[FeFe]-Hydrogenase Synthetic Mimics Based on Peri-Substituted Dichalcogenides.

Eightdithiolato-, diselenolato-, and mixed S,Se-Fe2(CO)6complexes based on peri-substitutednaphthalene and phenanthrene dichalcogenides are prepared by oxidativeinsertion of Fe3(CO)12into the dichalcogenbonds 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 replacingsulfur 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 (naphthalenevs phenanthrene) on the reduction potential is evaluated by cyclicvoltammetry. The electrocatalytic activity of these [FeFe]-hydrogenasesynthetic mimics for proton reduction in the presence of increasingconcentrations of p-TsOH is investigated. Diselenolate-based[FeFe]-complexes show enhanced catalytic activity for proton reductioncompared with their sulfur congeners. [ABSTRACT FROM AUTHOR]