Chemistry of Diphosphinidenecyclobutenes

Preparation and characterization of sterically protected diphosphinidenecyclobutenes bearing two phosphorus atoms of coordination number 2 are described from the viewpoint of development of a novel type of bidentate ligand for transition metal complexes. They form the complexes with group 6 metals such as chromium, molybdenum, and tungsten, and group 10 metals such as palladium and platinum. Some of them can be used as a catalyst for synthetic reactions such as cross-coupling of the Sonogashira type, polymerization of ethylene, dehydrogenative hydrosilylation of ketones, hydroamination of 1, 3-butadienes, and direct alkylation or amination of allylic alcohols.