Choosing between Ti(II) and Ti(III): selective reduction of titanocene dichloride by elemental lanthanides.

The reduction of titanocene dichloride CpTiCl with lanthanide metals has led to the discovery of a surprising lanthanide effect: while with most lanthanides, a divalent [CpTi] equivalent was obtained, the use of samarium or ytterbium only led to the reduction to trivalent [CpTiCl]-type complexes, including the structurally characterized heterobimetallic complex [CpTi(μ-Cl)SmCl(THF)]. These results were corroborated by reactivity studies (alkyne coupling and radical reactions), EPR spectroscopy and electrospray mass spectrometry, providing new insights into the reduction chemistry of lanthanide metals.