Researchers in Portugal have developed high-valent metal oxides for hydrogenating alkynes and sulfoxides, using inexpensive hydrogen.

Beatriz Royo and co-workers of the University of Lisbon exploited catalysts normally used for oxidations, such as olefin epoxidation and oxygen transfer. An earlier unconventional hydrosilylation of carbonyl groups with a high-valent rhenium oxide catalyst prompted us to further investigate these catalysts, said Royo. The team has extended the role of this and a similar molybdenum catalyst to reductive processes using hydrogen, a cheaper and more convenient reducing agent than silane. The catalysts are even capable of catalysing the selective hydrogenation of alkynes to alkanes - a challenging task in organic synthesis, said Royo.

The molybdenum catalyst, MoO₂Cl₂, also possesses high catalytic activity in the deoxygenation of sulfoxides using hydrogen, which may have important advantages in terms of green chemistry, explained Royo.  The procedure replaces phosphines, expensive metals and environmentally hazardous reducing agents, and has the added advantage of producing only water as a by-product.

Werner Thiel, professor of inorganic chemistry at the University of Kaiserslautern in Germany, is impressed by the work. He said that the researchers have exceeded the expectations for these types of catalysts, and that they have 'opened the door for other researchers to find further applications of high-valent transition metal compounds in reductions'.

Royo said that the team is now studying the mechanism of these processes, and an important goal for the future is to develop systems for enantioselective reductions.

Roxane Owen