Neodymium(III) complexes with bulky ansa-bis(cyclopentadienyl) ligands:: Synthesis and use in olefin oligomerization

The trivalent neodymium complexes [rac-{Me2Si(eta (5)-2-SiMe3-4-t-Bu-C5H2)(2))Nd(mu -Cl)(2)Li(THF)(2)] (rac-3),[rac-{Me2Si(eta (5)-2,4-(SiMe3)(2)C5H2)(2)}Nd(mu -Cl)(2)Li(THF)(2)] (rac-5), and [(Me2Si(eta (5)-2,4-(SiMe3)(2)C5H2)((eta (5)-3,4-(SiMe3)(2)C5H2)}Nd(mu -Cl)(2)Li(THF)(2)] (C-1-6) 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 C-1-6 gave significantly more active catalysts for 1-octene oligomerization (M-n = 400-1300, M-w/M-n = 1.11-1.65) than systems based on nonbridged complexes [(eta (5)-C5Me5)(2)Nd(mu -Cl)(2)Li(Et2O)(2)] (1) and [(eta (5)-1,3-(SiMe3)(2)C5H3)(2)Nd(mu -Cl)(2)Li(THF)(2)] (7). Ethylene oligomerization (M-n = 400-5000) was best achieved with complexes 1 and rac-3, as important catalyst decay occurred with bridged bis(trimethylsilyl) systems rac-5 and C-1-6.