Silver Trifluoroacetate Research Articles

Synthesis, Structure, and Theoretical Study of Lower Trifluoromethyl Derivatives of [60]Fullerene

AbstractA number of C60(CF3)n compounds with n = 2–10 have been synthesized by the reaction of C60 with silver trifluoroacetate and successfully isolated by means of HPLC. This resulted in the first crystal structure determination of six lower trifluoromethyl derivatives with n = 2 (single isomer), 4 (two isomers), and 6 (three isomers). A kinetic model of sequential trifluoromethylation based on the Bell–Evans–Polanyi principle has been used to explain the experimentally observed isomeric distribution in the mixtures of C60(CF3)n compounds up ton = 6. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Analysis of rosin and modified rosin esters in adhesives by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS)

The optimum method for analyzing glyceryl rosinate by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) was studied. The performances of dithranol, anthracene, and 2,5-dihydroxybenzoic acid, pyrene, trans, trans-1,4-diphenyl-1,3-butadiene, 9-nitroanthracene, indole-3-acrylic acid and retinoic acid as a matrix agent, and those of sodium trifluoroacetate (NaTFA) and silver trifluoroacetate (AgTFA) as a cationization agent were measured. Dithranol showed higher signal to noise ratio and lower base-line, and AgTFA showed better performance than NaTFA. In this study, however, NaTFA was chosen since the ester peaks with high signal to noise ratios were observed, and the spectra of sodium-cationized molecules are simpler than those of silver-cationized molecules. Rosin esters and modified rosin esters in 22 rubber-based pressure sensitive adhesives and a paper-cement were analyzed. Glyceryl rosinate, glyceryl disproportionated rosinate, pentaerythrityl rosinate and pentaerythrityl hydrogenated rosinate were easily detected despite the fact that rubber-based adhesives are complex mixtures of elastomers, tackifiers, antioxidants and other additives. The detection limit of this method was studied and 2% of glyceryl rosinate in a rubber-based pressure sensitive adhesive was detected. It has been proved that MALDI-TOF-MS is a useful analytical method to analyze rosin and modified rosin esters in adhesives.

Direct Formation of Silver Cluster Ions from Silver Salts by Laser Desorption/Ionization

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) has been used to characterize a wide range of polymers. In a MALDI mass spectrum, the protonated molecule and cation adduct of an analyte give an important information about the molecular ion mass. Some researchers reported that sliver clusters can be effectively produced under MALDI conditions from various silver salts in the presence of various matrices. During the analysis of organic molecules when Ag is used as the cationization agent, it can be recognized that besides the desired adduct ions, [M + Ag], an additional silver cluster ions, Agn is formed. Keki and coworkers studied the matrix effect on the formation of the silver cluster ions under MALDI conditions using reductive polar organic matrices and silver trifluoroacetate (AgTFA) and reported that the matrix greatly influenced the resulting cluster ion abundances. Metal clusters are very important in both theoretical and practical points of view. Investigation of cluster formation in mass spectrometry provides valuable information on the stability and electronic properties of clusters of different size. Studies on the formation of silver cluster ions under MALDI conditions have been performed in the presence of matrices such as 2,5-dihydroxybenzoic acid (DHB), 3,5dimethoxy-4-hydroxycinnamic acid (sinapinic acid, SA), trans-3-indoleacrylic acid (IAA), 2-(4-hydroxyphenylazo)benzoic acid (HABA), all-trans-retinoic acid (RTA), and 1,8,9-trihydroxyanthracene (dithranol, DIT). Formation of silver cluster ions directly from silver salts in the absence of matrix was not studied. In the present work, we investigated the silver cluster ions formed directly from silver salts of silver benzoate (AgBz), AgTFA, silver nitrate (AgNO3), and silver p-toluenesulfonate (AgTS) in the absence of any matrices. Scheme 1 shows their chemical structures. Figures 1, 2, 3, and 4 are the laser desorption/ionization (LDI) mass spectra of AgBz, AgTFA, AgNO3, and AgTS, respectively. Only the mass spectrum of AgBz shows a clear distribution of the silver cluster ions. It is a surprising result that the silver cluster ions are directly formed from AgBz in the absence of any matrix. Macha and coworkers investigated the formation of silver clusters from silver salts such as AgTFA, AgNO3, and silver acetylacetonate [Ag(acac)], but silver clusters were not detected. The cluster ion intensity distribution of AgBz shows an odd-even alternation pattern as shown in Figure 1. In other words, the intensity of the odd-number cluster ions tends to be stronger than that of the neighboring even-number cluster ions, especially in the low-mass range. The mass spectrum also shows a steep decrease of the ion intensities after some cluster ions called magic numbers. Figure 1 shows clear magic numbers of n = 9 and 21 of Agn. The specific ion intensity distribution of the silver cluster ions can be explained with the theoretical models. Since odd-number silver cluster ions have even numbers of valance electrons that become paired in the electronic shell of the formed clusters, they show stronger stabilities and higher ion intensities compared to those of even-number ones which have odd-number of electrons in their electronic shells. In addition, odd-number silver cluster ions tended to lose two silver atoms in their dissociation while even-number clusters lose a single atom. The magic numbers are in good agreement with the jellium model theory. In the jellium model one assumes that the positive ions of the cluster are smeared into a uniform background of spherical shape with density equal to that in the bulk. The electrons respond to this uniform background and fill the successive angular momentum states in accordance with the rules of quantum mechanics. A cluster shows pronounced stability when one of the angular momentum levels is filled. This shell closure occurs for alkali atoms at n = 2, 8, 20, 40, 58, 92, ... Formation of the silver cluster ions has been studied in the presence of matrix. In general, formation of the silver

