Wesley Ting Kwok Chan

Regioselective Synthesis of Polycyclic and Heptagon-embedded Aromatic Compounds through a Versatile π-Extension of Aryl Halides

A versatile π-extension reaction was developed based on the three-component cross-coupling of aryl halides, 2-haloarylcarboxylic acids, and norbornadiene. The transformation is driven by the direction and subsequent decarboxylation of the carboxyl group, while norbornadiene serves as an ortho-C-H activator and ethylene synthon via a retro-Diels-Alder reaction. Comprehensive DFT calculations were performed to account for the catalytic intermediates.

Chiral DOTA chelators as an improved platform for biomedical imaging and therapy applications

Despite established clinical utilisation, there is an increasing need for safer, more inert gadolinium-based contrast agents, and for chelators that react rapidly with radiometals. Here we report the syntheses of a series of chiral DOTA chelators and their corresponding metal complexes and reveal properties that transcend the parent DOTA compound. We incorporated symmetrical chiral substituents around the tetraaza ring, imparting enhanced rigidity to the DOTA cavity, enabling control over the range of stereoisomers of the lanthanide complexes. The Gd chiral DOTA complexes are shown to be orders of magnitude more inert to Gd release than [GdDOTA]−. These compounds also exhibit very-fast water exchange rates in an optimal range for high field imaging. Radiolabeling studies with (Cu-64/Lu-177) also demonstrate faster labelling properties. These chiral DOTA chelators are alternative general platforms for the development of stable, high relaxivity contrast agents, and for radiometal complexes used for imaging and/or therapy.MRI contrast agents containing the rare earth metal gadolinium are very effective, yet unstable and thus potentially hazardous. Here, the authors developed complexes between gadolinium and the scaffolding compound DOTA with increased stability, which also lend themselves to radiometal labelling.

Stereolabile chiral biphenyl hybrids: crystallization-induced dynamic atropselective resolution involving supramolecular interactions

Crystallization-induced dynamic atropselective resolutions of three simple chiral biphenyl hybrids, (1R,1′R)-1,1′-(biphenyl-2,2′-diyl)diethanol 1, (1R,1′R)-1,1′-(biphenyl-2,2′-diyl)bis(ethane-1,1-diyl)diacetate 2 and (1S,1′S)-1,1′-(biphenyl-2,2′-diyl)bis(2,2′-dimethylpropan-1-ol) 3 were achieved. The axial chirality of the biphenyl backbones of 1–3 were found to be determined by (i) the steric bulkiness at the α position of the ortho-substituents, and (ii) the intermolecular interactions between the molecules. 1, which possesses the least sterically demanding methyl substituents, was found to form stereoselectively the S-atropisomer and gave enantiomerically pure supramolecular right-handed helices through strong and directional intermolecular hydrogen bonds in its crystal.

Assembly of Lanthanide(III) Cubanes and Dimers with Single-Molecule Magnetism and Photoluminescence

Discrete lanthanide(III) tetranuclear cubane-like clusters seldom occur throughout the LnIII series and behave as single-molecule magnets (SMMs). Herein, a series of cubanes, [Ln4(μ3-OH)4(μ-tfa)4(hfa)4(phen)4] (1-9, Ln = La-Dy (except Pm), tfa = trifluoroacetate, hfa = hexafluoroacetylacetonate, phen = 1,10-phenanthroline), and dinuclear clusters, [Ln2(μ-OH)2(hfa)4(phen)2] (10-16, Ln = Tb-Lu), were synthesized and characterized. Two types of clusters were formed due to the change of preferred coordination geometry for lighter and heavier LnIII ions which favor nine-coordinated cubanes and eight-coordinated dimers, respectively. A magnetic study shows that 8-Tb4 and 9-Dy4 are ferromagnetically coupled and SMM in nature because of the larger Ln···Ln distance compared to other discrete cubanes. The anisotropic barriers, Ueff, of 9-Dy4 are determined to be 67.0 K. In addition, the photophysical properties of 6-Eu4, 8-Tb4, and 10-Tb2 owing to tfa, hfa, and phen sensitization and O-H quenching are discussed.

N,N′-(Ethane-1,2-di­yl)bis­(methane­sulfon­amide)

The molecular structure of the title compound, C4H12N2O4S2, has crystallographic inversion symmetry. The central N—C—C—N moiety was refined as disordered over two sets of sites with an approximate occupancy ratio of 3:1 [0.742 (15):0.258 (15). In the crystal, N—H⋯O hydrogen bonds link adjacent molecules into a thick sheet structure parallel to the b-axis direction.