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.W. Kläui, P. C. Kunz "Sodium (η5-Cyclopentadienyl)tris(dimethylphosphito-P)cobalt(III), Na[(C5H5)Co{P(O)(OMe)2}3]" Inorg. Synth., 2010 vol. 35, pp. 125–128. 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 (). 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.).
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