Synthesis of C,N-Glycosides via Brønsted Acid-Catalyzed Azidation of -Glycals.

The reaction of -glycals with azidotrimethylsilane in the presence of a Brønsted acid leads to the generation of the corresponding C,N-glycosyl azides. The majority of these glycosylation reactions proceed at room temperature with short reaction times. In addition, the targeted products were obtained in high yields with exclusive diastereoselectivity to the α-anomer in pyranose-based derivatives.

Stereoselective Palladium-Catalyzed Arylation of -Glycals with Aryl Iodides.

A novel methodology for the arylation of -glycals has been developed. A range of -glycals underwent reactions with aryl iodides in the presence of a palladium catalyst. The transformation proceeded in a stereoselective manner to afford -isomers.

Slow magnetic relaxation in Dy and Dy complexes of a versatile, trifunctional polydentate N,O-ligand.

A tridentate ligand LH (CHNO) comprising o-vanillin, hydrazone and oxime donor groups has been employed to prepare a new class of di- and tetranuclear Ln complexes. The reaction of LH with Ln(NO)·xHO in the presence of a suitable base yields the dinuclear Dy complex [Dy(LH)(CHOH)][NO] (1) and the tetranuclear complexes [Dy(LH)(LH)(OH)]·2HO (2) and [Gd(LH)(LH)(OMe)]·nHO, (3). In these complexes, LH is either monodeprotonated (1) or a mixture of mono- and doubly-deprotonated ligands (2 and 3) binding lanthanide ions via N, O, and O donors, while the remaining vacant coordination sites are occupied by O (1), O (2) and methoxides (3).

Dual-Property Supramolecular H-Bonded 15-Crown-5 Ln(III) Chains: Joint Magneto-Luminescence and ab Initio Studies.

Two complexes comprising 9-coordinate capped square antiprismatic [Ln(NO)(OH)(MeOH)] units [Ln(III) = Dy 6; Tb 7] are reported in which the metal complexes are hydrogen-bonded to 15C5 (15-crown-5) macrocycles to form supramolecular chains, {[Ln(NO)(OH)(MeOH)]·(15C5)}. Alternating current magnetic susceptibility measurements supported by ab initio studies show field-induced SMM (single-molecule magnet) behavior for 6, but rapid relaxation of the magnetization for 7 because of the presence of dominant quantum tunneling processes as evidenced by the presence of a significant calculated tunnel splitting within the ground-state multiplet. Modeling the high-resolution emission spectra for 6 afforded energies of 37 ± 5 and 28 ± 5 cm for the first-excited-state Stark sublevels of the two crystallographically independent Dy1 and Dy2 ions, in excellent agreement with the calculated values of 31 and 21 cm for ΔE derived from ab initio studies.

Large Energy Barrier and Magnetization Hysteresis at 5 K for a Symmetric {Dy} Complex with Spherical Tricapped Trigonal Prismatic Dy Ions.

The introduction of the Schiff base ligand N-salicylidene-2-amino-5-chlorobenzoic acid (sacbH) in 4f-metal chemistry has afforded a new dinuclear complex, [Dy(NO)(sacbH)(HO)(MeCN)] (1), with the metal ions adopting a rare spherical tricapped trigonal prismatic coordination geometry. The deprotonated phenoxido O atoms of the organic chelate occupy the axial triangular faces of the prism and were found to be very close to the main anisotropy axes of the two Dy ions. As a result, the {Dy} compound exhibits frequency- and temperature-dependent out-of-phase ac signals below ∼25 K in the absence of a static dc field, yielding an energy barrier of 109.