Conceptually, the direct hydrogenation of unsaturated compounds is an ideal reaction, one able to fulfil the principles of Green Chemistry. It exhibits perfect atom economy, as all employed atoms end up in the product and uses inexpensive hydrogen gas, which can be obtained from renewable sources. Hence, the process is both ecologically sustainable and cost-efficient. Its catalytic nature obviates the need for stoichiometric hazardous reagents and reduces waste. The high energy efficiency enabled by the often mild conditions further adds to its sustainability. Consequently, the hydrogenation of unsaturated substrates, such as ketones or olefins, has been widely explored and has been awarded with several Nobel Prizes.
The relatively unexplored hydrogenation of aromatic systems offers additional benefits, such as the conversion of readily available flat frameworks into elusive complex saturated (hetero)cycles. These are attractive motifs throughout the chemical sciences, especially for pharmaceutical and agrochemical research. Given effective control over chemo-, diastereo- and enantioselectivity, an astonishing amount of complexity can be built up in a single chemical step making it a dream reaction for use in an ideal synthesis. As the ultimate goal, this should provide efficient and unique access to valuable building blocks for the synthesis of pharmaceuticals and other important compounds.