AgOTf Research Articles

Silver triflate/p-TSA co-catalysed synthesis of 3-substituted isocoumarins from 2-alkynylbenzoates.

In this paper, we describe the silver triflate/p-toluenesulfonic acid co-catalysed synthesis of seventeen isocoumarins and two thieno[2,3-c]pyran-7-ones starting from 2-alkynylbenzoates and 3-alkynylthiophene-2-carboxylates, respectively. The reaction proceeds with absolute regioselectivity under mild reaction conditions and low catalyst loading, to afford the desired products in good to excellent yields. A conceivable reaction mechanism is proposed and supported by isotope-exchange tests, 1H NMR studies and ad hoc experiments.

Cobalt complexes with hemilabile o-iminobenzoquinonate ligands: a novel example of redox-induced electron transfer.

The tetracoordinated square-planar CoIII complex (imSQC(O)Ph)CoIII(APC(O)Ph) (1) bearing a radical anion and the closed-shell o-amidophenolate forms of the functionalized o-aminophenol H2LC(O)Ph were synthesized. The intermediate spin state (SCo = 1) CoIII center was found for compound 1. The cyclic voltammogram of derivative 1 contains two oxidative processes and one reductive redox process as well as an additional multi-electron wave at high negative potentials above -2 V, which can involve both the ligand and metal center. One-electron oxidation of 1 by silver triflate produces the [(imSQC(O)Ph)CoII(imQC(O)Ph)]OTf·2toluene (2) derivative with the trigonal prismatic coordination environment of the metal arising from the additional coordination of -C(O)Ph hemilabile groups. This is a first example of a trigonal prismatic coordination polyhedron in cobalt-based complexes featuring o-iminobenzoquinone ligands. The trigonal prismatic geometry achieved by the unique flexibility of the ligand allows metal-to-ligand redox-induced electron transfer (RIET). Chemical oxidation of complex 1 promotes the reduction of CoIII to CoII in compound 2 due to the redox-active nature of o-iminobenzoquinonate ligands. Remarkably, this is the first example of RIET in cobalt-based derivatives with this type of ligand. The oxidative states of the ligands and cobalt ion in both complexes were unequivocally established according to the X-ray data collection by using the utility of "metric oxidation state" (MOS). The spin states of the metal centers were unambiguously determined by density functional theory. The strong antiferromagnetic exchange via metal-ligand interactions is dominant in compounds 1 and 2, giving the doublet (S = 1/2) and triplet (S = 1) ground spin state, respectively.

Cycloheptatrienyl Cyclopentadienyl Titanium Phosphane Ligands in Palladium‐Catalyzed Suzuki–Miyaura Cross‐Coupling Reactions

The reaction of the cycloheptatrienyl cyclopentadienyl (Cht‐Cp) titanium sandwich complexes [(η7‐C7H7)Ti(η5‐C5R5)] (R = H, Me) with nBuLi followed by treatment with the chlorophosphanes ClPR′2 (R′ = Cy, tBu) afforded the Cht‐substituted phosphanes [(η7‐C7H6PR′2)Ti(η5‐C5R5)] (R = H, Me; R′ = Cy, tBu). Together with their previously reported Cp‐substituted analogues [(η7‐C7H7)Ti(η5‐C5H4PR2)] (R = Cy, tBu), these complexes were employed as ancillary phosphane ligands in palladium‐catalyzed Suzuki–Miyaura coupling between sterically encumbered aryl bromides and aryl boronic acids. The unusually short reaction times indicated rapid generation of catalytically active Pd0 species, and the reaction of Pd(OAc)2 with an excess of the phosphorus ligands afforded linear bis‐phosphane palladium(0) complexes. These reactions gave no indication of phosphane oxide formation, and it is supposed that the Cht‐Cp titanium sandwich moiety serves as an integrated reducing agent. Accordingly, the reaction of [(η7‐C7H7)Ti(η5‐C5M5)] with Pd(OAc)2 or Ag(OAc) resulted in a three‐electron redox reaction with formation of the half‐sandwich complex [(η5‐C5Me5)Ti(OAc)3] together with 7,7′‐bi‐1,3,5‐cycloheptatriene (ditropyl) and elemental Pd or Ag metal. On reaction with silver(I) trifluoromethanesulfonate, a four‐electron redox process furnished the tropylium titanate complex [C7H7][(η5‐C5Me5)Ti(OTf)4].

Inverting Steric Effects: Using "Attractive" Noncovalent Interactions To Direct Silver-Catalyzed Nitrene Transfer.

