ABSTRACT
A series of 2-(N-methyl)benzylamino-1,3-thiazolium-4-olates (2-aminothioisomunchnones) react with chiral 1,2-diaza-1,3-butadienes derived from carbohydrates to afford a diastereomeric mixture of (4R,5S)- and (4R,5R)-4,5-dihydrothiophenes. These substrate-controlled cycloadditions are chemoselective, regiospecific, and proceed with a high facial diastereoselection. A theoretical rationale at semiempirical level does justify the stereochemical outcome observed in the experiments.
ABSTRACT
The geometries of four-coordinate CuI and CuII complexes in the Cambridge Structural Database (CSD) have been analysed systematically and compared using symmetry-deformation coordinates and principal component analysis. The observed stereochemistries have been rationalized in terms of the d-electron configurations, interligand repulsion and pi-bonding effects. The results confirm that the majority of four-coordinate copper(I) complexes in the CSD adopt tetrahedral geometries and deviations from tetrahedral symmetry are caused by the presence of chelating ligands or by the incorporation of copper centres into dimeric or polymeric structures. Four-coordinate copper(II) complexes generally adopt geometries close to square planar; this is particularly evident for bis(chelate) complexes where pi-bonding is important. Distortions towards tetrahedral geometries are attributable to steric interactions of bulky substituents in the bidentate ligands.
ABSTRACT
A methodology has been developed for the semi-automatic assignment and checking of formal oxidation states for metal atoms in the majority of metallo-organic complexes stored in the Cambridge Structural Database (CSD). The method uses both chemical connectivity and bond-length data, via ligand donor group templates and bond-valence sums, respectively. In order to use bond-length data, the CSD program QUEST has been modified to allow the coordination sphere of metal atoms to be recalculated using user-defined criteria at search time. The new methodology has been used successfully to validate the +1, +2 and +3 oxidation states in 743 four-coordinate copper complexes in the CSD for which atomic coordinates are available in ca 99% of structures using one or other method, and both succeed for >86% of structures.
ABSTRACT
Lithium cages containing hydride: The reaction of tBuLi with Me(2)AlN(2-Pyr)Ph in toluene gave [Li(8)(H){N(2-Pyr)Ph}(6)](+)[Li(Me(2)AltBu(2))(2)](-), whose cation is the first molecular main group metal species to contain interstitial hydride (the cluster core is shown in the picture). Treatment of the reaction mixture with THF gave the neutral hydride Li(7)(H)[N(2-Pyr)Ph](6), which has a capped octahedral (Li(+))(7) cluster core. 2-Pyr=2-pyridyl.
