Phosphine Atoms Research Articles

Versatile Synthesis of Trisphosphines Bearing Phenylene and Vinylene Backbones Useful for Metal Catalysis and Materials Applications

AbstractTrisphosphines, in which two phenylene or vinylene backbones connect three phosphine atoms, belong to an emerging class of ligands in metal-catalyzed organic synthesis and materials applications. However, these ligands were previously known only in a small variety because of the synthetic limitations. We report herein two versatile synthetic routes to a hitherto unavailable variety of trisphosphines. The compounds bearing phenylene backbones were synthesized by sequential addition of two different organolithium reagents to triphenyl phosphite and that with vinylene backbones by stereoretentive addition of lithium diarylphosphide to a cis-bromoalkene. The new trisphosphine compounds will serve as valuable tools for the development of transition-metal-catalyzed reactions and functional materials.

Three half-sandwiched iron(II) monocarbonyl complexes with PNP ligands: Their chemistry upon reduction and catalysis on proton reduction

Three half-sandwiched iron(II) monocarbonyl cationic complexes (1+−3+) containing a azadiphoshine ligand (PNP, L1–3) and an iodide as the counter anion, [Fe(II)Cp(CO)(L1–3)]Ι (Cp = η5-cyclopentadienyl; L1 = Ph2PN(cyclohexyl)PPh2, 1+; L2 = Ph2PN(phenyl)PPh2, 2+; L3 = Ph2PN(benzyl)PPh2, 3+) were reported. All the complexes were fully characterized, of which complexes 2+ and 3+ were crystallographically analysed to confirm their “piano stool” geometry. Electrochemically, complexes 1+−3+ exhibited two major reduction events at about −1.9 V and −2.3 V, respectively, assigned to Fe(II) → Fe(I) and Fe(I) → Fe(0), respectively. The first reduction produces a 19e-species, [Fe(I)Cp(CO)(L1–3)] (1, 2, and 3) whereas the second event is not assigned to the further reduction of the 19e-species but a 17e-intermediate ([Fe(I)Cp(CO)(m-L1–3)]; 1′, 2′ and 3′) which is chemically generated from the 19e-species by cleaving one of the two Fe−P bonds. However, the 19e-species 3 is considerably more stable than the other two analogues (1 and 2) due to H−π interaction between the ortho-H atoms from one of the four phenyl rings on the phosphine atom and the phenyl ring of the benzyl group as revealed by theoretic calculations. Therefore, species 3 is stable enough for the reduction of 3 → 3− to be electrochemically detected right before the second major reduction. To further shed some light on the electrochemical mechanism, both bulk electrolysis and chemical reduction of complexes 1+−3+ with cobaltocene as the reducing agent were conducted. Under N2 atmosphere, the neutral 17e-species, [Fe(I)Cp(CO)(m-L1–3)] (1′-3′) was spectroscopically detected whereas under CO atmosphere, CO-adducts, [Fe(I)Cp(CO)2(m-L1–3)], were generated. The formation of CO-adduct explains the loss of reversibility of the first reduction (3+) under CO atmosphere in its electrochemistry. With acetic acid as the proton source, only the second major reduction of the complexes exhibited significant catalytic activity, of which complex 1+ possessed the best performance. Significant proton-coupled electron transfer (PCET) effect was observed for complex 1+ due to the strong electron-donating capability of the ligand (L1).

Rhodium-Catalyzed Asymmetric Hydrogenation of All-Carbon Aromatic Rings.

Compared with heteroarenes, homogeneous asymmetric hydrogenation of all-carbon aromatic rings is a longstanding challenge in organic synthesis due to the strong aromaticity and difficult enantioselective control. Herein, we report the rhodium/diphosphine-catalyzed asymmetric hydrogenation of all-carbon aromatic rings, affording a series of axially chiral cyclic compounds with high enantioselectivity through desymmetrization or kinetic resolution. In addition, the central-chiral cyclic compounds were also obtained by asymmetric hydrogenation of phenanthrenes bearing a directing group. The key to success is the introduction of chiral diphosphine ligands with steric hindrance and strong electron-donating properties. The axially chiral monophosphine ligands could be obtained by simple conversion of the hydrogenation products bearing the phosphine atom.

