UNPRECEDENTED COORDINATION OF A SI-CL BOND TO A TRANSITION-METAL - SYNTHESIS AND STRUCTURE OF [RAC-C2H4(INDENYL)2ZR(CH(SIME2CL)(SIME3))][AL2CL6.5ME0.5] FORMED BY REVERSIBLE SI-C BOND ACTIVATION

Reaction of Cp'2Zr{CH(SiMe3)2}Cl with a 2-fold excess of AlCl3 affords the novel Si-C bond activation products [Cp'2Zr{CH(SiMe2Cl)(SiMe3)}][Al2ClnMe7-n] (Cp'2 = rac-C2H4(indenyl)2 (1), (C5H5)2 (2)); the Lewis acid adducts Cp'2Zr{CH(SiMe3)2}Cl.AlCl3 are obtained with 1 equiv of AlCl3. In contrast, Cp'2Zr(CH2SiMe3)Cl (Cp'2 = rac-C2H4(indenyl)2, (C5Me5)2) undergoes rapid alkyl-chloride exchange with AlCl3, giving Cp'2ZrCl2.(Me3SiCH2)AlCl2. The structure of [rac-C2H4(indenyl)2 activated Zr{CH(SiMe2Cl)(SiMe3)}][AlCl6.5Me0.5] (1) has been determined by X-ray crystallography. Crystal data: C26.5H33.5Al2Cl7.5Si2Zr, M(r) 819.3, monoclinic, P2(1)/n, a = 9.419 (2) angstrom, b = 23.134 (5) angstrom, c = 17.418 (4) angstrom, Z = 4, final R = 0.053 for 5215 ''observed'' reflections. The unusual chelating alkyl ligand shows the first example of Si-Cl bond coordination to a transition metal (Zr-Cl = 2.573 (1) angstrom; Si-Cl = 2.266 (2) angstrom; Zr-Cl-Si = 80.4 (1)-degrees). The Si-C bond activation reaction leading to 1 is reversible, as shown by formation of rac-C2H4(indenyl)2Zr{CH(SiMe3)2}Cl on reaction of 1 with a 2-fold excess of AlMe3. Sterically and electronically saturated 1 is inert toward unsaturated substrates. Treatment of 1 with Lewis bases affords rac-C2H4(indenyl)2Zr{eta(1)-CH(SiMe2Cl)(SiMe3)}Cl (3).