Solvent Effects on Catalytic Epoxidation of Alkenes by Tetra‐ n ‐butylammonium Periodate and (Tetraarylporphyrinato)manganese(III)

The epoxidation of cyclooctene and cis ‐stilbene was performed by tetra‐ n ‐butylammonium periodate ( n Bu 4 NIO 4 )in the presence of (tetraarylporphyrinato)manganese(III) [Mn(por)] and imidazole (im) in various CH 2 Cl 2 /alcohol solvents (alcohol = CH 3 OH, C 2 H 5 OH, n ‐C 3 H 7 OH, i ‐C 3 H 7 OH, t ‐C 4 H 9 OH). In accord with the coordinating abilities of the alcohols to [Mn(por)], the epoxidation yields increased from CH 2 Cl 2 /CH 3 OH to CH 2 Cl 2 / t ‐C 4 H 9 OH. In the epoxidation of cis ‐stilbene in the presence of (acetato)(tetraphenylporphyrinato)manganese(III) [Mn(tpp)(OAc)], the cis ‐ to trans ‐stilbene oxide ratio increased consistently with the bulk of the alcohol in CH 2 Cl 2 /alcohol solvents. Also, it was found that the interaction of [Mn(tpp)(OAc)] and (acetato)(tetramesitylporphyrinato)manganese(III) [Mn(tmp)(OAc)] with n Bu 4 NIO 4 in the presence of imidazole but in the absence of alkenes yields [Mn(tpp)(O)(im)] + and [Mn(tmp)(O)(im)] + complexes. The formation of the Mn=O species for the small linear alcohols was faster than that for the larger ones, whereas the stability of the Mn=O complex was greater in the presence of the bulkier alcohols. Attempts were made to explain these effects.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)