The Kläui ligand is the anion {(C5H5)Co[(CH3O)2PO]3}−. The ligand, popularized by Wolfgang Kläui, binds metals and metalloids via a facial O3 donor set. Related tridentate and tripodal anionic ligands include trispyrazolylborates. The ligand is derived from the cationic complex of trimethylphosphite {(C5H5)Co[P(OCH3)3]3}2+ via an Arbuzov reaction. Using other phosphites and other cyclopentadienyl ligands, a large variety of derivatives are possible. The parent acid {(C5H5)Co[(CH3O)2PO]3}H is highly soluble in water (270 g/100 mL). Its pKa is about 2. Many complexes have been described, including bis(chelate) complexes of the type {M[{(C5H5)Co[(CH3O)2PO]3}2]n+ (M = Co(II), Mn(II), Bi(III), etc.). References Organocobalt compounds Half sandwich compounds Cyclopentadienyl complexes Phosphites Tripodal ligands