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  • Ruthenium  (23)
  • Photochemistry  (16)
  • Wiley-Blackwell  (38)
  • 2015-2019
  • 1995-1999  (38)
  • 1999  (38)
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  • 2015-2019
  • 1995-1999  (38)
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  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 57-60 
    ISSN: 1434-193X
    Keywords: Benzyne ; Dehydroanthracene ; Matrix isolation ; Photochemistry ; Bergman reaction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -9,10-Didehydroanthracene (1) is an interesting derivative of p-benzyne that has been subject of several studies. In contrast to an earlier report, the photochemical decarbonylation of 9,10-dicarbonyl-9,10-dihydroanthracene (2) does not lead to 1 but rather to the ring-opened ene-diyne 4. The key intermediate for this reaction is keto carbene 7 which is formed by monodecarbonylation of 2. Carbene 7 is labile towards visible-light irradiation and easily looses the second CO molecule to give 4. Carbene 7 and diyne 4 are characterized by IR and UV/Vis spectra, the IR spectra are compared to calculations at the B3LYP/6-31G(d,p) level of theory.
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  • 2
    ISSN: 1434-193X
    Keywords: meta Photocycloaddition ; Photochemistry ; Steric hindrance ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Irradiation of a series of 5-(2-methoxyphenyl)pent-1-enes substituted with a hydroxy or trimethylsilyloxy group at the α-, β-, or γ-position of the side-chain yields in all cases meta photocycloadducts, in which the configuration at the substituted carbon atom is mainly endo. This indicates that the diastereoselectivity originates from minimization of steric interactions between the side-chain substituent and the ortho-methoxy group at the arene unit. Hydrogen bonding does not seem to be involved. The introduction of the side-chain substituents also influences the regioselectivity of the addition: The linear to angular adduct ratios are significantly increased compared to the case of the parent compound.
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  • 3
    ISSN: 1434-193X
    Keywords: 1β-Methylcarbapenems ; Palladium ; Ruthenium ; Catalysis ; Cyclizations ; Stereoselective hydrogenation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -An efficient diastereoselective multi-step synthesis of bicyclic 1β-methylcarbapenem antibiotic precursors has been developed, starting from the commercially available 4-acetoxyazetidin-2-one 4. Chiral ruthenium catalysts are used in the hydrogenation step to control the β-stereochemistry at the 1-position, and a π-allylpalladium ring-closure strategy is used to form the functionalized carbapenem skeleton.
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  • 4
    ISSN: 1434-193X
    Keywords: Crystal engineering ; Diynes ; Photochemistry ; Solid-state chemistry ; Polymers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The 1,6-bis(2,5-dimethoxyphenyl)hexa-2,4-diynes 4a-c were obtained from the corresponding 2,5-dimethoxybenzenes 1 by bromination followed by a copper-catalyzed Grignard reaction with 3-bromoprop-1-yne. Catalyzed coupling of the resulting 3-(2,5-dimethoxyphenyl)prop-1-ynes 3 under Hay conditions gave the hexa-2,4-diynes 4a-c in good yields. The molecular structures of the diynes 4a and 4b were determined by X-ray diffraction analysis. In each crystal structure, an unusual 1,6-synperiplanar conformation of the hexa-2,4-diyne unit is observed, with the 1,6-diphenyl substituents arranged in a coplanar orientation. According to the crystal structure data obtained, irradiation of diynes 4a and 4b afforded the deeply-colored, highly-ordered polymers 5a and 5b under topochemical control. Oxidation of 4a and 4b with cerium(IV) ammonium nitrate gave the corresponding 1,6-bis(2,5-dimethoxyphenyl)hexa-2,4-diyne-1,6-diones 6a and 6b.
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1005-1009 
    ISSN: 1434-193X
    Keywords: Hydrogen migration ; Anthronylidene ; Quinone methide ; Matrix isolation ; Photochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The photochemistry of 4-methyl-9,10-diazoanthrone (7a) and 1,4-dimethyl-9,10-diazoanthrone (7b) was investigated in argon matrices at 10 K. Visible-light irradiation results in the formation of the anthronylidenes 5a and b, respectively, which were identified by oxygen trapping, by comparison of the IR and UV/Vis spectra with that of the parent anthronylidene 6, and by comparison of the IR spectrum with that calculated by DFT methods. The carbenes 5 are thermally stable under the conditions of matrix isolation; however, irradiation with visible or UV light results in the rearrangement to the quinone methides 10a and b.
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1595-1600 
    ISSN: 1434-193X
    Keywords: Photochemistry ; Anthracenes ; Fluorescence spectroscopy ; Cycloaddition reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The novel 2,6-donor-acceptor-substituted anthracene, namely 6-methoxy-2-anthracene carboxylic acid (7), was synthesized. The emission of this compound exhibits significant solvatochromism. The fluorescence band position and intensity are also remarkably sensitive to H+. Irradiation of the anthracene 7 in solution yields the syn and anti head-to-tail dimers exclusively. A synergistic electronic effect between the donor and acceptor substituents is proposed to operate on the photophysical and photochemical properties of anthracene 7.
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  • 7
    ISSN: 1434-1948
    Keywords: Ruthenium ; Coordination chemistry ; Paramagnetic complexes ; Magnetic properties ; Ion exchange ; Antitumor agents ; Colon tumors ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Indazolium trans-tetrachlorobis(indazole)ruthenate(III) exhibits excellent results against different tumor models in vitro and in vivo. To improve the water solubility necessary for the introduction of this tumor-inhibiting compound into clinical trials, we synthesized the corresponding sodium salt in a two-step ion exchange via the tetramethylammonium salt. The sodium salt shows a 35-fold higher solubility in water relative to the indazolium salt. We also synthesized the n-butylammonium, n-octylammonium, and tetraphenylphosphonium salts, all of which showed improved solubility in organic solvents. The X-ray crystal structure of the latter could be solved, proving the trans configuration of the complex anion. In spite of the paramagnetic RuIII center an assignement of the coordinated indazole protons could be made with the help of a COSY experiment.
