Metalloporphyrins as Catalysts of Chain Transfer in Radical Polymerisation and Stereoselective Oxidation

The 25th anniversary of catalytic chain transfer

“…The exact mechanism of CIRP remains unclear. A hydride transfer to a radical to explain CIRP was suggested 4 as being naturally related to CCT. According to that mechanism, LCoH that forms via reaction 1 reacts with the excess of free radicals rather then with the monomer:…”

“…Cobaloximes, with their rich chemistry of axial ligands, helped me to compose a general reaction scheme (Scheme 1) for the reaction of CCT catalysts under the conditions of radical polymerization. It appeared first in my Ph.D. thesis in 1983 and was soon published in the first review 4 of CCT. The inner circle of the scheme is the only working cycle of CCT.…”

“…4 This strange difference in cobalt phthalocyanine (II) was soon explained. The cobalt complex of unsubstituted phthalocyanine (II) is not soluble in most organic solvents.…”

Shining a light on catalytic chain transfer

“…In some solvents or in the presence of certain axial bases these can be rather stable, thereby reducing the amount of cobalt available for transfer. 60,73 A last deactivation pathway is hydrolysis or oxidation of the macrocyclic ligand.…”

The role of monomer in the chain transfer reaction in cobaloxime-mediated free-radical polymerization

“…In the early 1980s, catalytic chain transfer by certain lowspin Co(II) complexes emerged as a very effective technique for molecular weight control in free-radical polymerization [1][2][3] . It was found that these complexes catalyze the chain transfer to monomer reaction, and although it has since long been established that a hydrogen atom is abstracted from a b position (preferably from an a-methyl group) in the growing radical and transferred to a monomer molecule to give a monomeric free radical, no conclusive evidence regarding the actual chain transfer reaction exists.…”