A carbon-free sandwich complex [(P₅)₂Ti]^2-

Reactions of highly reduced titanium complexes with white phosphorus, P₄, at or below 25°C yielded brown to deep red-brown salts of the first entirely inorganic metallocene, [(η⁵-P₅)₂Ti]^2-(1). Like ferrocene and other carbon-based metallocenes, the structure of 1 has parallel and planar five-membered rings symmetrically positioned about the central metal atom. Despite its electron-deficient (16 electron) and formally zerovalent titanium character, salts of 1 are highly stable toward heat and air, both in solution and in the solid state. Computational studies show that the pentaphosphacyclopentadienyl unit, P₅, functions as an unusually effective acceptor ligand, and this results in substantial stabilization of 1.