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  • 8
    ISSN: 1434-1948
    Keywords: Boranes ; Ruthenium ; Sandwich Complexes ; Diboroles ; Triple-decker ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The addition products of lithium alkyls and the pentaalkyl-2,3-dihydro-1,3-diborole derivatives 5a-f react with [{(C5Me5)RuCl}4] and [{(C5Me4Et)RuCl}4] to form the violet sandwich compounds 2*c-f and 2∧c, f. These formally 16 VE complexes are in fact electron-poor 18 VE species, because a high-lying combination of σ(B-C) orbitals interacts with the dxz orbital of the Ru atom. Addition of tert-butyl isocyanide to 2*a, or 2*d leads to the isonitrile complexes 6*a, and 6*d, as indicated by the spectroscopic data and X-ray structure analyses. At low temperature the interaction of 2*a, c, or e with H2 yields the classic dihydride complexes 7*a, c, and e, respectively, which have been studied by NMR. Oxidative addition of H3B·THF to the ruthenium atom of 2*a or c, followed by a reductive elimination of H2 and migration of the boranediyl group gives the yellow closo-RuC3B3 ruthenacarboranes 8*a and 8*c, respectively. The reaction of [(C2H4)2RhCl]2 and 2*c generates the tetranuclear complex 9*c.
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 341-348 
    ISSN: 1434-1948
    Keywords: N ligands ; S ligands ; Iron ; Ruthenium ; Pentadentate ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In order to obtain iron and ruthenium complexes which are analogous to [M(L)(′NHS4′)] and [M(L)(′N2H2S3′)] complexes [′NHS4′2- = 2,2′-bis(2-mercaptophenylthio)diethylamine(2-), ′N2H2S3′2- = 2,2′-bis(2-mercaptophenylamino)diethylsulfide(2-)] but have electron-richer metal centers, the new pentadentate amine thiolate ligand ′N3H3S2′-H2 [ = 2,2′-bis(2-mercaptophenylamino)diethylamine] (4) was synthesized. The dianion ′N3H3S2′2- reacted with FeII salts to give high-spin [Fe(′N3H3S2′)] (5) [μeff (293 K) = 3.94 μB], which yielded diamagnetic [Fe(CO)(′N3H3S2′)] (6) upon reaction with CO. Complex 6 exhibits a low-frequency ν(CO) band (1934 cm-1 in THF) indicating an electron-rich Fe center and a strong Fe-CO bond. In spite of this, 6 readily dissociated in solution to 5 and CO. The reaction of [RuCl2(PPh3)3] with ′N3H3S2′2- yielded [Ru(PPh3)(′N3H3S2′)] (7), which proved inert with respect to PPh3 substitution but could be methylated at the thiolate donors. The resulting [Ru(PPh3)(′N3H3S2′-Me2)]I2 (8) proved as inert towards substitution as 7. Complex 8 could reversibly be deprotonated to give [Ru(PPh3)(′N3H2S2′-Me2)]I (11), in the course of which the [RuPN3S2] cores rearrange from CS to C1 symmetry. Reversible protonation/deprotonation was also found with [Ru(NO)(′N3H2S2′)] (9) which formed from [RuCl3(NO)(PPh3)2] and ′N3H3S2′2- in the presence of one additional equivalent of LiOMe. Protonation of 9 with HBF4 gave [Ru(NO)(′N3H3S2′)]BF4 (10). The NMR spectra and the X-ray structure analysis of 8 proved that the [RuPN3S2] cores of 7 and 8 exhibit a CS-symmetrical meso structure. In all other complexes, however, the [MLN3S2] cores exhibit a C1-symmetrical structure. It results from the fac-mer coordination mode of the ′N3H3S2′2- ligand and favors the planarization of amide donors when NH functions are reversibly deprotonated.
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 651-654 
    ISSN: 1434-1948
    Keywords: Manganese ; Coordination modes ; 1-Hydronaphthalene complexes ; Trimethylphosphite addition ; Photochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Tricarbonyl(2-4,4a,8a-η-1-hydronaphthalene)manganese (1) reacts readily with trimethyl phosphite to afford tricarbonyl(2-4-η-1-hydronaphthalene)(trimethyl phosphite)manganese (2), by a simultaneous η5-η3-hapticity change. Upon UV irradiation, one carbonyl ligand is preferentially cleaved from 2 to yield dicarbonyl(2-4,4a,8a-η-1-hydronaphthalene)(trimethyl phosphite)manganese (3), with a η5-coordinated 1-hydronaphthalene ligand. In a similar fashion 3 also reacts with trimethyl phosphite and forms dicarbonyl(2-4-η-1-hydronaphthalene)bis(trimethyl phosphite)manganese (4), which loses carbon monoxide upon UV irradiation to afford carbonyl(2-4,4a,8a-η-1-hydronaphthalene)bis(trimethyl phosphite)manganese (5). All compounds were characterized by IR and NMR spectroscopy. The η5-1-hydronaphthalene complexes 1, 3 and 5 show hindered 1,4-H shifts of 1-Hendo. Considerable energy barriers were also found for the rotation of the 1-hydronaphthalene ligand in 2-5.