Nitrene transfer (NT) reactions represent powerful and direct methods to convert C-H bonds into amine groups that are prevalent in many commodity chemicals and pharmaceuticals. The importance of the C-N bond has stimulated the development of numerous transition-metal complexes to effect chemo-, regio-, and diastereoselective NT. An ongoing challenge is to understand how subtle interactions between catalyst and substrate influence the site-selectivity of the C-H amination event. In this work, we explore the underlying reasons why Ag(tpa)OTf (tpa = tris(pyridylmethyl)amine) prefers to activate α-conjugated C-H bonds over 3° alkyl C(sp3)-H bonds and apply these insights to reaction optimization and catalyst design. Experimental results suggest possible roles of noncovalent interactions (NCIs) in directing the NT; computational studies support the involvement of π···π and Ag···π interactions between catalyst and substrate, primarily by lowering the energy of the directed transition state and reaction conformers. A simple Hess's law relationship can be employed to predict selectivities for new substrates containing competing NCIs. The insights presented herein are poised to inspire the design of other catalyst-controlled C-H functionalization reactions.

Synthesis of Disaccharide Nucleosides Utilizing the Temporary Protection of the 2',3'-cis-Diol of Ribonucleosides by a Boronic Ester.

Disaccharide nucleosides are an important class of natural compounds that have a variety of biological activities. In this study, we report on the synthesis of disaccharide nucleosides utilizing the temporary protection of the 2′,3′-cis-diol of ribonucleosides, such as adenosine, guanosine, uridine, 5-metyluridine, 5-fluorouridine and cytidine, by a boronic ester. The temporary protection of the above ribonucleosides permits the regioselective O-glycosylation of the 5’-hydroxyl group with thioglycosides using a p-toluenesulfenyl chloride (p-TolSCl)/silver triflate (AgOTf) promoter system to afford the corresponding disaccharide nucleosides in fairly good chemical yields. The formation of a boronic ester prepared from uridine and 4-(trifluoromethyl)phenylboronic acid was examined by 1H, 11B and 19F NMR spectroscopy.

Baylis–Hillman Reaction: In Situ Generated Isoquinolinium Species as Excellent Electrophiles for Coupling with Alkyl Acrylates and Acrylonitrile

Isoquinolinium species, generated in situ from 2‐alkynylbenzaldehydes, arylamines, and silver trifluoromethanesulfonate, were successfully employed as excellent electrophiles for Baylis–Hillman coupling with alkyl acrylates (or acrylonitrile) under the influence of 1,4‐diazabicyclo[2.2.2]octane to provide 1,2,3‐trisubstituted dihydroisoquinoline derivatives in high yields.

Reactivity of Silanes with (tBu PONOP)Ruthenium Dichloride: Facile Synthesis of Chloro-Silyl Ruthenium Compounds and Formic Acid Decomposition.

The coordination of tBu PONOP (tBu PONOP=2,6-bis(ditert-butylphosphinito)pyridine) to different ruthenium starting materials, to generate (tBu PONOP)RuCl2 , was investigated. The resultant (tBu PONOP)RuCl2 reactivity with three different silanes was then investigated and contrasted dramatically with the reactivity of (iPr PONOP)RuCl2 (DMSO) (iPr PONOP=2,6-bis(diisopropylphosphinito)pyridine) with the same silanes. The 16-electron species (tBu PONOP)Ru(H)Cl was produced from the reaction of triethylsilane with (tBu PONOP)RuCl2 . Reactions of (tBu PONOP)RuCl2 with both phenylsilane or diphenylsilane afforded the 16-electron hydrido-silyl species (tBu PONOP)Ru(H)(PhSiCl2 ) and (tBu PONOP)Ru(H)(Ph2 SiCl), respectively. Reactions of all three of these complexes with silver triflate afforded the simple salt metathesis products of (tBu PONOP)Ru(H)(OTf), (tBu PONOP)Ru(H)(PhSiCl(OTf)), and (tBu PONOP)Ru(H)(Ph2 Si(OTf)). Formic acid dehydrogenation was performed in the presence of triethylamine (TEA), and each species proved competent for gas-pressure generation of CO2 and H2 . The hydride species (tBu PONOP)Ru(H)Cl, (tBu PONOP)Ru(H)(OTf), and (tBu PONOP)Ru(H)(PhSiCl2 ) exhibited faster catalytic activity than the other compounds tested.

