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)]·KOR (R = CCH3(CF3)2) 1, featuring a stabilizing ONO pincer ligand, initiates
the controlled living polymerization of strained dibenzocyclooctynes
at T > 60 °C to give high molecular weight
polymers
with exceptionally low polydispersities (PDI ∼ 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 (kp/ki ∼ 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.