Ar Cl Research Articles

Kinetics and Mechanism of PPh3/Ni-Catalyzed, Zn-Mediated, Aryl Chloride Homocoupling: Antagonistic Effects of ZnCl2/Cl.

The Ni/PPh3-catalyzed homocoupling of aryl chlorides in DMF using Zn as the stochiometric reducing agent is one of a general class of Ni-catalyzed processes, where the mechanism has been a matter of long-standing debate. This study re-evaluates prior conclusions and insights. NMR spectroscopy is used to identify [(PPh3)2NiII(Ar)Cl] as a key intermediate and to explore the indirect roles of using Zn as the reductant. The [ZnCl2] coproduct is responsible for several features, including a sequential transmetalation pathway involving [ArZnCl]. [ZnCl2] also abstracts halide from [(PPh3)2NiCl2] to generate [NiIICl(DMF)5]+[ZnCl3(DMF)]-, and in doing so, affects the NiII + Ni0 ↔ 2 NiI speciation. [ZnCl2] thus acts as an accelerator and inhibitor, resulting in mildly sigmoidal reaction profiles. When the [ZnCl2] concentration becomes too high or the phosphine ligand concentration too low, catalysis stalls. Turnover is restored by the addition of further phosphine ligand, or chloride ion. In the presence of an exogenous chloride ion, turnover is rapid, again proceeding via [(PPh3)2NiII(Ar)Cl] but via dinuclear metathesis. The generation of [ZnCl3(DMF)]- results in mutually antagonistic effects between [ZnCl2] and [Cl]- such that turnover proceeds via one mechanism or the other, depending on which species is in excess. The intermediacy of [ArZnCl] suggests a solution to the long-standing anomaly that many other reductants were found to be much less effective than Zn in inducing turnover of Ni/PPh3 catalyzed aryl chloride homocoupling in DMF. The use of DMAc as a solvent in place of DMF inhibits stalling through the steric inhibition of mixed metalate generation.

Palladium-catalyzed selective Buchwald–Hartwig C–N coupling of chloroaryl triflates with amines

The chemoselective Buchwald–Hartwig amination developed here showed that the reactivity of the Ar–Cl bond is higher than that of the Ar–OTf bond. Catalyzed by PdCl2/P(t-Bu)3, the reaction selectively aminated the Ar–Cl bond in an aryl system containing both Ar–Cl and Ar–OTf with moderate yield and excellent chemoselectivity, and the significant effect of additives was also found. With the aid of this methodology, we also efficiently synthesized a bicarbazole scaffold that can serve as a valuable precursor for alkaloids such as murrastifoline A&B.

Shake-Off Process in Non-Sequential Single-Photon Double Ionization of Closed-Shell Atomic Targets

Amusia and Kheifets in 1984 introduced a Green’s function formalism to describe the effect of many-electron correlation on the ionization spectra of atoms. Here, we exploit this formalism to model the shake-off (SO) process, leading to the non-sequential single-photon two-electron ionization (double photoionization—DPI) of closed-shell atomic targets. We separate the SO process from another knock-out (KO) mechanism of DPI and show the SO prevalence away from the DPI threshold. We use this kinematic regime to validate our model by making a comparison with more elaborate techniques, such as convergent and time-dependent close coupling. We also use our model to evaluate the attosecond time delay associated with the SO process. Typically, the SO is very fast, taking only a few attoseconds to complete. However, it can take much longer in the DPI of strongly correlated systems, such as the H− ion as well as the subvalent shells of the Ar and Xe atoms and Cl− ion.

Palladium-catalyzed chemoselective direct α-arylation of carbonyl compounds with chloroaryl triflates at the C-Cl site.