HeI Photoelectron Spectroscopy and Theoretical Study of Trichloromethanesulfenyl Acetate, CCl3SOC(O)CH3, and Trichloromethanesulfenyl Trifluoroacetate, CCl3SOC(O)CF3

Two novel species, trichloromethanesulfenyl acetate, CCl(3)SOC(O)CH(3), and trichloromethanesulfenyl trifluoroacetate, CCl(3)SOC(O)CF(3), have been generated in situ by the heterogeneous reactions between trichloromethanesulfenyl chloride, CCl(3)SCl, and corresponding silver salts, silver acetate (AgOC(O)CH(3)) and silver trifluoroacetate (AgOC(O)CF(3)), respectively. Photoelectron spectroscopy and quantum chemical calculations are performed to investigate these two molecules, together with their precursor, CCl(3)SCl. Both of these two compounds may exist in the gas phase as a mixture of gauche and trans conformations. As for the dihedral angles delta(RSOR') of the gauche conformers, 107.0 degrees and 108.5 degrees are derived by theoretical calculations (at the B3LYP/6-311+G(3df) level) for CCl(3)SOC(O)CH(3) and CCl(3)SOC(O)CF(3), respectively. The first vertical ionization energies of CCl(3)SOC(O)CH(3) and CCl(3)SOC(O)CF(3), which have been determined by photoelectron spectroscopy, are 9.67 and 10.34 eV, respectively. According to the experimental results and theoretical analysis, the first ionization energy of these two molecules both come from the ionization of the lone pair electron of S atom.

Transfer of heterocyclic carbene ligands from chromium to gold, palladium and platinum

The reaction of pentacarbonyl(pyrazolin-3-ylidene)chromium complexes, ▪ ( 2a– c) (R = Ph ( a), C 6H 4NMe 2-4 ( b); (C 5H 4)FeCp ( c)), with [AuCl(SMe 2)], H[AuCl 4], [PdCl 2(NCPh) 2] and [PtCl 2(NCPh) 2] gives, by transfer of the heterocyclic carbene ligand, new chloro pyrazolin-3-ylidene complexes of gold(I) and gold(III), dichloro bis(pyrazolin-3-ylidene) palladium and dichloro bis(pyrazolin-3-ylidene) platinum in high yield. The chloride ligand in ▪ (Fc = (C 5H 4)FeCp) is readily displaced by trifluoroacetate. The analogous substitution of iodide for the chloride ligands in ▪ (M = Pd, Pt) give the corresponding diiodo complexes although in a much slower reaction. In contrast, the reaction of silver trifluoroacetate with ▪ affords a binuclear Pd–Ag complex containing two pyrazolin-3-ylidene and three trifluoroacetate ligands two of whom occupy bridging positions between Pd and Ag. The reactions of the pyrazolidin-3-ylidene complex ▪ (R = C 6H 4NMe 2-4) with [AuCl(SMe 2)] and [PdCl 2(NCPh) 2] yield chloro pyrazolidin-3-ylidene gold and dichloro bis(pyrazolidin-3-ylidene) palladium complexes. The related dichloro bis(tetrahydropyrimidin-4-ylidene) palladium complex is formed in the reaction of ▪ with the palladium complex [PdCl 2(NCPh) 2]. The solid-state structures of several of these heterocyclic carbene complexes including the structure of the binuclear Pd–Ag complex are established by X-ray structure analyses.

