Arsenic Ligands Research Articles

Synthetic Strategy for AB2-Type Arsines via Bidentate Dithiolate Leaving Groups.

Despite their potential for several transition-metal-catalyzed reactions, arsenic ligands are poorly diversified. In this work, we developed an efficient synthetic methodology for AB2-type ligands, which is a typical motif in phosphorus systems, for example, in Buchwald ligands. The introduction of 1,2-benzenedithiol to tribromoarsine reduces the reactivity of two of the three reaction sites. After the substitution reaction with the first nucleophile involving the elimination of bromide, the substitution reaction with the second nucleophile produced AB2-type arsines through the elimination of the dithiolate anion. Among the various types of obtained AB2-type arsines, the arsa-Buchwald ligands, which are arsenic analogues of Buchwald ligands, were applied to the Suzuki-Miyaura cross-coupling reaction. Some of the arsa-Buchwald ligands showed activity comparable to that of the well-known Buchwald ligand, SPhos. Furthermore, the arsenic analogue of SPhos showed higher activity and stability than SPhos under open-air conditions.

Tertiary arsine ligands for the Stille coupling reaction.

The Stille coupling reaction is one of the most important coupling reactions. It is well known that the triphenylarsine ligand can accelerate the reaction rate of Stille coupling. However, other arsine ligands have never been investigated for the Stille coupling reaction so far. In this work, we prepared 13 kinds of C3-symmetrical tertiary arsine ligands and discovered that tri(p-anisyl)arsine is the best ligand for the reaction of tributylvinyltin and p-iodoanisole. The reaction mechanism was studied by dispersion-corrected density functional theory calculations to demonstrate the energetic feasibility of the Stille coupling reactions mediated by tri(p-anisyl)arsine.

Multi-Mode Switchable Luminescence of Tetranuclear Cubic Copper(I) Iodide Complexes with Tertiary Arsine Ligands

Abstract Tetranuclear cubic copper(I) iodide (CuI) complexes were synthesized by utilizing tertiary arsine ligands such as triphenylarsine, tri(p-tolyl)arsine, 9-phenyl-9-arsafluorene, and 1-phenylarsolane; except for triphenylarsine, these ligands were prepared by the practical methods that we previously developed. The obtained complexes exhibited intense emission in the crystalline states even at room temperature. Their emission colors were drastically changed by mechanical stimulus, temperature, and excitation wavelength. These complexes are the first examples of cubic Cu4I4 complexes with arsenic ligands exhibiting stimuli-responsive and excitation wavelength-dependent luminescence.

Terahertz physical mechanism of arsenic (III) restoring p53 mutant protein activity

Recovering the protein activity of p53 mutants through small molecule ligand binding (eg. arsenic) is an important strategy for tumor suppressor therapy. However, the mechanistic basis on the changes of collective dynamics and their roles of p53 protein in functional recovery process has not been fully elucidated. Herein, the normal mode calculations based on all-atom elastic network model are employed to characterize the terahertz low frequency motions of core DNA-binding domain (p53C) which is essential for p53 protein activities in transcriptional transactivation. We find that the lowest-frequency collective vibration mode of the p53C mutant is effectively restored by the binding of arsenic (III) ligand. In R249S mutant, the L1 loop is stabilized through restricting the swing-out movement. The results obtained from atomic backbone fluctuations suggest that the arsenic binding can significantly improve the L1 loop and L2 loop fluctuations. The statistical analysis of low frequency vibration mode reflects that the arsenic-bound R249S mutant has an apparent recovery of frequency shift in the terahertz range. The residue-residue motion correlation also suggests that structural components binding to arsenic are dynamically coupled. In the H2 helix with arsenic-binding residues, the motions of C124, C135, M133 and C141, are correlated with the arsenic recovery. These results provide the terahertz biophysical mechanism for the recovery effect of arsenic (III) on the p53 protein activity and new evidence for the coupling of the low-frequency vibration characteristics of protein structures with its function, thus giving a new physical insight into the p53 related cancer therapies.

