Two new Ru-aqua complexes containing a phosphonated trpy ligand with the general formula [Ru(trpy-P)(B)(H2O)]2+ (trpy-P is diethyl [2,2′:6′,2′′-terpyridin]-4′-ylphosphonate (1); B = bpm (5a) is 2,2′-bipyrimidine; (or) B = azpy (cis- and trans-5b) is 2-phenylazopyridine) are reported. These complexes and their synthetic intermediates have been characterized by the usual analytic techniques and by spectroscopic and electrochemical methods. X-ray structures of the cis and trans Ru-Cl complexes that are synthetic intermediates to the corresponding Ru-aqua complexes have also been obtained. The phosphonated complexes 4a and trans-4b have been anchored onto MNPs of Fe3O4 (6.2 ± 2 nm), via covalent bonds to generate 6a and trans-6b, respectively. These new materials have been characterized by UV-vis, IR, TEM and CV. The Ru-aqua complexes were generated in situ by dissolving the Ru-Cl complexes in water. The Ru-aqua complexes 5a and trans-5b are excellent catalysts for the epoxidation of olefins and are stereoselective for cis-alkenes such as cis-β-methylstyrene and cis-stilbene. Remarkably, the analog supported onto MNPs, 7a, displays practically the same behavior as its homogeneous counterpart. Multiple recycling experiments for the epoxidation of cis-β-methylstyrene involving magnetic decantation of the catalyst were carried out with 7a without significant loss of activity.
Molecular ruthenium complexes anchored on magnetic nanoparticles that act as powerful and magnetically recyclable stereospecific epoxidation catalysts
Catal. Sci. Technol. 2013, 3, 706-714.