A porous metal–organic aerogel based on dirhodium paddle-wheels as an efficient and stable heterogeneous catalyst towards the reduction reaction of aldehydes and ketones

Abstract

A new metal–organic aerogel (MOA-Rh-2) containing dirhodium paddle-wheels has been prepared from the reaction of dirhodium(II) tetracarboxylate (Rh₂(OAc)₄) and tetrakis(4-carboxyphenyl)porphyrin (TCPP) in a mixed solvent of DMF and water, followed by supercritical CO₂ extraction. MOA-Rh-2 has been fully characterized by ICP-OES, EDS, XPS, PXRD, SEM, TEM and TGA. Its porosity has been confirmed by N₂ adsorption isotherms at 77 K, and the Barrett–Joyner–Halenda pore size is centered at 3.5 nm. The existence of mesopores has been further verified by dye adsorption tests using methylene blue (14.4 × 6.1 Ų) and rhodamine B (15.8 × 11.8 × 6.8 ų). MOA-Rh-2 is air and moisture-stable. The catalytic results show that, under an air atmosphere and at ambient temperature, a low loading (0.1–0.4 mol%) of MOA-Rh-2 can efficiently promote the hydrosilylation of aldehydes and ketones with the commercially available silane of PhSiH₃. After catalytic reactions, MOA-Rh-2 can be recycled and reused for 5 runs without significant loss of the activity, and the reaction conversions are in the range of 89–99%.