Influence of the departing group on the electrophilic cleavage of silicon-carbon bonds adjacent to zirconocene dichloride. Preparation of electrophile-functionalized zirconocene dibromides

(EtMe2SiC5H4)CpZrCl2 (5) reacts with BBr3 in 1,2-dichloroethane (reflux, 24 h) to afford a 4:1 mixture of (EtMeBrSiC5H4)CpZrBr2 (10) and (BrMe2SiC5H4) CpZrBr2 (11) in a nearly quantitative conversion. Similarly, ((BuMe2SiC5H4) -Bu-t)CpZrCl2 (6) reacts with BBr3 to afford a 15:1 mixture of ((BuMeBrSiC5 H4)-Bu-t)CpZrBr2 (13) and 11. The product 11 is obtained independently by t reating (Me3SiC5H4)CpZrCl2 (12) with BBr3. In contrast, Si-Ph bonds are cle aved with complete selectivity in the presence of Si-Me groups. (PhMe2SiC5H 4)(2)-ZrCl2 (8) reacts with excess BCl3 in dichloromethane (reflux, 15 h) t o afford (ClMe2SiC5H4)(2)-ZrCl2 (14) in 72% yield. (Ph2MeSiC5H4)(2)ZrCl2 (9 ) reacts with excess BBr3 in 1,2-dichloroethane (reflux, 15 h) to afford (B r2MeSiC5H4)(2)ZrBr2 (15) in 79% yield. Complexes 9 and 15 were analyzed by single-crystal X-ray diffraction. Crystalline 9 adopts a pseudo-C-2 conform ation in which the face of the Ph group of one ligand shows a weak interact ion with a C-H bond of the other ligand. Crystalline 15 also adopts a pseud o-C-2 conformation, in which the SiBr2 groups are directed away from the Zr Br2 group.