科研之友
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摘要
Bis(cyclopentadienyl)aluminum and -gallium species of the type (Pytsi)ECp2 [E = Al (2a), Ga (2b); Pytsi = C(SiMe3)(2)SiMe2(2-C5H4N)] have been prepared from NaCp and respective dichlorides (Pytsi)ECl2 in isolated yields of 65% (2a) and 83% (26). In addition to applying standard methods of characterization (NMR spectroscopy, CHN analysis, and MS), the molecular structures of both compounds were solved by single-crystal X-ray crystallography. Reactions between 2a or 2b with Zr(NMe2)(4) in benzene, followed by addition of an excess of ClSiMe3, gave the first ansa-zirconocene dichlorides with aluminum (4a) or gallium (4b) in bridging position. The gallium compound 4b was isolated in a yield of 40% and characterized by NMR spectroscopy, CHN analysis, and mass spectrometry. The aluminum species 4a could not be obtained in an analytically pure form; it was characterized by NMR spectroscopy, and its molecular structure was determined by single-crystal X-ray analysis. The angle between the two planes of the Cp ligands in 4a was found to be 57.17(11)degrees, which is larger than in Cp2ZrCl2 (alpha = 53.5 degrees) and smaller than in silicon-bridged ansa-zirconocene dichlorides (e.g., Me2Si(C5H4)(2)ZrCl2: alpha = 60.1 degrees). Crystallization attempts of 4a from DCCl3 solutions gave crystals of the new species (Pytsi)AlCl[(C5H4)ZrCp] (7), which was characterized by NMR spectroscopy and single-crystal X-ray analysis. In comparison to the Pytsi-containing species 2a and 2b, the less sterically protected compound [2-(Me2NCH2)C6H4]ALCp(2) (6), which was prepared from NaCp and [2-(Me2NCH2)C6H4]AlCl2 in yields of 94% and characterized by standard methods (NMR, CHN, and MS), reacted with Zr(NMe2)(4) to give the known Cp2Zr(NMe2)(2). The targeted ansa-species was not formed, as judged by H-1 NMR spectroscopy. The gallium-bridged compound 4b and Cp2ZrCl2, respectively, had been tested for polymerizations of ethylene utilizing MAO as an activator (300 equiv of MAO; 5 or 10 mu mol of precatalyst; 15 or 70 psi), resulting in activities of 637 to 1080 for 46 and of 640 to 2601 kg PE (mol Zr)(-1) h(-1) atm(-1) for Cp2ZrCl2.
- 出版日期2010-11-22