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  • 11
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 655-661 
    ISSN: 1434-1948
    Keywords: Manganese complexes ; Organyl complexes ; C-C coupling ; [5+2] Cycloaddition ; Cumulenes ; Photochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: [Mn(η5-C6H7)(CO)3] (1) forms highly reactive [Mn(η5-C6H7)(CO)2(THF)] (2) upon UV irradiation in THF at 208 K. Solvent complex 2 reacts between 208 and 293 K with 1,1-disubstituted allenes C3H2RR′ [R, R′ = CH3, CH3 (A); CH3, C6H5 (B); C2H5, C6H5 (C); C6H5, C6H5 (D); OCH3, Si(CH3)3 (E)] to four different types of complexes: The [5+2] cycloadduct [Mn(η3:2-C9H9RR′)(CO)3] (3E), rearranged [5+2] cycloadducts [Mn(η3:2-C9H9RR′)(CO)3] (4B, 4C, 4D), 1:2 adducts [Mn(η3:2-C12H11R2R′2)(CO)3] (5A-5E), and the 1:3 adduct [Mn{η3:2:2-C15H13(CH3)6}(CO)2] (6A). The constitutions of the products were established by IR and NMR spectroscopy, as well as by C,H elemental analysis and mass spectrometry. The crystal and molecular structure of 6A was determined by X-ray structure analysis. A formation mechanism for the complexes is proposed.
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  • 12
    ISSN: 1434-1948
    Keywords: Ruthenium ; Thiolate ligands ; Dithiolate ligands ; Substitution reactions ; Electrophilic additions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The known dithiolate-bridged ruthenium(I) complex [Ru2(μ-bdt)(CO)6] (1) (bdt = benzene-1,2-dithiolate) has been prepared in fair yield (55%) by the sequential treatment of RuCl3·nH2O with carbon monoxide, benzene-1,2-dithiol and zinc in a one-pot reaction. Complex 1 reacts readily with monodentate phosphanes to give, stepwise, the penta- and tetracarbonyl derivatives [Ru2(μ-bdt)(CO)6-n(PR3)n] (n = 1, 2; R = Ph, Cy, iPr). However, the reaction of 1 with one equivalent of bis(diphenylphosphanyl)methane (dppm) affords a mixture of complex 1 and the disubstituted derivative [Ru2(μ-bdt)(CO)4(η1-dppm)2], in which the dppm ligands are monodentate. This mixture is subsequently transformed into a polymeric material of formula [{Ru2(μ-bdt)(CO)4}(μ-dppm)]n, which consists of binuclear {Ru2(μ-bdt)(CO)4} units linked to each other by bridging dppm ligands. The use of two equivalents of dppm leads to [Ru2(μ-bdt)(CO)4(η1-dppm)2] in quantitative yield. The X-ray diffraction structure of [Ru2(μ-bdt)(CO)4(PiPr3)2] (3c) confirms that the phosphane ligands are located in axial positions, cis to both sulfur atoms, and that the Ru-Ru distance is short [2.6753(7) Å]. A comparative study of the reactivity of complexes 1 and 3c with the electrophiles H+, [Au(PPh3)]+, and HgCl2 has allowed the isolation of the derivatives [Ru2(μ-H)(μ-bdt)(CO)6-n(PiPr3)n][BF4] (n = 0, 2), [Ru2Au(μ-bdt)(CO)6-n(PiPr3)n(PPh3)][BF4] (n = 0, 2) and [Ru2HgCl2(μ-bdt)(CO)6-n(PiPr3)n] (n = 0, 2), respectively.
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  • 13
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1523-1529 
    ISSN: 1434-1948
    Keywords: Boron ; Iron ; Ruthenium ; Boryl Complexes ; Borylene Complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reactivity of aminodihaloboranes R2NBX2 (R = Me, SiMe3; × = Cl, Br) towards transition metal complexes of the type Na[(η5-C5R′5)M(CO)2)] (M = Fe, Ru; R′ = H, Me) was investigated. In the case of Me2NBBr2 and M = Fe the borylcomplexes [(η5-C5R′5)(CO)2Fe{BBr(NMe2)}] (C5R′5 = C5H59a; C5R′5 = C5H4Me 9b; C5R′5 = C5Me510) were obtained. The compounds 9aand 9bwere formed together with the corresponding bridged borylene complexes [μ-BNMe2(μ-CO){(η5-C5R′5)Fe(CO)}2] (C5R′5 = C5H511a; C5R′5 = C5H4Me 11b) in a 1:1 ratio, the latter, however, could be isolated from these mixtures as pure materials. In addition the novel boryl and borylene ruthenium complexes [(η5-C5H5)(CO)2Ru{BX(NMe2)}] (X = Cl 12a; × = Br 12b), [(η5-C5H5)(CO)2Ru{BCl{NSiMe3{BClN(SiMe3)2}}}] (13) and [μ-BN(SiMe3)2(μ-CO){(η5-C5H5)Ru(CO)}2] (14) were obtained by similar methods. All compounds were characterized by multinuclear NMR and IR spectroscopy. The structure of 13 in the solid state was determined by a single-crystal X-ray diffraction study.
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  • 14
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1707-1713 
    ISSN: 1434-1948
    Keywords: Carbene complexes ; Carbonyl complexes ; Diazoalkanes ; Hydrido complexes ; Ruthenium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The five-coordinate compound [RuHCl(CO)(PiPr2Ph)2] (1), which was prepared from RuCl3· 3 H2O and PiPr2Ph in methanol in the presence of NEt3, reacts with CO and with diazoalkanes RCHN2 (R = Ph, H) to give the six-coordinate complexes [RuHCl(CO)2(PiPr2Ph)2] (4) and [RuHCl(CO)(=CHR)(PiPr2Ph)2] (5, 6), respectively. If the reaction of 1 with CH2N2, which at -78 °C affords 6, is carried out at room temperature, the ionic compound [MePiPr2Ph][RuHCl2(CO)(PiPr2Ph)2] (7) is formed. The corresponding PPN salt was obtained from 1 and [PPN]Cl. The X-ray crystal structure analysis of 7 revealed, that the anionic species [RuHCl2(CO)(PiPr2Ph)2]- contains the chloro ligands in cis and the phosphanes in trans disposition. The Ru=CH2 bond of compound 6 is quite labile and, therefore, the CH2 unit is easily displaced by CO or pyridine. From 1 and pyridine, an isomeric mixture of [RuHCl(CO)(py)(PiPr2Ph)2] (9a, b) is formed. Treatment of 1 with HC≡CR (R = H, Ph) yields the five-coordinate vinylruthenium(II) complexes [Ru(CH=CHR)Cl(CO)(PiPr2Ph)2] (12, 13) by insertion of the alkyne into the Ru-H bond. The preparation of [RuHX(CO)-(PiPr2Ph)2] (X = CF3CO2, I) is also reported.
