The catalytic formation of C-C bonds is one of the most useful transformations in organic synthesis. Over the last decade, the use of transition metal nanoparticles (NPs) in catalysis has attracted much interest and their use in C-C bond formation reactions constitutes one of their most important applications, including the Suzuki, Heck, and Sonogashira reactions. This tutorial review highlights recent work in this active area, considering the stabilising agents used to prepare the NPs, the catalytic results and the recycling possibilities.
homogeneous phase occur via an "Interaction of 2 M-O units" (I2M) might still be able to carry out the catalytic water oxidation reaction at the surface of an electrode, but will need to proceed through higher energy pathways that can lead to catalyst degradation. 6 Further, given the intrinsic high energy demands for the water oxidation catalysis, it is essential that the anchoring groups that act as an interface between the catalysts and surface are oxidatively resistant.Here on, we report new hybrid materials consisting of molecular WOCs anchored onto Multi-Walled Carbon Nanotubes (MWCNTs) via π-stacking interactions. 9 The resulting materials are extremely stable and allow the anchoring of a large amount of catalyst giving Turnover Numbers (TNs) over a million without apparent deactivation.In a recent publication, 10 we have reported the synthesis of complex {Ru II (tda)(py)2}, 1a, (for a drawing of tda 2-see Scheme 1) and have shown that in its high oxidation states (IV) acts as a precursor for the formation of {Ru V (O)(tda)(py)2} + . The latter is the most powerful molecular water oxidation catalyst described to date achieving Turnover Frequencies (TOF) in the range of 50.000 s -1 . In addition, we showed that the rate determining step for the water oxidation reaction is the O-O bond formation, which in this case occurs via WNA, as evidenced by kinetics and further supported by DFT calculations.Scheme 1. Drawing of the ligands discussed in the present work (top) and complex labelling strategy (bottom).[a]
In the last decade, the semi-hydrogenation of alkynes has experienced significant advances in terms of fine control of alkene selectivity and prevention of the over-hydrogenation reaction. Such advances have been possible to a large extent through the progress in colloidal methods for the preparation of metallic nanoparticles. The present review describes the contributions in the field of the selective hydrogenation of alkynes involving the utilization of colloidal methodologies. These approaches permit the fine modulation of several parameters affecting the catalytic performance of the active phase such as the particle size, the bulk and the surface structure and composition. For the transformation of liquid substrates, the nature of the stabilizers, the reducing agents and the metal precursors employed for the synthesis of the catalysts can be tuned to enhance the alkene selectivity. In contrast, in catalytic transformations of gaseous substrates, the presence of adsorbed species at the metal surface usually gives detrimental results while the interplay between the support and the active phase appears to be a more convincing alternative for catalyst tuning.
The study of reaction mechanisms by NMR spectroscopy normally suffers from limitations in sensitivity that arise from the physical constraints of the detection method. An overview is presented of how chemical reactions can be studied using parahydrogen assisted NMR spectroscopy where detected signal strengths can exceed those normally seen by factors of over 28,000.
Over the last decade, the hydrogenation of arenes catalysed by soluble nanoparticles has attracted much interest from both academic and industrial research groups due to the milder conditions and the interesting selectivities achieved when compared to those obtained with classical heterogeneous catalysts. When substituted arenes are used as substrates in this reaction, the stereoselectivity is a key objective, and high levels of enantioselectivity are yet to be achieved.
para-Hydrogen-induced polarization methods are shown to enable the in situ detection of linear and branched monophosphine-containing intermediates during hydroformylation when Co(eta3-C3H5)(CO)2(PCy3) is the catalyst precursor. The NMR signal characteristics of the alkyl arms of these species provide direct evidence for the rapid interconversion of linear and branched cobalt alkyls prior to the CO insertion step. The observation of additional para-hydrogen-enhanced signals for the corresponding linear and branched aldehydes enables the reactions selectivity to be rapidly monitored as a function of H2 and CO pressure or reaction temperature.
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