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

Abstract

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(C(6) F(5) )(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.

Cyclopolymerizations: Synthetic Tools for the Precision Synthesis of Macromolecular Architectures

“…The Hf complex with a tridentate phenoxyamine ligand ( VI ) brings about cyclopolymerization of 1,5-hexadiene in the presence of B­(C 6 F 5 ) 3 to afford a polymer rich in cis -diisotactic structure (cis = 70–74%, α = 0.93–0.96; Figure ). The catalyst also promotes the highly isotactic cis-selective cyclopolymerization of 1,6-heptadiene ( cis -diisotactic = 97%). The tridentate pyridylamide Hf complex VII in combination with [Ph 3 C]­[B­(C 6 F 5 ) 4 ] promotes the cyclopolymerization of 1,5-hexadiene and 1,7-octadiene ( i- Bu 3 Al is used as scavenger) .…”

Cycloterpolymerization of 1,6-Heptadiene with Ethylene and Styrene Catalyzed by a THF-Free Half-Sandwich Scandium Complex

“…However, no catalyst has been reported to date to effect such terpolymerization reactions. Previously, a few transition metal catalysts were reported for the homopolymerization of HPD. − However, attempts to copolymerize HPD with another monomer such as ethylene often gave a mixture of homopolymers . A cobalt catalyst was reported recently by Osakada and co-workers to effect the copolymerization of HPD with ethylene to give HPD−ethylene copolymers with relatively low molecular weights .…”

Synthesis of Long-Chain Branched Polyolefins by Coordinative Chain Transfer Polymerization

“…If a 5-hexenyl group participates as a comonomer in the chain growth process as shown in Scheme , the growing two PO chains are connected, and hence, the counted number of PO chains should be less than the value of “2 × Zn (μmol)”. The cyclocopolymerization of 1,5-hexadiene or 1,6-heptadiene is a well-known process, in which successive insertions of both vinyl groups in 1,5-hexadiene or 1,6-heptadiene occur to form a cyclopentane or cyclohexane ring. − After the 5-hexenyl group is transferred from the Zn site to the Hf center, a similar cyclization process must favorably occur, and consequently, the 5-hexenyl group is transformed to cyclopentylmethyl through intramolecular 1,2-insertion process (Scheme a) . Owing to the occurrence of such a reaction, LCBs were not generated.…”