Rhodium‐Catalyzed Asymmetric Hydrogenation of All‐Carbon Aromatic Rings

AbstractCompared with heteroarenes, homogeneous asymmetric hydrogenation of all‐carbon aromatic rings is a longstanding challenge in organic synthesis due to the strong aromaticity and difficult enantioselective control. Herein, we report the rhodium/diphosphine‐catalyzed asymmetric hydrogenation of all‐carbon aromatic rings, affording a series of axially chiral cyclic compounds with high enantioselectivity through desymmetrization or kinetic resolution. In addition, the central‐chiral cyclic compounds were also obtained by asymmetric hydrogenation of phenanthrenes bearing a directing group. The key to success is the introduction of chiral diphosphine ligands with steric hindrance and strong electron‐donating properties. The axially chiral monophosphine ligands could be obtained by simple conversion of the hydrogenation products bearing the phosphine atom.

Rhodium catalyzed asymmetric synthesis of Chiraphos derivatives

Herein, we report a highly efficient versatile synthetic route to Chiraphos derivatives through Rh/Ph-bod catalyzed asymmetric addition of aryl boronic acids to phosphinyl dienes. Various substituted phosphinyl dienes, both on the parent skeleton and the phosphine atoms, were well tolerated with this method and provided chiral phosphine oxides in satisfied yield and up to 95% ee. The corresponding Chiraphos derivative displayed an advantage over Chiraphos in the representative Pd-catalyzed asymmetric 1,4-addition reaction.

Synthesis and full characterizations of poly acrylate cyclotriphosphazene and blended it with PMMA

Poly acrylate cyclotriphosphazene (poly PN-A) was successfully synthesized by polymerization reaction using benzoyl peroxide as an initiator in dry 1,4-dioxane to form poly PN-A. After that the blended polymer with poly(methyl methacrylate) (PMMA) were prepared for synthesized polymer (poly PN-A) by using ratio 10:1 per weight of synthesized polymer to PMMA hence they were mixed using dioxane. Many techniques were used to characterize the chemical structures of synthesized material. Infrared spectroscopy was used to identify the functional groups within the chemical structure of the compounds. Three types of nuclear magnetic resonance (1H NMR, 13C NMR, and 31P NMR) were used to confirm the chemicals structures of the products. 31P NMR was used because all units and their polymers have phosphine atoms in their chemical structures. Thus, all used spectra confirmed the chemical structure of synthesised materials with high percentage of purity

Pursuit of an Electron Deficient Titanium Nitride.

The nitride salt [(PN)2Ti≡N{μ2-K(OEt2)}]2 (1) (PN- = (N-(2-PiPr2-4-methylphenyl)-2,4,6-Me3C6H2) can be oxidized with two equiv of I2 or four equiv of ClCPh3 to produce the phosphinimide-halide complexes (NPN')(PN)Ti(X) (X- = I (2), Cl (3); NPN' = N-(2-NPiPr2-4-methylphenyl)-2,4,6-Me3C6H22-), respectively. In the case of 2, H2 was found to be one of the other products; whereas, HCPh3 and Gomberg's dimer were observed upon the formation of 3. Independent studies suggest that the oxidation of 1 could imply the formation of the transient nitridyl species [(PN)2Ti(≡N•)] (A), which can either oxidize the proximal phosphine atom to produce the Ti(III) intermediate [(NPN')(PN)Ti] (B) or, alternatively, engage in H atom abstraction to form the parent imido (PN)2Ti≡NH (4). The latter was independently prepared and was found to photochemically convert to the titanium-hydride, (NPN')(PN)Ti(H) (5). Isotopic labeling studies using (PN)2Ti≡ND (4-d1) as well as reactivity studies of 5 with a hydride abstractor demonstrate the presence of the hydride ligand in 5. An alternative route to putative A was observed via a photochemically promoted incomplete reduction of the azide ligand in (PN)2Ti(N3) (6) to 4. This process was accompanied by some formation of 5. Frozen matrix X-band EPR studies of 6, performed under photolytic conditions, were consistent with species B being formed under these reaction conditions, originating from a low barrier N-insertion into the phosphine group in the putative nitridyl species A. Computational studies were also undertaken to discover the mechanism and plausibility of the divergent pathways (via intermediates A and B) in the formation of 2 and 3, and to characterize the bonding and electronic structure of the elusive nitrogen-centered radical in A.

