Metal-free catalytic hydrogenation of polar substrates by frustrated Lewis pairs.

In 2006, our group reported the first metal-free systems that reversibly activate hydrogen. This finding was extended to the discovery of "frustrated Lewis pair" (FLP) catalysts for hydrogenation. It is this catalysis that is the focal point of this article. The development and applications of such FLP hydrogenation catalysts are reviewed, and some previously unpublished data are reported. The scope of the substrates is expanded. Optimal conditions and functional group tolerance are considered and applied to targets of potential commercial significance. Recent developments in asymmetric FLP hydrogenations are also reviewed. The future of FLP hydrogenation catalysts is considered.