Showing papers on "Substituent published in 2008"

Substituent effects in the benzene dimer are due to direct interactions of the substituents with the unsubstituted benzene.

Abstract: The prevailing views of substituent effects in the sandwich configuration of the benzene dimer are flawed. For example, in the polar/π model of Cozzi and co-workers (J. Am. Chem. Soc. 1992, 114, 5729), electron-withdrawing substituents enhance binding in the benzene dimer by withdrawing electron density from the π-cloud of the substituted ring, reducing the repulsive electrostatic interaction with the nonsubstituted benzene. Conversely, electron-donating substituents donate excess electrons into the π-system and diminish the π-stacking interaction. We present computed interaction energies for the sandwich configuration of the benzene dimer and 24 substituted dimers, as well as sandwich complexes of substituted benzenes with perfluorobenzene. While the computed interaction energies correlate well with σm values for the substituents, interaction energies for related model systems demonstrate that this trend is independent of the substituted ring. Instead, the observed trends are consistent with direct elect...

n-channel polymers by design: optimizing the interplay of solubilizing substituents, crystal packing, and field-effect transistor characteristics in polymeric bithiophene-imide semiconductors.

Abstract: Electron transporting (n-channel) polymer semiconductors for field-effect transistors are rare. In this investigation, the synthesis and characterization of new electron-depleted N-alkyl-2,2′-bithiophene-3,3′-dicarboximide-based π-conjugated homopolymers and copolymers containing the 2,2′-bithiophene unit are reported. A novel design approach is employed using computational modeling to identify favorable monomer properties such as core planarity, solubilizing substituent tailorability, and appropriate electron affinity with gratifying results. Monomeric model compounds are synthesized to confirm these properties, and a crystal structure reveals a short 3.43 A π−π stacking distance with favorable solubilizing substituent orientations. A family of 10 homopolymers and bithiophene copolymers is then synthesized via Yamamoto and Stille polymerizations, respectively. Two of these polymers are processable in common organic solvents: the homopolymer poly(N-(2-octyldodecyl)-2,2′-bithiophene-3,3′-dicarboximide) (P1...

Synthesis of Benzocyclobutenes by Palladium-Catalyzed C−H Activation of Methyl Groups: Method and Mechanistic Study

Abstract: An efficient catalytic system has been developed for the synthesis of benzocyclobutenes by C−H activation of methyl groups. The optimal conditions employed a combination of Pd(OAc)2 and PtBu3 as catalyst, K2CO3 as the base, and DMF as solvent. A variety of substituted BCB were obtained under these conditions with yields in the 44−92% range, including molecules that are hardly accessible by other methods. The reaction was found limited to substrates bearing a quaternary benzylic carbon, but benzocyclobutenes bearing a tertiary benzylic carbon could be obtained indirectly from diesters by decarboxylation. Reaction substrates bearing a small substituent para to bromine gave an unexpected regioisomer that likely arose from a 1,4-palladium migration process. The formation of this “abnormal” regioisomer could be suppressed by introducing a larger subsituent para to bromine. DFT(B3PW91) calculations on the reaction of 2-bromo-tert-butylbenzene with Pd(PtBu3) with different bases (acetate, bicarbonate, carbonate)...

Light emitting device material and light emitting device

Abstract: Disclosed is a light-emitting device material which is characterized by containing an anthracene compound represented by the general formula (1) below or the general formula (3) below. With such a light-emitting device material, there can be obtained a light-emitting device having high luminous efficiency and excellent durability. (1) (In the formula, R1-R10 respectively represent a hydrogen atom, alkyl group, cycloalkyl group, heterocyclic group or the like, and at least one of the R1-R10 represents a substituent represented by the following formula (2).) (In the formula, R11-R18 respectively represent a hydrogen atom, alkyl group or cycloalkyl group; X represents an oxygen atom or sulfur atom; Y represents a single bond, arylene group or heteroarylene group; at least one of R11-R18 is used for linking with Y; and α is used for linking with the anthracene skeleton.) (3) (In the formula, R19-R37 respectively represent a hydrogen atom, alkyl group, cycloalkyl group, heterocyclic group or the like; n is 1 or 2; A represents a heteroarylene group or arylene group; and at least one of R19-R27 and at least one of R28-R37 are used for linking with A.)

