Green electrochemical template synthesis of CoPt nanoparticles with tunable size, composition, and magnetism from microemulsions using an ionic liquid (bmimPF6)

Altres ajuts: Substrates have been prepared in IMB-CNM (CSIC),supported by the (CSIC) NGG-258 project.Electrodeposition from microemulsions using ionic liquids is revealed as a green method for synthesizing magnetic alloyed nanoparticles, avoiding the use of aggressive reducing agents. Microemulsions containing droplets of aqueous solution (electrolytic solution containing Pt(IV) and Co(II) ions) in an ionic liquid (bmimPF) define nanoreactors in which the electrochemical reduction takes place. Highly crystalline hcp alloyed CoPt nanoparticles, in the 10-120 nm range with a rather narrow size distribution, have been deposited on a conductive substrate. The relative amount of aqueous solution to ionic liquid determines the size of the nanoreactors, which serve as nanotemplates for the growth of the nanoparticles and hence determine their size and distribution. Further, the stoichiometry (PtCo) of the particles can be tuned by the composition of the electrolytic solution inside the droplets. The control of the size and composition of the particles allows tailoring the room-temperature magnetic behavior of the nanoparticles from superparaparamagnetic to hard magnetic (with a coercivity of H = 4100 Oe) in the as-obtained state. © 2014 American Chemical Society

Synergic effects between N-heterocyclic carbene and chelating benzylidene-ether ligands toward the initiation step of Hoveyda-Grubbs type Ru complexes

Synergic effects between ancillary N-heterocyclic carbenes [(1,3-bis(2,4,6-trimethylphenyl)-1,3-imidazoline-2-ylidene or 1,3-bis(2,6-diisopropylphenyl)-1,3-imidazoline-2-ylidene] and chelating benzylidene ether ligands were investigated by studying initiation rates and kinetic profiles of Hoveyda-Grubbs (HG) type Ru complexes. A newly designed Ru-benzylidene-oxazinone precatalyst 4 was compared with Grela and Blechert complexes bearing modified isopropyloxy chelating leaving groups and with the standard HG complex to understand how the ancillary and the leaving ligands interact and influence the catalytic activity

Olefin metathesis by Grubbs−Hoveyda complexes : computational and experimental studies of the mechanism and substrate-dependent kinetics

The potential energy surfaces for the activation of Grubbs−Hoveyda-type precatalysts with the substrates ethene, propene, 1-hexene, and ethyl vinyl ether (EVE) have been probed at the density functional theory (DFT) (M06-L) level. The energetically favored pathway of the reaction leading to a 14e Fischer carbene and styrene starts with an initiation step in which the incoming substrate and outgoing alkene ligand are both clearly associated with the ruthenium center. For these substrates, with the exception of ethene, the rate determining step is predicted to be the formation of the metallocyclobutane (MCB). We have taken the initial reactant to be a weak van der Waals complex between substrate and precatalyst. This model yields good agreement between the computed activation parameters for both the parent Grubbs−Hoveyda and Grela complex with EVE substrate, and the experimental values, reported here. The alternative model which takes the initial reactant to be two isolated molecules requires an estimate of the entropy loss on formation of the initial complex in solution which is difficult to evaluate. Our estimate of this quantity yields a barrier for the rate determining step for the interchange mechanism which is close to the value we find for the alternative mechanism in which the rate determining step is the initial dissociation of the precatalyst. The relative energetics of these two mechanisms involving different initiation steps but with similar activation barriers, could well be dependent upon the precatalyst and substrate in line with the recent experimental findings of Plenio and co-workers