Jan Hvoslef

Rupture and realignement of the bridging phosphine framework in the reactions of polynuclear rhodium complexes of 2,6-bis(diphenylphosphino)pyridine

Exemple de rupture et de realignement dans le traitement du complexe Rh 4 [μ-(Ph 2 P) 2 py] 2 (μ-CO)(CO) 2 (μ-Cl) 2 Cl 2 avec le monoxyde de carbone dans le chloroforme. Formation de [Rh 2 (μ-Ph 2 P) 2 Py] 2 (CO) 2 (CH 3 OH)Cl[PF 6 ] dont on etudie la structure

Structure of dehydroisoascorbic acid isomers in solution

Abstract N.m.r. spectroscopy ( 1 H and 13 C) shows that dehydroisoascorbic acid ( d - erythro -2,3-hexodiulosono-1,4-lactone) in solution is only partially similar to dehydroascorbic acid ( l - threo -2,3-hexodiulosono-1,4-lactone). In N,N -dimethylformamide, the preponderant species is an asymmetric dimer, only 7% of the symmetric dimer is present, and other species are also detected. In water, significant differences between dehydroascorbic acid and dehydroisoascorbic acid are observed. In fresh, aqueous solutions, both acids are present as bicyclic lactones, but, with time, dehydroisoascorbic acid is transformed irreversibly into approximately equal amounts of two pyranose anomers. In contrast, dehydroascorbic acid mainly changes into a hydrated 1,4-lactone having a free side-chain. This difference is probably caused by strain in the lactone ring of dehydroisoascorbic acid, because of the proximity of O-4 and O-5 after formation of the furanoid ring. In water, this leads to opening of the lactone ring prior to the furanoid ring, and a simple equilibrium between iso-ascorbic acid and its primary oxidation product is lost.

On the stability of symmetric dimers of dehydroascorbic acid: a study of the esters in the crystalline and the solute state

Abstract Acetylated and benzoylated dimeric dehydroascorbic acid have the same molecular structure as the crystalline parent compound. X-Ray analysis of the tetra-acetate reveals only moderate deviation from two-fold symmetry, caused, presumably, by the packing requirements of the acetate groups. The central dioxane ring is stabilised by the conversion of OH into OAc or OBz. In methyl sulfoxide or N,N-dimethylformamide solutions, no anomerisation occurs as is found with dehydroascorbic acid.

Syntheses and X-ray crystal structures of lithium and chromium(II) complexes of the tri-t-butylmethoxide ligand

The syntheses and X-ray crystal structures of Li and CrII complexes of the tri-t-butylmethoxide ligand are described, these are [{Li(OCBut3)(thf)}2] and [Cr(OCBut3)2·LiCl(thf)2](thf = tetrahydrofuran); the latter compounds has a rare distorted T-shaped geometry at chromium and when dissolved in n-hexane gives LiCl and a complex that analyses as [Cr(OCBut3)2(thf)2].