HIGHLY OXIDATION RESISTANT INORGANIC-PORPHYRIN ANALOG POLYOXOMETALATE OXIDATION CATALYSTS .2. CATALYSIS OF OLEFIN EPOXIDATION AND ALIPHATIC AND AROMATIC HYDROXYLATIONS STARTING FROM ALPHA-2-P2W17O61(MN+.BR)(N-11) (MN+ = MN3+, FE3+, CO2+, NI2+, CU2+), INCLUDING QUANTITATIVE COMPARISONS TO METALLOPORPHYRIN CATALYSTS

Several well-characterized transition-metal-substituted polyoxotungstate complexes, alpha-2-[(n-C4H9)4N](11-n)P2W17O61(Mn+.Br) (P2W17M) with M = Mn(III), Fe(III), or Co(II), catalyze the epoxidation of cyclooctene and cyclohexene, with P2W17Mn performing much better than P2W17Fe and P2W17Co; the complexes P2W17Cu, P2W17Ni, and P2W18 were almost inactive. P2W17Mn also catalyzes the oxidation of cyclohexane, adamantane, and heptane, with the formation of the corresponding alcohols and ketones (respective yields around 38, 40, and 5%), as well as the hydroxylation of naphthalene with the formation of 1- and 2-naphthol (43 and 3%). cis-Stilbene was epoxidized in anonstereoselective manner. Many of the characteristics of P2W17Mn-catalyzed oxidations, particularly the regioselectivity of limonene epoxidation and of adamantane and heptane oxidation, are similar to those of the oxidations of the same substrates catalyzed by the hindered Mn-porphyrin Mn(TDCPP)Cl. This suggests a high-valent Mn-oxo intermediate with a difficult substrate access, as the active oxygen species involved in P2W17Mn-catalyzed monooxygenation reactions by PhIO. However, in cyclooctene epoxidations using large excess of PhIO relative to the Mn catalyst, the rates and yields were higher with Mn(TPP)Cl and Mn(TDCPP)Cl than with P2W17Mn.