Dioxidomolybdenum(VI) and -tungsten(VI) complexes with tripodal amino bisphenolate ligands as epoxidation and oxo-transfer catalysts

The molybdenum(VI) and tungsten(VI) complexes [MO₂(L)] (M = Mo (1), W (2), H₂L = bis(2-hydroxy-3,5-di-tert-butybenzyl)morpholinylethylamine) were synthesized and the complexes were used to catalyze oxotransfer reactions, viz. sulfoxidation, epoxidation and benzoin oxidation. For comparison, the same reactions were catalyzed using the known complexes [MO₂(L′)] (M = Mo (3), W (4), H₂L′ = bis(2-hydroxy-3,5-di-tert-butybenzyl)ethanolamine) and [MO₂(L″)] (M = Mo (5), W (6), H₂L″ = bis(2-hydroxy-3,5-di-tert-butybenzyl)diethyleneglycolamine). The oxo atom transfer activity between DMSO and benzoin at 120 °C was identical for all studied catalysts. Reasonable catalytic activity was observed for sulfoxidation by the molybdenum complexes, but all tungsten complexes were found to be inactive. Similarly, the molybdenum complex 1 exhibited relatively good epoxidation activity, while the corresponding tungsten complex 2 catalyzed only the epoxidation of cis-cyclooctene with low activity.