Tris(2-pyridyl) tripod ligands

This review covers the recent literature involving tris(2-pyridyl) tripod ligands which use nitrogen, phosphorus, arsenic, or carbon as central bridging atoms. In general, tripod ligands are facially coordinating, tridentate chelate ligands which have received considerable attention in both coordination and organometallic chemistry. Over the past 20 years, there have been hundreds of published reports concerning various aspects of metal complexes which contain tripod ligands, with the majority of these reports involving polypyrazolylborate ligands. In light of the extensive and also very recent literature coverage of ligands which contain pyrazole donors, this review is a timely examination of the literature concerning tripod ligands that use pyridine donors. Further, this review contains the first summary of the chemistry of carbon-bridged tris(2-pyridyl) tripod ligands as well as an examination of recent studies involving nitrogen-bridged, phosphorus-bridged and arsenic-bridged analogues to the carbon-bridged ligands. There is a particular focus on tris(2-pyridyl) tripod ligands that coordinate in a facial manner to a single metal center through the pyridyl nitrogens.