177,076 research outputs found
Synthesis, X-Ray Structure, and Reactivity with Lewis Acids of Metallacyclopentane Derivatives of Rhodium(III) and Iridium(III). Observation of the First Boron Trifluoride-promoted C-H Bond Activation in Transition Metal Alkyls
No full textThe metallacyclopentanes [M{CH 2CH(R)CH(R′)CH 2}(η 5-C 5Me 5)(PPh 3)] [(1b) M = Rh, R = Me, R′ = H; (1c) M = Rh, R = R′ = Me; (1e) M = Ir, R = Me, R′ = H; (1f) M = Ir, R = R′ = Me; (1g) M = Ir, R = Pr i, R′ = H] were prepared by reacting the appropriate alkylating reagent M′[CH 2CH(R)CH(R′)CH 2]M′ (M′ = Li or MgCl) with the dichlorides of formula [MCl 2(η 5-C 5Me 5)(PPh 3)]. Complexes (1) were characterized by elemental analysis, 1H n.m.r., and mass spectrometry. The X-ray crystal structures of (1c), (1e), and (1f) have been determined. (1c) and (1f) give isostructural P2 1/c crystals, while (1e) crystallizes in the space group C2/c. The cell constants are: (1c), a = 14.982(9), b = 11.058(6), c = 18.421(10) Å, β = 101.13(2)°, Z = 4, R (3 964 reflections, 493 parameters) = 0.0443; (1e), a = 33.63(4), b = 9.29(1), c = 20.56(2) Å, β = 116.6(2)°, Z = 8, R (3 196, 476) = 0.0472; (1f), a = 15.01(2), b = 11.10(1), c = 18.44(2) Å, β = 100.90(4)°, Z = 4, R (4 136, 446) = 0.0334. All compounds possess a structure of the 'three-legged piano stool' type, the major differences lying in the puckering of the metallacyclopentane rings which is larger in the dimethylated derivatives (1c) and (1f) than it is in (1e), where the metallacyclic moiety is rather flattened. The endocyclic C β-C β′, bond in (1e) is 1.34(3) Å, while it is 1.51(1) and 1.52(1) Å in (1c) and (1f), respectively. The rhoda- and irida-cyclopentanes (1a) (M = Rh, R = R′ = H), (1b), (1c), (1d) (M = Ir, R = R′ = H), (1e), and (1f) react under very mild conditions, with BF 3·Bu n 2O and with [CPh 3][PF 6] to give the η 3-allyl complexes [M{η 3-CH 2C(R)C(R′)Me}(η 5-C 5Me 5)(PPh 3)][BF 4] (2) and [M{η 3-CH 2C(R)C(R′)Me}(η 5-C 5Me 5)(PPh 3)][PF 6] (3) [(a) M = Rh, R = R′ = H; (b) M = Rh, R = Me, R′ = H; (c) M = Rh, R = R′ = Me; (d) M = Ir, R = R′ = H; (e) M = Ir, R = Me, R′ = H; (f) M = Ir, R = R′ = Me], respectively, via the regiospecific hydrogen abstraction from the alkyl-substituted β-carbon atom by Lewis acids. Complexes (2) and (3) were characterized by elemental analysis, 1H n.m.r., and fast atom bombardment mass spectrometry
Structure and conformation of two gamma-substituted derivatives of alpha,beta-unsaturated carbonyl compounds
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The crystal and molecular structure of 7α-bromo-17β-acetoxy-4,13β-dimethyl(5,6-dihydro-1,4-Dithian)[1,2-b]estra1,3,5(10)triene
No full textINTRAOPERATIVE ILIAC ANGIOPLASTY AND DISTAL REVASCULARIZATION: IS IT AN EFFICACIOUS METHOD IN THE HIGH-RISK PATIENT?
No full textAlumina/Chloroform-promoted conversion of the ruthenacycles [Ru(CH2CMe2CH2)(eta-6-C6Me6)(PRPh2)] (R = Me or Ph) into the Chloro orthometallated derivatives [Ru(C6H4PRPh)Cl(eta-6-C6Me6)]
No full textInteraction of the ruthenacyclobutanes [Ru(CH2CMe2CH2)(eta6-C6Me6)(PRPh2)] (R = Me 1 or Ph 3) with neutral alumina causes the decomposition of the metallacyclic moiety, with the formation of 1,1-dimethylcyclopropane, neopentane and alumina-adsorbed metal complexes which lead to the corresponding chloro orthometallated compounds [Ru(C6H4PRPh)CI(eta6-C6Me6)] (R - Me 2 or Ph 4) by reaction with CHCl3. The X-ray crystal structure of complex 2 reveals the presence of clathrated benzene. Crystal data: space group P2(1)/c, a = 14.068(14), b = 15.392(13), c = 13.064(14) angstrom, beta = 116.38(6)-degrees, Z = 4, R = 0.0510
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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