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New silyl substituted monocyclopentadienyl complexes of Zr(IV) were synthesized from the precursor [Zr{@-CsH4(SiMe2C1)}CI 3] (1). The reaction of 1 with the lithium benzamidinate salt Li[C(Ph){N(SiMe3)} 2] leads to the complex [Zr{r/5-CsHa(SiM%C1)}{C(Ph)[N(SiMe3)]2}C12 ] (2), which decomposes slowly in solution with elimination of SiMe3C1. Complex 1 reacts with alkyl, amido and alkoxo transfer reagents (4 equiv.) to afford complexes [Zr{@-CsH4(SiMe2X)}X 3] (X = NMe 2 (3), OSiMe 3 (4), CH2CMe2Ph (5), C6H 5 (6), C6F 5 (7) and CH2SiMe 3 (8)) in good yields. Compounds 6 and 7 retain diethyl ether used as solvent but decompose as soon as they are desolvated under high vacuum conditions. Reaction of 1 with Mg(CH2Ph) 2 • 2THF (4 equiv.) yields the tetrabenzyl complex [Zr{@-CsHa(SiMe2CH2Ph)}(CH2Ph) 3] (9). The lH and 13C NMR data of the latter compound are discussed in terms of the non-classical coordination mode of the CH 2 Ph ligand, The molecular structure of [Zr{~75-C 5H4(SiMe2CH 2 Ph)}(CH2 Ph)3] 9 has been determined by X-ray diffraction methods. The coordination geometry around the zirconium atom shows a substituted @-cyclopentadienyl ring and three different benzyl ligands: a distorted ~2-benzyl group; a normal r/l-benzyl group; and a benzyl ligand with an intermediate coordination mode. The benzyl fragment bonded to silicon points away from the metal center. 9 crystallized in monoclinic space group P21/c with a = 11.268(3) A, b = 10.846(3) A, c = 27.734(6) A, /3 = 100.29(1) °, V = 3334.9(15) ~3 for Z = 4. The tetraalkylated compounds 6, 7 and 9 are excellent precursors for the preparation of the chloro derivatives. Reactions of these complexes with 3 equiv, of HC1 gave the corresponding trichloro [Zr{@-CsH4(SiMezR)}C13] (R = C6H 5 (10), C6F' 5 (11), CHePh (12)). The monochloro [Zr{@-CsH4(SiM%CH2Ph)}(CH2Ph)2C1] (13) and the dichloro derivative [Zr{@-CsH4(SiMezCHzPh)}(CHzPh)C12] (14) are observed, at 60°C and 90°C, respectively, by NMR experiments in deuterated chloroform. Complexes 10 and 11 also retain coordinated solvent, decomposing slowly when it is removed. 1 and 12 in the presence of MAO as cocatalyst, at 25°C and 1 atm of monomer pressure, cause the polymerization of ethylene with moderate activities, while under similar conditions, polymerization of propylene and styrene proceeds giving only traces of atactic materials. © 1997 Elsevier Science S.A.

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