Catalytic homogeneous system

As depicted above, there is a large variety of NHCs, and their access is relatively easy. This is a veritable advantage in the use of NHCs for homogeneous catalytic systems. However, it is probably their unique electronic and steric properties that make NHCs an exceptional class of molecules. These unique features are described in the following sections. 

A variety of amides has been formed in moderate to high yields with aryl bromides or iodides as aryl precursors and single-mode microwave heating for 15 min at 150 °C (Eq. 11.15) [29]. Under these conditions, aliphatic, unhindered primary, and secondary amines reacted readily, whereas sterically hindered amines or amines of low nucleophilicity, e.g. anilines, afforded low yields and incomplete conversions. Among the homogeneous catalytic systems tested the most suitable for the use with aryl bromides was a 2 1 mixture of BINAP and Herrmann s palladacycle. 

Section 3 will deal with catalytic systems whose stereospecificity is mainly controlled by the chirality of the environment of the transition metal, independently of the possible chirality of the growing chain (chiral site stereocontrol). In particular, in Section 3.1 the chirality and stereospecificity of homogeneous catalytic systems based on metallocenes of different symmetries and in different experimental conditions will be reviewed. In Section 3.2 the chirality of model catalytic sites, which have been supposed for isospecific first-generation TiCl3-based and high-yield MgC -supported catalysts, is described. In Section 3.3 we will present a comparison between model catalytic sites proposed for heterogeneous and homogeneous stereospecific site-controlled catalysts. 

As an example, C2-symmetric isospecific models for homogeneous catalytic systems based on the (R, / -coordinated isopropyl-bis(l-indenyl) ligand and for heterogeneous catalytic systems based on TiCLt supported on MgCl2 are compared in Figure 1.19. These models correspond to minimum-energy preinsertion intermediates calculated to be suitable for primary propene insertion... 

An analysis of the most significant homogeneous catalytic systems reported in the literature reveals a structural variety for Pd which is not found for Pt. In fact, although in most cases Pd is incorporated into the (pre)catalyst as divalent ion, active Pd(0) -catalysts have also been reported. By contrast, Pt(0) -catalysts are a rarity. Moreover, Pd complexes containing mono-, di-, tri-, and even tetra-dentate ligands have found application as hydrogenation catalysts, and often their activity and selectivity is governed by the steric and electronic features of... 

As for homogeneous catalytic systems, the plateau current is independent of the scan rate, here being equal to kr°CIf the amount of catalyst on the electrode surface is known, the kinetic constant, kr°, and the rate constant, k, are easily derived from the plateau current. The half-wave potential is simply equal to the P/Q standard potential. 

Since the catalyst is large and has a high degree of conformational variability, the ab initio molecular dynamics simulations have been used to provide an initial scan of the potential energy surfaces. This approach has been previously applied to study homogeneous catalytic systems [47, 52-54],... 

The metallacyclobutane mechanism of olefin metathesis has been discussed in Sections 1.3 and 3.1.7. For metathesis of acetylenes carbyne complexes are generally required (Figure 3.44), and both heterogeneous and homogeneous catalytic systems have been developed for this purpose. 

The interconversion of a- and 7r-allyl complexes has been observed by Kwiatek, Mador, and Seyler in the interesting homogeneous catalytic system of potassium pentacyanocobaltate(II), K3Co(CN)5 (46). This solution absorbs molecular hydrogen to form the active hydride species, Kj[Co (CN)jH]. Addition of butadiene to the hydride results in the formation of a [Pg.36]

In homogeneous catalytic systems we witnessed a new process for the production of acetic acid from methanol and carbon monoxide using a transition metal complex, thus displacing the earlier process employing ethylene as the starting material. The use of immobilized enzymes makes possible the commercial conversion of glucose into fructose. 

Dark Reactions If a homogeneous catalytic system is studied with the total exclusion of (1) stray light, (2) intense microwave irradiation or photo irradiation, and (3) spectrometer photon sources with hv > NIR radiation, then the reactive system will be considered to be thermally activated. Only dark reactions occur. 

Initial Times Immediately after the introduction of a reagent into a CSTR-recycle system, and for the first ca. 100 s, the compositions of the fluid elements throughout the liquid phase homogeneous catalytic system are measurably different. 

Longer Reaction Times For homogeneous catalytic systems without reactants in a second phase (P or Pl), the fluid elements in the CSTR, recycle loop, and cells are quite similar at times greater than ca. 100 s. Furthermore, for homogeneous catalytic systems with reactants in a second phase (Pq or Pj ), the fluid elements in the CSTR, recycle loop, and cells are quite similar at times greater than ca. 100 s if transport is fast compared to reaction i. e. Hatta regimes F-H. 

In this section, the historical context for Eq. (2) is formulated, the concept of signal entropy is discussed, and a solution for Eq. (2) is shown. The repeated application of Eq. (2) to organometallic and homogeneous catalytic systems is shown. 

PCA techniques have been applied to various data sets. From the open literature, I have been unable to find reference to their application to homogeneous catalytic systems. Having said that, it is important to note that the new ReactIR system by Mettler Toledo contains a program ConcIRT. It is a proprie-... 

In Section 4.5.3, discussion was restricted to the application of BTEM to organome-tallic and homogeneous catalytic systems using MIR spectroscopy. However, it should also be noted that BTEM has been successfully applied to other problems in the chemical sciences using FTIR [104], RAMAN, FTIR and RAMAN [105, 106], as well as MS [107, 108]. A one-to-one comparison between BTEM and SIMPLISMA, OPA-ALS, has appeared [109]. 

This chapter has focused on formulating the context for Eq. (2) and demonstrating that a solution exists. The results to date show that a genuine and robust solution to Eq. (2) is available in the absence of a priori information. The solution, BTEM, is a very powerful tool in the investigation of homogeneous catalytic systems using in situ spectroscopies. 

The two variables change their role with respect to their dependent versus independent, intensive versus extensive nature. This is also true of e.g. calorimetric, conductometric and spectrophotometric titrations using UV-, IR- or NMR-spectrosco-py We additionally have to consider that in the titration of the catalytic process only the external dynamics are measured a direct comparison with the actual metal fraction of the related intermediate complexes is generally not possible We call this analysis of homogeneous catalytic systems by a metal-ligand titration the method of inverse titration and for the resulting diagrams we use the term li nd-concentration control maps ([L]-control maps) . 

The monomers dealt with can be polymerized by various mechanisms, not only by ROMP. For example, a rapid polymerization of norbornadiene occurs using a homogeneous catalytic system consisting of nickel acetylacetonate or a nickel-phosphine complex, such as nickel bis-(tri-n-butylphosphine) dichloride (NiCl2(TBP)2) or nickel bis-(tricyclohexylphosphine) dichloride (NiCl2(TBP)2). Nickel acetylacetonate as catalyst is known to initiate rather a classical vinyl polymerization (7). The classical vinyl polymerization... 

Roundhill has recently reported the catalytic oxidation of CO to C02 by 02 using noble metal complexes, but no mechanistic details are given (91). Another direct transfer of oxygen to CO may take place in certain homogeneous catalytic systems for the reduction of nitric oxide by carbon monoxide according to (28) when no water is present to serve as the oxygen transfer agent (92,98). The catalyzed reductions of NO by CO are examined in the nitric oxide section of the review. 

The cone angles of optical isomers are, of course, identical, but it has been demonstrated that chiral phosphines in homogenous catalytic systems can determine a reaction pathway to form asymmetric products.199 Clearly the chirality of the phosphine is the determining factor in these systems, although other essential characteristics of the phosphine ligand s bulk and the it acidity still... 

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