Eight dithiolato-, diselenolato-, and mixed S,Se-Fe2(CO)6 complexes based on peri-substituted naphthalene and phenanthrene dichalcogenides are prepared by oxidative insertion of Fe3(CO)12 into the dichalcogen bonds of 2,7-dimethoxynaphtho­[1,8-cd]­[1,2]­dithiole, three naphtho­[1,8-cd]­[1,2]­diselenoles, two naphtho­[1,8-cd]­[1,2]­thiaselenoles, phenanthro­[1,10-cd]­[1,2]­dithiole, and phenanthro­[1,10-cd]­[1,2]­diselenole. Complexes are characterized by 1H, 13C NMR, UV/vis, and IR spectroscopy and by X-ray analysis. The effect of replacing sulfur with selenium, incorporating electron-donating groups (2,7-di-tert-butyl, 2,7-dimethoxy) on the naphthalene ring system, and changing the degree of conjugation in the aromatic backbone (naphthalene vs phenanthrene) on the reduction potential is evaluated by cyclic voltammetry. The electrocatalytic activity of these [FeFe]-hydrogenase synthetic mimics for proton reduction in the presence of increasing concentrations of p-TsOH is investigated. Diselenolate-based [FeFe]-complexes show enhanced catalytic activity for proton reduction compared with their sulfur congeners.

Stereogenic main group elements, a promising strategy for metal-free enantioselective catalysis.

Click and bio-orthogonal reactions are dominated by cycloaddition reactions in general and 1,3-dipolar cycloadditions in particular. Among the dipoles routinely used for click chemistry, azides, nitrones, isonitriles, and nitrile oxides are the most popular. This review is focused on the emerging click chemistry that uses mesoionic compounds as dipole partners. Mesoionics are a very old family of molecules, but their use as reactants for click and bio-orthogonal chemistry is quite recent. The facility to derivatize these dipoles and to tune their reactivity toward cycloaddition reactions makes mesoionics an attractive opportunity for future click chemistry development. In addition, some compounds from this family are able to undergo click-and-release reactions, finding interesting applications in cells, as well as in animals. This review covers the synthetic access to main mesoionics, their reaction with dipolarophiles, and recent applications in chemical biology and heterocycle synthesis.