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-ⁱPr) 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.