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  • 15
    ISSN: 1434-1948
    Keywords: Macrocycles ; Photochemistry ; Fluorescence spectroscopy ; Coordination chemistry ; Zinc ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The macrocyclic ligands L2 and L3, containing a triethylenetetraamine and a tetraethylenepentaamine moiety linked to the methyl groups of 2,9-dimethyl-1,10-phenanthroline, bind H+ and Zn2+ ions giving rise to modulation of the fluorescence emission intensity. The equilibrium constants and the enthalpy changes for ligand protonation were determined by means of pH-metric and microcalorimetric methods in 0.1 M Me4NCl solutions at 298.1±0.1 K. Also the stability constants of the Zn2+ complexes were determined under the same experimental conditions. L2 forms only mononuclear complexes, while L3 also forms dizinc(II) species. The phenanthroline group has fluorescence emission properties, but interaction with the lone pairs of benzylic nitrogen atoms produces an efficient quenching of the emission. Such a quenching effect can be avoided by deactivation of the benzylic nitrogen atoms by means of protonation or Zn2+ complexation. Hence, L2 and L3 behave as chemosensor for H+ and Zn2+, the photochemical properties of the ligands being modulated by the formation of different protonated and complexed species. In the case of L3, the fluorescence emission is also controlled by the metal to ligand molar ratio, because of the formation of an emissive binuclear complex.
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  • 16
    Electronic Resource
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    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1919-1930 
    ISSN: 1434-1948
    Keywords: Ruthenium ; Chirality ; Cyclopentadienyl complexes ; Kinetics ; Asymmetric catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Novel, functionalized, chiral Cp-ligands with S- and P-donor atoms were designed. Together with known analogues containing ether side-chains they were complexed to ruthenium for use as chiral Lewis-acid catalysts. In the ether complexes [RuCl(η5-C5H4CH2CH2OR)(PPh3)2] {R = Me, (1S)-isobornyl, (1R)-menthyl, (1R)-fenchyl} the Cp-ligand is only η5-coordinated; all attempts to provoke a bidentate, Cp/O coordination were unsuccessful. The sulfide complex [Ru{η5:η1-C5H4CH2CH2S[(1R)-neomenthyl]}(PPh3)2][OTf] contains a bidentate Cp/S-coordinated ligand, but it is unstable. The stable phosphane complex [RuCl(η5:η1-C5H4CH2CH(Me)PPh2)(PPh3)] exists as a 77:23 mixture of diastereomers containing a strongly bidentate Cp/P ligand. The diastereomers interchange, with Ru-Cl bond cleavage as the rate-determining step.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2005/1999/99126_s.pdf or from the author.
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  • 17
    ISSN: 1434-1948
    Keywords: Ruthenium ; Photochemistry ; Photosubstitution ; Diimine chelates ; Sterically hindered ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Mixed ruthenium(II) complexes containing 1,10-phenanthroline (or 2,2′-bipyridine) and a sterically congested bidentate ligand such as 2,9-diphenyl-1,10-phenanthroline, 6,6′-dimethyl- or 6,6′-diphenyl-2,2′-bipyridine, or 1-(2′-pyridyl)-3,5-dimethylpyrazole undergo clean and selective ligand substitution under irradiation with visible light. For instance, Ru(phen)2(dmbp)2+ in CH3CN is quantitatively converted to Ru(phen)2(CH3CN)22+ in a photochemical reaction accompanied by expulsion of the sterically hindering chelate dmbp (phen = 1,10-phenanthroline; dmbp = 6,6′-dimethyl-2,2′-bipyridine). Interestingly, 2,2′-bipyridine was found to be photochemically ejected in one case, probably as a consequence of its greater flexibility.
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  • 18
    Electronic Resource
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    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 729-737 
    ISSN: 1434-1948
    Keywords: Ab initio calculations ; Matrix isolation ; Rare-gas compounds ; Solid-state chemistry ; Photochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of novel neutral rare-gas-containing molecules of type HXY, where × = Xe or Kr and Y is an electronegative atom or fragment, is discussed. The molecules are characterised experimentally by their vibrational spectra and computationally by extensive ab initio calculations. They are formed in low-temperature rare-gas solids from neutral reagents and their bonding consists of both covalent and ionic contributions. Our recent studies add to the previously known class of rare-gas chemical bonds in neutral ground-state molecules the new bonds Xe-H, Xe-I, Xe-Br, Xe-S, Kr-H, Kr-C, and Kr-Cl.
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  • 19
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    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2121-2126 
    ISSN: 1434-1948
    Keywords: Ruthenium ; Allenylidene complexes ; Butadiyne ; Electrochemistry ; Thio-Claisen rearrangements ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ruthenium-butatrienylidene cations trans-[Cl(L2)2Ru=C=C=C=CH2]+ are key intermediates in the synthesis of the first thioallenylidene complexes trans-[Cl(L2)2Ru=C=C=C(SR)R′]+ (L2 = dppm, R = Et, R′ = Me: 3a, L2 = dppm, R = Me, R′ = C4H7: 3b, L2 = dppe, R = C3H5, R′ = C4H7: 3c). Spectroscopic and electrochemical data for 3a-c are presented and are compared with those of their aminoallenylidene analogues. Aminoallenylidene complexes are best represented by the iminiumalkynyl resonance form, while a true cumulene description is much more appropriate for thioallenylidene complexes 3a-c. Based on a combination of spectroscopic and electrochemical data, we present evidence that the NMR shifts of the carbon atoms of the unsaturated ligand in these allenylidene complexes are correlated to the HOMO-LUMO gap. In situ EPR-, UV/Vis-, and IR-spectro-electrochemistry reveals that the one-electron oxidation occurs at the metal center, while reduction occurs at the carbon-heteroatom terminus.
