Phosphorus-bridged ansa-metallocene complexes of titanium, zirconium, and hafnium: The syntheses and structures of [PhP(C5Me4)(2)]MX2 and [Ph(E)P(C5Me4)(2)]MX2 (E = O, S, Se) derivatives

A series of phosphorus-bridged ansa-metallocene complexes of titanium, zirc onium, and hafnium, [PhP(C5Me4)(2)]MX2 and [Ph(E)P(C5Me4)(2)]MX2 (X = Cl, M e, CO, (Se-3)(0.5), (Te-3)(0.5); E = O, S, Se), has been synthesized. Struc tural characterization by X-ray diffraction indicates that, in comparison t o their non-ansa counterparts (C5Me5)(2)MX2, the cyclopentadienyl groups in phosphorus-bridged complexes are displaced from symmetric eta(5)-coordinat ion toward eta(3)-coordination. Such eta(3), eta(3)-coordination creates mo re electrophilic metal centers than those in their permethylcyclopentadieny l counterparts, as judged by the nu(CO) stretching frequencies of the zirco nium dicarbonyl complexes Cp*Zr-2(CO)(2) (1946 and 1853 cm(-1)) and [PhP(C5 Me4)(2)]Zr(CO)(2) (1959 and 1874 cm(-1)).