Triarylselenonium salts

Many different photoinitiators based on onium -type compounds with anions of low nucleophilicity also have been described in the literature as effective catalysts for the polymerization of epoxides Thus, diaryliodonium salts diaryliodosyl salts triarylsulfonium salts and related compoundstri-phenylsulfoxonium saltsdialkylphenacylsulfonium salts and dialkyl-4-hydroxyphenylsulfonium salts seem to be most suitable as photoinitiators for epoxy curing. Some of the principles of the reaction mechanism involving these initiators are discussed in detail in the following Sections. Various other onium photoinitiators such as diarylchloronium and diarylbromonium salts , thiopyrylium salts 3), triarylselenonium salts and onium salts of group Va elements >... 

Another interesting process is the elec-trosynthesis of triarylselenonium salts, hard to obtain through traditional chemical ways [143]. 

The 5-arylation of sulfides is greatly improved by copper catalysis. The uncatalysed reaction requires heating under reflux to afford modest to moderate yields of the 5-aryl sulfonium derivatives. By contrast, upon copper catalysis, the reaction proceeds at room temperature to afford good to high yields of the 5-aryl sulfonium derivatives. 2-146,151 Moreover, the reaction was extended to the double arylation of the more readily available aiylthiols.l Similarly, the reaction of areneselenolates with diaryliodonium salts led to diarylselenides and triarylselenonium salts were easily obtained by copper catalysed arylation of diarylselenides. 2... 

Of these, only the triarylsulfonium and triarylselenonium salts have been investigated as photoinitiators for cationic polymerization. Triarylsulfonium salts, in particular, are attractive photoinitiators since they can be readily prepared in high yields by straightforward synthetic techniques. 

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