Synthesis, Characterization Of Half-sandwich Rare Earth Bis (Amide) Complexes And Their Catalytic Behavior For Polymerization

A series of half-sandwich scandium bis(amide) complexes were synthesized and characterized. These complexes can serve as precatalysts for syndiospecific polymerization of styrene.1. Treatment of ScCl3 with 2.9 equiv. of LiN(SiRMe2)2 (R= H, Me) afforded the scandium tris(amide) complexes Sc[N(SiRMe2)3](THF)n (R= H, n= 1; R= Me, n= 0). Amine elimination of Sc[N(SiRMe2)3](THF)n with 1 equiv. of cyclopentadienyl derivatives C5Me4R'H (R= H, Me, SiMe3) in toluene at 100℃afforded a series of half-sandwich scandium bis(amide) complexes (C5Me5)Sc[N(SiHMe2)2]2 (1), (C5Me4SiMe3)Sc[N(SiHMe2)2]2 (2), (C5Me5)Sc[N(SiMe3)2]2 (3), (C5Me4H)Sc[N(SiMe3)2]2 (4) in 72-81% isolated yields. These complexes were characterized by elemental analysis, NMR spectroscopy, FT-IR spectroscopy. Single crystal structural determination of 1-3 revealed that the central metal adopts a trigonal geometry.2. A dimeric yttrium complex [Y(C5Me4SiMe3){μ-O(CH2)3CH3}{N(SiHMe2)2}]2 (5) was isolated as one of the co-products from the reaction of Y{N(SiHMe2)2}3(THF)2 with C5Me4HSiMe3 in 1:1 molar ratio in toluene at 100℃. Complex 5 was characterized by elemental analysis, NMR spectroscopy, FT-IR spectroscopy, and X-ray single crystal structural analysis. X-ray diffraction revealed that complex 5 is a symmetric dimer, and the center metal is eight-coordinated by one nitrogen atom from the amide group, two bridging oxygen atoms from the O(CH2)3CH3 groups, and one cyclopentadienyl ringη5-fashion to adopt a distorted tetrahedron geometry. The formation of complex 5 was postulated to be a result from C-O bond cleavage reaction of THF by (C5Me4SiMe3)Y[N(SiHMe2)2]2.3. In the presence of Al'Bu3, and activated by one equimolar amount of [Ph3C][B(C6F5)4] or [PhNMe2H][B(C6F5)4], (C5Me5)Sc[N(SiHMe2)2]2 (1), (C5Me4SiMe3)Sc[N(SiHMe2)2]2 (2), (C5Me5)Sc[N(SiMe3)2]2 (3), and (C5Me4H)Sc[N(SiMe3)2]2 (4) showed high activity towards styrene polymerization to give polystyrenes with high syndiotacticity (rrrr> 99%). The polystyrenes were characterized by 1H NMR,13C NMR,DSC and GPC.