This study described palladium-catalyzed chemoselective direct α-arylation of carbonyl compounds with chloroaryl triflates in the Ar–Cl bond. The Pd/SelectPhos system showed excellent chemoselectivity toward the Ar–Cl bond in the presence of the Ar–OTf bond with a broad substrate scope and excellent product yields. The electronic and steric hindrance offered by the –PR2 group of the ligand with the C2-alkyl group was found to be the key factor affecting the reactivity and chemoselectivity of the α-arylation reaction. The chemodivergent approach was also successfully employed in the synthesis of flurbiprofen and its derivatives (e.g., –OMe and –F).

Exploring benzylic gem-C(sp3)-boron-silicon and boron-tin centers as a synthetic platform.

A stepwise build-up of multi-substituted Csp3 carbon centers is an attractive, conceptually simple, but often synthetically challenging type of disconnection. To this end, this report describes how gem-α,α-dimetalloid-substituted benzylic reagents bearing boron/silicon or boron/tin substituent sets are an excellent stepping stone towards diverse substitution patterns. These gem-dimetalloids were readily accessed, either by known carbenoid insertion into C–B bonds or by the newly developed scalable deprotonation/metallation approach. Highly chemoselective transformations of either the C–Si (or C–Sn) or the C–B bonds in the newly formed gem-Csp3 centers have been achieved through a set of approaches, with a particular focus on exploiting the synthetically versatile polarity reversal in organometalloids by λ3-aryliodanes. Of particular note is the metal-free arylation of the C–Si (or C–Sn) bonds in such gem-dimetalloids via the iodane-guided C–H coupling approach. DFT calculations show that this transfer of the (α-Bpin)benzyl group proceeds via unusual [5,5]-sigmatropic rearrangement and is driven by the high-energy iodine(iii) center. As a complementary tool, the gem-dimetalloid C–B bond is shown to undergo a potent and chemoselective Suzuki–Miyaura arylation with diverse Ar–Cl, thanks to the development of the reactive gem-α,α-silyl/BF3K building blocks.

Nondipole Effects in Time Delay of Photoelectrons from Atoms, Negative Ions, and Endohedrals

In this Letter, we investigate the non-dipole effects in time delay of photoelectrons emitted by multi-electron atoms, negative ions, and respective endohedrals. We present the necessary general formulas in the frame of the random phase approximation with exchange (RPAE) applied to atoms, negative ions, and properly adjusted to endohedrals. We concentrate on low photon energy region, where non-dipole effects are very small in the cross-sections but become observable in angular distributions. We not only derive the formulas for non-dipole effects in time delay, but perform corresponding numeric calculations. We demonstrate how the non-dipole corrections can be isolated in experiment. Concrete calculations are performed for noble gas atoms Ar and Xe, isoelectronic to them negative ions Cl- and I- and endohedrals Ar(Cl-)C60 and Xe(I-)@C60. We found that the forward-backward photoelectron time delay differences give direct information on non-dipole effects. They proved to be quite measurable and prominently affected by the presence of the fullerenes shell.

Small Phosphine Ligands Enable Selective Oxidative Addition of Ar-O over Ar-Cl Bonds at Nickel(0).

Current methods for Suzuki-Miyaura couplings of nontriflate phenol derivatives are limited by their intolerance of halides including aryl chlorides. This is because Ni(0) and Pd(0) often undergo oxidative addition of organohalides at a similar or faster rate than most Ar-O bonds. DFT and stoichiometric oxidative addition studies demonstrate that small phosphines, in particular PMe3, are unique in promoting preferential reaction of Ni(0) with aryl tosylates and other C-O bonds in the presence of aryl chlorides. This selectivity was exploited in the first Ni-catalyzed C-O-selective Suzuki-Miyaura coupling of chlorinated phenol derivatives where the oxygen-containing leaving group is not a fluorinated sulfonate such as triflate. Computational studies suggest that the origin of divergent selectivity between PMe3 and other phosphines differs from prior examples of ligand-controlled chemodivergent cross-couplings. PMe3 effects selective reaction at tosylate due to both electronic and steric factors. A close interaction between nickel and a sulfonyl oxygen of tosylate during oxidative addition is critical to the observed selectivity.

