Phosphine Research Articles

Synthesis of P-Chiral Tertiary Phosphine Oxides by Copper-Catalyzed Dynamic Kinetic Asymmetric C–P Cross-Coupling

Abstract P-Stereogenic phosphorus compounds are of importance in various areas. Some strategies have been developed for the enantioselective formation of C–P bonds, among which transition-metal-catalyzed asymmetric C–P cross-coupling of secondary phosphine oxides (SPOs)—bench-stable, odorless, and nontoxic—is more appealing. Due to the elusive racemization of SPOs, reactions with them usually proceed in a kinetic resolution fashion, thus being less practical. Highlighted here is a copper-catalyzed, highly enantioselective dynamic kinetic intermolecular C–P coupling of SPOs and aryl iodides. The successful development of this reaction relies on two key factors: the facile racemization of SPOs under the reaction conditions and the high enantioselectivity of the carefully tuned copper catalysts. P-Stereogenic tertiary phosphine oxide (TPO) products were obtained in high yields and with good enantioselectivities and were further converted into structurally diverse P-chiral scaffolds that are highly valuable as ligands and catalysts in asymmetric synthesis.

Ni-Catalyzed Asymmetric C-P Cross-Coupling Reaction for the Synthesis of Chiral Heterocyclic Phosphine Oxides.

Nickel performs excellently in C-C and C-X cross-coupling reactions. Here, we disclose a Ni(II)-catalyzed asymmetric C-P cross-coupling reaction to afford valuable chiral heterocyclic tertiary phosphine oxides. The method is mild and efficient, which invokes a self-sustained nickel catalytic cycle without an external reductant, light irradiation, or electricity.

Stereoelectronic Effect in the Reaction of α-Methylene Lactones with Tertiary Phosphines and Its Application in Organocatalysis.

The kinetic data indicate that the addition of tertiary phosphines to α-methylene lactones in acetic acid is strongly accelerated in comparison to the reactions of related open-chain esters. Six-membered α-methylene-δ-valerolactone exhibited a more pronounced rate increase than five-membered α-methylene-γ-butyrolactone. The use of α-methylene-γ-butyrolactam as a nitrogen analogue of α-methylene-γ-butyrolactone resulted in a total loss of the reaction acceleration. The observed reactivities were rationalized by DFT calculations at the RwB97XD/6-31+G(d,p) level of theory, showing that the intramolecular interaction between phosphonium and enolate oxygen centers provided by the locked s-cis-geometry of the heterocycles plays an important role in the stabilization of intermediate zwitterions. The reactivity is also controlled by the conformational flexibility of the heterocycle. The geometries of five-membered and, especially, six-membered lactone cycles are slightly changed upon the nucleophilic attack of phosphine, leading to the stabilizing stereoelectronic effect by the Ρ···Ο interaction. The addition of phosphine to α-methylene-γ-butyrolactam significantly distorts the initial geometry of the heterocycle, making the nucleophilic attack unfavorable. The application of the stereoelectronic effect to enhance the efficiency of the phosphine-catalyzed Michael and Pudovik reactions of α-methylene lactones was demonstrated.

Synthesis and Assembly of Core–Shell Nanorods with High Quantum Yield and Linear Polarization

AbstractThe seeded growth method offers an efficient way to design core–shell semiconductor nanocrystals in the liquid phase. The combination of seed and shell materials offers wide tunability of morphologies and photophysical properties. Also, semiconductor nanorods (NRs) exhibit unique polarized luminescence which can potentially break the theoretical limit of external quantum efficiency in light emitting diodes based on spherical quantum dots. Although rod‐in‐rod core–shell NRs present higher degree of polarization, most studies have focused on dot‐in‐rod core–shell NRs due to the difficulties in achieving uniform NR seeds. Here, this study prepares high‐quality uniform CdSe NRs by improving the reactivity of the Se source, using a secondary phosphine, namely diphenylphosphine, to dissolve the Se power, along with the conventional tertiary phosphine, namely trioctylphosphine. Starting from these high‐quality NR seeds, this study synthesizes CdSe/CdxZn1−xS/ZnS core–shell NRs with narrow emission bandwidth (29 nm at 620 nm), high PLQY (89%) and high linear polarization (p = 0.90). This study then assembles these core–shell NRs using the confined assembly method and fabricates long‐range‐ordered microarrays with programmable patterns and displaying highly polarized emission (p = 0.80). This study highlights the great potential of NRs for application in liquid crystal displays and full‐color light emitting diodes displays.

