14410.8 e ,k3 were found in the final difference Fourier map very near the methyl carbons of the diethylaluminum moiety. All other peaks were less than 0.6 e .k3. All calculations were carried out on a VAX 11/750 computer with the CRYRM system of programs.[Cp2Zr(C,0-~2-OCCHCH2CMe3)]z(p-H)(p-AIEt2) (X). A toluene solution of Ia (1.057 g, 1.58 mmol) was treated with several equivalents (0.400 mL, 3.77 mmol) of neat Et2A1H. A deep yellow solution formed and was stirred for 24 h at 80 OC. Removal of solvent in vacuo afforded a dark brown waxy residue that was washed with four 15-mL portions of cold (-30 "C) hexane to yield X as a white powder (0.444 g, 0.589 mmol). The dark brown washings were evacuated to dryness, redissolved in toluene, and stirred at 80 OC for an additional 6 h. Workup in a similar manner provided an additional 0.094 g (0.125 mmol) of X. Recrystallization of 0.100 g of X from 5 mL of Et,O-hexane (3/2) at -20 OC afforded crystals suitable for X-ray diffraction: IR (Nujol) 2800 (vs), 2750 (vs), 1630 (m) (uC4), 1630 (s), 1310 (m), 1290 (m), 1255 (w), 1195 (w), 1180 (w), 1155 (w), 1020 (m), 1110 (m), 975 (m), 940 (m), 900 (m), 875 (m). 820 (s), 780 (s) cm-'. X-ray Structure Determination of [Cp2Zr(C,0-v2-OCCHCH,CMe,)h(~H)(r-ALEt,) (X). A crystalline block (0.35 X 0.30 X 0.25 mm) of X was mounted approximately along (I in a glass capillary under N,. A series of oscillation and Weissenberg photographs indicated monoclinic symmetry and the space group C2/c (hkl absent for h + k odd, hOl absent for I odd); data were collected on a Enraf-Nonius CAD-4 diffractometer with a graphite monochromator and Mo K a radiation (A = 0.7107 A). The unit cell parameters (Table 11) were calculated from the setting angles of 25 reflections in the range 20 < 28 < 35O. A total of 9443 reflections, comprising four symmetry-equivalent data sets, were averaged to give a total of 2845 reflections. The three check reflections, collected every loo00 s of exposure time, showed no significant deviations in their intensities. The correction for absorption was negligible (w = 0.544 mm-I). The form factors were taken from Table 2.2B, Vol. IV, "International Tables for X-Ray Crystallography" (1 974) for all atoms.The position of the Zr atoms was derived from the Patterson map, and the Fourier map phased on this atom revealed the remainder of the structure. All H atoms were introduced into the model with fixed coordinates at idealized positions and individual isotropic W s equal in magnitude to that of the adjacent heavy atom, plus 10-20%. Leastsquares refinement of all non-hydrogen atoms with anisotropic U,;? the scale factor, and the two parameters of the hydride H atom 0, coordinate and U), minimizing x w [ F 2 -(F,/k)2]2, with all the data (2845 reflections) led to S = 1.76, RF = 0.049, and RF = 0.033;s6 final shift/errors <0.10. The maximum deviation found in the Ap map is less than 0.8 e A-3. All calculations were carried out on a Vax 11/750 computer with the CRYRM system of programs.