マトリックス支援レーザー脱離イオン化飛行時間型質量分析法によるゴム系粘着剤中のポリβ−ピネンの分析

In order to develop an analytical method that allows effective discrimination of pressure-sensitive adhesives (PSAs), polyβ-pinene, one of the representative tackifiers that constitute PSAs, was identified using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. In this study, the optimum analytical method was obtained using trans,trans-1,4-diphenyl-1,3-butadiene as the matrix without silver trifluoroacetate, the cationization agent. Acetone extracts of PSAs were analyzed by this method and polyβ-pinene was identified.

Resequencing of Comonomer Units of Well-Defined Vectra Oligomers during MALDI-TOF Mass Spectral Measurements

To aid in the detailed characterization of the LCP polymer Vectra A950, 20 alternating dimers and 10 alternating tetrameric model oligomers were synthesized and subjected to detailed MALDI and ESI spectral characterization. The model compounds were synthesized using stepwise reactions on 4-hydroxybenzoic and 6-hydroxy-2-naphthoic acids using protection−deprotection strategies. MALDI-TOF spectra of these compounds in both the positive and negative modes were determined using dithranol, 2-(4-hydroxyphenylazo)-benzoic acid (HABA), and and its methyl ester (MHABA) as matrixes and in the presence or absence of silver trifluoroacetate. The “coolest” matrix, leading to least fragmentation, proved to be dithranol with silver trifluoroacetate, while the “hottest” was dithranol alone. On the positive side, the majority of ions detected other than the parent ions proved to be acylium ions resulting from cleavage of the unexpectedly fragile aryloxy-to-carbonyl bond. At higher applied laser power, the extrusion of oxybenzoyl groups as p-quinonemethide molecules from both the chain middles and ends, followed by recombination, led to extensive resequencing of the original monomer units. Similar behavior was observed in the negative ion spectra, allowance being made for the suppression of negative ions by carboxylic and phenolic functional groups. ESI spectra on the positive side, in contrast, gave much less fragmentation but more complicated spectra resulting from the occurrence of noncovalent molecular complexes. On the negative side, much fragmentation accompanied the complex spectra, reasonably resulting from the ready formation of carboxylate and phenoxide anions. In the ESI spectra, the original monomer sequences were cleanly maintained and identified. Our results demonstrate both the power and limitations of MALDI and ESI in the characterization of Vectra A950, which by implication extend to the characterization of other commercially important polymers based on 4-hydroxybenzoic acid as well.

Pyrolytic Trifluoromethylation of [76]‐, [78]‐, [84]‐, and Aza[60]Fullerenes with Silver Trifluoroacetate; Evidence for Coordination of Fullerenes to Silver

Pyrolytic trifluoromethylation of [76], [78], [84], and aza[60]fullerenes with silver trifluoroacetate at 300°C results in extensive polyaddition of up to 18, 18, 20 and 20 CF3 groups, respectively. In contrast to trifluoromethylation of [60]‐ and [70]fullerenes that give a full range of derivatives ranging upwards from C n (CF3)2, [76]‐, [78]‐, and [84]‐fullerenes only give C n (CF3)6‐18 derivatives, largely in the 10–12 CF3 range; reaction with [76]fullerene is accompanied by formation of C60(CF3)6 attributed to cage fragmentation. For aza[60]fullerene the hexa‐addition level dominates, in contrast to its other reactions which give predominantly penta‐addition products. All the compounds showed peaks at 1256±2 and 1180–1190 cm−1, due to the CF3 group, and peaks in this region are shown also by the soluble extract obtained on trifluoromethylation of nanotubes. As in trifluoromethylation of [60]‐ and [70]‐fullerenes, the products obtained initially are involatile, attributed to formation os silver complexes; these are decomposed on subsequent solution in toluene. Mixed isomeric trifluoromethylated C60F8 derivatives viz. C60F7CF3, C60F6(FG3)2, C60F5(CF3)3 and C60F4(CF3)4, and C60F4CF3CF2CF3 (a C60F6 derivative) have been isolated from fluorination of [60]fullerene with MnF3/K2NilF6 at 510°C. *Deceased