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  • 20
    ISSN: 1434-1948
    Keywords: Biaryls ; Lactones ; Nucleophilic additions ; Ruthenium ; S ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The substitution-labile thiophene complex [CpRu{(S,S)-CHIRAPHOS}(SC4H4)]BF4 (2) [(S,S)-CHIRAPHOS = (2S,3S)bis(diphenylphosphanyl)butane], prepared from [CpRu{(S,S)-CHIRAPHOS}Cl] (1), thiophene, and AgBF4, reacted with the biaryl-thionolactones 3a-f to give the corresponding S-coordinated complexes 4a-f in high yields. The structure of 4c, which crystallized as the pure (S,S,P) diastereoisomer, was determined by X-ray crystallography. Coordination of the ruthenium fragment caused an elongation of the C=S bond, a contraction of the C-O bond within the lactone ring and a flattening of that ring. Single hydride transfer with LiBEt3H converted 4a-f into the thiolactolate complexes 5a-f in good yields and diastereoselectivities. An X-ray structure determination of the major isomer of 5a revealed it to be the (S,S,S,P) diastereoisomer. Protonation with NH4PF6 converted 5a-f into the corresponding ring-opened thioaldehyde complexes 6a-f. Alkylation of 5a with methyl iodide resulted in Ru-S cleavage to give the oxothioacetal 7a and [CpRu{(S,S)-CHIRAPHOS}I] (8). Full reduction of 4a-f with LiAlH4 produced the thiolate complexes 9a-f in high yields and 6-74% de. Methylation at sulfur converted 9a-c into the corresponding thioether complexes 10a-c, which were cleaved to 8 and the free methyl thioethers 11a-c without isomerization of the biaryl axis.
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  • 21
    ISSN: 1434-1948
    Keywords: Asymmetric catalysis ; Transfer hydrogenation ; Ruthenium ; Amino alcohol ligands ; X-ray structure ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The nature of ruthenium-amino alcohol precursors in the catalytic cycle of asymmetric hydrogen transfer reactions was studied using two C2-symmetrical tetradentate ligands (1 and 2) that were synthesised from (nor)ephedrine. The structure of the catalyst precursor was examined through catalysis and NMR experiments. It was shown that the active catalyst contains one ligand per metal, which coordinates in a didentate N,O fashion (9). In addition, a RuIICl2 complex, in which N,N′-bis(2-hydroxy-1-methyl-2-phenylethyl)-1,2-diaminoethane (1) coordinates through two nitrogen atoms, was structurally characterised by X-ray diffraction (8). - Based on the results of this study a series of new amino alcohol ligands was synthesised from easily available starting materials. Optimisation of the amino alcohol ligand structure resulted in the most effective chiral amino alcohol ligand (5) so far that is capable of reducing acetophenone at 0 °C with up to 97% ee in the RuII-catalysed transfer hydrogenation.
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  • 22
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1-5 
    ISSN: 1434-1948
    Keywords: Terpyridine ligands ; Ferrocenes ; Iron ; Ruthenium ; Cyclic voltammetry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2,2′:6′,2′′-Terpyridines bearing a substituent × in the 4′-position [3a: × = Fc-C≡C-p-C6H4; 3b: × = Fc#-C≡C-p-C6H4; Fc = (C5H5)Fe(C5H4), Fc# = (C5Me4H)Fe(C5Me4)] were prepared by Pd0-catalysed cross-coupling reactions. 3b was characterised by X-ray structure analysis. [(3a)RuCl2(DMSO)] (4a) and [(3b)RuCl2(DMSO)] (4b) were obtained by reaction of [RuCl2(DMSO)4] with 1 equivalent of 3a and 3b, respectively, while the analogous reaction with 2 equivalents afforded [(3a)2Ru][PF6]2 (5a) and [(3b)2Ru][PF6]2 (5b), respectively, after precipitation with aqueous [NH4][PF6]. Similarly, [(3a)Ru(tpy)][PF6]2 (6) was isolated from the reaction of 4a with 2,2′:6′,2′′-terpyridine (tpy). Compounds 3 and 5 were investigated by cyclic voltammetry, which revealed that the introduction of eight methyl groups leads to the expected cathodic shift of the E0′ values of ca. 0.44 V for the ferrocenyl-centered redox processes.
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  • 23
    ISSN: 1434-1948
    Keywords: Ruthenium ; Halogens ; Carbonyl complexes ; Structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Aqueous hydrogen halides HX (X = Cl, Br, I) are shown to be excellent halogen sources for the synthesis of a series of halogen-containing ruthenium mono(2,2′-bipyridine) carbonyl complexes Ru(dmbpy)(CO)2X2 (dmbpy = 4,4′-dimethyl-2,2′-bipyridine), as well as effective reagents for the attack of the Ru-Ru bond in the dimer [Ru(dmbpy)(CO)2Cl]2. Selective syntheses were established for both cis- and trans-halogen complexes in the case of Cl- and of Br-containing derivatives, but the only stable isomer containing iodine was trans(I)-Ru(dmbpy)(CO)2I2. The failure to obtain the cis isomer was probably due to sterical effects. Furthermore, a novel S-bound trans(SCN) analogue was synthesized and structurally characterized. In all experiments, the reaction conditions selected led to complete halogen exchange; no mixed halogen or pseudohalogen complexes were detected.
