Reactivity of a Metastable Cobalt(III) Trisulfide Complex: Multiple C—H Functionalization of p-Xylene and Disulfides to Afford Photofunctional Cobalt Complexes

摘要

The chemistry of sterically restricted systems is becoming increasingly important. By protecting otherwise unfavored and unattainable chemical species, sterically restricted systems often give rise to unusual properties and reactivity. Supramolecular cages, frustrated Lewis pairs, and bowl-shaped reaction spaces are types of sterically restricted systems that have been intensively studied. Such systems inside a bowl-shaped η-C_(60)R5 ligand are known to effectively perturb the structure and electronic structures of η~5-Cp metal complexes to afford unconventional species (Figure 1). In particular, cobalt trisulfide complex 2, which can be synthesized only inside a bowl-shaped C_(60)Ar5 ligand, is of great interest because of the characteristic coexistence of stabilization (6π-aromaticity and strong steric protection) and destabilization (high ring strain and a coor-dinatively unsaturated metal center). Although a wide range of structures of metal polysulfide complexes have been studied as models of catalysts and enzyme active centers, and this area of research is rather mature, cobalt trisulfide has a rare and unexplored type of structure. Thus, elucidation of its reactivity is promising for gaining new perspectives on novel chemical reactions, such as inert bond activation. Against this background, we herein report on unprecedented reactivity of cobalt trisulfide and demonstrate applications of C—H functionalization reactions to syntheses of a series of photofunctional cobalt complexes.