NEW ZIRCONOCENE PSEUDOHALOGENO COMPLEXES - CRYSTAL-STRUCTURE OF BIS[BIS(CYCLOPENTADIENYL)ISOCYANATOZIRCONIUM(IV)], [(ZR(ETA(5)-C5H5)(2)(NCO))(2)O]

The isothiocyanato complexes [Zr(eta(5)-C5H4Me)(2)(NCS)(2)] and [Zr(et a(5)-(C5H4Bu)-Bu-t)(2)(NCS)(2)] have been prepared from the correspond ing zirconocene dichlorides and KSCN in acetone. Analogous reactions w ith KOCN or KSeCN, led to the formation of the stable dinuclear ore-br idged complexes [(Zr(eta(5)-C5H5)(2)(NCO))(2)O] and [(Zr(eta(5)-C5H4Me )(2)(NCSe))(2)O], respectively. The molecular structure of [(Zr(eta(5) -C5H5)(2)(NCO)](2)O] has been determined by X-ray diffraction methods and consists of two (eta(5)-C5H5)(2)Zr(NCO) units linked by an oxo bri dge. The Zr-O-Zr bridge [angle 165.7(2)degrees] is non linear. The rel atively short Zr-O bond lengths of 1.949(3) and 1.942(3) Angstrom supp ort the presence of partial double-bond character. The compound contai ns N-coordinated cyanato ligands which are almost linear.