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  • 24
    ISSN: 1434-1948
    Keywords: Cleavage reactions ; C-S cleavage ; Ligand synthesis ; Osmium ; Ruthenium ; S ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In search of a tetradentate thioether thiolate ligand that is more stable toward reductive C-S bond cleavage than the parent ligand ′S4′-H2 [′S4′-H2 = 1,2-bis(2-mercaptophenylthio)ethane], the novel tris-phenylene ligand ′tpS4′-H2 (3) [′tpS4′-H2 = 1,2-bis(2-mercaptophenylthio)phenylene] was synthesized via the nitro and amine compounds ′tpS2(NO2)2′ (1) and ′tpS2(NH2)2′ (2). The coordination of ′tpS4′2- to ruthenium centers resulted in the formation of six-coordinate [Ru(L)(PR3)(′tpS4′)] complexes (R = Et, L = PEt34; R = Ph, L = PPh35, CO 6, DMSO 7). The X-ray structure analyses of 4 and 6 revealed that the thiolate donors occupy trans positions; consequently the ′tpS4′2- ligand coordinates in the same way as the ′S4′2- ligand. The stability of the ′tpS4′2- ligand toward reductive C-S cleavage reactions was shown by the synthesis of [Os(PEt3)2(′tpS4′)] (8). In contrast to [Os(PEt3)2(′S4′)], 8 is stable for unlimited periods of time. The X-ray structure analysis of [Ru(Cl)2(PPh3)(′tpS2(NH2)2′)] (9) demonstrates that the potentially tetradentate ligand ′tpS2(NH2)2′ coordinates in 9 through three donors leaving one NH2 donor dangling.
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  • 25
    ISSN: 1434-1948
    Keywords: Spectroelectrochemistry ; Cyclic voltammetry ; Photochemistry ; Copper(II) complexes ; Thiolate complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electrochemical and photoredox properties of copper(II) thiopyrazolone Schiff base complexes 1-9 with imine and thiolate coordination, showing variable degrees of tetrahedral distortion, were investigated by means of combined electrochemical and spectroscopic techniques in the temperature range of 193-293 K. The cyclic voltammograms of 1-9 in butyronitrile revealed that the reduction and oxidation paths are strongly dependent on the geometry of the CuN2S2 moiety. Due to the strong delocalization of the singly occupied redox orbital (SOMO) the oxidations and reductions occur in a narrow potential range. The one-electron-reduced 1(r)-9(r) and oxidized 1(o)-9(o) products were electrogenerated and stabilized inside optically transparent thin-layer electrochemical (OTTLE) cells at variable temperatures and could be characterized for the first time by UV/Vis spectroscopy. The reduced formal d10 copper(I) species absorb only weakly in the visible region. The oxidized products 1(o)-9(o) show several strong absorptions in the visible region due to the presence of formal d8 copper(III) species. The spectral information allowed assignment of the initial photoproducts. Irradiations in donor media such as THF or EtOH initially produces 1(r)-9(r). No photoreduction was observed in tBuOH which cannot liberate reducing Hα. The primary oxidized species 1(o)-9(o) were formed in chlorinated acceptor solvents (CHCl3) on UV irradation. Fast relaxation to the ground state prevents the photoredox reactions from CT or LF excited states.
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  • 26
    ISSN: 1434-1948
    Keywords: Ruthenium ; Triazole ; Titanium ; Electron Transfer ; Sensitizers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The complexes [Ru(dcb)2(L)] {L = 3-(2-hydroxyphenyl)-5-(pyridin-2-yl)-1,2,4-triazole (2-ppt), 3-(4-hydroxyphenyl)-5-(pyridin-2-yl)-1,2,4-triazole (4-ppt), 3,5-bis(pyrazin-2-yl)-1,2,4-triazole (bpzt), 3-(2-hydroxyphenyl)-5-(pyrazin-2-yl)-1,2,4-triazole (2-ppzt) and dcb = 4,4′-(CO2H)2-2,2′-bipyridine} have been synthesized, spectroscopically characterized and anchored to nanocrystalline TiO2 electrodes for the conversion of light into electricity in regenerative solar cells. The different efficiencies observed have been rationalized on the basis of an analytical expression relating the incident photon-to-current conversion efficiency (IPCE) to the kinetic parameters of the relevant electron transfer processes involved in the solar cell.
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  • 27
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 917-930 
    ISSN: 1434-1948
    Keywords: Halides ; Homogeneous catalysis ; Organometallics ; Ruthenium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: While the primary motivation of fundamental studies on carbonylhalotriruthenium complexes was to understand the promoter effect of halides on certain ruthenium-based catalytic systems of industrial relevance, such complexes have gained significance in their own right due to their remarkable ability to provide low-activation energy pathways for the coordination of organic substrates. Limitations inherent to the fragility of these prototypes led to the design and development of a related family of more sophisticated derivatives where an aminopyridyl group serves as an alternate hemilabile ancillary ligand. Studies of their reactivity have revealed the possibility of achieving a number of stoichiometric or moderately catalytic “cluster-mediated” transformations of organic substrates under very mild conditions. Yet, the viability of these systems is still limited to a narrow low-energy domain. By contrast, halotriruthenium derivatives are still seen to function as catalyst precursors under the actual conditions of certain catalytic reactions where they act as sources of ruthenium(II) halide complexes that become the active components of the system. The second part of the review focuses on novel aspects of their fascinating chemistry.