Synthesis, Characterization, and Theoretical Study of Stable Isomers of C70(CF3)n (n = 2, 4, 6, 8, 10)

Reaction of C70 with ten equivalents of silver(I) trifluoroacetate at 320-340 degrees C followed by fractional sublimation at 420-540 degrees C and HPLC processing led to the isolation of a single abundant isomer of C70(CF3)n for n = 2, 4, 6, and 10, and two abundant isomers of C70(CF3)8. These six compounds were characterized by using matrix-assisted laser desorption ionization (MALDI) mass spectrometry, 2D-COSY and/or 1D 19F NMR spectroscopy, and quantum-chemical calculations at the density functional theory (DFT) level. Some were also characterized by Raman spectroscopy. The addition patterns for the isolated compounds were unambiguously found to be C1-7,24-C70(CF3)2, C1-7,24,44,47-C70(CF3)4, C2-1,4,11,19,31,41-C70(CF3)6, Cs-1,4,11,19,31,41,51,64-C70(CF3)8, C2-1,4,11,19,31,41,51,60-C70(CF3)8, and C1-1,4,10,19,25,41,49,60,66,69-C70(CF3)10 (IUPAC numbering). Except for the last compound, which is identical to the recently reported, crystallographically characterized C70(CF3)10 derivative prepared by a different synthetic route, these compounds have not previously been shown to have the indicated addition patterns. The largest relative yield under an optimized set of reaction conditions was for the Cs isomer of C70(CF3)8 (ca. 30 mol % of the sublimed mixture of products based on HPLC integration). The results demonstrate that thermally stable C70(CF3)n isomers tend to have their CF3 groups arranged on isolated para-C6(CF3)2 hexagons and/or on a ribbon of edge-sharing meta- and/or para-C6(CF3)2 hexagons. For Cs- and C2-C70(CF3)8 and for C2-C70(CF3)6, the ribbons straddle the C70 equatorial belt; for C1-C70(CF3)4, the para-meta-para ribbon includes three polar hexagons; for C1-7,24-C70(CF3)2, the para-C6(CF3)2 hexagon includes one of the carbon atoms on a C70 polar pentagon. The 10.3-16.2 Hz 7JF,F NMR coupling constants for the end-of-ribbon CF3 groups, which are always para to their nearest-neighbor CF3 group, are consistent with through-space Fermi-contact interactions between the fluorine atoms of proximate, rapidly rotating CF3 groups.

Polymeric silver(I) and mercury(II) complexes with chiral bis(pyridyl) ligands

The racemic binaphthol derivatized ligands LL= rac−1,1′-C 20H 12(OCH 2-4-C 5H 4N) 2, 1, and rac−1,1′-C 20H 12(OCH 2-3-C 5H 4N) 2, 2, react with silver trifluoroacetate or with mercury(II) salts to give the polymeric complexes [Ag(O 2CCF 3)(μ-LL)] n or [HgX 2(μ-LL)] n . Individual polymer chains may be chiral or racemic, with sequences of binaphthyl groups with chirality …RRR…, …SSS… or …RSRS…, respectively. The polymer chains may associate, through Ag⋯Ag or Hg–X⋯Hg secondary bonding, to give more complex double-stranded polymer or sheet structures.

Homochiral and Heterochiral Coordination Polymers and Networks of Silver(I)

The self-assembly of racemic and enantiopure binaphthylbis(amidopyridyl) ligands 1,1'-C(20)H(12){NHC(O)-4-C(5)H(4)N}(2), 1, and 1,1'-C(20)H(12){NHC(O)-3-C(5)H(4)N}(2), 2, with silver(I) salts (AgX; X = CF(3)CO(2), CF(3)SO(3), NO(3)) to form extended metal-containing arrays is described. It is shown that the self-assembly with racemic ligands can lead to homochiral or heterochiral polymers, through self-recognition or self-discrimination of the ligand units. The primary polymeric materials adopt helical conformations (secondary structure), and they undergo further self-assembly to form sheets or networks (tertiary structure). These secondary and tertiary structures are controlled through secondary bonding interactions between pairs of silver(I) centers, between silver cations and counteranions, or through hydrogen bonding involving amide NH groups. The self-assembly of the enantiopure ligand R-1 with silver trifluoroacetate gave a remarkable three-dimensional chiral, knitted network composed of polymer chains in four different supramolecular isomeric forms.

