Fe(III)-Based Phenylsilsesquioxane/Acetylacetonate Complexes: Synthesis, Cage-like Structure, and High Catalytic Activity.

Unprecedented iron-based silsesquioxane/acetylacetonate complexes were synthesized. The intriguing cage-like structure of compounds is alkaline metal-dependent: the Fe 2 Li 2 complex includes condensed Si 6 -silsesquioxane and four acetylacetonate ligands; the Fe 4 Na 4 complex exhibits two cyclic Si 4 -silsesquioxane and eight acetylacetonate ligands, while the Fe 3 K 3 complex features two cyclic Si 3 -silsesquioxane and six acetylacetonate ligands. The latter case is the very first observation of small trimeric silsesquioxane ligands in the composition of cage-like metallasilsesquioxanes. The Fe 4 Na 4 -based complex exhibits a record high activity in the oxidation of inert alkanes with peroxides (55% yield of oxygenates in cyclohexane oxidation). It also acts as a catalyst in the cycloaddition of CO 2 with epoxides, leading to cyclic carbonates in good yields (58-96%).