Highly Selective Molybdenum ONO Pincer Complex Initiates the Living Ring-Opening Metathesis Polymerization of Strained Alkynes with Exceptionally Low Polydispersity Indices

The pseudo-octahedral molybdenum benzylidyne complex [TolC Mo(ONO)(OR)]center dot KOR (R = CCH3(CF3)(2)) 1, featuring a stabilizing ONO pincer ligand, initiates the controlled living polymerization of strained dibenzocyclooctynes at T > 60 degrees C to give high molecular weight polymers with exceptionally low polydispersities (PDI similar to 1.02). Kinetic analyses reveal that the growing polymer chain attached to the propagating catalyst efficiently limits the rate of propagation with respect to the rate of initiation (k(p)/k(i) similar to 10(-3)). The reversible coordination of KOCCH3(CF3)(2) to the propagating catalyst prevents undesired chain-termination and -transfer processes. The ring-opening alkyne metathesis polymerization with 1 has all the characteristics of a living polymerization and enables, for the first time, the controlled synthesis of amphiphilic block copolymers via ROAMP.