Arene complexes crosslinking

Transition metal organometallic complexes like dicarbonyl cyclopentadienyl iron [128], tricarbonyl cyclopentadienyl manganese [129] and iron-arene complexes [130,131] have also been reported as photoinitiators for photochemical crosslinking of cyanate esters. Photosubstitution of carbonyl groups by -OCN during irradiation initiates the reaction in the former case whereas photochemical dissociation of arene triggers it in the latter system. 

Commercially important photoinitiators for crosslinking by cationic polymerization are onium salts, particularly the thermally and hydrolytically stable diaryliodonium and triarylsulfonium salts,and mixed ligand arene cyclopentadienyl metal salts with complex metal halide anions. Direct and sensitized photolysis of these systems have been reviewed " and are discussed in detail in Volume 4, Chapter 20. 

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