Competition between Ring-Closing Migratory Insertion Polymerization and Monomer Cyclization

Abstract

Migratory insertion polymerization (MIP) of PFpR [PFp = (PPh2(CH2)3Cp)Fe(CO)2, R = (CH2)4CH═CH2 or (CH2)5CH3] (1) involved competitive MIP ring-closing polymerization and monomer cyclization (MC), producing P(PFpR) macrocycles (2) and PFpR rings (3), respectively. MC, generating 3, occurred at the early stage of MIP, while the growing polymer chains exclusively underwent ring-closing cyclization without producing any linear analogues. The effect of solvent, temperature, and the concentration of 1 on the competition between the ring-closing MIP and MC was investigated. 3 was synthesized as the only product in THF with a low concentration of 1 (1 wt %), while the ring-closing MIP predominated under the condition at 60 °C with a high concentration of 1 in THF (>70 wt %), resulting in 2 with Mn up to 17 500 g/mol. This effective synthesis of ring molecules is attributed to the piano-stool coordination geometry and the low rotation barrier of Cp–Fe bond and will facilitate further exploration of ring molecules as functional materials and supramolecular building blocks.