Non-Classical Molecular Activation by Phosphines and N-Heterocyclic Carbenes and Its Application to Catalytic Reactions

Abstract This Award Account reports our recent studies concerning the catalytic transformations that involve a non-classical mode of molecular activation by tertiary phosphines and N-heterocyclic carbenes (NHCs). Regarding organophosphine catalysis, we successfully designed reactions based on a P(III)/P(V) redox couple. A catalytic protocol for generating pentacoordinate P(V) species was devised by the reaction of tertiary phosphines, acyl fluorides and alkynoates. The ability of the thus generated fluorophosphoranes to participate in ligand coupling and ligand metathesis with organosilicon nucleophiles enables synthetic transformations that are otherwise unattainable, including the intermolecular carbofluorination of alkynes and the hydroalkenylation of enol ethers. Regarding nucleophilic NHC catalysis, the use of imidazolium-based NHCs can generate deoxy-Breslow intermediates that are sufficiently nucleophilic to promote the aromatic substitution of aryl halides, aryl ethers and anilides. The protocol can also be used for the nucleophilic activation of styrene derivatives, allowing for the generation of a series of ylide intermediates that can serve as non-stabilized vinyl anion equivalents. These results demonstrate that synthetic transformations involving non-stabilized carbanions can be conducted under catalytic conditions without the use of strong organometallic nucleophiles.

Sterically Demanding Novel Triazole Based Tertiary Phosphines: Synthesis, Transition Metal Chemistry and Catalytic Applications

AbstractSterically demanding 2,6‐dibenzhydryl‐4‐methylphenyl and 1,2,3‐triazole based tertiary phosphines, [Ar*{1,2,3‐N3C(Ph)C(PR2)}] (R=Ph, 3; R=iPr, 4) were obtained by the temperature‐controlled lithiation of 1‐(2,6‐dibenzydryl‐4‐methyl)‐5‐iodo‐4‐phenyl‐1H‐1,2,3‐triazole (2) followed by the reaction with R2PCl (R=Ph, iPr). Treatment of 3 with H2O2, elemental sulfur and selenium yielded chalcogenides [Ar*{1,2,3‐N3C(Ph)C(P(E)Ph2)}] (E=O, 5; E=S, 6; E=Se, 7). The reaction of 3 with [Pd(COD)Cl2] in 1 : 1 molar ratio, afforded dimeric complex [Pd(μ2‐Cl)Cl{Ar*{1,2,3‐N3C(Ph)C(PPh2)}‐κ1‐P}]2 (8), whereas the reactions of 3 and 4 with [Pd(η3‐C3H5)Cl]2 in 2 : 1 molar ratios produced complexes [Pd(η3‐C3H5)Cl{Ar*{1,2,3‐N3C(Ph)C(PR2)}‐κ1‐P}] (R=Ph, 9; R=iPr, 10). Treatment of 3 with [Pd(OAc)2] in 1 : 1 molar ratio afforded a rare trinuclear complex [{Pd3(OAc)4}{Ar*{1,2,3‐N3C(C6H4)C(PPh2)}‐κ2‐C,P}2] (11). Treatment of 3 and 4 with [AuCl(SMe2)] resulted in [AuCl{Ar*{1,2,3‐N3C(Ph)C(PR2)}‐κ1‐P}] (R=Ph, 12; R=iPr, 13). Bulky phosphine 4 was very effective in Suzuki‐Miyaura coupling and amination reactions with very low catalyst loading. Molecular structures of 3–5, and 8–13 were confirmed by single‐crystal X‐ray diffraction studies.

