Complex sentence: Because of their "unquenched" reactivity, such systems are very reactive and are able to split the hydrogen molecule heterolytically, which makes them potentially useful as metal-free catalysts for hydrogenation reactions.
Split into simpler sentences: Because of their "unquenched" reactivity, such systems are very reactive toward substrates that can undergo heterolysis. They have potential use as metal-free catalysts for hydrogenation reactions.