Aasif Helal

The rhodium complex of bis(diphenylphosphinomethyl)dopamine-coated magnetic nanoparticles as an efficient and reusable catalyst for hydroformylation of olefins

A new bis(diphenylphosphinomethyl)dopamine (bpd) ligand has been prepared and anchored on the surface of magnetic nanoparticles (MNPs). The obtained ligand and the surface functionalized nanoparticles of type MNP@bpd have been characterized by various analytical techniques, such as NMR, IR, TEM, XRD, and VSM. TEM shows homogeneous distribution of the particles with the size ranging 5–7 nm. XRD Rietveld analysis confirms the formation of a pure and single Fe3O4 phase with high crystallinity. The ligands anchored on the magnetic nanoparticle surface have been confirmed by the shift of the characteristic Fe–O vibration band in the FT-IR spectrum, and have been supported by the stepwise weight loss in TGA as a function of temperature. The phosphorus content determined by ICP-MS is approximately 0.39 mmol of phosphine per gram of the nanoparticles. Magnetization-field curves recorded at room temperature reveal superparamagnetic behavior. MNP@bpd materials have proven to be excellent catalysts after in situ addition of the rhodium (Rh) metal precursor for the hydroformylation reaction of styrene and its derivatives. The extent of reusability of the catalyst has been tested and was found to be active even after seven consecutive cycles.

Magnetic nanoparticle-supported ferrocenylphosphine: a reusable catalyst for hydroformylation of alkene and Mizoroki–Heck olefination

We present dopamine (dop) conjugated bis(diphenylphosphino)ferrocenylethylamine (BPPFA) functionalized magnetic nanoparticles (Fe3O4). A ferrocene ({η5-C5H4-PPh2}Fe{η5-C5H3-1-PPh2-2-CH(Me)NH-CH2-CH2-4Ph-1,2-OH}) ligand (dop-BPPF) has been prepared by reaction of (1-[1′,2-bis(diphenylphosphino)-ferrocenyl]ethyl acetate) and dopamine hydrochloride to form dop-BPPF, which was characterized by NMR, IR, FTIR, EA and FAB-MS. This ligand was anchored on ultrasmall (6–8 nm) magnetic nanoparticles (MNP) to yield Fe3O4@dop-BPPF. The resulting ferrocenylphosphine on magnetic nanoparticles was characterized by SEM, EDS, XRD, TEM, TGA, and VSM. The magnetic nature of the materials was investigated. Fe3O4@dop-BPPF exhibits very high catalytic activity for the Pd-catalyzed Mizoroki–Heck reaction and exceptionally high regioselectivity for the Rh-catalyzed hydroformylation reaction with branched aldehydes (up to > 99%). The potential of this Fe3O4@dop-BPPF as a reusable catalyst has been studied for the Mizoroki–Heck reaction, and this catalyst was robustly active even after eleven consecutive cycles.

Facile hydrogenation of N-heteroarenes by magnetic nanoparticle-supported sub-nanometric Rh catalysts in aqueous medium

The hydrogenation of nitrogen-containing heterocyclic precursors in aqueous medium at low temperature without imposing molecular hydrogen pressure is quite challenging. Herein, we report the synthesis and performance of a novel catalyst capable of facile hydrogenation (employing tetrahydroxydiboron (THDB) as the reductant) of N-heteroarenes in water at 80 °C with good recyclability. Rhodium particles in the sub-nano range (<1 nm) were produced by in situ reduction of a Rh precursor on freshly prepared superparamagnetic iron oxide nanoparticles (SPIONs, Fe3O4), using aqueous ammonia as a reducing agent at 50 °C. HRTEM and elemental mapping images reveal a homogeneous distribution of <1 nm Rh particles within the matrix of Fe3O4 nanoparticles having an average size within a narrow range of 7–9 nm. The superparamagnetic nature of the composite was confirmed by VSM analysis. The Rh@Fe3O4 catalyst was found to be highly efficient in the heterogeneous hydrogenation of nitrogen-containing heterocyclic compounds with quantitative conversion. It showed selectivity towards the hydrogenation of 1,2,3,4-tetrahydroquinoline (py-THQ) in water using THDB with a high TOF of 1632 h−1. These results are compared with the conversion and selectivity data obtained from reduction with molecular hydrogen gas pressure. The catalytic activity is extended to the successful hydrogenation of simple aromatics like benzene, toluene etc. Isotopic labelling studies were performed to determine the source of hydrogen in quinoline hydrogenation in the presence of THDB. It was found that it could be used for 16 consecutive cycles with gaseous hydrogen, without any undesired by-products; it also retained its original crystallinity.