Kinetics and photophysical behavior of the P,N-ReI complex [P,N-{(C6H5)2(C5H4N)P}Re(CO)3(O-O3SCF3)]: A directly coordinated (and labile) triflate

The reaction of [P,N-{(C6H5)2(C5H4N)P}Re(CO)3Br] (RePNBr) with silver triflate leads to the complex [P,N-{(C6H5)2(C5H4N)P}Re(CO)3(O-CF3SO3)] (RePNTfO) with moderate yield. This new P,N-ReI triflate compound contains the anion directly coordinated to the metal, completing an octahedral environment. RePNTfO displays in dichloromethane (DCM) solution an irreversible oxidation about +1.35V and three irreversible reduction processes at −1.38V, −2.03V and −2.30V. Oxidation has been attributed to the ReI/ReII couple, while the reduction corresponds to PN-ligand processes, which is consistent with those computed by means of DFT. The absorption spectrum of RePNTfO in DCM displays a maximum at 295nm (ε=7.1×103M−1cm−1) and a shoulder around 350nm (ε=1.8×103M−1cm−1), which have been assigned to intraligand (π→π∗) and metal to ligand charge transfer (MLCT, dπ→π∗) transitions with the help of DFT/TDDFT. Excitation of RePNTfO in DCM at 350nm leads to an emission spectrum centered at 535nm. The analysis of the variation of the absorption and emission spectra in coordinating solvents compared to non-coordinating DCM, DFT/TDDFT calculations modeling and ELF analysis suggests for coordinating solvents that triflate ligand is replaced in the coordination sphere of ReI in solution. Kinetics of the exchange of triflate by bromide measured in DCM at different temperatures allowed to estimate the Eyring parameters: ΔH≠, ΔS≠ and ΔG≠, 50.8kJmol−1, −109.6JK−1mol−1 and 83.5kJmol−1 respectively. The high negative entropy is indicative of a compact transition state, compatible with an associative mechanism, Ia, for the exchange.

Coordination of Piano‐Stool Complexes to a Hydrogen‐Bonded Rosette‐Type Assembly

A new melamine (ME)–barbituric acid (BA) rosette‐type system has been prepared and characterized. The introduction of a pyridyl group on the barbituric acid moiety allows coordination of metal ions at the periphery of the ME3·BA3 rosette. Reactions of 1.5 equiv. of [Ru(cym)Cl2]2 (cym = p‐cymene) or [M(Cp*)Cl2]2 (Cp* = pentamethylcyclopentadienyl; M = Rh, Ir) with the rosette afford the corresponding ME3·[BA{Ru(cym)Cl2}]3 and ME3·[BA{M(Cp*)Cl2}]3 assemblies. The neutral metal‐containing rosettes ME3·[BA{Ru(cym)Cl2}]3 and ME3·[BA{Rh(Cp*)Cl2}]3 can also be obtained by adding the mononuclear complexes [BA{Ru(cym)Cl2}] and [BA{Rh(Cp*)Cl2}] to N,N′‐bis(4‐tert‐butylphenyl)melamine in chloroform. In addition, the triphenylphosphine derivatives [Ru(cym)(PPh3)Cl2] or [M(Cp*)(PPh3)Cl2] react with ME3·BA3 in the presence of silver triflate to generate the ionic rosette‐type assemblies ME3·[BA{Ru(cym)(PPh3)Cl}+]3·3CF3SO3– and ME3·[BA{M(Cp*)(PPh3)Cl}+]3·3CF3SO3–, respectively.

Synthesis of 2,3-Disubstituted Quinazolinone Derivatives Using Silver Triflate as a Efficient Catalyst at Room Temperature

Synthesis of 2,3-Disubstituted Quinazolinone Derivatives Using Silver Triflate as a Efficient Catalyst at Room Temperature

Coinage Metal Complexes of Phosphonite Analogues of 2‐Diphenylphosphino‐1,1′‐binaphthyl (H‐MOP) and 2‐Diphenylphosphino‐2′‐methoxy‐1,1′‐binaphthyl (MeO‐MOP)

Chiral MOP‐phosphonites containing two phenoxy substituents (S)‐1a/(R)‐1b, a biphenoxy group (S)‐2a/(R)‐2b or the 3,3′‐dimethylbiphenoxy group (S)‐3a/(R)‐3b, have been coordinated to the coinage metals. Six [Au(LP)Cl] complexes have been prepared and five were characterised by X‐ray crystallography, as well as complex [Au{(S)‐3a}2]SbF6. Six [Ag(LP)OTf] complexes were synthesised, studied by VT NMR spectroscopy and, in the case of [Ag{(R)‐2b}OTf], by X‐ray crystallography. Six [Cu(LP)(MeCN)2]PF6 complexes were prepared, and [Cu{(R)‐3b}(MeCN)2]PF6 was characterised crystallographically, as was the decomposition product [Cu{(S)‐1a}(O2PF2)]2.

