Five-coordinate gold(III) complexes of the Kläui ligands [(η5-C5H5)Co{P(O)(OR)2}3]− (R = Me, Et)

The reactions of cycloaurated gold(III) dichloride complexes [LAuCl2] (L = 2-C6H4CH2NMe2 or 2-C6H4PPh2double bond; length as m-dashNPh) with monoanionic tripodal oxygen donor Kläui ligands [(η5-C5H5)Co{P(O)(OR)2}3]− (R = Me or Et) results in the formation of cationic gold(III) salts [LAu{OP(OR)2}3Co(η5-C5H5)]+. An X-ray structure determination on [(2-C6H4PPh2double bond; length as m-dashNPh)Au{OP(OR)2}3Co(η5-C5H5)]BF4 shows that the Kläui ligand coordinates strongly to the gold through two oxygen atoms, and weakly through the third, giving the gold(III) a distorted square pyramidal geometry. This is the first structurally characterised example of this geometry for gold(III) with ligands other than those containing rigid bipyridine or phenanthroline backbones. In solution at room temperature there is rapid interchange (on the NMR timescale) between the oxygen atoms of the Kläui ligands, which is frozen out on cooling.