Highly Disordered Polymer Field Effect Transistors: N-Alkyl Dithieno[3,2-b:2′,3′-d]pyrrole-Based Copolymers with Surprisingly High Charge Carrier Mobilities

Abstract: A series of novel electroactive and photoactive conjugated copolymers based on N-alkyl dithieno[3,2-b:2′,3′-d]pyrroles (DTP) and thiophene (TH) units (DTP-co-THs) were synthesized using a Stille coupling reaction and exhibited molecular weights of 1.6 × 104 to 5.0 × 104 g/mol. The incorporation of soluble substituted thiophenes and planar DTP units resulted in low band gap, highly conductive polymers. DTP-co-THs exhibited excellent solubility in common organic solvents and formed high-quality films. Optical characterization revealed that the band gaps of DTP-co-THs were between 1.74 and 2.00 eV, lower than regioregular poly(3-alkylthiophenes). Electrochemical characterization showed that the HOMO energy levels of DTP-co-THs are between −4.68 and −4.96 eV. When doped, DTP-co-THs exhibited high conductivities up to 230 S/cm with excellent stability. The different thiophene substituent patternsʼ effect on the polymers’ optical and electronic properties was then examined by density functional theory computati...

Trifluoromethyl ethers – synthesis and properties of an unusual substituent

Abstract: After nitrogen, fluorine is probably the next most favorite hetero-atom for incorporation into small molecules in life science-oriented research. This review focuses on a particular fluorinated substituent, the trifluoromethoxy group, which is finding increased utility as a substituent in bioactives, but it is still perhaps the least well understood fluorine substituent in currency. The present review will give an overview of the synthesis, properties and reactivity of this important substituent.

Aromatic amine derivative and organic electroluminescent device using the same

Abstract: Provided are: an aromatic amine derivative in which a terminal substituent such as a dibenzofuran ring or a dibenzothiophene ring is bonded to a nitrogen atom directly or through an arylene group or the like; an organic electroluminescence device including an organic thin film layer formed of one or more layers including a light emitting layer and interposed between a cathode and an anode in which a layer of the organic thin film layer contains the aromatic amine derivative by itself or as a component of a mixture, and the device has a long lifetime and high luminous efficiency; and an aromatic amine derivative for realizing the device.

InBr3-promoted divergent approach to polysubstituted indoles and quinolines from 2-ethynylanilines: switch from an intramolecular cyclization to an intermolecular dimerization by a type of terminal substituent group.

Abstract: Use of a 2-ethynylaniline having an alkyl or aryl group on the terminal alkyne selectively produced a variety of polyfunctionalized indole derivatives in moderate to excellent yields via indium-catalyzed intramolecular cyclization of the corresponding alkynylaniline. In contrast, employment of a substrate with a trimethylsilyl group or with no substituent group on the terminal triple bond, exclusively afforded polysubstituted quinoline derivatives in good yields via indium-promoted intermolecular dimerization of the ethynylaniline. This indium catalytic system successfully accommodated the intramolecular cyclization of other arylalkyne skeletons involving a carboxylic acid and an amide group.

Polyfluoroalkyl, Polyethylene Glycol, 1,4-Bismethylenebenzene, or 1,4-Bismethylene-2,3,5,6-Tetrafluorobenzene Bridged Functionalized Dicationic Ionic Liquids: Synthesis and Properties as High Temperature Lubricants

Abstract: A new class of geminal dicationic ionic liquids was formed with a bridging moiety, such as a polyalkyl ether, polyfluoroalkyl, 1,4-bismethylenebenzene, or 1,4-bismethylene-2,3,5,6-tetrafluorobenzene link, between alkyl-substituted imidazolium rings. Their properties were modified by varying the linker chains and/or alkyl substituents on the imidazolium ring. The polyfluoroalkyl bridged dicationic ionic liquids exhibit the highest densities and viscosities. Although melting points are directly proportional to the length of the alkyl substituent, the densities decrease concomitantly. With 1,4-bismethylene-2,3,5,6-tetrafluorobenzene as the linking chain and with longer alkyl substituents on the imidazolium rings, the nonpolar character of the ionic liquid greatly increases, e.g., the solubilities in toluene of dicationic ionic liquids 36 and 37, where the ring substituents are C10H21 and C14H29, increase markedly. Some of the salts exhibit higher conductivities than an equimolar tetrabutylammonium iodide sol...

