Cyclic zinc-porphyrin trimer

SCHEME 3 Cyclic zinc-porphyrin trimer catalysts for Diels-Alder reactions of pyridine-substituted dienes and dienophiles the structure of the catalyst dictates the stereochemistry of the reaction (45-48). 

FIGURE 13 CAChe-generated model of an exo-adduct bound inside the cavity of the 2,2,2-cyclic zinc-porphyrin trimer devised by Sanders and coworkers (45,46)... 

The Diels-Alder reaction can also be catalysed by simple artificial systems. A recent example is the reversible reaction between 7 and 8, which is accelerated by (stoicheiomet-ric amounts of) a cyclic zinc-porphyrin trimer host which binds pyridine derivatives inside the cavity. [22] The product is the exo-adduct, produced up to 1(X)0 times faster than the cor-... 

Anderson, H.L., A. Bashall, K. Henrick, M. McPartlin, and J.K.M. Sanders (1994). Crystal-structure of a supramolecular dimer formed by n—n interactions between 2 interlocked cyclic zinc porphyrin trimers. Angew. Chem. Int. Ed. Engl. 33, 429 31. 

Starting from zinc(II) 5,15-dioxo-10,20-bis(aryl)porphyrin [Zn(L1798)] the corresponding dimer [Zn2(L1799)] and trimer [Zn3(L1800)] are produced nearly quantitatively in the presence of bipy and tptz as templates. The yield of cyclic tetramer [Zn4(L1801)] assembled in the presence of H2LI796 exceeds 70% (Eq. 8.60) [146]. 

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