Ru complexes containing N-methyl-1,3,5-triaza-7-phosphaadamantane (mPTA) as catalysts for the isomerization of 2-cyclohexen-1-ol.

Abstract

The complex [RuCp(H2O-κO)(mPTA)2](CF3SO3)3 MeOH (4 MeOH) was synthesized and characterized by spectroscopic techniques and its crystal structure determined by single-crystal X-ray diffraction (mPTA = N-methyl-1,3,5-triaza- 7-phosphaadamantane). The catalytic activity of 4 for the redox isomerization of 2-cyclohexen-1-ol into cyclohexanone was studied in water, methanol/ water, and biphasic systems, reaching the highest conversion rate in biphasic water/cyclohexane (1:1) at pH 1.7 and under N2. The aqueous phase containing 4 was recycled up to 7 consecutive runs, reaching a total turnover number (TON) of 471 without significant losses of catalyst. Therefore, this reaction is a unique procedure for the isomerization of cyclic allylic alcohols without metal contamination of the product. The catalytic reaction mechanism was studied by nuclear magnetic resonance (NMR), showing that the reaction probably proceeds through the formation of an intermediate in which the substrate is η2-coordinated to the metal.