page_title: Vinyl iodide functional group
section_title: Properties
hierarchical_section_title: Vinyl iodide functional group / Properties
caption_attribution_description: English: Properties of vinyl iodide
context_page_description: In organic chemistry, a vinyl iodide functional group is an alkene with one or more iodide substituents. Vinyl iodides are versatile molecules that serve as important building blocks and precursors in organic synthesis. They are commonly used in carbon-carbon forming reactions in transition-metal catalyzed cross-coupling reactions, such as Stille reaction, Heck reaction, Sonogashira coupling, and Suzuki coupling. Synthesis of well-defined geometry or complexity vinyl iodide is important in stereoselective synthesis of natural products and drugs.
context_section_description: Vinyl iodides are generally stable under nucleophilic conditions. In SN2 reactions, back-attack is difficult because of steric clash of R groups on carbon adjacent to electrophilic center (see figure 1a). In addition, the lone pair on iodide donates into the ╥* of the alkene, which reduces electrophilic character on the carbon as a result of decreased positive charge. Also, this stereoelectronic effect strengthens the C-I bond, thus making removal of the iodide difficult (see figure 1b). In SN1 case, dissociation is difficult because of the strengthened C-I bond and loss of the iodide will generate an unstable carbocation(see figure 1c)
  In cross-coupling reactions, typically vinyl iodides react faster and under more mild conditions than vinyl chloride and vinyl bromide. The order of reactivity is based on the strength of carbon-halogen bond. C-I bond is the weakest of the halogens, the bond dissociation energies of C-I is 57.6kcal/mol, while fluoride, chloride and bromide are 115, 83.7, 72.1 kcal/mol respectively. As a result of having weaker bond, vinyl iodide does not polymerize as easily as its vinyl halide counterparts, but rather decompose and release iodide.
  It is generally believed that vinyl iodide cannot survive common reduction conditions, which reduces the vinyl iodide to an olefin or unsaturated alkane. However, there is evidence in literature, in which a propargyl alcohol's alkyne was reduced in presence of a vinyl iodide using hydrogen over Pd/CaCO₃ or Crabtree's catalyst.
caption: Figure 1.
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