J. Appl. Cryst.の発刊に際して

: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Several ruthenium-based olefin metathesis catalysts of the formula (PR3)2X2RuCHCHCPh2 have been synthesized, and relative catalyst activities were determined by monitoring the ring-closing metathesis of the acyclic diene diethyl diallylmalonate. The following order of increasing activity was determined:  X = I < Br < Cl and PR3 = PPh3 ≪ PiPr2Ph < PCy2Ph < PiPr3 < PCy3. Additional studies were conducted with the catalyst (PCy3)2Cl2RuCH2 to probe the mechanism of olefin metathesis by this class of catalysts. The data support a scheme in which there are two competing pathways:  the dominant one in which a phosphine dissociates from the ruthenium center and a minor one in which both phosphines remain bound. Higher catalyst activites could be achieved by the addition of CuCl to the reaction.

Well-defined ruthenium olefin metathesis catalysts: Mechanism and activity

Structural chemistry of transition metal complexes of oximes

Chemistry and enzymology of vitamin B12.

Kinetic evidences for pre-equilibria in the substitution reactions of alkylbis(dimethylglyoximato)aquocobalt(III) complexes in aqueous solution

EXAFS Data Analysis of Vitamin B12 Model Compounds − A Methodological Study

Cleavage by halogens of carbon-cobalt bonds in organometallic complexes of cobalt(III)

Subsitution reactions of methylbis(dimethylglyoximato)rhodium(III) as a function of pH

Cobalt(III) complexes of the type [CoIII(chel)(OH)(H2O)], where chel is a tetradentate conjugated chelating ligand, react in water with CO yielding, in the pH range 4–13, [CoII(chel)]. Formation of [CoIII(chel)(CO2H)(H2O)] through nucleophilic attack of OH– on the intermediate [CoIII(chel)(CO)(OH)] is assumed. The carboxy-derivative decomposes yielding CO2 and [CoI(chel)]– species which, in turn, gives [CoII(chel)] by different reaction paths depending on pH of the solution. The same mechanism operates for the complex with the 2,3,9,10-tetramethyl-1,4,8,11-tetra-azaundeca-1,3,8,10-tetraen-11-ol-1-olato anion(tn) up to pH 8. In more alkaline solution (pH 13) the corresponding carbonyl derivative [CoI(chel)(CO)] can be isolated. With all chel complexes investigated the reaction in alkaline solution appears to be autocatalytic. Mono- and di-organometallic derivatives can be prepared by the same reaction in the presence of organic halides.

Giovanni Tauzher

Papers

Kinetic evidences for pre-equilibria in the substitution reactions of alkylbis(dimethylglyoximato)aquocobalt(III) complexes in aqueous solution

EXAFS Data Analysis of Vitamin B12 Model Compounds − A Methodological Study

Cleavage by halogens of carbon-cobalt bonds in organometallic complexes of cobalt(III)

Subsitution reactions of methylbis(dimethylglyoximato)rhodium(III) as a function of pH

Reduction of cobalt complexes by carbon monoxide and synthesis of mono- and bis-organometallic derivatives