Synthesis and reactivity of new silyl substituted monocyclopentadienyl zirconium complexes. X-ray molecular structure of [Zr{η5-C5H4(SiMe2CH2Ph)}(CH2Ph)3]

Article abstract of DOI:10.1016/S0022-328X(97)00443-9

New silyl substituted monocyclopentadienyl complexes of Zr(IV) were synthesized from the precursor [Zr{η⁵-C₅H₄(SiMe₂Cl)}Cl₃] (1). The reaction of 1 with the lithium benzamidinate salt Li[C(Ph){N(SiMe₃)}₂] leads to the complex [Zr{η⁵-C₅H₄(SiMe₂Cl)}{C(Ph)[N(SiMe₃)]₂}Cl₂] (2), which decomposes slowly in solution with elimination of SiMe₃Cl. Complex 1 reacts with alkyl, amido and alkoxo transfer reagents (4 equiv.) to afford complexes [Zr{η⁵-C₅H₄(SiMe₂X)}X₃] (X = NMe₂ (3), OSiMe₃ (4), CH₂CMe₂Ph (5), C₆H₅ (6), C₆F₅ (7) and CH₂SiMe₃ (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{η⁵-C₅H₄(SiMe₂CH₂Ph)}(CH₂Ph)₃] (9). The ¹H and ¹³C NMR data of the latter compound are discussed in terms of the non-classical coordination mode of the CH₂Ph ligand. The molecular structure of [Zr{η⁵-C₅H₄(SiMe₂CH₂Ph)}(CH₂Ph)₃] 9 has been determined by X-ray diffraction methods. The coordination geometry around the zirconium atom shows a substituted η⁵-cyclopentadienyl ring and three different benzyl ligands: a distorted η²-benzyl group; a normal η¹-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, β = 100.29(1)°, V = 3334.9(15) A³ 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{η⁵-C₅H₄(SiMe₂R)}Cl₃] (R = C₆H₅ (10), C₆F₅ (11), CH₂Ph (12)). The monochloro [Zr{η⁵-C₅H₄(SiMe₂CH₂Ph)}(CH₂Ph)₂Cl] (13) and the dichloro derivative [Zr{η⁵-C₅H₄(SiMe₂CH₂Ph)}(CH₂Ph)Cl₂] (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.