Chapter 24, Problem 24.28P

Interpretation Introduction

Interpretation:

The proper reactant and the proper coupling reaction pathway have to be suggested for the given polymers in the question.

Concept Introduction:

Cross coupling:

A cross coupling reaction is defined as a reaction that creates a $\text{C}-\text{C}$ bond by coupling together two alkyl, aryl, alkenyl or alkynyl groups.  Cross coupling reactions involve a transmetallation step.  A transmetallation is a pairwise interchange of ligands between two different metals or metalloids.

In the case of palladium catalysed cross-coupling reactions the other metal or metalloids are commonly $\text{Zr,}\text{Sn}\text{,}\text{B}\text{,}\text{ZN}\text{,}\text{Cu}\text{,}\text{Mg}$ which are designated as M in the following general example,

$\text{R-Pd}\text{+R'-M}\stackrel{}{\to }\text{R'-Pd}\text{+}\text{R-M}$

Sonogashira coupling:

The $\text{Pd(0)}$ catalyzed cross coupling reaction that involves transmetallation of an alkynyl $\text{Cu(I)}$ species to $\text{Pd}$ follow by the coupling to an aryl or vinyl iodide or triflate.  The $\text{Cu(I)}$ alkynyl complex is created in situ by the reaction of terminal alkyne with $\text{CuI}$ in the presence of trimethylamine.  This reaction is most commonly used to create diaryl alkynyl product.

Generalized reaction,

Suzuki coupling:

The Suzuki coupling uses a boron compound and an alkenyl, aryl or alkyl halide or triflate as the carbon sources with a palladium salt as a catalyst.  The reaction is mainly used to form biaryls.  The mechanism of the reaction starts with an oxidative addition followed by transmetallation in which the substituent on the borane replaces the ligand on the palladium concluding with the reductive elimination of the palladium to form the new carbon-carbon bond.  The base may serve as a new labile ligand to palladium or it may activate the borane by coordination.

Generalized reaction,

$\text{RX}\text{+}{\text{R'BY}}_{\text{2}}\underset{\text{base}}{\overset{{\text{PdL}}_{\text{4}}}{\to }}\text{R-R'}\text{+}{\text{XBY}}_{\text{2}}$

Oxidative addition and ligand exchange,

$\text{RX}\stackrel{{\text{PdL}}_{\text{n}}}{\to }\text{R-PdX}\stackrel{{\text{RO}}^{\text{-}}}{\to }\text{R-Pd-OR}$

Borane activation

${\text{BY}}_{\text{3}}\stackrel{{\text{RO}}^{\text{-}}}{\to }{\left[{\text{RO-BY}}_{\text{3}}\right]}^{\text{-}}$

Reaction,

$\text{R-Pd-OR}\text{+}{\left[{\text{R'-BY}}_{\text{3}}\right]}^{\text{-}}\stackrel{}{\to }\text{R-Pd-R'}\stackrel{}{\to }\text{R-R'}\text{+}\text{Pd(0)}\text{+}{\left[{\text{RO-BY}}_{\text{3}}\right]}^{\text{-}}$