Optical and Electrical Characteristics of Silver Ion Conducting Nanocomposite Solid Polymer Electrolytes Based on Chitosan

Optical and electrical properties of nanocomposite solid polymer electrolytes based on chitosan have been investigated. Incorporation of alumina nanoparticles into the chitosan:silver triflate (AgTf) system broadened the surface plasmon resonance peaks of the silver nanoparticles and shifted the absorption edge to lower photon energy. A clear decrease of the optical bandgap in nanocomposite samples containing alumina nanoparticles was observed. The variation of the direct-current (DC) conductivity and dielectric constant followed the same trend with alumina concentration. The DC conductivity increased by two orders of magnitude, which can be attributed to hindrance of silver ion reduction. Transmission electron microscopy was used to interpret the space-charge and blocking effects of alumina nanoparticles on the DC conductivity and dielectric constant. The ion conduction mechanism was interpreted based on the dependences of the electrical and dielectric parameters. The dependence of the DC conductivity on the dielectric constant is explained empirically. Relaxation processes associated with conductivity and viscoelasticity were distinguished based on the incomplete semicircular arcs in plots of the real and imaginary parts of the electric modulus.

Synthesis, structure, and properties of a new multiredox-active Sn(IV) complex based on 3,6-di-tert-butyl-o-benzoquinone and ferrocenylaldimine phenol

A new mixed-ligand tin(IV) complex 2 derived from 3,6-di-tert-butyl-o-benzoquinone and ferrocenylaldimine phenol 1 has been prepared and characterized by different physicochemical methods (IR, 1HNMR, and 119Sn NMR spectroscopies). Electrochemical transformations of complex 2 have been studied by cyclic voltammetry. Catecholate and ferrocenyl groups have been found to take part in the redox transformations. Chemical oxidation of complex 2 with silver triflate in a dichloromethane solution has been studied. Formation of monocationic complex 2 + has been detected by EPR spectroscopy. The catecholate ligand has been found to be the primary redox center subjected to oxidation.

Metal‐Catalyzed Synthesis of Functionalized 1,2,4‐Oxadiazoles from Silyl Nitronates and Nitriles

AbstractThe metal‐catalyzed cycloaddition of silyl nitronates and nitriles leading to 1,2,4‐oxadiazoles is described. Silver(I) triflate (AgOTf) and and ytterbium(III) triflate [Yb(OTf)3] are suitable catalysts. A variety of functional groups is tolerated in the nitrile. The reaction works well for alkenyl and aryl silyl nitronates while the use of alkyl silyl nitronates is less efficient. Mechanistic studies are in favour of an elimination of tert‐butyl(dimethyl)silanol (TBSOH) after the cycloaddition step. The new approach has also been applied for the synthesis of the drug ataluren.magnified image

Synthesis of Pentafluoroethyl Ethers by Silver-Mediated Oxidative Pentafluoroethylation of Alcohols and Phenols.

A silver triflate (AgOTf)-mediated oxidative pentafluoroethylation of alcohols and phenols with nucleophilic (pentafluoroethyl)trimethylsilane (TMSCF2CF3) using selectfluor as oxidant under mild reaction conditions was developed. This oxidative coupling protocol utilizes broadly available substrates and easily handled reagents to afford various pentafluoroethyl ethers in moderate to excellent yields. Furthermore, this method was extended to the oxidative heptafluoropropylation and ethoxycarbonyldifluoromethylation of alcohols and phenols for preparation of the corresponding fluoroalkyl ethers.

Silver‐Catalysed Domino Approach to 1,3‐Dicarbo‐Substituted Isochromenes

We report herein the first example of the silver triflate catalysed synthesis of 1,3‐dicarbo‐substituted isochromene derivatives starting from 2‐alkynyl(hetero)arylaldehydes and enolizable ketones. The reaction proceeds in a cascade fashion under mild heating with complete regioselectivity and moderate‐to‐good yields. In some cases, the reaction gives unexpected homodimeric products. Two competitive mechanistic paths for the formation of the desired isochromene derivatives and the homodimeric products are described.

