Boronic Acid-Catalyzed Regioselective Koenigs-Knorr-Type Glycosylation.

Boronic acid-catalyzed regioselective Koenigs-Knorr-type glycosylation is presented. The reaction of an unprotected or partially protected glycosyl acceptor with a glycosyl halide donor in the presence of silver oxide and a low catalytic amount of imidazole-containing boronic acid was found to proceed smoothly, which enables construction of a 1,2-trans glycosidic linkage with high regioselectivities. This is the first example of the use of a boronic acid catalyst to initiate regioselective glycosylation via the activation of cis-vicinal diols in glycosyl acceptors.

Contrasting magnetism of [Mn(III)(4)] and [Mn(II)(2)Mn(III)(2)] squares.

Two tetranuclear manganese distorted square-shaped clusters, [Mn(III)(4)(L1)(4)(mu(2)-OMe)(4)].2.5H(2)O (1) and [Mn(II)(2)Mn(III)(2)(L2)(4)(H(2)O)(2)](PF(6))(2).CHCl(3).CH(3)OH.1.5H(2)O (2) (H(2)L1 = 2-[3-(2-hydroxyphenyl)-1H-pyrazol-5-yl]-6-pyridinecarboxylic acid methyl ester; H(2)L2 = 2-[3-(2-hydroxyphenyl)-1H-pyrazol-5-yl]-6-pyridinecarboxylic acid ethyl ester), exhibit antiferromagnetic and ferromagnetic interactions between neighboring manganese ions, respectively.

Triple-stranded ferric helices: a π-π interaction-driven structural hierarchy of Fe5, Fe7, and Fe17 clusters.

Three polypyridine ligand-supported multinuclear iron complexes, [Fe5], [Fe7] and [Fe17], were synthesized and their physical properties were investigated. The complexes had triple-stranded helical structures with pseudo threefold symmetry, and were stabilized by varying degrees of intramolecular π-π stacking. The pentanuclear iron complex consisted of two Fe(II) and three Fe(III) ions, supported by three ligands, while the heptanuclear complex comprised four Fe(II) centres, three Fe(III) ions, and six ligands, and the heptadecanuclear complex contained seventeen Fe(III) ions and nine ligands. Electrochemical studies revealed that the pentanuclear and heptanuclear iron complexes showed pseudo-reversible three- and five-step redox behaviours, respectively. Magnetic measurements conducted on the pentanuclear and heptanuclear complexes revealed that antiferromagnetic interactions were operative between neighbouring iron ions through the oxo- and pyrazole-bridges.