Manganese porphyrin hosts as epoxidation catalysts - activity and stability control by axial ligand effects

The catalytic performance of a cavity-containing [(porphyrin)Mn] in the epoxidation of alkenes is described. Inside the catalyst cavity, nitrogen-containing axial ligands can be bound to the porphyrin metal with high association constants, resulting in strong activation of the catalyst in the presence of only one equivalent of the ligand. Complexation of a sterically demanding ligand to the outside of the cavity-containing catalyst can prevent catalyst decomposition through the formation of ν-oxo dimers

Highly negative homotropic allosteric binding of viologens in a double-cavity porphyrin

The synthesis of a double-cavity porphyrin with interesting allosteric binding properties toward viologens (N,N′-disubstituted 4,4′-bipyridines) is described. The porphyrin host forms very strong 1:2 complexes with viologens, displaying a negative allosteric behavior. The first viologen guest binds exceptionally tight (K > 107 M-1), and the second guest binds much more weakly (ΔΔG = 9-15 kJ mol-1). The allosteric effect, one of the highest reported so far, originates in structural changes upon binding the first ligand, closely following the sequential (or induced-fit) theory of allosteric interactions by Koshland, Némethy, and Filmer (the KNF-model)