Carbohydrates as ligands: coordination equilibria and structure of the metal complexes

Directed assembly metallocyclic supramolecular systems for molecular recognition and chemical sensing

'Chirality switching' is one of the most important chemical processes controlling many biological systems. DNAs and proteins often work as time-programmed functional helices, in which specific external stimuli alter the helical direction and tune the time scale of subsequent events. Although a variety of organic foldamers and their hybrids with natural helices have been developed, we highlight coordination chemistry strategies for development of structurally and functionally defined metal helicates. These metal helicates have characteristic coordination geometries, redox reactivities and spectroscopic/magnetic properties as well as complex chiralities. Several kinds of inert metal helicates maintain rigid helical structures and their stereoisomers are separable by optical resolution techniques, while labile metal helicates offer dynamic inversion of their helical structures via non-covalent interactions with external chemical signals. The latter particularly have dynamically ordered helical structures, which are controlled by the combinations of metal centres and chiral ligands. They further function as time-programmable switches of chirality-derived dynamic rotations, translations, stretching and shape flipping, which are useful applications in nanoscience and related technology.

Coordination chemistry strategies for dynamic helicates: time-programmable chirality switching with labile and inert metal helicates

Transition metal-based chiroptical switches for nanoscale electronics and sensors

The synthesis, characterization, and circular dichroism (CD) spectra of optically active mixed, neutral-charged Pt/Pt and Pt/Pd macrocyclic complexes are described as well as the CD spectra of their corresponding precursors. Interaction between the chiral monomers (R(−)-DIOP or S(+)-DIOP) of cis-Pt(DIOP)(4-ethynylpyridine)2 and the bistriflates of chiral (R(+)-BINAP or S(−)BINAP)) Pt(II) or Pd(II) bisphosphines or cis-Pd(PEt3)2(OSO2CF3)2, in CH2Cl2 at room temperature results in the formation of cyclic, chiral molecular squares in 84−99% yields via self-assembly. CD studies and optical rotation of the chiral macrocycles and their corresponding precursors reveal that the chiroptical properties are mainly determined by the BINAP moiety. The host−guest chemistry of the chiral 4-ethynylpyridine tetramers with silver triflate and the capture of neutral guests via the resulting square Lewis acid/base receptors have been monitored by CD.

Self-Assembly, Chiroptical Properties, and Host−Guest Chemistry of Chiral Pt−Pt and Pt−Pd Tetranuclear Macrocycles. Circular Dichroism Studies on Neutral Guest Inclusion Phenomena

Novel seven-coordinated cage-type cobalt(II) complexes containing N-glycosides from mannose-type aldoses and tris(2-aminoethyl)amine (tren), [Co((aldose)3tren)]X2·nH2O (1a·5H2O, aldose = d-mannose (d-Man), X = Cl-; 1b·5H2O, aldose = 6-deoxy-l-mannose (l-Rha), X = Cl-; 2a·4H2O, aldose = d-Man, X = Br-; 2b·H2O, aldose = l-Rha, X = Br-) and [Co((aldose)3tren)]SO4·nH2O (3a·4H2O, aldose = d-Man; 3b·3H2O, aldose = l-Rha), where (aldose)3tren is tris(2-(aldosylamino)ethyl)amine, were prepared and characterized by elemental analysis, electronic absorption and circular dichroism spectroscopies, and X-ray crystallography. Crystal data are as follows. 2b·2CH3OH:  C26H56N4O14Br2Co, monoclinic, space group P21, a = 11.045(2) A, b = 17.283(6) A, c = 10.996(3) A, β = 117.371(6)°, V = 1864(1) A3, Z = 2, R = 0.072 for 2787 independent reflections. 3b·3H2O·CH3OH:  C25H58N4O20SCo, orthorhombic, space group P212121, a = 14.836(2) A, b = 22.489(2) A, c = 12.181(3) A, V = 4064(1) A3, Z = 4, R = 0.077 for 2010 independent refle...

and Hidehiro Uekusa

Papers

Chiral Inversion around a Seven-Coordinated Cobalt Center Induced by an Interaction between Sugars and Sulfate Anions