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  • 28
    ISSN: 1434-1948
    Keywords: Ruthenium ; Osmium ; Phosphane-thiolate ligands ; C-P bond activation ; C-S bond activation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2-(Diphenylphosphanyl)thiophenol (HSC6H4PPh2) reacts with the carbonyl clusters [Ru3(CO)12] and [Os3(CO)10(MeCN)2] to give mixtures of products, the composition of which depends upon the reaction conditions and the ratio of the reactants. The derivatives [M3(μ-H)(μ-η2-SC6H4PPh2)(CO)9] (1a: M = Ru; 1b: M = Os), [Ru3(μ3-S)(μ-η2-Ph)(μ-PPh2)(PPh3)(CO)6] (2), and [Ru2(μ-η2-SC6H4PPh2)2(CO)4] (3) have been isolated. The SC6H4PPh2 ligand of compounds 1a and 1b has the sulfur atom spanning the same M-M edge as the hydride ligand and the phosphorus atom attached to one of the bridged metal atoms. Compound 2, which contains sulfide, phenyl, diphenylphosphanyl and triphenylphosphane ligands that arise from HSC6H4PPh2, has the Ru3 triangle capped by the sulfide and two Ru-Ru edges spanned by bridging phenyl and diphenylphosphanyl ligands. In complex 3, the two SC6H4PPh2 ligands have the same coordination behavior as in 1a or 1b; this binuclear complex is more conveniently prepared by treating [Ru2(μ-η2-MeCO2)2(CO)4(MeCN)2] with HSC6H4PPh2.
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  • 29
    ISSN: 1434-1948
    Keywords: Ruthenium ; Nitrogen heterocycles ; Hydrogen bonds ; Antitumor agents ; Crystal structures ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The X-ray structure of the potential antitumour complex trans-[RuCl3(H2O)(admtp)2] · H2O (admtp = 2-amino-5,7-dimethyl[1,2,4]triazolo[1,5-a]pyrimidine) shows unique and very interesting intramolecular hydrogen-bonding properties with the non-bridgehead pyrimidinic nitrogen atom of admtp acting as hydrogen acceptor and the amino group acting as hydrogen donor.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2005/1999/98348_s.pdf or from the author.
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  • 30
    ISSN: 1434-1948
    Keywords: Cluster compounds ; Ruthenium ; Iridium ; Alkynes ; Butterfly structures ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The tetrahedral cluster anion [Ru3Ir(CO)13]- (1) reacts with internal alkynes RC≡CR′ to afford the alkyne derivatives [Ru3Ir(CO)11(RCCR′)]-(2: R = R′ = Ph; 3: R = R′ = Et; 4: R = Ph; R′ = Me; 5: R = R′ = Me) which have a butterfly arrangement of the Ru3Ir skeleton in which the alkyne is coordinated in a μ4-η2 fashion. Under CO pressure they undergo fragmentation to give the trinuclear cluster anions [Ru2Ir(CO)9(RCCR′)]- (6: R = R′ = Ph; 7: R = R′ = Et; 8: R = Ph; R′ = Me; 9: R = R′ = Me), in which the alkyne ligand is coordinated in a μ3-η2 parallel fashion. Protonation of these trinuclear anions leads to the formation of the corresponding neutral hydrido clusters [HRu2Ir(CO)9(RC≡CR′)] (10: R = R′ = Ph; 11: R = R′ = Et; 12: R = Ph; R′ = Me; 13: R = R′ = Me). The protonation of the butterfly anions 2 and 3, however, gives rise to the formation of the neutral tetrahedral clusters [HRu3Ir(CO)11(RCCR′)] (14: R = R′ = Ph and 15: R = R′ = Et), respectively. The analogous clusters [HRu3Ir(CO)11(PhCCCH3)] (16) and [HRu3Ir(CO)11(CH3CCCH3)] (17) are only accessible from the reaction of the neutral cluster [HRu3Ir(CO)13] with the corresponding alkynes. The complexes 2, 4, 5, 6, 10, 12 and 15 are characterised by X-ray structure analysis.
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  • 31
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1141-1149 
    ISSN: 1434-1948
    Keywords: C-C coupling ; Metallacycles ; Metallacyclobutane ; Ruthenium ; Tripodal ligands ; Vinylidene complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Selective coupling of olefins and terminal acetylenes is shown to be effected in the coordination sphere of RuII by the successive intermediacy of vinylidene and ruthenacyclobutane complexes. Subsequent deprotonation of one of the β-hydrogen atoms of the latter by NaOEt yields η3-butadienyl complexes, while in the presence of Cl- rearrangement takes place to give neutral η2-butadiene complexes by a β-hydrogen elimination/reductive elimination sequence. [Ru(tp)(COD)Cl] and [Ru(tp){η3-(P,C,C)-Ph2PCH=CHC(Ph)=CH2}Cl] were the starting materials which were treated with HC≡CR (R = Ph, C6H9, ferrocenyl, CH2Ph, nBu). The η3-butadienyl complexes are nucleophilic at the enynyl carbon atom reacting readily with the electrophiles H+ and I2 to give the corresponding η2-butadienyl complexes. X-ray structures of representative products are given.
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  • 32
    ISSN: 1434-193X
    Keywords: Proteins ; Cross coupling ; Drug research ; Photochemistry ; Toxicology ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -To gain insight into the chemical nature of drug-induced photoallergy, model studies have been carried out on the photochemical modification of proteins by tiaprofenic acid. Irradiation of decarboxylated tiaprofenic acid (DTPA) in the presence of p-cresol leads to C-C- and C-O-connected p-cresol “dimers”, together with DTPA hydrodimers. The p-cresol-DTPA cross-coupling product was not detected in this reaction. However, a product of this type is formed using a more hindered phenol, such as 2,6-di-tert-butylphenol. Similar results are obtained when tiaprofenic acid (TPA) or its methyl ester are used as photosensitizers. The observed formation of “dimers” can be related to protein photo-crosslinking, through the coupling of two tyrosine units. On the other hand, phenol-(D)TPA cross-coupling may be relevant to the understanding of drug-protein photobinding.
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  • 33
    ISSN: 1434-193X
    Keywords: Matrix isolation ; IR spectroscopy ; Photochemistry ; Diradicals ; Isomerizations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Bicyclopropylidene (3) and 1,2-dimethylenecyclobutane (7) have been irradiated in rare-gas matrices. If 1,2-dimethylenecyclobutane (7) is exposed to the light of a KrF excimer laser (λ = 248 nm), an isomeric species is produced, showing an absorption at 793.1 cm-1 (argon matrix) or 791.2 cm-1 (xenon matrix) in the IR spectrum. The back reaction can be induced with light of λ = 254 nm. This photochemical interconversion, together with the comparison between the experimental and calculated band positions, supports the assignment of the IR absorption near 790 cm-1 to tetramethyleneethane (5).
