Insertion versus migration

The important difference between the insertion mechanism (2.2) and the migration mechanism (2.3) is the following. In the insertion mechanism carbon monoxide inserts into the metal methyl bond and the acyl bond formed takes 

Formation of new o-bonds at the cost of the loss of the 7t-bond of the alkene during alkene hydrogenation, polymerisation etc. makes the overall processes of alkenes thermodynamically feasible and the process is highly exothermic. 

The metal hydride bond is stronger than a metal carbon bond and the insertion of carbon monoxide into a metal hydride is thermodynamically most often uphill. Alkene insertion into a metal hydride is thermodynamically allowed and often reversible. 

Suppression of P-elimination is often a desirable feature. It can be achieved in several ways  

Maintain co-ordinative saturation. In a catalytic cycle this may be a counterproductive suggestion, since the next reaction in the catalytic cycle will also require a vacant site. 

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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. 

T. The top part illustrates the spatial distribution of separated components in the capillary at two different times (to = 0 and ti > to) from the beginning of separation. The graph at the bottom shows concentrations of the separated components as functions of their position in the capillary at time ti. (C) Schematic NECEEM electropherogram (signal versus migration time) assuming a point detector at the distal end of the capillary. (See insert for color representation.)... 

A chiral metal center, as is found in a pseudotetrahedral iron complex with cyclopentudienyl. carbonyl, triphenylphosphine, and ethyl ligands, hus also beer used to address the question of alkyl migration versus carbonyl insertion. Inversion of... 

This cis-rearrangement (or cis-insertion) scheme, has been proposed more than 15 years ago by P. Cossee it involves essentially a TT-bonding of the moncmer (mono- or bidentate depending on the number of positions available) on a vacancy located in a cis-position versus the n-bonded polymer chain, followed by a purely electronic rearrangement (typical of the oericyclic type, and involving a small migration of the n -bonded chaiin, to the moncmer). This liberates a new coordination position, vhich can be used further, in a repetitive catalytic process. 

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