Novel complexes between methyltrioxorhenium (MTO) and natural polysaccharides like chitin and chitosan or modified chitosan-bearing N-substituted acyl or alkyl pyridine moieties were synthesized and used for the oxidation of alkenes including acid-sensitive styrene derivatives with urea hydrogen peroxide adduct (UHP) as primary oxidant High conversions and yields of the corresponding epoxides were obtained Silica-chitosan hybrid composites with increased surface area and mechanical properties were also prepared and used as MTO supports A correlation on the role played by the different MTO-coordinating ligand sites of supports on the experimental outcome of olefin catalytic oxidations is discussed (C) 2010 Elsevier Inc All rights reserved