OA3. Polar Oxidative Addition
The polar oxidative addition mechanism is very similar to an aliphatic nucleophilic substitution (SN1 or SN2) reaction.
Figure OA3.1. An example of a polar oxidative addition.
In an oxidative addition, the metal can act as a nucleophile in the first step in an SN2 process. In the second step, the liberated halide binds to the metal. That doesn't happen in a normal nucleophilic substitution. In this case, the metal has donated its electrons and is able to accept another pair from the halide.
Figure OA3.2. Mechanistic steps in a polar oxidative addition.
Polar oxidative addition has some requirements similar to a regular SN1 or SN2 reaction:
Requires good leaving group
Requires tetrahedral carbon (or a proton) as electrophile
- What do you think is the most difficult step (i.e. the rate-determining step) for the reaction in Figure OA3.2? Why?
- Suggest the probable rate law for this reaction.
The platinum compound shown below is capable of reductively eliminating a molecule of iodobenzene.
a) Show the products of this reaction.
The starting platinum compound is completely stable in benzene; no reaction occurs in that solvent. However, reductive elimination occurs quickly when the compound is dissolved in methanol instead.
b) Explain why the solvents may play a role in how easily this compound reacts.
The reaction in methanol is inhibited by added iodide salts, such as sodium iodide.
c) Provide a mechanism for the reductive elimination of iodobenzene from the platinum complex, taking into account the solvent dependence and the inhibition by iodide ion.
For the following reaction,
- Identify the oxidation state at platinum in the reactant and the products.
- Assign stereochemical configuration in the product and the reactant.
- Explain the steresochemistry of the reaction.
Reaction of the following deuterium-labeled alkyl chloride with tetrakis(triphenylphosphine) palladium produces an enantiomerically pure product (equation a). Draw the expected product.
However, reaction of a very similar alkyl halide produces a compound that is only 90% enantiomerically pure. Draw the major product and explain the reason that there is some racemization.