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. 400 ºC) and fluorescent properties. Ring-opening metathesis polymerization (ROMP) of a high strained norbornene derivative (NBE-ⁱPr) at 80 ºC using the ruthenium vinylidene generated from (1) is also investigated. The discovery of ROAlMP allows for the simple accesses of well-defined polyallenes from commercially available catalysts and will ultimately guide structure-property determinations of polyallenes.