Cobalt Pincer Complexes in Catalytic C-H Borylation: The Pincer Ligand Flips Rather Than Dearomatizes.

The mechanism for the borylation of an aromatic substrate by a cobalt pincer complex was investigated by density functional theory calculations. Experimental observations identified trans-(iPrPNP)CoH2(BPin) as the resting state in the borylation of five-membered heteroarenes, and 4-BPin-(iPrPNP)Co(N2)BPin as the resting state in the catalytic borylation of arene substrates. The active species, 4-R-(iPrPNP)CoBPin (R=H, BPin), were generated by reductive elimination of H2 in the former, through Berry pseudorotation to the cis isomer, and N2 loss in the latter. The catalytic mechanism of the resulting Co(I) complex was computed to involve three main steps: C-H oxidative addition of the aromatic substrate (C6H6), reductive elimination of PhBPin, and regeneration of the active complex. The oxidative addition product formed through the most favorable pathway, where the breaking C-H bond of C6H6 is parallel to a line between the two phosphine atoms, leaves the complex with a distorted PNP ligand, which rearranges to a more stable complex via dissociation and re-association of HBPin. Alternative pathways, σ-bond metathesis and the oxidative addition in which the breaking C-H bond is parallel to the Co-B bond, are predicted to be unlikely for this Co(I) complex. The thermodynamically favorable formation of the product PhBPin via reductive elimination drives the reaction forward. The active species regenerates through the oxidative addition of B2Pin2 and reductive elimination of HBPin. In the overall reaction, the flipping (refolding) of the five-membered phosphine rings, which connects the species with two phosphine rings folded in the same direction and that with them folded in different directions, is found to play an important role in the catalytic process, as it relieves steric crowding within the PNP ligand and opens Co coordination space. Metal-ligand cooperation based on the ligand's aromatization/dearomatization, a common mechanism for heavy-metal pincer complexes, and the dissociation of one phosphine ligand, do not apply in this system. This study provides guidance for understanding important features of pincer ligands with first-transition-row metals that differ from those in heavier metal complexes.

Recent progress in the development of advanced element-block materials

An element-block is defined as a minimum functional unit composed of heteroatoms. The concept of ‘element-block material’ for designing advanced materials was proposed in 2015. In this review, the recent progress in material designs based on this concept is described. From our research, several element-blocks as representative examples are selected, and their roles in each material are explained. Initially, research on the development of ‘designable hybrids’ by employing polyhedral oligomeric silsesquioxane (POSS) is illustrated. Multiple functions of hybrids composed of modified POSS and the significant roles of POSS in bio-related polymeric materials for solving critical problems in conventional 19F MR probes and for realizing new sensing technologies are demonstrated. Next, solid-state luminescent materials containing o-carborane and group 13 element-blocks are discussed. The materials’ highly efficient emission in the solid state and their origins are explained. Furthermore, stimuli-responsive luminescent chromism is summarized. The sensing mechanisms and the application of these materials as sensors are presented in this study. In the last part, we mention optically active element-blocks containing chiral P-stereogenic phosphorus. In this review, the characteristics originating from each element-block are explained. We review our recent studies on material designs based on element-blocks, which are defined as a minimum functional unit composed of heteroatoms, and particularly focus on the roles of element-blocks in these materials. To start, the development of ‘designable hybrids’ by employing polyhedral oligomeric silsesquioxane is illustrated. The following topics include solid-state luminescent materials containing o-carborane and group 13 element-blocks. Their highly efficient emission in the solid state and their photochemistry are explained. Furthermore, we mention chiral element-blocks containing optically active phosphine atoms. The unique properties of this series of element-block materials are illustrated.