Dinuclear Rhombic Copper(I) Iodide Complexes with Rigid Bidentate Arsenic Ligands

Abstract We have recently developed a series of arsenic ligands based on practical synthetic strategies. Herein, three kinds of bidentate arsenic ligands with rigid linkers were selected to construct dinuclear rhombic copper(I) iodide (CuI) complexes, whose structures were analyzed by X-ray crystallography. They had sufficient solubility in organic solvents, and it was confirmed that their coordination forms were kept in the solutions. Intense solid-state emissions were observed even at room temperature, and the emission colors were varied from yellow to red by the ligands.

Fundamental Study on Arsenic(III) Halides (AsX3; X = Br, I) toward the Construction of C3-Symmetrical Monodentate Arsenic Ligands.

Arsenic ligands have attracted considerable attention in coordination chemistry. Arsenic(III) halides are the most important starting materials in the preparation of monodentate arsenic ligands. In this work, we optimized the synthetic methodologies of arsenic(III) halides (AsX3; X = Br, I) and examined the difference of their physical properties such as solubility to organic solvent and reactivity to nucleophiles. In addition, a wide variety of monodentate arsenic ligands were prepared with the obtained AsX3. Finally, the obtained monodentate arsenic ligands were utilized for copper-free Sonogashira cross-coupling reaction in the reaction system with porphyrin. The results showed that monodentate arsenic ligands have higher catalytic activity compared with triphenylphosphine because of the difference of the electronic features of lone pairs between arsenic and phosphorus atoms.

Construction of a Bidentate Arsenic Ligand Library Starting from a Cyclooligoarsine

Bidentate ligands are, needless to say, pivotal in organometallic chemistry. In contrast to phosphorus ligands, practical synthetic protocols for the arsenic analogues remain to be developed, resul...

The syntheses and structures of a series of polyoxometalate-based metal-organic arsonates constructed from a dual-ligand strategy with organic arsenic acids and N-donor ligands

Seven polyoxometalate (POM)-based metal-organic arsenates, namely, [Ni(H2O)3(bipy)]2(Mo6O18)(L1)2·4H2O (POMAs-1), [Zn(H2O)2(bipy)]2(Mo6O18)(L1)2·4H2O (POMAs-2), [Cd(H2O)2(bipy)]2(Mo6O18)(L1)2·4H2O (POMAs-3), [Ni(phen)2]2(Mo6O18)(L1)2·2H2O (POMAs-4), [Cd(H2O)(phen)2]2(Mo12O34)(L1)4·H2O (POMAs-5), (Mo12O34)(L2)2∙H4(bipy)2·3H2O (POMAs-6), H2(Mo6O19)(L2)(HAsO4) ∙H4(bipy)2·4H2O (POMAs-7) (H2L1 = phenylarsonic acid, C6H5AsO3H2, PhAsO3H2; H2L2 = 3-NO2-4-OH-C6H3-AsO3H2; phen = 1,10-phenanthroline; bipy = 4,4′-bipyridine), have been successfully synthesized under similar hydrothermal conditions. Single-crystal X-ray diffraction analyses reveal that three types of polyoxoanions were obtained in the seven compounds, containing α-octamolybdate-type {(Mo6O18)(L1)2}4− in POMAs-1–4, very large molydoarsonate cluster {(Mo12O34)(L1)4}4− and {(Mo12O34)(L2)4}4− polyoxoanions in POMAs-5–6, and a totally new {(Mo6O19)(L2)(HAsO4)}6− cluster in POMAs-7. In POMAs-1–5, transition metal-organic unit built by metal centers and N-donor ligands as counter cations balance the charge of target structure, however, in POMAs-6–7, transition metal ions do not coordinate to the framework of polyoxoanion. In this work, the effects of metal cations and organic ligand containing N-donor ligands and organic arsenic ligands on target POM clusters were presented clearly and discussed in detail.

Dichotomy of Manganese Catalysis via Organometallic or Radical Mechanism: Stereodivergent Hydrosilylation of Alkynes

AbstractHerein, we disclose the first manganese‐catalyzed hydrosilylation of alkynes featuring diverse selectivities. The highly selective formation of E‐products was achieved by using mononuclear MnBr(CO)5 with the arsenic ligand, AsPh3. Whereas using the dinuclear catalyst Mn2(CO)10 and LPO (dilauroyl peroxide) enabled the reversed generation of Z‐products in good to excellent stereo‐ and regioselectivity. Such a way of controlling the reaction stereoselectivity is unprecedented. Mechanistic experiments revealed the dichotomy of manganese catalysis via organometallic and radical pathways operating in the E‐ and Z‐selective routes, respectively.