Exceptionally Simple Homologation of Protected α‐ to β‐Amino Acids in the Presence of Silica Gel

The Wolff rearrangement of α‐amino acid–derived diazoketones is simply achieved by gentle warming in a ethyl acetate/silica gel slurry containing catalytic amounts of silver trifluoroacetate. Without workup (not counting filtration and evaporation) the protected β‐amino acids are obtained in high yields (92–97%) without significant impurities. This variation avoids the laborious workup after a conventional silver‐catalyzed Wolff rearrangement. This method can be similarly applied to the synthesis of β‐amino acid methyl esters when methanol is used as solvent. No reaction occurs without silica gel.

Silver Ion Release from Polymethyl Methacrylate Silver Nanocomposites

Polymethyl methacrylate (PMMA) silver nanocomposites were prepared by the thermal reduction of silver(I) trifluoroacetate. Transmission electron microscopic investigations reveal that the silver nanoparticles were spherical and their particle sizes were between 5 nm and 50 nm. The particles were distributed randomly in the PMMA matrix. Immersion of the nanocomposites in water led to a release of silver ions. The silver ion release from the PMMA silver nanocomposites was measured by anodic stripping voltammetry. When a nanocomposite sample having a surface area of 36.8 cm2 and a silver content of 0.12 wt% was immersed in water, the silver ion concentration in the surrounding water was about 0.05 mg/l after two days. This is sufficient to kill bacteria. Using conventional silver powder as a filler, a silver content 30 times higher is necessary to achieve the same silver ion concentration in the surrounding water under the same conditions. The silver ion concentration in the water increased with increasing nanosilver content of the composites. The composites incorporating conventional silver powder are not transparent. In contrast, PMMA silver nanocomposites containing less than 0.25 wt% silver show a translucency sufficient for use in packaging materials.

Novel Ruthenium‐Based Metathesis Catalysts Containing Electron‐Withdrawing Ligands: Synthesis, Immobilization, and Reactivity.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis of Fullerenols from Halofullerenes

Halogenated fullerenes were used as reagents to prepare fullerenols. Depending on reaction conditions two types of substances (complex mixtures of products with average compositions C60OnHm, n=10–26, m=14–30 and C60OnHmMk, M=K, Na; n=17–24, m=16–28, k=3–8) possessing essentially different water solubility were obtained. Highly soluble metal‐containing species are most likely ionic compounds similar to metal derivatives of alcohols–alcoholates. An electron withdrawing effect of the carbon cage could make alkali metal fullerenolates (C60(OH)x(OM)y) inert towards hydrolysis. Halogens were selectively substituted when fullerene bromides and chlorides were treated with silver trifluoroacetate. Fullerenol esters C60(OOCCF3)n formed were then hydrolyzed to form C60(OOCCF3)x(OH)y. Attempts to cleave all ester groups in C60(OOCCF3)x(OH)y failed in acidic media, while alkaline hydrolysis was accompanied by unselective polyhydroxylation of the fullerene cage.

Tetraphosphinite Resorcinarene Complexes: Silver(I) Capsule Complexes

Resorcinarene tetraphosphinite ligands, P4, react with silver(I) trifluoroacetate or silver(I) triflate, AgX, to give the corresponding [Ag4X4(P4)] complexes. The resorcinarene skeleton in these complexes adopts a boat conformation with the silver(I) phosphinite units on the horizontal, rather than the upright, arene units of the resorcinarene. The [Ag4X4(P4)] complexes react with free P4 ligand to yield the [Ag2X2(P4)] or [AgX(P4)] complexes, which are characterized in solution by NMR spectroscopy to have a conformation opposite to that of the [Ag4X4(P4)] complexes; the silver(I) phosphinite groups are on the upright arene rings of the resorcinarene "boat" instead of the horizontal arene units. There is an easy equilibrium between these complexes. When X = triflate, the [Ag4X4(P4)] complexes disproportionate and add aqua ligands during slow crystallization to give "capsule complexes", which are characterized crystallographically as [Ag10(O3SCF3)10(OH2)6(P4)2], [Ag10(O3SCF3)6(OH2)8(P4)2][O3SCF3]4, or [Ag13(O3SCF3)13(OH2)7(P4)2] depending on the resorcinarene tetraphosphinite ligand P4 used. These unusual capsule complexes are formed by the tail-to-tail self-assembly of pairs of [Ag4(P4)]4+ units linked by additional silver ions that bind to the phenyl substituents of one resorcinarene through {Ag(eta2-C6H5)}+ binding and to the bridging triflate ligands, aqua ligands, or both of the other resorcinarene unit.