Cu(I) and Ag(I) complexes of two sterically demanding Xylyl-Substituted phosphine Ligands: Synthesis, Characterization, and structural examination

Two sterically demanding tertiary phosphines, PiPr2Xyl and PtBu2Xyl, (Xyl = 2,6-dimethylphenyl), the latter reported here for the first time, have been used to synthesize a series of dinuclear complexes of the general formula [M(μ-X)PR2Xyl]2, (R = iPr, tBu; M = Cu: X = Cl, Br, I, OTf; M = Ag: X = OTf, NTf2). All compounds have been characterized by multinuclear NMR spectroscopy in solution and, with the exception of AgNTf2(PtBu2Xyl), by X-ray diffraction analyses. The doubly halido-bridged compounds [Cu(μ-X)PR2Xyl]2 (R = iPr, tBu; X = Cl, Br, I) display Ci, C2-like, or C1 molecular symmetry, depending on the anion and the R group, and enclose planar or disphenoidal [CuX]2 cores with short, bonding Cu—Cu distances in case of X = I. On the other hand, centrosymmetric 8-membered rings with twist-chair conformations are found in the solid state structures of [M(μ-OTf)PR2Xyl]2 (R = iPr, tBu; M = Cu, Ag) and [Ag(μ-NTf2)PiPr2Xyl]2, with the anions in a κ2-μ2 coordination mode. Additionally, the cationic complex [Cu(PR2Xyl)2]+ has been obtained as a triflate or BArF salt (BArF- = B{3,5-(CF3)2C6H3}4-), and shows C2-like symmetry in the solid state, with PCuP angles of ca. 168-169° and synclinal dispositions of the Xyl groups with respect to the P∙∙∙P axis. Comparative discussion of relevant NMR data of Cu(I), Ag(I), and Au(I) adducts of the title phosphines is also provided.

Copper-Catalyzed Dynamic Kinetic Asymmetric P-C Coupling of Secondary Phosphine Oxides and Aryl Iodides.

Transition-metal-catalyzed enantioselective P-C cross-coupling of secondary phosphine oxides (SPOs) is an attractive method for synthesizing P-stereogenic phosphorus compounds, but the development of such a dynamic kinetic asymmetric process remains a considerable challenge. Here we report an unprecedented highly enantioselective dynamic kinetic intermolecular P-C coupling of SPOs and aryl iodides catalyzed by copper complexes ligated by a finely modified chiral 1,2-diamine ligand. The reaction tolerates a wide range of SPOs and aryl iodides, affording P-stereogenic tertiary phosphine oxides (TPOs) in high yields and with good enantioselectivity (average 89.2 % ee). The resulting enantioenriched TPOs were transformed into structurally diverse P-chiral scaffolds, which are highly valuable as ligands and catalysts in asymmetric synthesis.

Copper‐Catalyzed Dynamic Kinetic Asymmetric P−C Coupling of Secondary Phosphine Oxides and Aryl Iodides

AbstractTransition‐metal‐catalyzed enantioselective P−C cross‐coupling of secondary phosphine oxides (SPOs) is an attractive method for synthesizing P‐stereogenic phosphorus compounds, but the development of such a dynamic kinetic asymmetric process remains a considerable challenge. Here we report an unprecedented highly enantioselective dynamic kinetic intermolecular P−C coupling of SPOs and aryl iodides catalyzed by copper complexes ligated by a finely modified chiral 1,2‐diamine ligand. The reaction tolerates a wide range of SPOs and aryl iodides, affording P‐stereogenic tertiary phosphine oxides (TPOs) in high yields and with good enantioselectivity (average 89.2 % ee). The resulting enantioenriched TPOs were transformed into structurally diverse P‐chiral scaffolds, which are highly valuable as ligands and catalysts in asymmetric synthesis.

Phosphine-catalyzed acyl-transfer of heteroaryl ketones for the construction of N-fused heterocycles

An inexpensive phosphine catalyst was used effectively for a transition-metal-free acyl-transfer of N-containing heteroaryl ketones for the rapid synthesis of N-fused heterocycles. The key pre-aromatic spirocyclic intermediate initialized by the single electron transfer (SET) process of Togni's reagent II promoted by the tertiary phosphine resulted in an intriguing and alternative tactic for the cleavage of C‒C bonds. By using inexpensive tertiary phosphine as the catalyst, this skeleton-reorganizing approach of N-containing heteroaryl ketones allows a streamlined assembly of complex N-fused heterocycles with broad functional group tolerance.