Substituent position effect on the properties of isomeric photochromic diarylethenes bearing chlorine atoms

Abstract: Three new isomeric photochromic diarylethenes, namely 1,2-bis[2-methyl-5-(4-chlorophenyl)-3-thienyl]perfluorocyclopentene (1o), 1,2-bis[2-methyl-5-(3-chlorophenyl)-3-thienyl]perfluorocyclopentene (2o), and 1,2-bis[2-methyl-5-(2-chlorophenyl)-3-thienyl]perfluorocyclopentene (3o) which bear two chlorine atoms at the para-, meta-, and ortho-position of both terminal phenyl groups, have been synthesized. The substituent position effect of chlorine atoms on their optoelectronic properties, including photochromic behavior and fluorescence, both in solution and in PMMA amorphous film, and electrochemical properties were investigated in detail. The results elucidated that the chlorine atoms and their substituent positions had a significant effect on the optoelectronic properties of these compounds. These diarylethene derivatives bearing two chlorine atoms have shown good photochromic behavior and fluorescent switching both in solution and in PMMA film. For diarylethenes 1–3, the cycloreversion quantum yields were gradually increased when the chlorine atom was attached to the para-, meta- and ortho-positions of the two terminal benzene rings; but, their absorption maxima, cyclization quantum yields and the molar absorption coefficients both of their open-ring and closed-ring isomers were remarkably decreased one by one. Furthermore, the clear oxidation waves of diarylethenes 1c, 2c and 3c were observed at 1.01, 0.92 and 0.98 V by performing the cyclic voltammograms experiments.

π-Conjugated Organoboron Polymers via the Vacant p -Orbital of the Boron Atom

Abstract: A decade has passed since organoboron π-conjugated systems highly extended through the empty p-orbital of the boron atom emerged as a new class of π-conjugated materials. Making use of convenient hydroboration polymerization, a variety of π-conjugated organoboron polymers exhibiting fluorescence emission, n-type electrochemical activity, electrical conductivity, third order non linear optical property, anion sensing ability is easily prepared. The organoboron π-conjugated polymers having highly bulky substituent on the boron atom shows high stability under air and moisture and therefore, potentially useful for versatile applications.The design of electron deficient organoboron π-systems led to observation of unique photophysical behavior such as extraordinary high third order non linear optical susceptibility, facilitation of pπ-dπ* transition, intramolecular charge transfer, unusually activated σ-π conjugative interaction and so forth.In addition to boration polymerization methods, polycondensation using di-Grignard reagent, Sonogashira type polycondensation, polycondensation via tin-boron exchange are useful for synthesis of π-conjugated organoboron polymers.

Organocatalytic Asymmetric Synthesis of α,α-Disubstituted α-Amino Acids and Derivatives

Abstract: It is shown that racemic oxazolones are excellent reagents for the synthesis of chiral quaternary amino acids and its derivatives by the diastereo- and enantioselective nucleophilic addition to alpha,beta-unsaturated aldehydes catalyzed by diarylprolinol silyl ethers. The scope of this new organocatalytic reaction is demonstrated for different oxazolones having aromatic and alkyl groups at the reactive carbon atom and different aromatic and aliphatic substituted alpha,beta-unsaturated aldehydes, for which the stereoselective reaction proceeds with good yield, moderate to good to very high diastereoselectivity, and very high enantioselectivity. The potential of the reaction is shown for the synthesis of optically active alpha,alpha-disubstituted alpha-amino acids, alpha-quaternary proline derivatives, amino alcohols, lactams, and tetrahydropyranes. Furthermore, we have calculated by DFT-methods the transition-state structures that account for both the diastereo- and enantioselectivity observed for the addition of oxazolones to the alpha,beta-unsaturated aldehydes. For one class of compounds, the stereoselectivity is controlled by a hydrogen-bonding interaction of the enolate-form of the oxazolone with an ortho-hydroxy-phenyl substituent of the alpha,beta-unsaturated aldehyde, whereas the benzhydryl-protecting group in the oxazolone determines the diastereo- and enantioselectivity in a more general manner for both aromatic and aliphatic alpha,beta-unsaturated aldehydes.

