[{Me(4)C(2)(C(5)H(4))(2)}Zr(BH(4))(2)], a bis(tetrahydroborate) complex of a bridged zirconocene.

Bis(tetrahydroborato)[1,1,2,2-tetramethyl-1,2-ethylenebis(eta(5)-cyclopentadienyl)]zirconium, (I), was synthesized by the reaction of the zirconocene dichloride with lithium tetrahydroborate. Crystals suitable for X-ray structure analysis were obtained by recrystallization from toluene. The molecule adopts an appproximate C(2v) symmetry. Both tetrahydroborate ligands are eta(2)-coordinated and tilted by 18-19 degrees out of the equatorial plane; the angle B1-Zr1-B2 is 104.7 degrees. The cyclopentadienyl rings show a normal eta(5)-coordinaton, with a centroid-Zr-centroid angle of 124.3 degrees.