzylic acetates to deliver products with diaryl and triaryl quaternary stereocenters in high yields and ee's. This reaction employs an inexpensive, air-stable Ni(II) salt and commercially available phosphine ligand to transform tertiary alcohol derivatives, which are easily available in exceptional ee, into valuable products with stereoretention. [ABSTRACT FROM AUTHOR]

An Ir(ppy)3-catalyzed vic-diphosphination of styrenes with Me3Si-PPh2 and NFSI proceeds under blue LED irradiation to afford the corresponding bis(diphenylphosphino)ethane derivatives without any formation of hydrophosphination byproducts, which are inevitable and problematic under the previous Cu/NHC catalysis. Additionally, the visible-light-promoted photoredox catalysis enables the diphosphination of relatively challenging aliphatic alkenes and β-substituted styrene. [ABSTRACT FROM AUTHOR]

To develop Rh-catalyzed dehydrocoupling for stereocontrolled synthesis of P-P bonds, we prepared potential intermediates, chiral rhodium phosphine-phosphido complexes, and investigated their stoichiometric and catalytic transformations. Treatment of [Rh(diphos*)(COD)][X] with the bis(secondary phosphine) IsHPCH2PHIs (1, Is = 2,4,6-(i-Pr)3C6H2) gave the cations [Rh(diphos*)(IsHPCH2PHIs)][X] (diphos* = (R,R)-Me-DuPhos (2), (R,R)-i-Pr-DuPhos (3), or (R,R)-Me-BPE (4); X = BF4 or OTf) with high diastereoselectivity as single C2-symmetric diastereomers. Deprotonation of 2-4 with NaN(SiMe3)2 yielded phosphine-phosphido chelates Rh(diphos*)(IsHPCH2PIs) 5-7 with high diastereoselectivity. Thermolysis of 5-7 in toluene at 90°C caused isomerization to give Rh(diphos*)(IsMeP-PIs) (8-10) as mixtures of diastereomers. Under catalytic conditions, Rh-DuPhos precursors slowly converted 1 to a mixture of diastereomers of its isomer, the unsymmetrical diphosphine IsHP-PMeIs (12). We propose a possible mechanism for the isomerization and discuss its relationship to dehydrocoupling catalysis. [ABSTRACT FROM AUTHOR]

A silver-free palladium-catalyzed dehydrogenative phosphorylation of terminal alkynes with hydrogen phosphine oxides has been developed. Both aromatic and aliphatic terminal alkynes including those bearing functional groups coupled readily with hydrogen phosphine oxides, producing the corresponding value-added alkynylphosphine oxides in good to excellent yields. This reaction could be easily conducted at gram scales (10 mmol) without any decrease of the reaction efficiency, showing highly potential synthetic value in organic synthesis. A plausible Pd(0)/Pd(II) mechanism is proposed. [ABSTRACT FROM AUTHOR]

Reactions of silylated clusters [Ge9{Si(TMS)3}3]- or [Ge9{Si(TMS)3}2]2- with dialkylhalophosphines R2PCl (Cy, iPr, tBu) at ambient temperature yield the first tetrel Zintl cluster compounds bearing phosphine moieties. Varying reactivity of the dialkylhalophosphines toward the silylated clusters is observed depending on the bulkiness of the phosphine's alkyl substituents and on the number of hypersilyl groups at the tetrel cluster. Reactions between phosphines with small cyclohexyl- (Cy) or isopropyl- (iPr) groups and the tris-silylated cluster [Ge9{Si(TMS)3}3]- yield the novel neutral cluster compounds [Ge9{Si(TMS)3}3PR2] (R: Cy (1), iPr (2)) with discrete Ge-P exo bonds. By contrast, the bulkier phosphine tBu2PCl does not react with [Ge9{Si(TMS)3}3]- due to steric crowding. However, the reaction with the bis-silylated cluster [Ge9{Si(TMS)3}2]2- yields the novel cluster compound [Ge9{Si(TMS)3}2PtBu2]- (3). Subsequent reactions of compound 3 with NHCDippMCl (M: Cu, Ag, Au) yield the charge neutral zwitterionic compounds [(Ge9{Si(TMS)3}2)tBu2P]M(NHCDipp) (M: Cu, Ag, Au) (4-6), in which compound 3 acts as a phosphine ligand bearing a bulky tetrel Zintl cluster moiety. Compounds 4-6 also represent the first uncharged examples for 3-fold substituted tetrel Zintl clusters. [ABSTRACT FROM AUTHOR]

