Elementary steps migration reactions

Insertion of carbon monoxide and alkenes into metal-carbon bonds is one of the most important reaction steps in homogeneous catalysis. It has been found for insertion processes of platinum [16] that the relative positions of the hydrocarbyl group and the unsaturated fragment must be cis in the reacting complex [17], The second issue concerns the stereochemical course of the reaction, insertion versus migration as discussed in Chapter 2.2. 

Accidentally, one proof for the migration mechanism stems from the polyketone model work and we will present it here. When the two dents of the bidentate ligand are only slightly inequivalent, be it sterically or electronically, this would allow the identification of the sites during migration or insertion. In order to do this we need two phosphorus ligands that are very 

Rates of insertion of CO. The rate of CO insertion in the Pd-CH3 bond has been studied by Dekker, Vrieze, van Leeuwen et al. [23] for the complexes (P-P)Pd(CH3)Cl (P-P = dppe, dppp, dppb, dppf) and the ionic complexes [(P-P)Pd(CH3)(CH3CN)]+S03CF3-. The rate was found to decrease in the order dppb dppp dppf for the neutral chloro complexes with half-life times ranging from 18 to 36 minutes at 235 K and 25 bar of CO. The dppe complex reacted much more slowly with a half-life time of 170 minutes at 305 K. The rate of carbonylation of the Pd-CH3 bond in the ionic triflate complexes was at least 10 times higher than those of the analogous neutral complexes, the order 

It should be emphasized that this is only true within a series of diphenylphosphino ligands, i.e. the phenyl substituents are retained in the series. 

When the bite angle becomes too wide, as for dppb, the behaviour of the catalytic systems of palladium may also be different. When ligands have large 

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Insertion and migration refer to the process in which an unsaturated molecule inserts to a metal-anion bond. The two ways of describing this elementary step have been depicted in Figure 2.2 and 2.3 In the platinum complex shown an acetyl fragment is formed from a co-ordinated CO and a methyl group, both attached to platinum. Clearly, the two reacting groups should occupy positions cis to one another, otherwise the reaction cannot occur [1]. 

Elementary steps involving insertion or migration reactions are of prime importance for catalysis employing alkenes and carbon monoxide. Two examples taking place on a platinum centre have been depicted in Figs. 4.18 and 4.19. In these reactions an acetyl fragment is formed on the platinum centre from a coordinated CO and a methyl group. The important mechanistic difference... 

The first reaction we will discuss is the ligand migration reaction, or, as it is sometimes called, the insertion reaction. This well defined elementary reaction is a step in many important reactions of organometallics, including several catalytic processes of industrial importance. For a general review see Basolo and Pearson 36), or Schrauzer 37). 

Heterogeneous catalytic hydrogenation and dehydrogenation reactions proceed in a pathway of elementary steps that involve mass transfer of reactant molecules to the catalyst surface, adsorption and migration of reactant molecules on the catalyst surface to active sites, reaction conversion to the product on catalyst surface and then desorption of product molecules from the catalyst surface. Microreactors in their various geometries have the potential for detailed studies of reactions for multiple... 

Transition metal catalysts generally operate via elementary steps that can occur at the metal center, typically oxidative addition, substrate coordination, migration (insertion), reductive eUmination, and so on. This creates a reaction pathway by breaking down the reaction in several different steps. As a typical example, the reaction pathway of rhodium-catalyzed hydrogenation is depicted. The reaction profile of such a metal-catalyzed reaction therefore consists of various transition states and intermediates (Figure 4.7). Often one of the transition states has the highest energy barrier and represents the most difficult step, and it is this step of... 

Scheme 1.2 Elementary steps taking place in a photocatalytic cycle light absorption (i), electron excitation (ii), electron and hole migration (iii), oxidation and reduction reactions (iv), or geminate electron recombination (v)...

The n-pentane is dehydrogenated on the platinum to n-pentene, w hich migrates to the acidic sites I on the alumina, where it is adsorbed and isomerizes to z-pentene. Then the z-pentene is desorbed and migrates to the platinum, where it is hydrogenated to z-pentane. Step 3 is treated as elementary and rate-controlling the other four steps are treated as quasiequilibrium reactions. 

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