Triazolyl RuII, RhIII, OsII, and IrIII Complexes as Potential Anticancer Agents: Synthesis, Structure Elucidation, Cytotoxicity, and DNA Model Interaction Studies

Novel conjugated ruthenium(II), rhodium(III), and iridium(III) organometallic complexes of triazoles 1 and 2 synthesized and evaluated for anticancer activity against cervical (HeLa), kidney (HEK293), nonsmall lung cancer (A549), and leukemia (MT4) cancer cell lines are reported herein. The complexes are κ2-N,C coordinated and have the formula [ML(Ar)Cl] (where L is 1-benzyl-4-phenyl-1H-1,2,3-triazole for 1 and 1-benzyl-4-hydroxymethyl-1H-1,2,3-triazole for 2, Ar is p-cymene for RuII and OsII and Cp* for RhIII and IrIII, and M is metal). NMR studies, including HMBC and NOESY, were employed to unambiguously elucidate their structures and provide their conformational information in solution. Single-crystal X-ray diffraction data have been used to establish the solid-state structures of selected complexes, which further confirm the structural elucidation by NMR. Dynamic NMR studies, such as differential transferred NOE, have been employed to distinguish between isomers 1a_I and 1a_II of ruthenium(II) complexes of triazole 1. The rhodium(III) (1b) and iridium(III) (1c) complexes exhibited good cytotoxic activities (CC50 = 4–6 μM) comparable to that of the drug auranofin against lung cancer A549 cell lines (CC50 = 4.69 μM). While triazole 1 based ruthenium(II) (1a) and osmium(II) (1d) complexes displayed modest anticancer activities against HeLa and HEK293 cell lines, the analogous rhodium(III) and iridium(III) complexes exhibited good potential (CC50 = 9–54 μM versus auranofin (3–9 μM)) against these cancer cell lines. Insightful NMR studies on the interaction between the DNA model guanosine 5′-GMP and the complexes 1b,c reveal a possible mode of action of the aquated complexes involving carbenylation with DNA bases or purines through the triazolyl proton H-5. From the findings, these complexes could possibly confer their cytotoxic activities through intercalation with the DNA of pathological cells. Therefore, carbenylation of the triazolylrhodium(III) and iridium(III) complexes by DNA guanosine 5′-GMP is proposed as a novel mode of DNA intercalation of these complexes in cancer cells.

Suzuki–Miyaura reaction by heterogeneously supported Pd nanoparticles on thio-modified multi walled carbon nanotubes as efficient nanocatalyst

The palladium (Pd) supported on thio-modified multi walled carbon nanotubes (MWCNTs/CC-SH/Pd) was utilized as a useful and reusable nanocatalyst in Suzuki–Miyaura coupling reactions. The catalyst was really efficient for the Suzuki–Miyaura reaction of aryl halides (Ar–I, Ar–Br, Ar–Cl) with phenylboronic acid and conversion was good in most cases. The aryl iodides and aryl bromides reactions take place at room temperature, while reaction of aryl chlorides occurs at temperature of 80 °C. The products yields ranged between70% and 96%. The catalyst indicated excellent constancy and could be recycled and reused up to four cycles with no considerable change in its catalytic behavior.

Catalyst-Directed Chemoselective Double Amination of Bromo-chloro(hetero)arenes: A Synthetic Route toward Advanced Amino-aniline Intermediates

A chemoselective sequential one-pot coupling protocol was developed for preparing several amino-anilines in high yield as building blocks for active pharmaceutical ingredients (APIs). Site (Cl vs Br on electrophile) and nucleophile (amine vs imine) selectivity is dictated by the catalyst employed. A Pd-crotyl (t-BuXPhos) precatalyst selectively coupled the Ar-Br of the polyhaloarene with benzophenone imine, even in the presence of a secondary amine, while Pd-based RuPhos or (BINAP)Pd(allyl)Cl coupled the Ar-Cl site with secondary amines.

