ISOMERIC ZIRCONOCENOPHANE DICHLORIDES INVOLVING 2 DISILOXANE-BRIDGED INDENYL LIGANDS

The title complex 2 = [{O(Me(2)SiC(9)H(6))(2)}ZrCl2] (SiC9H6 = 2-silyl ated indenyl group) has been prepared in a way slightly different from that published recently by Rausch and coworkers (J. Organomet. Chem., 501 (1995) 375). In contrast to the earlier report, the H-1 NMR spect ra of 2 in C6D6 and CD2Cl2 reflect clearly the presence of both rac-2 and meso-2 (ca. 4:1). From toluene, 2 crystallizes as a racemic mixtur e; rac-2: monoclinic; space group P2(1)/c, a = 1278.2(4), b = 1196.2(4 ), c = 1567.8(6) pm; beta = 100.8(3)degrees; R(1) = 0.0314 (wR(2) = 0. 0771). The high-resolution H-1 NMR spectrum of rac-2 does not match wi th the crystal structure: most probably, rapid (on the NMR time scale) racemization takes place down to at least -80 degrees C.