Neodymium(III) Complexes with Bulky ansa-Bis(cyclopentadienyl) Ligands:  Synthesis and Use in Olefin Oligomerization

The trivalent neodymium complexes [rac-{Me2Si(η5-2-SiMe3-4-t-Bu-C5H2)2}Nd(μ-Cl)2Li(THF)2] (rac-3), [rac-{Me2Si(η5-2,4-(SiMe3)2C5H2)2}Nd(μ-Cl)2Li(THF)2] (rac-5), and [{Me2Si(η5-2,4-(SiMe3)2C5H2)(η5-3,4-(SiMe3)2C5H2)}Nd(μ-Cl)2Li(THF)2] (C1-6) have been prepared and their structures investigated by NMR and X-ray crystallography. These new chlorolanthanocenes, when combined in situ with a dialkylmagnesium cocatalyst, initiate the polymerization of ethylene and 1-octene to yield di(oligoalkyl)magnesium species, which can be finally hydrolyzed to oligomers. Bulky bridged complexes rac-3, rac-5, and C1-6 gave significantly more active catalysts for 1-octene oligomerization (Mn = 400−1300, Mw/Mn = 1.11−1.65) than systems based on nonbridged complexes [(η5-C5Me5)2Nd(μ-Cl)2Li(Et2O)2] (1) and [(η5-1,3-(SiMe3)2C5H3)2Nd(μ-Cl)2Li(THF)2] (7). Ethylene oligomerization (Mn = 400−5000) was best achieved with complexes 1 and rac-3, as important catalyst decay occurred with bridged bis(trimethylsilyl) systems rac-5 and C1-6.