201413-89-0Relevant academic research and scientific papers
Synthesis and reactivity of new silyl substituted monocyclopentadienyl zirconium complexes. X-ray molecular structure of [Zr{η5-C5H4(SiMe2CH2Ph)}(CH2Ph)3]
Ciruelo, Gemma,Cuenca, Tomas,Gomez, Rafael,Gomez-Sal, Pilar,Martin, Avelino,Rodriguez, Gema,Royo, Pascual
, p. 287 - 296 (2008/10/08)
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.
