Selective Ring-Opening Allene Metathesis: Polymerization or Ruthenium Vinylidene Formation.

Selective ring-opening allene metathesis polymerization (ROAlMP) and ruthenium vinylidene formation from 1,2-cyclononadiene ( 1 ) by simple catalyst selection are discussed. Grubbs second-generation catalyst (G2) favors the formation of an alkylidene leading to the ROAlMP of ( 1 ). Grubbs first-generation catalyst (G1) favors vinylidene formation and prevents the homopolymerization of ( 1 ) even at elevated temperatures. Isolation and characterization of poly( 1 ) by NMR analysis and MALDI-TOF confirms the generation of a well-defined polyallene that exhibits good thermal stability ( T D ca. 390 °C) and fluorescent properties. Ring-opening metathesis polymerization (ROMP) of a highly strained norbornene derivative (NBE- i Pr) at 80 °C using the ruthenium vinylidene generated from ( 1 ) is also investigated. The discovery of ROAlMP allows for the simple access of well-defined polyallenes from commercially available catalysts and will ultimately guide structure-property determinations of polyallenes.