Ruthenium(II) and Ruthenium(III) Complexes of p-Benziporphyrin: Merging Equatorial and Axial Organometallic Coordination.

A diamagnetic ruthenium(II) complex of 5,10,15,20-tetraphenyl-p-benziporphyrin [RuII(p-BzP)(CO)Cl] was obtained via the insertion of ruthenium into p-benziporphyrin using triruthenium(0) dodecacarbonyl [Ru3(CO)12] as the metal source. The procedure applying dichloro(cycloocta-1,5-diene)ruthenium(II) (polymer, [Ru(COD)Cl2]n) afforded the paramagnetic six-coordinate ruthenium(III) p-benziporphyrin [RuIII(p-BzP)Cl2]. As shown by X-ray crystallography, the p-phenylene ring in both complexes is sharply tilted out of the N3 plane, as reflected by the respective N3 (pyrrole)-C6 (p-phenylene) dihedral angle [RuII(p-BzP)(CO)Cl, 52.5°; RuIII(p-BzP)Cl2, 53.7°]. p-Phenylene is bound to the ruthenium cation in an η2 fashion, revealing the shortest ever Ru-C distance in the series of p-benziporphyrin complexes [RuII(p-BzP)(CO)Cl, 2.275(2) Å; RuIII(p-BzP)Cl2, 2.324(5) Å]. The reaction of RuII(p-BzP)(CO)Cl with ArMgCl or AlkMgCl results in the formation of diamagnetic six-coordinate ruthenium(II) p-benziporphyrin complexes containing the apically coordinated σ-alkyl or σ-aryl ligands, where the metal ion simultaneously coordinates to three carbon centers respectively accommodating η2 (phenylene) and σ (aryl and alkyl) modes. Reactions of σ-aryl (alkyl) carbanions with paramagnetic RuIII(p-BzP)Cl2 have been followed by 1H NMR spectroscopy. The procedure afforded the six-coordinate paramagnetic ruthenium(III) p-benziporphyrin [RuIII(p-BzP)(Ph)Cl], which binds one σ-aryl ligand, as reflected by the characteristic 1H NMR spectra spread within the +120 to -120 ppm range. Both paramagnetic complexes RuIII(p-BzP)(Ph)Cl and RuIII(p-BzP)(p-Tol)Cl are formed as a mixture of two stereoisomers differentiated by two nonequivalent locations of σ-aryl with respect to the puckered macrocyclic ring. The paramagnetic shifts of σ-aryls are indicative of π-spin delocalization patterns. Analysis of the contact shifts and parallel density functional theory calculations of the spin density distribution in RuIII(p-BzP)Cl2, RuIII(p-BzP)(Ar)Cl, and RuIII(p-BzP)(Alk)Cl reflect the features of the dxy2(dxzdyz)3 electronic ground state.

CuI heterogenized on thiosemicarbazide modified‐multi walled carbon nanotubes (thiosemicarbazide‐MWCNTs‐CuI): Novel heterogeneous and reusable nanocatalyst in the C‐N Ullmann coupling reactions

Herein we described the synthesis of novel thiosemicarbazide‐MWCNTs‐CuI nanocatalyst by covalent grafting of thiosemicarbazide on carbon nanotubes surface and subsequent coordination with CuI catalyst. The formation of nanocatalyst was analyzed by Raman spectroscopy, energy dispersive spectroscopy (EDS), wavelength‐dispersive X‐ray spectroscopy (WDX) and ICP analysis. The morphology of the nanocatalyst was characterized using scanning and transmission electron microscopes (SEM and TEM). Additionally, the (thiosemicarbazide‐MWCNTs‐CuI) nanocatalyst was successfully employed in the N‐arylation of indole, amines and imidazoles through intermolecular C(aryl)‐N bond formation from the corresponding aryl halides (Ar–I, Ar–Br, Ar–Cl) with amines through Ullmann‐type coupling reactions. Interestingly, the novel catalyst could be recovered and recycled five times.