Dichotomy of Manganese Catalysis via Organometallic or Radical Mechanism: Stereodivergent Hydrosilylation of Alkynes.

Herein, we disclose the first manganese-catalyzed hydrosilylation of alkynes featuring diverse selectivities. The highly selective formation of E-products was achieved by using mononuclear MnBr(CO)5 with the arsenic ligand, AsPh3 . Whereas using the dinuclear catalyst Mn2 (CO)10 and LPO (dilauroyl peroxide) enabled the reversed generation of Z-products in good to excellent stereo- and regioselectivity. Such a way of controlling the reaction stereoselectivity is unprecedented. Mechanistic experiments revealed the dichotomy of manganese catalysis via organometallic and radical pathways operating in the E- and Z-selective routes, respectively.

A Practical Screening Strategy of Arsenic Ligands for a Transition-metal-catalyzed Reaction

Organoarsenic ligands were synthesized via a safe and easy procedure, superior to the conventional synthetic methodologies. Diiodophenylarsine was prepared in situ, and was readily converted to diarylphenylarsines. Pd-catalyzed Mizoroki–Heck reaction was investigated using the obtained arsenic ligands. It was found that bulky and electron-donating ligands were effective for the reaction, meaning that the success in the screening of arsenic ligand structures was based on the present facile strategy.

Organometallic polyphosphorus and -arsenic ligands as linkers between pre-assembled linear Cu(I) fragments.

A simple and straightforward synthesis of a new linear trinuclear Cu(I) cluster with polyphosphine ligands is presented. The reaction of this pre-organized Cu3 precursor with En ligand complexes (E = P, As; n = 2, 5) affords discrete complexes exhibiting end-on η(1)-coordination of the E2 ligands or one-dimensional coordination polymers featuring σ-1,3-bridging E5 rings, respectively.

Palladium on charcoal-catalyzed ligand-free Stille coupling

An efficient ligand-free Stille coupling reaction catalyzed by palladium on charcoal was developed. Tetraphenyltin was reacted with a variety of aryl halides including aryl chlorides using LiCl as an additive. The reactions of tributyl organotin compounds with aryl iodides were effectively expedited by the addition of LiF. These reactions efficiently proceeded without a phosphine or arsenic ligand and no leached palladium was detected in the reaction mixture.

ChemInform Abstract: Ligand Steric Properties

Abstract Methods of estimating the steric requirements of ligands are reviewed. The most widely employed measure is the cone angle, ⊝, first proposed by Tolman. Elaborations on the cone angle concept include mathematical methods for its estimation, estimates based on X-ray structural data, and solid cone angle measures. The ligand repulsive parameter, E R , is based upon molecular mechanics calculations of the structures of Cr(CO) 5 complexes of the various ligands. The ⊝ and E R parameters correlate reasonably well, but significant disparities are found among a large group of phosphorus, arsenic and nitrogen ligands for which both ⊝ and E R , values are available. Consideration of the various approaches to estimating ligand steric requirements indicates that each ligand has a range of steric requirements relative to other ligands, depending on the details of the particular complex or reaction involved. Applications of ligand steric requirements include quantitative linear free energy relationships. Given the relative imprecision with which the steric (and probably also the electronic) parameters can be determined, the use of additional parameters to account for the relative importances of σ and π bonding, or the existence of a steric threshold may not be justified by the number and variety of data available. Nevertheless, despite their lack of high precision, linear free energy relationships can provide important information regarding the electronic and steric demands of the transition state relative to the ground state in chemical reactions.

Synthesis, properties and structures of eight-coordinate zirconium(IV) and hafnium(IV) halide complexes with phosphorus and arsenic ligands.