A large number of ligands have been used to stabilize and functionalize the gold surfaces and nanoclusters, but there has been no systematic comparison about their binding strengths with gold. In this work, we studied the interaction between 27 ligands of six different types (thiolates, phosphines, amines, aryl radicals, alkynyls, and N-heterocyclic carbenes) with the model Au surfaces by first-principles density functional theory (DFT). On the perfect Au(111), we found the order of binding strengths to be bulky N-heterocyclic carbenes (NHCs) ≈ alkynyls > thiolates ≈ phosphines > aryls ≈ less sterically bulky NHCs > alkylamines. The much stronger interaction of bulky carbenes to Au than the less sterically bulky NHCs arises from the van der Waals (vdW) attraction of bulky side groups with gold surface via the short Au···HCH2R contact. Further, we showed that the presence of a gold adatom on Au(111) leads to enhanced binding and a similar order for most of the ligands examined. Overall, bulky NHCs and alkynyl groups form the strongest interaction to both Au(111) and Auad-Au(111). This suggests that NHCs can be employed as alternatives to the currently widely used thiolates and the emerging alkynyl ligands for the preparation of more stable self-assembled monolayer structures on metal surfaces. Further, this insight allowed us to design viable magic-number gold clusters with NHCs as the protecting ligands. [ABSTRACT FROM AUTHOR]

(Dimesitylphosphino)ferrocene (FcPMes2) ( 1 ) reacted with HB(C6F5)2 (2 equiv) by disproportionation to give adduct FcPMes2.H2B(C6F5) ( 4 ) plus B(C6F5)3, whereas 1-(dimesitylphosphino)-1'-vinylferrocene ( 2 ) was cleanly hydroborated with HB(C6F5)2 to afford [Fe(η5-C5H4PMes2)(η5-C5H4CH2CH2B(C6F5)2)] ( 7 ). Compound 7 adopted an open non-interacting P/B frustrated Lewis pair (FLP) structure in the crystal state as well as in a solution. This frustrated Lewis pair heterolytically cleaved dihydrogen under mild conditions to give the respective zwitterionic [P]H+/[B]H- phosphonium/hydroborate product, [Fe(η5-C5H4PHMes2){η5-C5H4CH2CH2BH(C6F5)2}] ( 8 ), which served as a catalyst for the hydrogenation of the electron-rich π-systems (imine, enamine) as well as the electron-deficient carbon-carbon double and triple bonds in some enones and an ynone under more forcing conditions (50 bar H2 pressure, 50 °C). [ABSTRACT FROM AUTHOR]

Addition of the coupling promoter PEWO ligand 1-(Ph2P),2-(CH=CH-C(O)Ph)C6F4 (PhPEWO-F) to precursors with the displaceable AsPh3 ligand trans -[PdXAr(AsPh3)2] (X = I, F, CF3) fails to induce the pursued Ar-F or Ar-CF3 coupling and results in formation of products of olefin insertion into the Pd-Ar bond for X = I, CF3, and in Ar-Ar coupling for X = F. In the course of the processes, trans -[PdXAr(PhPEWO-F)(AsPh3)] intermediates are observed for X = I, F, CF3, with P-coordinated PhPEWO-F monodentate ligands and a dangling olefin group. For X = I, CF3, subsequent insertion of the double bond into the Pd-Ar bond and O-coordination gives rise to complexes with a P,C,O-pincer system. The observed insertion rates suggest that the limiting step toward insertion is the trans to cis isomerization, while insertion itself is very fast. This is supported by the fast insertion observed when PhPEWO-F is added to cis -[Pd(CF3)Ar(3-F-py)2]. The insertion mechanism in PhPEWO-F resembles the initial phase of the dearomative rearrangement mechanism reported for PdArBrL (L = dialkyl biaryl phosphine). [ABSTRACT FROM AUTHOR]