Development of Chiral Bicyclic Triazolium Salt Organic Catalysts : The Importance of the N-Aryl Substituent

Abstract: The development of a family of chiral bicyclic triazolium salts is described. Treatment of these salts with base provides a nucleophilic carbene which may be used as an organic catalyst for asymmet...

Substituent effects in parallel-displaced π–π interactions

Abstract: High-quality quantum-mechanical methods are used to examine how substituents tune π–π interactions between monosubstituted benzene dimers in parallel-displaced geometries. The present study focuses on the effect of the substituent across entire potential energy curves. Substituent effects are examined in terms of the fundamental components of the interaction (electrostatics, exchange-repulsion, dispersion and induction) through the use of symmetry-adapted perturbation theory. Both second-order Moller–Plesset perturbation theory (MP2) with a truncated aug-cc-pVDZ′ basis and spin-component-scaled MP2 (SCS-MP2) with the aug-cc-pVTZ basis are found to mimic closely estimates of coupled-cluster with perturbative triples [CCSD(T)] in an aug-cc-pVTZ basis. Substituents can have a significant effect on the electronic structure of the π cloud of an aromatic ring, leading to marked changes in the π–π interaction. Moreover, there can also be significant direct interactions between a substituent on one ring and the π-cloud of the other ring.

Antibacterial and Hemolytic Activities of Quaternary Pyridinium Functionalized Polynorbornenes

Abstract: In this study, amphiphilic polyoxanorbornene with different quaternary alkyl pyridinium side chains were synthesized. The biological efficiencies of these polymers, with various alkyl substituents, were determined by bacterial growth inhibition assays and hemolytic activity (HC 50 ) against human red blood cells (RBCs) to provide selectivity of these polymers for bacterial over mammalian cells. A series of polymers with different alkyl substituents (ethyl, butyl, hexyl, octyl, decyl and phenylethyl) and two different molecular weights (3 and 10 kDa) were prepared. The impact of alkyl chain length divided the biological activity into two different cases: those with an alkyl substituent containing four or fewer carbons had a minimum inhibitory concentration (MIC) of 200 μg. mL -1 and a HC 50 greater than 1650 μg. mL -1 , while those with six or more carbons had lower MICs < 12.5 μg. mL -1 and HC 50 ≤ 250 μg. mL -1 . Using MSI-78, the potent Magainin derivative which has an MIC=12.0 μg·mL -1 and HC 50 = 120 μg·mL -1 , as a comparison, the polymers with alkyl substituents ≤C 4 (four carbons) were not very potent, but did show selectivity values greater than or equal to MSI-78. In contrast, those with alkyl substituents ≥C 6 were as potent, or more potent, than MSI-78 and in three specific cases demonstrated selectivity values similar to, or better than, MSI-78. To understand if these polymers were membrane active, polymer induced lipid membrane disruption activities were evaluated by dye leakage experiments. Lipid composition and polymer hydrophobicity were found to be important factors for dye release.

