Solutions of the Lewis acid B(C6F5)(3) in 1,4-dioxane are found to effectively catalyze the hydrogenation of a variety of ketones and aldehydes. These reactions, the first to allow entirely metal-free catalytic hydrogenation of carbonyl groups under relatively mild reaction conditions, are found to proceed via a frustrated Lewis pair mechanism in which the solvent, a weak Bronsted base yet moderately strong donor, plays a pivotal role.