Mechanistically Designed Dual-Site Catalysts for the Alternating ROMP of Norbornene and Cyclooctene

Mechanistic work on the olefin metathesis reaction by well-characterized ruthenium carbene complexes
led to the rational design and synthesis of a modified, unsymmetrical “first-generation” catalyst, which,
in contrast to either first- or second-generation systems with symmetrical ligands, converts a mixture of
two cycloolefin monomers to a largely alternating copolymer. The mechanistic concept of a homogeneous
catalyst that switches between more than one state at each turnover is general. The structures of the
complexes, determined by mass spectrometry, NMR, and X-ray crystallography, reveal some unexpected
features, which explain sequence errors in the copolymer.