CONTRASTING THE CP(3)MCL LI(CH2)(CH2)PPH(2) (M=U, TH) SYSTEMS - SYNTHESIS AND STRUCTURE OF CP(2)TH[(CH2)(CH2)PPH(2)](2)/

The reaction of Cp(3)ThCl with Li[(CH2)(CH2)PPh(2)] produces Cp(2)Th[( CH2)(CH2)PPh(2)](2) in contrast to the analogous uranium system which yields Cp(3)U=CHPR(3). The structure of Cp(2)Th[(CH2)(CH2)PPh(2)](2) h as been determined by X-ray crystallography in the orthorhombic space group Pbcn, a=13.873(3) Angstrom, b=8.887(1) Angstrom, c=26.256(3) Ang strom, Z=4, V=3237(1) Angstrom(3), R=0.0530, Rg = 0.0624. The molecule has C-2 crystallographic symmetry with the Th bound to two Cp groups and two bidentate ylide chelates. All metrical parameters indicate a v ery sterically crowded molecule. H-1 NMR shows that the methylene carb ons of the ylide chelate are in rapid dynamic exchange at temperatures as low as -80 degrees C. Possible reasons for the different courses o f the reactions of the Th and U analogs are discussed.