A chiral Brønsted acid containing two different acidic sites, chiral carboxylic acid-monophosphoric acid 1a, was designed to be a new and effective concept in catalytic asymmetric hetero-Diels-Alder reactions of azopyridinecarboxylate with amidodienes. The multipoint hydrogen-bonding interactions among the carboxylic acid, monophosphoric acid, azopyridinecarboxylate, and amidodiene achieved high catalytic and chiral efficiency, producing substituted 1,2,3,6-tetrahydropyridazines with excellent stereocontrol in a single step. This constitutes the first example of regio-, diastereo-, and enantioselective azo-hetero-Diels-Alder reactions by chiral Brønsted acid catalysis.

Dinuclear (μ-η3-allyl)palladium(I) complexes supported by chelate-bridging ligands, (μ-η3-allyl)Pd2(μ-L) (L = N,N′-bis[2-(diphenylphosphino)phenyl]formamidinate, N-(2-diphenylphosphino)phenyl-N′-8-quinolylformamidinate, N,N′-di-8-quinolylformamidinate, N,N′-di-8-quinolylacetamidinate), were synthesized, and some of them were characterized by X-ray crystallography. A dinuclear (μ-η3-allyl)platinum(I) complex, (μ-η3-allyl)Pt2(μ-L), was also synthesized and crystallographically characterized.

New C,N,S-cyclometalated palladium­(II) and platinum­(II) complexes have been synthesized and their structural, electrochemical, and photochemical properties examined. The blue color of these complexes in solution changed to yellow under visible-light irradiation. By measurement of the absorption spectra for quantifying changes in color, isosbestic points for each complex clearly indicated the presence of only two species responsible for the change of color. X-ray analysis revealed that the visible-light-induced yellow species were S-oxygenated sulfinato complexes. Photosensitized generation of singlet oxygen (1O2) was confirmed by the direct detection of singlet oxygen luminescence at 1275 nm. The present cyclometalated palladium­(II) and platinum­(II) complexes are efficient photosensitizers of singlet oxygen, which rapidly reacts with coordinating sulfur atoms.

Square-planar Ni complexes with non-innocent ligands generated by one-electron reduction of octahedral Ni(ii) complexes with Schiff base ligands exhibited excellent catalytic activities via proton-coupled electron transfer for the H2 evolution reaction.