ChemInform Abstract: Pd Immobilized on Modified Magnetic Fe3O4 Nanoparticles: Magnetically Recoverable and Reusable Pd Nanocatalyst for Suzuki—Miyaura Coupling Reactions and Ullmann‐Type N‐Arylation of Indoles.

The Pd supported on amidoxime (AO)-functionalized Fe3O4 (Fe3O4/AO/Pd) hybrid material was used as an effective and recyclable nanocatalyst in Suzuki-Miyaura coupling reactions. The catalyst was very effective for the Suzuki-Miyaura reaction of aryl halides (Ar–I, Ar–Br, Ar–Cl) with phenylboronic acid and conversion was excellent in most cases. The yields of the products were in the range from 7–98%. The catalyst showed good stability and could be recovered and reused for six reaction cycles without a significant loss in its catalytic activity. Also, a wide range of N-arylated indoles are selectively synthesized through intermolecular C(aryl)–N bond formation from the corresponding aryl iodides and indoles through Ullmann-type coupling reactions in the presence of the prepared catalyst.

Pd immobilized on modified magnetic Fe3O4 nanoparticles: Magnetically recoverable and reusable Pd nanocatalyst for Suzuki-Miyaura coupling reactions and Ullmann-type N-arylation of indoles

The Pd supported on amidoxime (AO)-functionalized Fe3O4 (Fe3O4/AO/Pd) hybrid material was used as an effective and recyclable nanocatalyst in Suzuki-Miyaura coupling reactions. The catalyst was very effective for the Suzuki-Miyaura reaction of aryl halides (Ar–I, Ar–Br, Ar–Cl) with phenylboronic acid and conversion was excellent in most cases. The yields of the products were in the range from 7–98%. The catalyst showed good stability and could be recovered and reused for six reaction cycles without a significant loss in its catalytic activity. Also, a wide range of N-arylated indoles are selectively synthesized through intermolecular C(aryl)–N bond formation from the corresponding aryl iodides and indoles through Ullmann-type coupling reactions in the presence of the prepared catalyst. Pd supported on amidoxime (AO)-functionalized Fe3O4NPs (Fe3O4/AO/Pd) showed high catalytic activity in Suzuki and Ullmann coupling reaction.

Mor-Dalphos-Pd (II) oxidative addition complexes and related NH3 adducts: Insights into bonding and nonbonding interactions

The stabilizing effects and bonding properties of the Pd metallic center in [(κ2-P,N-Mor-Dalphos)Pd(Ar)Cl] complexes and related NH3 adducts were investigated by density functional theory (DFT), the intrinsic bond orbital (IBO) approach and the Su–Li energy decomposition method (Su–Li EDA). The IBO analysis showed that the P atom from the P,N-Mor-Dalphos structure has stabilizing contributions in all Pd-Cl and Pd-NH3 bonds in the complexes. According to the Su–Li energy decomposition analysis, the main energy that drives the interaction between the [Mor-Dalphos-Pd(Ar)] moiety and Cl− is the electrostatic term, therefore, the electrostatic energy interaction between them might be an important factor for taking into account when designing other [Mor-Dalphos-Pd(Ar)]-Cl precatalysts.

A Well-Defined Aluminum-Based Lewis Acid as an Effective Catalyst for Diels-Alder Transformations.

A catalytically active aluminum-based system for Diels-Alder transformations is reported. The system was generated by mixing a β-diketiminate-stabilized aluminum bistriflate compound with Na[BAr(Cl) 4 (Ar(Cl) =3,5-Cl2 C6 H3). Solid-state analysis of the catalytic system reveals a unique structure incorporating a two-dimensional coordination polymer. According to the experimental results obtained from several Diels-Alder transformations, the aluminum-based system appears to be a more practical and more robust alternative to the recently reported compounds based on carbon and silicon cations.

