Mainchain optically active vinyl copolymers via transition metal complex-templated asymmetric free radical polymerisation

摘要

4-Vinylpyridine coordinated to optically pure Cu(ii) amino acid salicylidene Schiff-base complexes as chiral templates has been copolymerised using standard free radical procedures with styrene, indene and 1,2-dihydronaphthalene. Following isolation of the copolymer products and decomplexation from the Cu(ii) complexes the copolymers with indene and 1,2-dihydronaphthalene proved to be optically active. Each copolymer has an optical rotation at 589 nm which has a sign opposite to that of the original Cu(ii) Schiff-base complex and to the copolymer still coordinated to the Cu(ii) complex. In contrast the 4-vinylpyridine with styrene displays no optical rotation. Systematic experiments have confirmed that the chiral Cu(ii) complexes induce a net asymmetry in the mainchain of the copolymers, and that the configuration of the stereogenic carbon centres on the backbone is the source of the asymmetry. A tentative mechanism is proposed to explain the nature of the induction process in these novel asymmetric free radical copolymerisations. [References: 21]