Eight-coordinate [MX(4)(L-L)(2)] (M = Zr or Hf; X = Cl or Br; L-L = o-C(6)H(4)(PMe(2))(2) or o-C(6)H(4)(AsMe(2))(2)) were made by displacement of Me(2)S from [MX(4)(Me(2)S)(2)] by three equivalents of L-L in CH(2)Cl(2) solution, or from MX(4) and L-L in anhydrous thf solution. The [MI(4)(L-L)(2)] were made directly from reaction of MI(4) with the ligand in CH(2)Cl(2) solution. The very moisture-sensitive complexes were characterised by IR, UV/Vis, and (1)H and (31)P NMR spectroscopy and microanalysis. Crystal structures of [ZrCl(4)[o-C(6)H(4)(AsMe(2))(2)](2)], [ZrBr(4)[-C(6)H(4)(PMe(2))(2)](2)], [ZrI(4)[o-C(6)H(4)(AsMe(2))(2)](2)] and [HfI(4)[o-C(6)H(4)(AsMe(2))(2)](2)] all show distorted dodecahedral structures. Surprisingly, unlike the corresponding Ti(iv) systems, only the eight-coordinate complex was found in each system. In contrast, the ligand o-C(6)H(4)(PPh(2))(2) forms only six-coordinate complexes [MX(4)[-C(6)H(4)(PPh(2))(2)]] which were fully characterised spectroscopically and analytically. Surprisingly the tripodal triarsine, MeC(CH(2)AsMe(2))(3), also produces eight-coordinate [MX(4)[MeC(CH(2)AsMe(2))(3)](2)] in which the triarsines bind as bidentates in a distorted dodecahedral structure. There is no evidence for seven-coordination as found in some thioether systems.

Synthesis, reactivity and structural characterization of some heterometallic complexes containing naked arsenic ligands †

The reactions of [Co2(µ-As2)(CO)6] with [Mo2Cp2(CO)4] (Cp = η5-C5H5) and with [(OC)4CoMCp(CO)3] [M = Mo or W] gave, respectively, the known product [Mo2(µ-As2)Cp2(CO)4] 1 and the new heterobimetallic complexes [(OC)3Co(µ-As2)MCp(CO)2] [M = Mo 2 or W 3]. The mixed-metal complexes have been treated with PPh3 to give the substituted complexes [(Ph3P)(OC)2Co(µ-As2)MCp(CO)2] [M = Mo 4 or W 5]. Complex 2 reacted with [Cr(CO)5]·THF to give [(OC)3Co{µ-As2[Cr(CO)5]2}MoCp(CO)2] 6. Reaction of [MoWCp2(CO)4] with [Co2(µ-As2)(CO)6] does not lead to the complex [MoW(µ-As2)Cp2(CO)4] although this can be obtained by co-thermolysis of [Mo2Cp2(CO)6] and [W2Cp2(CO)6] with grey arsenic which affords three bimetallic products, [MM′(µ-As2)Cp2(CO)4] (M = M′ = Mo 1; M = Mo, M′ = W 7; M = M′ = W), and four trimetallic products, [M2M′(µ3-As)Cp3(CO)6] (M = M′ = Mo; M = Mo, M′ = W 8; M = W, M′ = Mo 9; M = M′ = W). The new heterometallic complexes 2, 3, 5, 6 and 9 have been characterized by X-ray diffraction analyses.

Copolymerization of carbon monoxide and norbornadiene with a palladium catalyst

Carbon monoxide (CO) and norbornadiene (NBD) with Pd(CH 3 CN) 4 (BF 4 ) 2 were copolymerized under various conditions at 50°C. Elemental analysis, infrared spectra, UV, Raman, and NMR spectra showed that the copolymers contained both ketone and unsaturated ring structures. Bidentate nitrogen ligands and phosphorus ligands proved to be more effective at stabilizing catalytic activity than monodentate arsenic ligands or phosphorus ligands. Methanol, protic acid, and an oxidant served as the coinitiator and chain transfer agent, respectively. X-ray diffraction analysis showed the copolymer to be partially crystalline. Thermogravimetric analysis showed that the TG curve for the NBD/CO copolymer has two stages with two maxima peaks at 251 and 470°C. This phenomenon was probably due to increased instability of the copolymers as CO content is increased. Hydrogenation of norbornadiene/CO copolymer with LiAlH 4 and Pd/C in THF yields a hydroxyl-containing polymer and norbornene/CO copolymer, respectively.