Synthesis, Structure, and Characterization of Emissive Neutral Dinuclear CuI Complexes with a Tetraphosphane Bridging Ligand

A series of new dinuclear copper complexes with a tetraphosphane bridging ligand, [{(pz4B)Cu}2(µ‐tpbz)] (1), [{(pz2BH2)Cu}2(µ‐tpbz)] (2), and [{(tz2BH2)Cu}2(µ‐tpbz)] (3) [tpbz = 1,2,4,5‐tetrakis(diphenylphosphanyl)benzene, pz4B = tetrakis(pyrazol‐1‐yl)borate, pz2BH2 = bis(pyrazol‐1‐yl)borohydrate, and tz2BH2 = bis(1,2,4‐triazol‐1‐yl)borohydrate], have been synthesized and structurally characterized. The CuI atoms in these complexes are four‐coordinate and adopt a tetrahedral coordination geometry. In each complex, the copper centers are bridged by a tpbz ligand and each CuI is further terminally chelated by a borate diimine anion. The central phenylene ring and the phosphine atoms of the tpbz ligand are essentially planar. The two CuI atoms in each molecule are located above and below the (P2C6H2P2) mean plane, respectively, leading to a chair‐like conformation for the [Cu](P2C6H2P2)[Cu] fragment. The distances between the CuI atoms in each complex are about 8.7 Å. In the solid state, these complexes are emissive and exhibit yellow–orange photoluminescence [emission peaks, λmax = 580 nm (1), 569 nm (2), 540 nm (3)] with lifetimes of 7.4–20.5 µs and quantum yields Φ = 0.07–0.45 at room temperature. Theoretical and experimental results indicate that these complexes have the lowest singlet (S1) state and the lowest triplet (T1) state with very close energy levels, and display thermally activated delayed fluorescence (TADF) at ambient temperature.

Light-Activated Staudinger-Bertozzi Ligation within Living Animals.

The ability to regulate small molecule chemistry in vivo will enable new avenues of exploration in imaging and pharmacology. However, realization of these goals will require reactions with high specificity and precise control. Here we demonstrate photocontrol over the highly specific Staudinger-Bertozzi ligation in vitro and in vivo. Our simple approach, photocaging the key phosphine atom, allows for the facile production of reagents with photochemistry that can be engineered for specific applications. The resulting compounds, which are both stable and efficiently activated, enable the spatial labeling of metabolically introduced azides in vitro and on live zebrafish.

Group VI metal complexes of tris(diphenylphosphinomethyl)phenylborate: modulation of ligand donation via coordination of M(CO)3 units at the borate phenyl substituent.

A series of d(6) metal complexes of tris(diphenylphosphinomethyl)phenylborate ([PhB(CH2PPh2)3](-), PhBP3), including [Et4N][M(CO)3(PhBP3)] (M = Cr, Mo, W), inaugural group VI metal tris(phosphino)borate complexes, and zwitterionic Mn(CO)3(PhBP3) have been synthesized and fully characterized. An analysis of IR ν(CO) data for [Et4N][M(CO)3(PhBP3)] indicates that PhBP3 is significantly less strongly donating than Tp towards zerovalent M(CO)3 fragments; PhBP3 does not function as a strongly donating scorpionate in this system as its does towards cationic metal fragments suggesting that PhBP3 may not function as an effective surrogate of hydrotris(1-pyrazolyl)borate towards zerovalent metals. While the metal centers of [Et4N][M(CO)3(PhBP3)] are very likely still more electron-rich than those of M(CO)3(triphos), the anions of [Et4N][M(CO)3(PhBP3)] do not provide robust oxidative addition products analogous to those of M(CO)3(triphos). A new bi-functional role for PhBP3 was investigated via the synthesis of seven structurally characterized bimetallics in which zerovalent M(CO)3 and monovalent [Mn(CO)3](+) fragments bind the three phosphine atoms and the borate phenyl substituent. IR ν(CO) data support modest attenuation of PhBP3 donor ability at phosphorus upon η(6)-phenyl substituent binding, representing a new inductive strategy for tuning tris(phosphino)phenylborate donation at the κ(3)-phosphine-bound metal fragment.

Bis-(diphenylphosphino)methane as Mono- or Bi-dentate Ligand of Benzoate-Functionalized Diiron Propanedithiolate Complexes: Catalysis for the Reduction of Proton

Reaction of the diiron propanedithiolate complex [μ-(SCH2)2CHO2CC6H5]Fe2(CO)6 (A) with bis-(diphenylphosphino)methane (dppm) in the presence of Me3NO·2H2O in MeCN yielded a mono-substituted complex [μ-(SCH2)2CHO2CC6H5]Fe2(CO)5(κ-dppm) (1), whereas in refluxing xylene gave a bridged complex [μ-(SCH2)2CHO2CC6H5]Fe2(CO)4(μ-dppm) (2). The structures of both complexes were fully characterized by spectroscopic methods and X-ray crystallography. In solid state, one phosphine atom of dppm in complex 1 occupies an apical position of the square pyramidal geometries of the Fe center or two phosphine atoms of dppm in complex 2 bridge two Fe centers in a cisoid dibasal conformation. The cyclic voltammograms of both complexes in the presence of HBF4 were investigated.