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  • 34
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1723-1728 
    ISSN: 1434-193X
    Keywords: Oxygenations ; Singlet Oxygen ; Sulfides ; Photochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The photosensitised oxidation of benzyl ethyl sulfides in aprotic solvents (benzene or acetonitrile) gives the corresponding aldehydes under mild conditions. This is a general reaction which applies to benzyl derivatives containing either electron-donating or electron-withdrawing substituents and furthermore to hetero analogues such as 2-pyridinylmethyl sulfide (not to the 3-indolylmethyl sulfide, since reaction at the heterocycle moiety competes) as well as to allyl sulfides. In a protic solvent (methanol) these sulfides give the sulfoxides instead (except for the nitrobenzyl derivatives, where the aldehyde remains the major product). Among the α-substituted sulfides tested, the α-phenylbenzyl and the 3-cyclohexenyl sulfide give the corresponding ketone (the latter in a low yield), but the α-methylbenzyl sulfide gives the sulfoxide as the main product. The rate for singlet oxygen quenching and for chemical reaction have been measured for representative benzyl sulfides. The reaction is discussed in the frame of the currently accepted mechanism for sulfide photooxygenation. The key step for oxidative C-S bond cleavage appears to be hydrogen transfer from the activated α position in the first formed intermediate, the persulfoxide. This reaction is inhibited in methanol where the persulfoxide is hydrogen-bonded.
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  • 35
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2315-2321 
    ISSN: 1434-193X
    Keywords: Asymmetric catalysis ; Transfer hydrogenations ; Ruthenium ; Coordination chemistry ; Nitrogen heterocycles ; Synthetic methods ; Hydrogenations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chiral 1,2,3,4-tetrahydroisoquinoline intermediates in the Rice and Beyerman routes to morphine, (+)-(R)-1-(3-hydroxy-4-methoxybenzyl)-6-methoxy-1,2,3,4-tetrahydroisoquinoline (6) and (+)-(R)-1-(3,5-dibenzyloxy-4-methoxybenzyl)-6-methoxy-1,2,3,4-tetrahydroisoquinoline (5), were prepared in high ee by ruthenium-catalyzed asymmetric transfer hydrogenation of the corresponding imine precursors (Noyori method). The yield of the key raw material in the Beyerman route, 3,5-dibenzyloxy-4-methoxyphenylacetic acid (1), starting from gallic acid methyl ester (7) was improved by a factor of 5 over previously described syntheses. Key steps in the new procedure are the selective formation of methyl 3,5-dihydroxy-4-methoxybenzoate (9) via the 3,5-diacetate and an improved benzylation of the hydroxyl groups in 9.
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  • 36
    ISSN: 1434-193X
    Keywords: Photochemistry ; Cycloadditions ; Small ring systems ; Rearrangements ; Electron transfer ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Solutions of chloranil (CA) in toluene or benzene have been irradiated in the presence of the C7H8 valence isomers homobenzvalene (HB), norbornadiene (N), and quadricyclane (Q). In the case of HB, the adducts 3-6 were obtained, all of them having a rearranged structure. By a separate irradiation it was shown that 4 is a consecutive product of 3. The structure of 4 was established by X-ray diffraction analysis. These reactions are most probably initiated by an electron transfer (ET) from HB to 3CA, continue by bond formation between the radical ions to give the zwitterion 14, which undergoes Wagner-Meerwein rearrangements, and are completed by ring-closure between the charged centres of the resulting zwitterions. The oxidation potential of N is not larger than that of HB and the products 8-10 may well be formed through an ET to 3CA. However, the pathway leading to product 3 most probably involves diradical intermediates. This should also be the case for the adducts 11 and 12, which were produced upon irradiation of methyl phenylglyoxylate (PG) in the presence of N. In the case of Q, an ET to 3CA is again highly likely, followed by a combination of the radical ions to generate the zwitterion 29, which eventually collapses to produce the oxetane 8 as the sole identifiable product. The photoreactions of CA with N and Q proceeded much less efficiently in acetonitrile solution.
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  • 37
    ISSN: 1434-193X
    Keywords: Ruthenium ; Ring-closing metathesis ; Metathesis ; EPC synthesis ; 1,2-Diaminocyclohex-4-ene ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantiopure (1R,2R)-1,2-diaminocyclohex-4-ene derivatives have been synthesized by the ruthenium-catalyzed ring-closing metathesis reaction of (4R,5R)-N,N′-bis[(S)-1-phenylethyl]-4,5-diamino-1,7-octadiene dihydrochloride.
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  • 38
    ISSN: 1434-193X
    Keywords: Photochemistry ; Alkylation ; Radicals ; Radical ions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In aprotic media, photoinduced electron transfer from toluene to 1,4-naphthalenedicarbonitrile (DCN) is followed by in-cage proton transfer and radical coupling. However, in the presence of a protic co-solvent, the radical ions diffuse out of the cage and deprotonation of the toluene radical cation takes place from the free solvated species. With tBuOH, this results in reductive benzylation of DCN through coupling of benzyl radicals with DCN-·. With MeOH, secondary hydrogen abstraction by PhCH2· yields hydroxymethyl radicals, which couple with DCN-·. Both benzyl and hydroxymethyl radicals are efficiently trapped by electrophilic alkenes. Thus, in the presence of dimethyl maleate, DCN-photosensitized benzylation - or hydroxymethylation - of the substrate occurs through direct activation of the C-H bond. The same reaction has been accomplished with acrylonitrile, albeit with a lower yield.
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