Tetramethylphosphinane as a new secondary phosphine synthon

Secondary phosphines are important building blocks in organic chemistry as their reactive P—H bond enables construction of more elaborate molecules. In particular, they can be used to construct tertiary phosphines that have widespread applications as organocatalysts, and as ligands in metal-complex catalysis. We report here a practical synthesis of the bulky secondary phosphine synthon 2,2,6,6-tetramethylphosphinane (TMPhos). Its nitrogen analogue tetramethylpiperidine, known for over a century, is used as a base in organic chemistry. We obtained TMPhos on a multigram scale from an inexpensive air-stable precursor, ammonium hypophosphite. TMPhos is also a close structural relative of di-tert-butylphosphine, a key component of many important catalysts. Herein we also describe the synthesis of key derivatives of TMPhos, with potential applications ranging from CO2 conversion to cross-coupling and beyond. The availability of a new core phosphine building block opens up a diverse array of opportunities in catalysis.

Synthesis and Properties of Sulfur-Containing Organophosphorus Extractants Based on Red Phosphorus, Alkyl Bromides, and Elemental Sulfur.

In order to obtain sulfur-containing organophosphorus compounds that are promising as extractants of heavy metals, the interaction of elemental phosphorus and sulfur with alkyl bromides catalyzed using strong bases was studied. According to the task, the reaction of non-toxic and non-flammable red phosphorus with alkyl bromides under conditions of phase transfer catalysts (PTC), followed by the introduction of elemental sulfur into the reaction medium, were studied. It is shown that alkyl bromides interact with red phosphorus when heated (95-105 °C, 5-8 h) under conditions of phase transfer catalysts (PTC) in a two-phase system: a 60% aqueous solution of KOH-toluene-benzyltriethylammonium chloride (BTEAC) forming a mixture of organophosphorus compounds along with alkylphosphines (57-60%), are the main reaction products; alkylphosphine oxides are also formed (40-43%). The introduction of elemental sulfur (solution in toluene) at the final stage of the process into the reaction mass cooled to 40-60 °C leads to the expected alkylphosphine sulfides, which are the result of the interaction of alkylphosphines with sulfur. The formation of complex mixtures of products prevents the release of target alkylphosphine sulfides in individual form. However, the synthesized mixture of alkylphosphine sulfides and alkylphosphine oxides without separation into individual components is promising for studying its extraction properties in relation to heavy metals. Testing of the extraction properties of synthesized mixtures of alkylphosphine sulfides and alkylphosphine oxides in relation to heavy metals (Ni, Co, Zn, Pb) and noble metals (Ag) showed that the resulting mixtures of tertiary phosphine oxides and phosphine sulfides are highly effective extractants. The degree of extraction in relation to Ni, Co, Zn, and Pb varies from 99.90 to 99.99%, and for Ag from 99.56 to 99.59%.

Synthesis of Triarylphosphines via Cu-Catalyzed Coupling of Aryl Halides and Acylphosphines

AbstractA Cu-catalyzed C(sp2)–P bond forming reaction using an acylphosphine as the phosphorus source is reported; with CuCl2 as the catalyst, 34 examples of aryl iodides and bromides were converted into triarylphosphines in good to excellent yield. A preliminary study of the mechanism was carried out and found that a radical intermediate is not involved. This reaction is an extension of the application of acylphosphines in Cu-catalyzed reactions and shows their potential as a phosphination reagent in the synthesis of tertiary phosphines.

Renewable synthesis of novel acrylates from biomass‐derived 5‐substituted‐2‐furaldehydes by Morita‐Baylis‐Hillman reaction