Kinetics and mechanism of the racemization of aryl allenes catalyzed by cationic gold(I) phosphine complexes.

The kinetics of the racemization of aromatic 1,3-disubstituted allenes catalyzed by gold phosphine complexes has been investigated. The rate of gold-catalyzed allene racemization displayed first-order dependence on allene, and catalyst concentration and kinetic analysis of gold-catalyzed allene racemization as a function of allene and phosphine electron-donor ability established the accumulation of electron density on the phosphine atom and the depletion of electron density on the terminal allenyl carbon atoms in the rate-limiting transition state for racemization. These and other observations were in accord with a mechanism for allene racemization involving rapid and reversible inter- and intramolecular allene exchange followed by turnover-limiting, unimolecular conversion of a chiral gold η(2)-allene complex to an achiral η(1)-allylic cation intermediate through a bent and twisted η(1)-allene transition state. With respect to proper ligand selection, these studies reveal that both electron-poor phosphine ligands and polar solvents facilitate racemization.

Mercury(II) complexes of unsymmetric phosphorus ylides: Synthesis, spectroscopic and antibacterial activity studies

The reaction of Ph2PCH2PPh2 (dppm) with 2-bromo-3-nitroacetophenone and 2,2′,4′-trichloroacetophenone in chloroform produce the new phosphonium salts [Ph2PCH2PPh2CH2C(O)C6H4NO2]Br (1) and [Ph2PCH2PPh2CH2C(O)C6H3Cl2]Cl (2). Further, by reaction of the monophosphonium salts of dppm with the strong base triethylaminethe corresponding bidentate phosphorus ylides, Ph2PCH2PPh2C(H)C(O)C6H4NO2 (3) and Ph2PCH2PPh2C(H)C(O)C6H3Cl2 (4) were obtained. The reaction of these ligands with mercury(II) halides in dry methanol led to the formation of the mononuclear complexes {HgX2[(Ph2PCH2PPh2C(H)C(O)C6H4NO2)]} [X=Cl (5), Br (6), I (7)] and {HgX2[(Ph2PCH2PPh2C(H)C(O)C6H3Cl2)]} [X=Cl (8), Br (9), I (10)]. Characterization of the obtained compounds was performed by elemental analysis, IR, 1H, 31P and 13C NMR. The structure of compound 1 being unequivocally determined by single crystal X-ray diffraction techniques. The mass spectrum of compound 6 (as an instance) also demonstrates the synthesize of these compounds. In all complexes the title ylides are coordinated through the ylidic carbon and the phosphine atom. These compounds form five membered ring under complexation. The antibacterial effects of DMSO solutions of the ligands and their metal complexes were evaluated by the disc diffusion method against six Gram positive and negative bacteria. All compounds represent antibacterial activity against these bacteria with high levels of inhibitory potency exhibited against the Gram positive species.

Mercury(II) complexes of new bidentate phosphorus ylides: synthesis, spectra and crystal structures

AbstractThe reaction of dppm (1,1-bis(diphenylphosphino)methane) with 2-bromo-4-phenylacetophenone and benzyl bromoacetate in chloroform produces new phosphonium salts, [Ph2PCH2PPh2CH2C(O) C6H4Ph]Br (I) and [Ph2PCH2PPh2CH2COOCH2Ph]Br (II). By allowing the phosphonium salts to react with the appropriate base, the bidentate phosphorus ylides, Ph2PCH2PPh2=C(H)C(O)C6H4Ph (III) and Ph2PCH2PPh2=C(H)C(O)OCH2Ph (IV), were obtained. The reaction of these ligands with mercury(II) halides in dry methanol led to the formation of the mononuclear complexes {HgX2[(Ph2PCH2PPh2C(H)C(O)C6H4Ph)]} (X = Cl (V); X = Br (VI); X = I (VII)) and {HgX2[(Ph2PCH2PPh2C(H)COOCH2Ph)]} (X = Cl (VIII); X = Br (IX); X = I (X)). The FTIR and 1H, 31P and 13C NMR spectra were studied. The structure of compound III was unequivocally determined by the single-crystal X-ray diffraction technique. Single-crystal X-ray analysis of the {HgBr2[(Ph2PCH2PPh2C(H)C(O)C6H4Me)]} complex (XI) revealed the presence of a mononuclear complex containing the Hg atom in a distorted tetrahedral environment. In all complexes, the ylides referred to above were coordinated through the ylidic carbon and the phosphine atom.

