Agent, electrophilic surface active

Markwell (1982) reported that the reaction mechanism for creating the electrophilic iodine species may be somewhat different for lodobeads than other oxidizing agents. It was demonstrated that the active component remained at or near the surface of the beads during the course of the iodination process. Markwell speculated that an intermediate reactive species, N-iodobenzenesulfonamide, is formed from substitution of the chlorine atoms on the bead (Figure 12.4). It is possibly that this intermediate is involved in the direct iodination of target molecules that approach the bead surface. 

Recently, Pt DENs were used as an electrophilic catalyst in an intramolecular addition of phenols to alkynes (intramolecular hydroalkoxylation), as shown in Fig. 4.13b [100], The Pt DENs were supported on a mesoporous silica material known as SBA-15 (Fig. 4.13a). Since the as-synthesized SBA-15 consists of micrometer-sized particles, the supported Pt DENs can be easily separated from the reaction solution by centrifugation. This reaction has only been catalyzed by homogeneous catalysts (e.g., PtCy before this report. The use of the supported Pt DENs to catalyze this reaction was the first demonstration that a heterogeneous catalyst could also catalyze this conversion. It was also found that adding an oxidation agent, PhICF, would dramatically increase the benzofuran yield from 10 to 98 %, as shown in Fig. 4.13b. The authors proposed that PhICl2 could render the surface of the Pt nanoparticles more electrophilic, which is required for the Pt DENs to be active for the hydroalkoxylation reaction. 

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