New chemoselective, recyclable, environmentally friendly and low-cost catalysts for selective hydrogenation of alkynes into (E)-or (Z)-alkenes are highly desirable, as it is an important process for fine chemical and polymerization industry. The main challenge in this process is the control of the selectivity towards the alkene and to avoid the over-reduction to the corresponding alkane by the catalyst. Metallic nanoparticles (MNPs) represent an alternative catalyst as they are higly active in hydrogenation reactions and their selectivity can be modified by using organic ligands. As regards the separation of MNPs from the products, magnetic nanoparticles (MagNPs) are ideal catalysts since they can be precipitated from the reaction medium in the presence of an external magnetic field, favoring their recycling. Therefore, the magnetic properties of MNPs together with their potential as catalysts in hydrogenation reactions, make them perfect candidates for selective semi-hydrogenation reactions in an environmentally friendly way. Herein, we report a series of new magnetically recoverable nickel nanoparticles (NiNPs) stabilized by three different imidazolium-amidinate ligands (L1: ICy(p-tol)NCN, L2: ICy(p-anysil)NCN and L3: ICy(p-ClC6H4)NCN). NiNPs were fully charaterized by TEM, HRTEM, WAXS, XRD, ICP-AAS, VSM and XPS. These new nanocatalysts present a remarkable selectivity in the semi-hydrogenation of 3-hexyne into (Z)-3-hexene under very mild reaction conditions (room temperature and 1 bar H2). The catalytic behavior of NiNPs was influenced by the electron donor/acceptor (-Me, -OMe, -Cl) groups in the N substituents of the amidinate moiety of the ligands. Taking profit of magnetic character of NiNPs, recycling experiments were successfully performed, allowing recovery and reuse of the catalysts without notable loss of activity and selectivity.

Magnetic and recyclable nickel nanoparticles for selective semi-hydrogenation of alkynes to (Z)-alkenes

2019 Spring National Meeting

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