AbstractBiomass‐derived furfurals are becoming increasingly popular as renewable chemical building blocks for synthesizing specialty chemicals. Morita‐Baylis‐Hillman (MBH) reaction is a classic carbon‐carbon bond‐forming transformation between the α‐position of an activated alkene and a carbon electrophile (e. g., aldehyde) using a nucleophilic catalyst, such as a tertiary amine or phosphine. The MBH reaction is highly atom economical, affords excellent yields of adducts under mild reaction conditions, introduces substantial molecular complexity, and enjoys broad substrate scope. In this work, several novel MBH adducts have been synthesized starting from biomass‐derived 5‐substituted‐2‐furaldehydes and acrylates using 1,4‐diazabicyclo[2.2.2]octane (DABCO) as the organocatalyst. This work reports the first systematic study of the MBH reaction of 5‐substituted‐2‐furaldehydes and acrylates. A general synthetic protocol for the high‐yielding synthesis of MBH adducts has been developed. The reactions were performed at room temperature under solvent‐free conditions, and the spectroscopically pure products were produced in good to excellent isolated yields. Moreover, DABCO was recovered from the reaction mixture and successfully recycled.

Catalytic Asymmetric Hydrophosphinylation of 2‐Vinylazaarenes to Access P‐Chiral 2‐Azaaryl‐Ethylphosphine Oxides

AbstractA chiral Brønsted acid‐catalysed asymmetric hydrophosphinylation of 2‐vinylazaarenes by secondary phosphine oxides is described. A variety of P‐chiral 2‐azaaryl‐ethylphosphine oxides are synthesized with high yields and ees, of which both the substituents of phosphines and azaarenes can be flexibly modulated, underscoring an exceptionally broad scope of substrates. These adducts are valuable to asymmetric metal catalysis since the resultant P‐chiral tertiary phosphines from the reduction of them are verified as a kind of effective C1‐symmetric chiral 1,5‐hybrid P,N‐ligands. Importantly, this catalysis platform enables the generic and efficient kinetic resolution of P‐chiral secondary phosphine oxides. It thus provides an expedient approach to access the enantiomers of the P‐chiral tertiary phosphine oxides derived from asymmetric hydrophosphinylation, further improving the utility of the method.

Catalytic Asymmetric Hydrophosphinylation of 2-Vinylazaarenes to Access P-Chiral 2-Azaaryl-Ethylphosphine Oxides.

A chiral Brønsted acid-catalysed asymmetric hydrophosphinylation of 2-vinylazaarenes by secondary phosphine oxides is described. A variety of P-chiral 2-azaaryl-ethylphosphine oxides are synthesized with high yields and ees, of which both the substituents of phosphines and azaarenes can be flexibly modulated, underscoring an exceptionally broad scope of substrates. These adducts are valuable to asymmetric metal catalysis since the resultant P-chiral tertiary phosphines from the reduction of them are verified as a kind of effective C1 -symmetric chiral 1,5-hybrid P,N-ligands. Importantly, this catalysis platform enables the generic and efficient kinetic resolution of P-chiral secondary phosphine oxides. It thus provides an expedient approach to access the enantiomers of the P-chiral tertiary phosphine oxides derived from asymmetric hydrophosphinylation, further improving the utility of the method.

Cd(II) and Pd(II) Mixed Ligand Complexes of Dithiocarbamate and Tertiary Phosphine Ligands-Spectroscopic, Anti-Microbial, and Computational Studies.

Mixed ligand complexes of Pd(II) and Cd(II) with N-picolyl-amine dithiocarbamate (PAC-dtc) as primary ligand and tertiary phosphine ligand as secondary ligands have been synthesized and characterized via elemental analysis, molar conductance, NMR (1H and 31P), and IR techniques. The PAC-dtc ligand displayed in a monodentate fashion via sulfur atom whereas diphosphine ligands coordinated as a bidentate mode to afford a square planner around the Pd(II) ion or tetrahedral around the Cd(II) ion. Except for complexes [Cd(PAC-dtc)2(dppe)] and [Cd(PAC-dtc)2(PPh3)2], the prepared complexes showed significant antimicrobial activity when evaluated against Staphylococcus aureus, Pseudomonas aeruginosa, Candida albicans and Aspergillus niger. Moreover, DFT calculations were performed to investigate three complexes {[Pd(PAC-dtc)2(dppe)](1), [Cd(PAC-dtc)2(dppe)](2), [Cd(PAC-dtc)2(PPh3)2](7)}, and their quantum parameters were evaluated using the Gaussian 09 program at the B3LYP/Lanl2dz theoretical level. The optimized structures of the three complexes were square planar and tetrahedral geometry. The calculated bond lengths and bond angles showed a slightly distorted tetrahedral geometry for [Cd(PAC-dtc)2(dppe)](2) compared to [Cd(PAC-dtc)2(PPh3)2](7) due to the ring constrain in the dppe ligand. Moreover, the [Pd(PAC-dtc)2(dppe)](1) complex showed higher stability compared to Cd(2) and Cd(7) complexes which can be attributed to the higher back-donation of Pd(1) complex.

