Ligands tailoring

The features of homogeneously catalyzed hydrocyanations described above prompted attempts to prepare 2-aryl-2-propionitriles 32 (eq. (8)). The development of a synthesis for naproxen demonstrates the successful application of ligand tailoring , the adjustment of the catalyst ligand system to the demands of the reaction. In this case it is of particular importance to achieve a high stereoselectivity because the 7 -enantiomer has a number of undesirable health effects [55],... 

The family of heteroscorpionate ligands tailored around acetamidinate fragments disclosed by Smchez-Barba and coworkers constimtes another useful class of nitrogen-containing ancillaries particularly suited to the synthesis of heteroleptic Mg complexes, fri a first study [67], they prepared tbpamd MgR (R = C3H5, 31 ... 

Collins TJ, Slebodnick C, Uffelman ES. 1990. Cr(V)-oxo complexes of macrocyclic tetraamido-N ligands tailored for highly oxidized middle transition metal complexes. Inorg Chem 29(18) 3433-3436. 

For L=NH3 (1) and L=Pr2NH (3), the isotherms are of type II as expected for non-porous materials [27]. Sample 2 shows a significant uptake at 0.6

narrow particle-size distribution which results in a more regular packing with interparticle pores of size similar to that of the particles [27]. The latter shows that the ligand-assisted synthesis does not only allow one to affect the total surface area and particle size, but also the size distribution which is an important tool for tailoring the particle properties. 

The key to the successful development of homogeneous catalysts has been the exploitation of the effects that ligands exert on the properties of metal complexes by tailoring the electronic and steric properties of a catalytically active metal complex, activities and selectivities can be altered considerably. This especially holds for phosphorus based ligands, which are the most commonly encountered ligands as.sociated with organometallic compounds. 

An interesting and potentially u.seful variant is deployment of thermoreversibility, a situation where the reaction occurs at relatively high temperature in a homogeneous phase, which becomes a two-pha.se system at lower temperatures, facilitating catalyst recovery. Here, tailored ligands have to be u.sed. Ethoxylated phosphines have been suggested by Jin, Fell, and co-workers (1996, 1997). 

The catalysts used in hydroformylation are typically organometallic complexes. Cobalt-based catalysts dominated hydroformylation until 1970s thereafter rhodium-based catalysts were commerciahzed. Synthesized aldehydes are typical intermediates for chemical industry [5]. A typical hydroformylation catalyst is modified with a ligand, e.g., tiiphenylphoshine. In recent years, a lot of effort has been put on the ligand chemistry in order to find new ligands for tailored processes [7-9]. In the present study, phosphine-based rhodium catalysts were used for hydroformylation of 1-butene. Despite intensive research on hydroformylation in the last 50 years, both the reaction mechanisms and kinetics are not in the most cases clear. Both associative and dissociative mechanisms have been proposed [5-6]. The discrepancies in mechanistic speculations have also led to a variety of rate equations for hydroformylation processes. 

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