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.

Treatment of R = −CH2X (X = halogen) derivatives of the type [RCoIII(LNH-py)(HLNH-py)]+, where HLNH-py = 2-(2-pyridyl-ethyl)amino-3-butanone oxime and LNH-py its conjugated base with diluted NaOH, afforded a new complex containing a three-membered ring by a pathway involving the intramolecular nucleophilic addition of an equatorial nitrogen donor to the axial carbon. The X-ray analysis reveals a highly distorted structure. The C−Co−N angle is acute (42.8°) with the distortion of the coordination sphere concentrated in the Co−C axial and Co−N bonds, which move away from the pseudo-octahedral positions in the CH2X parent complex to form the C−N bond of the metallocycle. Kinetic studies of the formation of this novel complex starting from [(XCH2CoIII(LNH-py)(HLNH-py)]+ (X = Cl,Br,I) showed that the metallocycle formation rates increase in the order Cl < Br < I. Kinetic data are consistent with a mechanism involving an intermediate species resulting from the deprotonation of an amine equatorial nitrogen in a ...

A new organocobalt complex containing a CO-N-C three membered ring.

The reactions of methylaquacobaloxime and ethylaquacobaloxime with 3-aminophenylboronic acid in water produce supramolecular triangles 3a and 3b respectively, through the reaction of boron with the oxime oxygens of the alkylcobaloxime and the coordination of pyridine to cobalt. The reaction is reversible and strongly pH dependent. The complexes 3a and 3b precipitate immediately from the solution at pH 7, but dissolve quickly at both acidic (below 4) and basic (above 9) pH values. The aggregates are re-formed by readjusting the pH to neutrality and the precipitation-dissolution cycle may be repeated several times without an apparent decrease in yield. The complexes were fully characterised by 1H and 13C NMR spectroscopy. The X-ray structure shows that the neutral chiral supramolecule 3a is a triangle of cobalt atoms with an approximate C3 symmetry. The side of the triangle is about 9.5 A. The ring closure is ensured by the torsion angles around the B−C and C−NH2 bonds, which vary in the range 25−30° and 97−109°, respectively. The reaction of methylaquarhodoxime with 3-aminophenylboronic acid in water at pH 7 results in the displacement of H2O by 3-aminophenylboronic acid only. The polymeric form 4 precipitates from CD3OD in the NMR tube with time. The X-ray structure shows that 4 is a polymeric species with a zig-zag chain arrangement, with Rh···Rh distances of 9.2 A. The chain arrangement is characterized by torsion angles around the B−C and C-NH2 bonds of 61° and 92°, respectively. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Self‐Assembly of Cobaloximes and Rhodoximes with 3‐Aminophenylboronic Acid: A Molecular Triangle and a Polymer

The reaction of a cis β folded organocobalt derivative with a salen-type ligand, 1, isolated as racemic compound of Δ and Λ enantiomers, with enantiomerically pure α-l amino acids is reported. The ...

Synthesis, characterization, and solution behavior of optically active cis β organocobalt salen complexes with L-amino acids

The reaction of methylaquobis(dimethylglyoximato)cobalt(III) with 3-pyridylboronic acid in CH2Cl2/CH3OH affords a dinuclear complex containing two methylcobaloxime units held together by two B(OCH3)(3-Py) residues, which is very stable in solution. The dimer is arranged around a crystallographic symmetry center so that the pendant pyridine residue of one moiety coordinates to the Co atom of the other in one axial position, the two pyridine rings being nearly coplanar.

Giovanni Tauzher

Papers

A new organocobalt complex containing a CO-N-C three membered ring.

Self‐Assembly of Cobaloximes and Rhodoximes with 3‐Aminophenylboronic Acid: A Molecular Triangle and a Polymer

Synthesis, characterization, and solution behavior of optically active cis β organocobalt salen complexes with L-amino acids

A New Dinuclear Complex Derived from Cobaloxime Units Held Together by 3-Pyridylboronic Acid Residues.

Kinetics of transfer of coordinated carbanions from cobalt to mercury(II) in two families of model vitamin B12 compounds