Double-Linear Insertion Mode of α,ω-Dienes Enabled by Thio-imino-quinoline Iron Catalyst

An unprecedented coordination–insertion mode, double-linear insertion of α,ω-dienes, has been discovered. Iron complexes of thio-imino-quinoline (TIQ) ligands, upon activation by modified methylaluminoxane (MMAO), were found to catalyze the oligomerization of α,ω-dienes (1,7-octadiene, 1,8-nonadiene, and 1,9-decadiene) and the copolymerization of such dienes with ethylene. The reactions furnish highly linear structures with internal double bonds, indicating the incorporation of both vinyl groups of α,ω-dienes into the polymer chain in a linear insertion fashion. Iron complexes with large substituents (e.g., iPr, Cy) on the S atom and small substituents (e.g., Et, Me) at the ortho positions of the N-aryl ring in the TIQ ligand afforded superior catalytic activity, high linear selectivity, and high α,ω-diene content in the ethylene-α,ω-diene copolymers. Density functional theory (DFT) calculations reveal that the diene enchainment involves 2,1-insertion of the first vinyl group into a Fe–C bond and β-H elimination, followed by 1,2-insertion of the second vinyl group into a Fe–H bond. The linear enchainment can be attributed to the low activation barriers for the β-H elimination and subsequent 1,2-insertion. The formation of internal double bonds in the ethylene-α,ω-diene copolymer chain allows for facile postpolymerization functionalization, which was demonstrated by olefin hydrosilylation to access Si-functionalized materials.