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 [TolCMo(ONO)(OR)]<b>·</b>KOR (R = CCH<sub>3</sub>(CF<sub>3</sub>)<sub>2</sub>) <b>1</b>, featuring a stabilizing ONO pincer ligand, initiates
the controlled living polymerization of strained dibenzocyclooctynes
at <i>T</i> > 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 (<i>k</i><sub>p</sub>/<i>k</i><sub>i</sub> ∼ 10<sup>–3</sup>). The reversible coordination
of KOCCH<sub>3</sub>(CF<sub>3</sub>)<sub>2</sub> to the propagating
catalyst prevents undesired chain-termination and -transfer processes.
The ring-opening alkyne metathesis polymerization with <b>1</b> has all the characteristics of a living polymerization and enables,
for the first time, the controlled synthesis of amphiphilic block
copolymers via ROAMP