Lewis base catalyzed asymmetric <italic>C</italic>-acylation

<p indent="0mm">Asymmetric <italic>C</italic>-acylation is one of the most useful methods for the convenient construction of quaternary stereocenters. Asymmetric <italic>C</italic>-acylation can be divided into indirect <italic>C</italic>-acylation and direct <italic>C</italic>-acylation. Lewis base catalysts play key roles in this type of reactions. These catalysts can be divided into tertiary amines, tertiary phosphines and the catalysts bearing an oxygen nucleophilic site. Among them, tertiary amines, including aminopyridines, amidines and imidazoles, are most widely used due to its structural diversity and stability. This review outlines the development of the asymmetric <italic>C</italic>-acylation catalyzed by Lewis base especially the direct <italic>C</italic>-acylation catalyzed by chiral bicyclic imidazoles, and focuses on the performance and mechanism of the catalysts in these reactions.

Synthesis, characterization and study of mercury(II) complexes with phosphine and heterocyclic thiones

Many new mixed ligand complexes of mercury(II) have been synthesized with LH = 4,5-(diphenyl)-1,2,4-triazole-3-thione (diptSH) and tertiary phosphines as co-ligands. The compounds have been characterized by elemental analyses, IR, UV–Vis, molar conductivity, and NMR spectroscopy. In the binuclear complexes (2-5), both Hg atoms have tetrahedral geometry, the Hg atom bonded to three halide ions and one thione ligand (LH) through the sulfur atom. The complex (6) show that thiolate ligand(diptS-) is coordinated as monodentate through the sulfur atom. The dppm behave as bidentate bridging ligand to bonded two Hg(II) ions in the complex (7), Whereas in the complexes (7-10), the thionlate ligand bonded as a monodentate fashion via the sulfur atom, while the diphosphines ligands coordinated as bidentate chelating ligands, and the geometry around the Hg center ion is tetrahedral. And in the complexes (11 and 12), the phosphine bonded as monodentate ligand, and the thionlate bonded via the sulfur atom as monodentate to give tetrahedral complexes

Trioctylphosphine- and Octanethiol-Induced Photoluminescence Recovery of CdSe/ZnS Quantum Dots after Dilution–Quenching: Implications for Quantum Dot Films

In this work, CdSe/ZnS core/shell quantum dots (QDs) were synthesized. Dilution of the as-synthesized QDs would lead to instability with photoluminescence (PL) quenching. It was found that the addition of tertiary phosphine and alkylthiol could recover the PL intensity of diluted QDs and make these QDs stable. Specifically, the recovery efficiency of tertiary phosphine was stronger than that of alkylthiol. Trioctylphosphine (TOP) and octanethiol (OT) were chosen as the representative ligands, respectively. Isothermal titration calorimetry (ITC) demonstrated that interactions between both TOP/OT and QDs were exothermic and spontaneous. The interaction between TOP and QDs was mainly driven by van der Waals forces due to the branched structure. This interaction had a negative entropy change, while the interaction between OT and QDs had a positive entropy change. There were about ∼12 TOP molecules and ∼17 OT molecules bound to a QD particle. The binding constants of TOP/OT to QDs were 1.6 × 103 and 12.8 × 103 M–1, respectively. The reaction rate between TOP and QDs was fast, and the addition of OT could slow the reaction rate constant from 0.081 to 0.024 min–1. PL decay indicated that TOP and OT could increase the radiative recombination of excitons. Furthermore, both TOP and OT could greatly improve the brightness of the QD films, which was a prerequisite for the efficient improvement of quantum dot light-emitting diodes. This work explicitly investigated the dilution process of QDs, explored the methods for keeping diluted QDs stable and bright, and highlighted the importance of surface ligands.