A Carbon-Free Sandwich Complex [(P₅)₂Ti]^2-

Urnezius, E.; Brennessel, W. W.; Cramer, C. J.; Ellis, J. E.; Schleyer, P. v. R.
Science 2002, 295, 832.

Reactions of highly reduced titanium complexes with white phosphorus, P₄, at or below 25^o C yielded brown to deep red-brown salts of the first entirely inorganic metallocene, [(h⁵-P₅)₂Ti]^2- (1). Like ferrocene and other carbon-based sandwich complexes, 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 remarkably 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.

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