Cross-metathesis of the vinyl group on tetrapyrrolic macrocycles: reactivity, selectivity, and mechanism

To find a general strategy for modifying the peripheral structure of vinylchlorin and porphyrin substrates, cross-metathesis on the vinyl group of these tetrapyrrolic macrocycles was investigated. The N-heterocyclic carbene-containing ruthenium complex 3 efficiently catalyzed the cross-metathesis (CM) of vinylchlorins and vinylporphyrins with a variety of olefins in high E-stereoselectivity. Different substituents on the olefin dramatically influenced the reaction. While the chlorins were more reactive than the porphyrins (as free bases), the corresponding zinc complexes showed higher activity. The reaction mechanism was investigated, and an empirical model for selective CM was applied to our studies to direct further reactions.