Ring-opening metathesis polymerization of norbornene by Cp*2Os2Br4 and related compounds

The dinuclear complex Cp*2Os2Br4 (Cp* = pentamethylcyclopentadienyl) and related mono(pentamethylcyclopentadienyl)osmium compounds are catalysts for the ring-opening metathesis polymerization (ROMP) of norbornene, The most active catalyst prepared to date is made by treatment of Cp*2Os2Br4 with methylaluminoxane. This catalyst polymerizes norbornene with yields up to 167 kg of polymer per mol of catalyst at room temperature. The C-13 NMR spectra show that the polymer is slightly blocky and that cis double bonds predominate. The polymer is insoluble in organic solvents but is swelled by many of them.