Stable, cationic alkyl-olefin complexes of ruthenium(II) and rhodium(III): Effects of ligand geometry upon olefin insertion/alkyl migration

The syntheses of ruthenium(II) and rhodium(III) model complexes of the putative active species in the iron(II)/MMAO polymerization system are reported. The cationic ruthenium methyl ethylene complex 3 is a stable, isolable compound, which does not produce polyethylene under a variety of conditions. Likewise, the analogous rhodium complex 12 shows no appreciable polymerization activity, despite its similarity to existing rhodium complexes which are active catalysts for olefin polymerization. X-ray crystal structures of the cationic ruthenium bis(ethylene) complex 7 and the five-coordinate rhodium bis(triflate) methyl complex 9 are also presented.