Crabtree's catalyst is an air-stable, iridium-based organometallic complex \([Ir(COD)(PCy_3)(py)]PF_6\). Developed in the 1970s, it is a highly reactive, homogeneous catalyst used primarily for the directed hydrogenation of unactivated and sterically hindered alkenes. It excels at selectively adding hydrogen to specific faces of molecules that contain coordinating groups like hydroxyls (-OH)