- Oxidative addition reactions of compounds of the type (η5-C5Me5)Os(CO)LR (L = CO, PMe2Ph; R = alkyl). The role of oxidized intermediates in electrophilic cleavage reactions of osmium-carbon σ-bonds
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Compounds of the type Cp*Os(CO)LR (Cp* = η5-C6Me5; L = CO, PMe2Ph; R = Me, Et, i-Pr, CH2Ph), most of them new, have been prepared and their reactions with the electrophiles CF3CO2H, Br2, and HgBr2 have been investigated. All of the electrophiles oxidatively add to give labile, formally osmium(IV) complexes of the type [Cp*Os(CO)(L)(R)(E)]+X-, one of which, [Cp*Os(CO)(PMe2Ph)(Me)(HgBr)]+, has been isolated as the PF6- salt. In all cases, the osmium(IV) complexes decompose in solution to give the normal products of electrophilic cleavage.
- Johnston, Laura J.,Baird, Michael C.
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p. 2469 - 2475
(2008/10/08)
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- A Raman spectroscopic study of the complexation of the methylmercury(II) cation by amino acids
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A systematic Raman spectroscopic investigation of the complexation of CH3Hg(1+) by the standard amino acids is reported.It is shown that the vibrational bands due to the ligand-Hg and Hg-CH3 stretching modes and to the symmetric -CH3 bending mode of the -HgCH3 unit are well suited to characterize the extent of complexation and the sites of attachment of the cation.Coordination, which occurs mostly on sulfur and nitrogen atoms by substitution of a proton on the thiol group of cysteine or on amino groups in general, is best identified by the frequency of the ligand-Hg stretching vibration in the 250-550 cm-1 region of the spectrum.
- Alex, Serge,Savoie, Rodrigue
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p. 491 - 496
(2007/10/02)
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- Oxidative cleavage reactions of compounds of the type CpRuLL′R (L, L′ = CO, PPh3; R = Me, PhCH2)
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The compounds CpRuLL′R (Cp = η5-C5H5; L, L′ = CO, PPh3; R = Me, PhCH2) have been prepared, some by improved routes. Alkyl cleavage reactions with halogens, hydrogen chloride, mercury(II) halides, and
- Joseph, Michael F.,Page, John A.,Baird, Michael C.
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p. 1749 - 1754
(2008/10/08)
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- OXIDATION-REDUCTION MECHANISMS - INNER-SPHERE AND OUTER-SPHERE ELECTRON TRANSFER IN THE REDUCTION OF IRON(III), RUTHENIUM(III), AND OSMIUM(III) COMPLEXES BY ALKYL RADICALS. MECHANISMS -
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Alkyl radicals are readily oxidized by the tris(phenanthroline) and tris(bipyridine) complexes ML//3**3** plus of iron(III), ruthenium(III), and osmium(III) in acetonitrile solution, the second-order rate constants easily exceeding 10**6 M** minus **1s** minus **1 at 25 degree C. Two oxidative processes are identified as (a) ligand substitution on the coordinated 1,10-phenanthroline to yield various alkylphenanthrolines and (b) cation formation to afford alkenes and N-alkylacetamides (after hydrolysis). Cation formation is characterized by extensive skeletal rearrangement of neopentyl, isobutyl, and n-propyl groups, whereas ligand substitution by the same alkyl radicals occurs without any rearrangement.
- Rollick,Kochi
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p. 1319 - 1330
(2007/10/02)
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- Electron-Transfer Activation in Electrophilic Mechanisms. Cleavage of Alkylmetals by Mercury(II) Complexes
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The disappearance of the transient charge-transfer (CT) absorption bands coincides with the electrophilic (SE2) cleavage of homologous series of alkyltin compounds by various mercury(II) halides, cyanide, and carboxylates.The second-order kinetics for HgCl2 cleavage afford rate constants which vary in a rather unaccountable way with the structure of the alkyltin compound and with the polarity of the solvent.Furthermore, the relative reactivities of these alkyltin compounds in the analogous electrophilic cleavage by I2 or Br2 show poor correlations with HgCl2 cleavages, in different solvents.However, the description of the activation process as an electron transfer in the precursor complex, e.g., -> +HgCl2->, stems from the CT transition energy and leads to a linear free energy relationship in which the activation free energy is equal to the driving force for the formation of the ion pair.The latter is readily dissected by eq 18 into separate changes in electronic, steric and solvation energies.With this mechanistic formulation, the reactivities of various alkyltin compounds follow a remarkably simple linear correlation with the ionization potentials and the solvent effects, in the comparison with I2 and Br2 cleavages.Moreover, the reactivities of the various mercury(II) derivatives relate directly to differences in their electron affinities.
- Fukuzumi, S.,Kochi, J. K.
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p. 7290 - 7297
(2007/10/02)
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