R-Isophthalate (R = –H, –NO2, and –COOH) as modular building blocks for mixed-ligand coordination polymers incorporated with a versatile connector 4-amino-3,5-bis(3-pyridyl)-1,2,4-triazole

Abstract: A series of nine CoII, CuII, and CdII mixed-ligand coordination complexes with a 3,3′-dipyridyl connector 4-amino-3,5-bis(3-pyridyl)-1,2,4-triazole (3-bpt) have been achieved, by changing the incorporated benzenedicarboxylic co-ligands from isophthalic acid (H2ip) to its 5-substituted derivatives 5-nitroisophthalic acid (–NO2, H2nip) and trimesic acid (–COOH, H3tma). All compounds have been structurally determined by the X-ray diffraction technique. It is indicated that most of them are coordination polymers, with the ligands of benzenecarboxylic acids being doubly deprotonated to compensate the charge and bridge the metal ions, except for a monomeric ion-pair product [Co(3-bpt)2(H2O)4]·(H2tma)2·(H2O)2 (1c). These polymers display a variety of coordination frameworks, such as 1-D double-strand chain, 2-D layer with (4,4) topology, 2-D double layer, 2-D layer with (6,3) topology and 1-D molecular ladder etc. The results evidently reveal the profound substituent effect of the R-isophthalate building blocks on engineering such coordination arrays, in virtue of the versatility of 3-bpt with diversiform configurations and binding fashions. Nevertheless, the choice of metal ion is also significant in the structural assembly, and the low-dimensional coordination networks are further extended to diverse 3-D supramolecular crystalline lattices via noncovalent interactions especially hydrogen bonding. Solid-state properties such as thermal stability and fluorescence have also been investigated.

Doubly bonded systems between heavier Group 15 elements.

Abstract: There has been much interest in the synthesis and properties of doubly bonded systems between heavier Group 15 elements, i. e. heavier analogues of azo-compounds (dipnictenes), from the viewpoints of fundamental and material chemistry. Although such double-bond compounds between heavier main group elements are known to be highly reactive, too much so to be isolated as stable compounds, a number of reports on the synthesis of kinetically stabilized diphosphenes (RPPR), diarsenes (RAsAsR), and phosphaarsenes (RPAsR) bearing bulky substituent have been published since 1980. We have also succeeded in the synthesis of the first stable distibene (RSbSbR) and dibismuthene (RBiBiR) by taking advantage of efficient steric protection groups, 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl (Tbt) and 2,6-bis[bis(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyl (Bbt), and revealed their structures and properties systematically. Thus, the doubly bonded compounds between heavier Group 15 elements are no longer imaginary species but are those with real existence which are stable, even in the case of the heaviest non-radioactive element bismuth, when they are appropriately protected by bulky substituents. This Perspective describes our research on the chemistry of kinetically stabilized double-bond compounds between heavier Group 15 elements.

Access to Enantioenriched α-Amino Esters via Rhodium-Catalyzed 1,4-Addition/Enantioselective Protonation

Abstract: Conjugate addition of potassium trifluoro(organo)borates 2 to dehydroalanine derivatives 1, mediated by a chiral rhodium catalyst and in situ enantioselective protonation, afforded straightforward access to a variety of protected α-amino esters 3 with high yields and enantiomeric excesses up to 95%. Among the tested chiral ligands and proton sources, Binap, in combination with guaiacol (2-methoxyphenol), an inexpensive and nontoxic phenol, afforded the highest asymmetric inductions. Organostannanes have also shown to participate in this reaction. By a fine-tuning of the ester moiety, and using Difluorophos as chiral ligand, increased levels of enantioselectivity, generally close to 95%, were achieved. Deuterium labeling experiments revealed, and DFT calculation supported, an unusual mechanism involving a hydride transfer from the amido substituent to the α carbon explaining the high levels of enantioselectivity attained in controlling this α chiral center.

Material for organic electroluminescent element and organic electroluminescent element using the material

Abstract: PROBLEM TO BE SOLVED: To provide: an organic EL element which has high phosphorescence efficiency and long life, accompanies no pixel defect, and offers superior heat resistance; and a material for achieving the organic EL element. SOLUTION: The material for the organic EL element is represented by the general formula (1), and the organic EL element is provided by using that material. In the formula (1), X denotes oxygen or sulfur, Y denotes a single bond, a carbonyl group, a 1-20C alkylene group that may have a substituent, oxygen, or sulfur, R 1 denotes a 1-20C alkyl group that may have a substituent or an aryl group having 6 to 18 ring-forming carbon atoms that may have a substituent, R 2 to R 5 each independently denote the 1-20C alkyl group that may have a substituent or an aryl group having 6 to 18 ring-forming carbon atoms that may have a substituent, m, p, and q separately denote an integer of 0 to 4, n denotes an integer of 0 to 3, and L 1 and L 2 each independently denote a bivalent bond group selected from a carbonyl group, an arylene group having 6 to 18 ring-forming carbon atoms that may have a substituent, a fluorenediyl group, etc. COPYRIGHT: (C)2010,JPO&INPIT