Unsaturated Selenacrown Ethers: Synthesis, Structure, and Formation of Silver Complexes

The unsaturated selenacrown ethers, (Z,Z,Z,Z,Z)-1,4,7,10,13-pentaselenacyclopentadeca-2,5,8,11,14-pentaene (15-US-5) (2), (Z,Z,Z,Z,Z,Z)-1,4,7,10,13,16-hexaselenacyclooctadeca-2,5,8,11,14,17-hexaene (18-US-6) (3), (Z,Z,Z,Z,Z,Z,Z)-1,4,7,10,13,16,19-heptaselenacycloheneicosa-2,5,8,11,14,17,20-heptaene (21-US-7) (4), (Z,Z,Z,Z,Z,Z,Z,Z)-1,4,7,10,13,16,19,22-octaselenacyclotetracosa-2,5,8,11,14,17,20,23-octaene (24-US-8) (5), and (Z,Z,Z,Z,Z,Z,Z,Z,Z)-1,4,7,10,13,16,19,22,25-nonaselenacycloheptacosa-2,5,8,11,14,17,20,23,26-nonaene (27-US-9) (6), were obtained together with 1,4-diselenin (1) by reacting sodium selenide with cis-dichloroethene in the presence of a phase-transfer catalyst. The crystal structures of 2-5 were determined by X-ray crystallographic analysis. The UV spectra of the selenacrown ethers showed absorption maximums in the range of 251-262 nm, which were assigned to n-->pi transitions. The cyclic voltammograms indicated that the large unsaturated selenacrown ethers were oxidized more easily than the small ones. The thermal reactions of the unsaturated selenacrown ethers afforded 1,4-diselenin (1) along with polymeric materials, whereas 1 was thermally stable even at 100 degrees C. The reactions of 1 or unsaturated selenacrown ethers 2-5 with silver ion yielded various novel silver complexes, Ag(C(4)H(4)Se(2))(CF(3)COO) (7), Ag(C(4)H(4)Se(2))(2)(CF(3)COO) (8), Ag(15-US-5)(CF(3)COO) (9), Ag(5)(18-US-6)(3)(CF(3)COO)(5) (10), Ag(7)(21-US-7)(CF(3)COO)(5) (11), Ag(24-US-8)(2)(CF(3)COO) (12), Ag(2)(24-US-8)(CF(3)COO)(2) (13), Ag(3)(24-US-8)(2)(CF(3)COO)(3) (14), Ag(15-US-5)NO(3) (15), and Ag(21-US-7)BF(4) (16). The stoichiometry for the complexation with silver trifluoroacetate in solution was examined by (1)H NMR measurement. The titration plots of 2 and 5 under the dilution conditions showed a distinct inflection point at the 1/1 metal/macrocycle ratio, whereas the plots of 1 and 3 showed gradual change.

Catalytic Asymmetric Synthesis of Chiral Allylic Amines. Evaluation of Ferrocenyloxazoline Palladacycle Catalysts and Imidate Motifs.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Novel Ruthenium-Based Metathesis Catalysts Containing Electron- Withdrawing Ligands: Synthesis, Immobilization, and Reactivity