Aryl carbon–chlorine (Ar–Cl) and aryl carbon–fluorine (Ar–F) bond cleavages by rhodium porphyrins

Aryl carbon–chlorine (Ar–Cl) bond cleavage has been achieved with rhodium(III) tetrakis-4-tolylporphyrin chloride (Rh(ttp)Cl) to give Rh(ttp)Ar. For 4-chlorofluorobenzene, the aryl carbon–fluorine (Ar–F) bond cleavage competes with the Ar–Cl bond cleavage. Mechanistic investigations show that the Ar–Cl bond cleavage goes through metalloradical ipso-substitution mechanism, while the Ar–F bond cleavage goes through nucleophilic aromatic substitution. The selectivity of the Ar–F or Ar–Cl bond cleavage can be controlled by tuning the temperature and substrate concentration.

A highly stable and efficient magnetically recoverable and reusable Pd nanocatalyst in aqueous media heterogeneously catalysed Suzuki C–C cross‐coupling reactions

Surface modification of Fe3O4 nanoparticles with triethoxyethylcyanide groups was used for the immobilization of palladium nanoparticles to produce Fe3O4/Ethyl‐CN/Pd. The catalyst was characterized using Fourier transform infrared, wavelength‐dispersive X‐ray, energy‐dispersive X‐ray and X‐ray photoelectron spectroscopies, field‐emission scanning electron and transmission electron microscopies, and X‐ray diffraction, vibrating sample magnetometry and inductively coupled plasma analyses. In this fabrication, cyano groups played an important role as a capping agent. The catalytic behaviour of Fe3O4/Ethyl‐CN/Pd nanoparticles was measured in the Suzuki cross‐coupling reaction of various aryl halides (ArI, ArBr, ArCl) with phenylboronic acid in aqueous phase at room temperature. Interestingly, the novel catalyst could be recovered in a facile manner from the reaction mixture by applying an external magnet device and recycled seven times without any significant loss in activity. Copyright © 2015 John Wiley & Sons, Ltd.

Platinum carbon bond formation via Cu(I) catalyzed Stille-type transmetallation: reaction scope and spectroscopic study of platinum-arylene complexes.

The preparation of Pt(ii) complexes of the type trans-L2Pt(Ar)Cl, L2Pt(Ar)2, and L2Pt(Ar)(Ar') (L = PBu3, Ar = arylene) by CuI catalyzed reaction of cis-(PBu3)2PtCl2 with aryl-stannanes is reported. The reactions proceed at 25-60 °C in moderate to good yields. The reaction is demonstrated to occur with phenyl- and 2-thienyl-stannanes that include a variety of functionality, and all of the resulting Pt-aryl complexes were fully characterized by (1)H, (13)C, and (31)PNMR spectroscopy, as well as mass spectroscopy. Photophysical properties of the L2Pt(Ar)2, and L2Pt(Ar)(Ar') complexes were measured, including steady-state absorption, photoluminescence, and photoluminescence quantum yields, in order to understand how attachment of the platinum metal influences the excited state properties of the arylene ligands. This work affirms that CuI catalyzed coupling between Ar-SnR3 and L2PtCl2 is a useful platinum-carbon bond formation reaction.

Silver(i) and thallium(i) cations as unsupported bridges between two metal bases

Stirring Lewis-basic transition metal complexes with the salts M[BAr(Cl)4] (M = Ag, Tl; Ar(Cl) = 3,5-C6H3Cl2) resulted in the formation of diplatinum complexes [{(Cy3P)2Pt}2(μ-Ag)][BAr(Cl)4] (3) and [{(Cy3P)2Pt}2(μ-Tl)][BAr(Cl)4] (4) and the diiron compound [{(OC)3(Me3P)2Fe}2(μ-Ag)] (5) featuring bridging, unsupported metal cations. Their properties were investigated by multinuclear NMR spectroscopy, as well as X-ray diffraction and infrared measurements.