Synthesis and reactivity of new silyl substituted monocyclopentadienyl zirconium complexes. X-ray molecular structure of [Zr η5-C 5H 4 (SiMe 2CH 2Ph)(CH 2Ph) 3

Abstract

New silyl substituted monocyclopentadienyl complexes of Zr(IV) were synthesized from the precursor [Zr η 5-C 5H 4(SiMe 2Cl)Cl 3] ( 1). The reaction of 1 with the lithium benzamidinate salt Li[C(Ph)N(SiMe 3) 2] leads to the complex [Zr η 5-C 5H 4(SiMe 2Cl)C(Ph)[N(SiMe 3)] 2Cl 2] ( 2), which decomposes slowly in solution with elimination of SiMe 3Cl. Complex 1 reacts with alkyl, amido and alkoxo transfer reagents (4 equiv.) to afford complexes [Zr η 5-C 5H 4(SiMe 2X)X 3] (X = NMe 2 ( 3), OSiMe 3 ( 4), CH 2CMe 2Ph ( 5), C 6H 5 ( 6), C 6F 5 ( 7) and CH 2SiMe 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(CH 2Ph) 2 · 2THF (4 equiv.) yields the tetrabenzyl complex [Zr η 5-C 5H 4(SiMe 2CH 2Ph)(CH 2Ph) 3] ( 9). The 1H and 13C NMR data of the latter compound are discussed in terms of the non-classical coordination mode of the CH 2Ph ligand. The molecular structure of [Zr η 5-C 5H 4(SiMe 2CH 2Ph)(CH 2Ph) 3] 9 has been determined by X-ray diffraction methods. The coordination geometry around the zirconium atom shows a substituted η 5-cyclopentadienyl ring and three different benzyl ligands: a distorted η 2-benzyl group; a normal η 1-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 P2 1/c with a = 11.268(3) Å, b = 10.846(3) Å, c = 27.734(6) Å, β = 100.29(1)°, V = 3334.9(15) Å 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 HCl gave the corresponding trichloro [Zr η 5-C 5H 4(SiMe 2R)Cl 3] (R = C 6H 5 ( 10), C 6F 5 ( 11), CH 2Ph ( 12)). The monochloro [Zr η 5-C 5H 4(SiMe 2CH 2Ph)(CH 2Ph) 2Cl] ( 13) and the dichloro derivative [Zr η 5-C 5H 4(SiMe 2CH 2Ph)(CH 2Ph)Cl 2] ( 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.