The syntheses and reactivity of seven different ruthenium-based metathesis catalysts are described. Ru(CF3COO)2(PCy3)(=CH-2-(2-PrO)C6H4) (1), Ru(CF3COO)2(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4) (2), and Ru(CF3COO)2(PCy(3))(1,3-dimesityldihydroimidazolin-2-ylidene)(=CHC6H5) (3) were prepared via chlorine exchange by reacting RuCl2(PCy3)2(=CH-2-(2-PrO)C6H4), RuCl2(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4), and RuCl2(PCy3)(1,3-dimesityldihydroimidazolin-2-ylidene)(=CHC6H5), respectively, with silver trifluoroacetate (Cy =cyclohexyl). In analogy, Ru(CF3CF2COO)2(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4) (4) and Ru(CF3CF2CF2COO)2(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4) (5) were prepared from RuCl2(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4) via reaction with CF3CF2COOAg and CF3CF2CF2COOAg, respectively. Ru(C6F5COO)2(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4) (6) and Ru(C6F5O)2(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4) (7) were prepared from RuCl2(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4) via reaction with C6F5COOTl and C6F5OTl, respectively. Supported catalysts Ru(PS-DVB-CH2OOCCF2CF2CF2COO)(CF3COO)(PCy3)(1,3-dimesityldihydroimidazolin-2-ylidene)(=CHC6H5) (8), Ru(PS-DVB-CH2OOCCF2CF2CF2COO)(CF3COO)(PCy3)(=CH-2-(2-PrO)C6H4) (9), and Ru(PS-DVB-CH2OOCCF2CF2CF2COO)(CF3COO)(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4) (10) were synthesized by reaction of RuCl2(PCy3)(1,3-dimesityldihydroimidazolin-2-ylidene)(=CHC6H5), RuCl2(PCy3)(=CH-2-(2-PrO)C6H4), and RuCl2(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4), respectively, with a perfluoroglutaric acid-derivatized poly(styrene-co-divinylbenzene) (PS-DVB) support (silver form). Halogen exchange in PCy3-containing systems had to be carried out in dichloromethane in order to suppress precipitation of AgCl.PCy3. The reactivity of all new catalysts in ring-closing metathesis (RCM) of hindered electron-rich and -poor substrates, respectively, at elevated temperature (45 degrees C) was compared with that of existing systems. Diethyl diallylmalonate (DEDAM, 11), diethyl allyl(2-methylallyl)malonate (12), N,N-diallyl-p-toluenesulfonamide (13), N-benzyl-N-but-1-en-4-ylbut-2-enecarboxylic amide (14), and N-allyl-N-(1-carboxymethyl)but-3-en-1-yl-p-toluenesulfonamide (15) were used as educts. Supported catalysts were prepared with high loadings (2.4, 22.1, and 160 mg of catalyst/g PS-DVB for 8, 9, and 10, respectively). Catalyst 8 showed higher and catalysts 9 and 10 sowed significantly reduced activities in RCM compared to their homogeneous analogues. Thus, with 8, turnover numbers (TONs) up to 4200 were realized in stirred-batch (carousel) RCM experiments. To elucidate the nature of the bound species, catalysts 8-10 were subjected to 13C- and 31P-MAS NMR spectroscopy. These investigations provided evidence for the proposed structures. Leaching of ruthenium into the reaction mixture was low, resulting in ruthenium contents <85 ppb (ng/g) in the final RCM-derived products.

Metal Salts for Molecular Ion Yield Enhancement in Organic Secondary Ion Mass Spectrometry: A Critical Assessment

In a search for molecular ion signal enhancement in organic SIMS, the efficiency of a series of organic and inorganic salts for molecular cationization has been tested using a panel of nonvolatile molecules with very different chemical characteristics (leucine enkephalin, Irganox 1010, tetraphenylnaphthalene, polystyrene). The compounds used for cationization include alkali bromide and group Ib metal salts (XBr with X = Li, Na, K; CF3CO2Ag; AgNO3; [CH3COCH=C(O-)CH3]2Cu; AuCl3). Alkali ions, very good for polar molecule cationization, prove to be of limited interest for nonpolar molecules such as polystyrene. Silver trifluoroacetate displays excellent results for all the considered molecules, except for leucine enkephalin (which might be due to the use of different solvents for the analyte and the salt). Instead, silver nitrate mixed with leucine enkephalin in an ethanol solution provides intense molecular signals. The influence of the respective concentrations of analyte and salt in solution, of the silver trifluoroacetate solution stability, and of the sample microstructure on the secondary ion intensities are also investigated. The results of other combinations of analyte and salts are reported. Finally, the use of salts is critically compared to other sample preparation procedures previously proposed for SIMS analysis of large organic molecules.