Bridging and Chelating Roles of Bis(2-(diphenylphosphino)ethyl)phenylphosphine in Stabilizing Binuclear Platinum(II) Complexes

The diorganoplatinum(II) complexes [PtR2(triphos-P,P′)] (1; R = Me, p-MeC6H4 and triphos = bis(2-(diphenylphosphino)ethyl)phenylphosphine), containing one free phosphine atom, react with cyclometalated platinum complexes [PtR′(C∧N)(SMe2)] (2; R′ = Me, p-MeC6H4 and C∧N is deprotonated 2-phenylpyridine (ppy) or deprotonated benzo[h]quinoline (bhq)) to give the cyclometalated diplatinum(II) complexes [Pt2R2R′(C∧N)(triphos)] (3). In these binuclear platinum(II) compounds, triphos acts as both a chelating and bridging ligand to stabilize the produced diplatinum complexes. The complexes 3 were readily characterized by multinuclear NMR spectroscopy and elemental microanalysis. The crystal structure of complex 3f (R = Me, R′ = p-MeC6H4, and C∧N = bhq) was further determined by X-ray crystallography, giving the first example of an X-ray structural determination of a diplatinum complex with a triphos ligand acting simultaneously as both a chelating and bridging ligand.

Electron-Beam Mediated Rearrangement and Fragmentation of Bis(diphenylphosphino)alkane Derivatives in Gas Phase

The irradiation of electron-beam onto bis- (diphenylphosphino)methane, ethane, propane and butane initiated phenyl-shift from a phosphine to another phosphine atom and subsequent fragmentation resulted in the formation of triphenylphosphine derivative as key intermediate. The mechanism of those processes is speculated.

Camphane-based phosphino-carboxamide ligands as P,O-chelates in Pd-catalyzed enantioselective allylic alkylation

A practical synthesis for new chiral phosphino-carboxamide ligands has been accomplished. These ligands were effectively modified both on the amide moiety and the phosphine atom. Application of these ligands in the Pd-catalyzed allylic alkylation of (E)-1,3-diphenyl-2-propenyl acetate proceeded with excellent conversions and with ee’s of up to 92%. The use of a camphane based chiral auxiliary was found to be crucial for the asymmetric induction.

Dinuclear copper complexes of pyridylphenylphosphine ligands: Characterization of a mixed-valence Cu II/Cu I dimer

Homo bi-copper complexes [Cu 2{PhP(2-py) 2} 2(NO 3) 3] ( 1) and [Cu 2{P(2-py) 3} 2Cl 2] ( 2), were synthesized from the reaction of Cu(NO 3) 2·3H 2O and CuCl 2·2H 2O with their corresponding 2-pyridylphosphine ligands. Compound 1 has a mixed valence Cu(I)–Cu(II) core with electron acceptor phosphine atoms and two NO 3 − anions coordinated in a monodentate fashion to Cu(I), giving it a distorted tetrahedral geometry. The environment of Cu(II) in 1 is composed of four nitrogen atoms from pyridyl and another NO 3 − anion in a square pyramidal geometry. This complex shows luminescence and a low energy absorption band at 969 nm corresponding to intermetallic electron transfer between the copper centers. Complex 2 was prepared from the treatment of copper(II) chloride with tris(2-pyridyl)phosphine, producing a binuclear copper complex which possesses a crystallographic inversion center. The copper geometry in this complex is distorted tetrahedral with coordination of one Cl −, two nitrogens from one bridging tris(2-pyridyl)phosphine ligand and one P atom from the other bridging tris(2-pyridyl)phosphine ligand, in a similar way observed in related complexes. The products have been characterized by spectroscopic methods and also by the single-crystal X-ray diffraction method.