Cyclopolymerization of Nonconjugated Dienes with a Tridentate Phenoxyamine Hafnium Complex Supported by an sp3‐C Donor: Isotactic Enchainment and Diastereoselective cis‐Ring Closure

Cyclopolymerization of nonconjugated dienes produces poly(methylene‐1,3‐cycloalkanes) and provides a pathway to a number of stereochemically complex polymers. Activation of a diastereomeric mixture of a six‐membered metallacycle complex (rac‐ 1 ) in the presence of 1,5‐hexadiene produced poly(methylene‐1,3‐cyclopentane) (PMCP) with >98% cyclization of the diene monomer. The catalyst was found to cyclopolymerize 1,5‐hexadiene with relatively high activity. The microstructure of the PMCP furnished by rac‐ 1 was found to contain a high proportion of cis‐cyclopentane rings (σ = 0.70–0.74) and a relatively high isotactic content (α = 0.93–0.96). These are the first cis‐enriched isotactic cyclopolymers of 1,5‐hexadiene. Cyclopolymerization of 1,6‐heptadiene with rac‐ 1 /B(C₆F₅)₃ produced poly(methylene‐1,3‐cyclohexane) containing 97% cis‐isotactic rings. This is the first report of this highly isotactic and diastereomerically‐pure microstructure.