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

The dinuclear complex Cp*2Os2Br4 (Cp* = pentamethylcyclopentadienyl) and re lated mono(pentamethylcyclopentadienyl)osmium compounds are catalysts for t he ring-opening metathesis polymerization (ROMP) of norbornene, The most ac tive catalyst prepared to date is made by treatment of Cp*2Os2Br4 with meth ylaluminoxane. This catalyst polymerizes norbornene with yields up to 167 k g 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 predomin ate. The polymer is insoluble in organic solvents but is swelled by many of them.