A comparison of cis- and trans-cobalt(III) complexes with phosphorus and arsenic ligands; the effect of stereochemistry on redox and spectroscopic properties

The spectroscopic (UV-vis, 1H, 31P and 59Co NMR) properties of cis- and trans- [Co(LL) 2X 2]Y [LL = o-C 6H 4(PMe 2) 2 or o-C 6H 4(AsMe 2) 2; X = Cl or Br, Y = X pr BF 4] and ( cis) [Co{ o-C 6H 4AsMe 2) 3}X 2]X (X = Cl, Br or I) are compared. Cyclic voltammetry has been used to probe the redox chemistries as a function of metal geometry. The structure of [Co{As( o-C 4H 4AsMe 2) 3}Br 2]BF 4 has been determined [CoAs = 2.242(2)−2.363(2), CoBr = 2.394(2), 2.435(2) Å].

The Role of Arsenic-Thiol Interactions in Metalloregulation of the ars Operon

The ars operon of the Escherichia coli plasmid R773 that confers arsenical and antimonial resistance is negatively regulated by the ArsR repressor. ArsR residues Cys-32 and Cys-34 were previously identified as involved in induction by arsenite and antimonite, suggesting coordination between As(III) and the two cysteine thiolates. However, in small molecule thiolate-As(III) complexes, arsenic is frequently three-coordinate. A site-directed mutagenic approach was employed in a search for a third arsenic ligand. ArsR proteins with C32G, C34G, and C32G/C34G substitutions were active repressors, but were not inducible in vivo. In vitro, the altered repressor-ars DNA complexes could not be dissociated by inducers. Alteration of Cys-37 and Ser-43, residues located in or near the putative helix-turn-helix DNA-binding region of the protein, had no effect on the inducibility of the operon. While these results indicated that neither the thiolate of Cys-37 nor the hydroxyl oxygen of Ser-43 is required for induction, they did not eliminate either atom as a potential arsenic ligand. Another approach involved reaction with an alternative inducer, phenylarsine oxide, which can form only two coordinations. Phenylarsine oxide was shown to be as effective as or more effective than arsenite or antimonite in induction in vivo. In vitro, the organic arsenical was more effective than either arsenite or antimonite in dissociating the repressor-promoter complex. Thus, two ArsR-arsenic bonds are sufficient for induction. The interaction of ArsR proteins with As(III) was examined using a phenylarsine oxide affinity resin. ArsR proteins containing any two of the three cysteine residues Cys-32, Cys-34, and Cys-37 bound to the resin. Alteration of any two of the three resulted in loss of binding. Arsenic X-ray absorption spectroscopy of ArsR treated stoichiometrically with arsenite confirmed the average arsenic coordination as AsS3 These results suggest that all three cysteine thiolates are arsenic ligands, but binding to only two, the Cys-32 and Cys-34 thiolates, is required to produce the conformational change that results in release of the repressor from the DNA and induction.

Synthesis and properties of ruthenium and palladium iodide complexes of phosphorus, arsenic and antimony ligands

Iodoruthenium (II) complexes trans-[Ru(L-L)2I2] (L-L=Ph2PCH2CH2PPh2, cis-Ph2PCHCHPPh2, Ph2AsCH2CH2AsPh2, o-C6H4-(AsMe2)2), trans-[Ru(SbPh3)4I2] and [Ru(PPh3)3I2] have been made by reaction of [Ru(H2O)6] [BF4]2 with the ligand and NaI in aqueous ethanol. Oxidation with conc. HNO3-HBF4 yielded trans-[Ru(L-L)2I2]BF4. The complexes were characterised by spectroscopy (IR, UV-Vis, 31P NMR) and cyclic voltammetry, and their properties compared with chloro- and bromo-analogues. Unsuccessful attempts to prepare palladium (IV) iodo complexes [Pd(L-L)2I2][BF4]2 are described. The crystal structures of [Ru(Ph2AsCH2CH2AsPh2)2I2]BF4 Pd∗o-C6H4(PMe2)2∗2Cl2][BF4]2 are reported.