Benzochrysene derivative and organic electroluminescent device using the same

Abstract: Disclosed is a fused aromatic ring derivative represented by the following formula (1). (In the formula, Ra and Rb independently represent a hydrogen atom or a substituent; p represents an integer of 1-13; q represents an integer of 1-8; when p is not less than 2, a plurality of Ra's may be the same as or different from each other, and adjacent Ra's may combine together to form a saturated or unsaturated ring; when q is not less than 2, a plurality of Rb's may be the same as or different from each other, and adjacent Rb's may combine together to form a saturated or unsaturated ring; L1 represents a single bond or a substituted or unsubstituted divalent linking group; and Ar1 represents a substituted or unsubstituted aryl group having 6-50 nuclear carbon atoms, or a substituted or unsubstituted heteroaryl group having 5-50 nuclear carbon atoms.)

Implications of monomer and initiator structure on the dissociative electron-transfer step of SET-LRP

Abstract: The heterolytic dissociation process associated with the activation of Single Electron-Transfer Living Radical Polymerization is examined through the use of energy profile modeling. Monomer and initiator structure is correlated with the approximate activation barriers, energies of electrostatic ion-radical pair formation, and stability of ion-radical pair generated from the counteranion halide leaving group and the radical atom with partial positive charge density induced by its electron-withdrawing substituent. Energy profiles permit access not just to one, but to all local minima, in the dissociation pathway and the identification of a global minimum. The location and energy of this global minimum allows for the placement of various initiators and dormant propagating macroradicals on the spectrum between stepwise and concerted dissociative electron-transfer. The barrier for the activation step for alkyl-halides derived from acrylates, vinyl halides, and styrenes, as well as from initiators bearing electron-withdrawing groups is decreased in comparison to relatively more electron-rich alkyl halides. This rate enhancement is explained through the sticky dissociative model wherein electron-transfer is accelerated by the formation of strong ion-radical pairs between radicals with partial positive charge density and their counteranion leaving group. Greater electron-withdrawing capacity of the alkyl halide substituent increases the stability of the ion-radical pair, reduces its equilibrium bond length, and accelerates electron-transfer. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5663–5697, 2008

Substituent position effect on the properties of new unsymmetrical isomeric diarylethenes having a chlorine atom

Abstract: Three new unsymmetrical photochromic diarylethenes bearing a chlorine atom at para-, meta- and ortho-position of one terminal benzene ring, namely {1-(2-methyl-5-phenyl-3-thienyl)-2-[2-methyl-5-(4-chlorophenyl)-3-thienyl]}perfluorocyclopentene (para 1o), {1-(2-methyl-5-phenyl-3-thienyl)-2-[2-methyl-5-(3-chlorophenyl)-3-thienyl]}perfluorocyclopentene (meta 2o), and {1-(2-methyl-5-phenyl-3-thienyl)-2-[2-methyl-5-(2-chlorophenyl) -3-thienyl]}perfluorocyclopentene (ortho 3o), have been synthesized. The substituent position effect on their properties, including photochromism, fluorescence both in solution and in PMMA amorphous film and their electrochemical properties were investigated in detail. The results elucidated that the chlorine atom and its substituent position had a remarkable effect on the absorption characteristics, photochromic reactivity, fluorescence, as well as the electrochemical performances of these diarylethene compounds. For diarylethenes 1, 2 and 3, the cycloreversion quantum yields were gradually increased when the chlorine atom was attached to the para-, meta- and ortho-positions of the one terminal benzene rings; but their molar absorption coefficients both of their open-ring and closed-ring isomers were remarkably decreased. The fluorescent properties of para-substituted diarylethene embedded in poly(methyl methacylate) (PMMA) amorphous film showed good fluorescent switches (quenched to 28%). Furthermore, the cyclic voltammograms experiments elucidated that the electrochemical properties of these diarylethene derivatives were also remarkably dependent on the chlorine atom position effect, which may be attributed to the different electron-inducing ability and steric effect when the chlorine atom was substituted on the different position of the terminal benzene ring.