Synthesis, characterization and catalytic application of some novel PNP-Ni(II) complexes: Regio-selective [2+2+2] cycloaddition reaction of alkyne

Some novel Ni(II) complexes of PN(H)PPh, PN(Me)PiPr and PN(Me)PtBu ligands have been synthesized and characterized using standard analytical and spectroscopic methods such as 1H NMR, 31P NMR, elemental analysis, ESI-MS, UV-Visible spectroscopy and single-crystal X-ray crystallography. In the presence of silver triflate, complex [PN(H)PPhNiBr]2NiBr4(5) activated the C−Cl bond of dichloromethane at room temperature and afford complex [PN(H)PPhNiCl]OTf (6). We have also performed alkyne [2+2+2] cycloaddition reaction using Ni(II) complexes and observed high regioselectivity of the products. The observed selectivity is well correlating with the electronic feature of alkynes. The [2+2+2] cycloaddition of electron rich alkynes produced 1,3,5-substituted benzene derivatives as a major product whereas the electron deficient alkynes produced 1,2,4-substituted benzene derivatives as a major product.

Iminophosphanes: Synthesis, Rhodium Complexes, and Ruthenium(II)-Catalyzed Hydration of Nitriles

Highly stable iminophosphanes, obtained from alkylating nitriles and reaction of the resulting nitrilium ions with secondary phosphanes, were explored as tunable P-monodentate and 1,3-P,N bidentate ligands in rhodium complexes. X-ray crystal structures are reported for both κ1 and κ2 complexes with the counterion in one of them being an unusual anionic coordination polymer of silver triflate. The iminophosphane-based ruthenium(II)-catalyzed hydration of benzonitrile in 1,2-dimethoxyethane (180 °C, 3 h) and water (100 °C, 24 h) and under solvent free conditions (180 °C, 3 h) results in all cases in the selective formation of benzamide with yields of up to 96%, thereby outperforming by far the reactions in which the common 2-pyridyldiphenylphosphane is used as the 1,3-P,N ligand.

Coordination-driven self-assembly of arene ruthenium metalla-rectangles

Series of tetranuclear arene ruthenium complexes of the general formula [Ru4(p-cymene)4(μ2-N∩N)2(μ4-OO∩OO)2][CF3SO3]4 (N∩N=2,5-dipyridyl-thiophene (dptp), 3,6-dipyridyl-1,2,4,5-tetrazine (dptz), 3,6-dipyridyl-1,4-dihydro-1,2,4,5-tetrazine (dpdt)) were prepared by reacting the dinuclear arene ruthenium complexes Ru2(p-cymene)2(μ4-OO∩OO)Cl2 (OO∩OO=oxalato (oxa), 2,5-dioxido-1,4-benzoquinonato (dobq), 2,5-dichloro-1,4-benzoquinonato (dClbq), 2,5-dioxido-3-undecyl-1,4-benzoquinonato (dubq), 5,8-dioxido-1,4-naphtoquinonato (donq)) with silver trifluoromethanesulfonate, followed by the addition of the corresponding N∩N linkers. All metalla-rectangles were characterized by standard techniques, including infrared, UV–visible, 1H, 13C NMR spectroscopy and ESI mass spectrometry: Thus confirming the rectangular structure of the complexes, and showing the facility of forming tetranuclear arene ruthenium metalla-rectangles.

New Method for the Development of Plasmonic Metal-Semiconductor Interface Layer: Polymer Composites with Reduced Energy Band Gap

Silver nanoparticles within a host polymer of chitosan were synthesized by using in situ method. Ultraviolet-visible spectroscopy was then carried out for the prepared chitosan : silver triflate (CS : AgTf) samples, showing a surface plasmonic resonance (SPR) peak at 420 nm. To prepare polymer composites with reduced energy band gap, different amounts of alumina nanoparticles were incorporated into the CS : AgTf solution. In the present work, the results showed that the reduced silver nanoparticles and their adsorption on wide band gap alumina (Al2O3) particles are an excellent approach for the preparation of polymer composites with small optical band gaps. The optical dielectric loss parameter has been used to determine the band gap experimentally. The physics behind the optical dielectric loss were interpreted from the viewpoint of quantum mechanics. From the quantum-mechanics viewpoint, optical dielectric loss was also found to be a complex equation and required lengthy numerical computation. From the TEM investigation, the adsorption of silver nanoparticles on alumina has been observed. The optical micrograph images showed white spots (silver specks) with different sizes on the surface of the films. The second semicircle in impedance Cole-Cole plots was found and attributed to the silver particles.