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

Abstract

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.