Benzamide compounds and applications thereof

Abstract: Novel benzamide compounds and intermediate compounds thereof, as shown by formula I and II respectively, wherein the definition of each substituent see the description. Compounds with formula I has excellent insecticidal and fungicidal activities and can be used to control insect pest and diseases.

Ruthenium Complexes with Vinyl, Styryl, and Vinylpyrenyl Ligands: A Case of Non-innocence in Organometallic Chemistry

Abstract: We herein describe a systematic account of mononuclear ruthenium vinyl complexes L-{Ru}-CH=CH-R where the phosphine ligands at the (PR'3)2Ru(CO)Cl={Ru} moiety, the coordination number at the metal (L = 4-ethylisonicotinate or a vacant coordination site) and the substituent R (R = nbutyl, phenyl, 1-pyrenyl) have been varied. Structures of the enynyl complex Ru(CO)Cl(PPh3)2(eta1:eta2-nBuHC=CHCCnBu), which results from the coupling of the hexenyl ligand of complex 1a with another molecule of 1-hexyne, of the hexenyl complexes (nBuCH=CH)Ru(CO)Cl(PiPr3)2 (1c) and (nBuCH=CH)Ru(CO)Cl(PPh3)2(NC5H4COOEt-4) (1b), and of the pyrenyl complexes (1-Pyr-CH=CH)Ru(CO)Cl(PiPr3)2 (3c) and (1-Pyr-CH=CH)Ru(CO)Cl(PPh3)3 (3a-P) have been established by X-ray crystallography. All vinyl complexes undergo a one-electron oxidation at fairly low potentials and a second oxidation at more positive potentials. Anodic half-wave or peak potentials show a progressive shift to lower values as pi-conjugation within the vinyl ligand increases. Carbonyl band shifts of the metal-bonded CO ligand upon monooxidation are significantly smaller than is expected of a metal-centered oxidation process and are further diminished as the vinyl CH=CH entity is incorporated into a more extended pi-system. ESR spectra of the electrogenerated radical cations display negligible g-value anisotropies and small deviations of the average g-value from that of the free electron. The vinyl ligands thus strongly contribute to or even dominate the anodic oxidation processes. This renders them a class of truly "non-innocent" ligands in organometallic ruthenium chemistry. Experimental findings are fully supported by quantum chemical calculations: The contribution of the vinyl ligand to the HOMO increases from 46% (Ru-vinyl delocalized) to 84% (vinyl dominated) as R changes from nbutyl to 1-pyrenyl.

New Simple Hydrophobic Proline Derivatives as Highly Active and Stereoselective Catalysts for the Direct Asymmetric Aldol Reaction in Aqueous Medium

Abstract: New 4-substituted acyloxyproline derivatives with different hydrophobic properties of the acyl group were easily synthesized and used as catalysts in the direct asymmetric aldol reaction between cyclic ketones (cyclohexanone and cyclopentanone) and several substituted benzaldehydes. Reactions were carried out using water, this being the best reaction medium examined. Screening of these catalysts showed that compounds bearing the most hydrophobic acyl chains [4-phenylbutanoate and 4-(pyren-1-yl)butanoate] provided better results. The latter catalysts were successfully used in only 2 mol% at room temperature without additives to give aldol products in excellent stereoselectivities. These results demonstrate that derivatization of the proline moiety with the proper simple hydrophobic substituent in the 4-position can furnish highly active and stereoselective catalysts without the need of additional chiral backbones in the molecule. Finally, an explanation of the observed stereoselectivities in the presence of water is provided.