Synthesis of porphyrin-containing [3]rotaxanes by olefin metathesis

A ruthenium-carbene-stoppered [2]rotaxane acts an intermediate in the synthesis of porphyrin-containing [3]rotaxanes by an olefin-metathesis protocol. The thread of these [3]rotaxanes can be extended to a polybutadiene strand by using them as chain-transfer agents in the ring-opening-metathesis polymerization of cyclooctadiene to give macromolecular porphyrin rotaxanes (see picture).