芳基亚胺-脒基稀土烷基化合物的合成及其催化异戊二烯聚合研究

Synthesis and Catalytic Isoprene Polymerization of Rare-Earth Alkyl Complexes Supported by An Arylimine-amidinate Ligand

制备了芳基亚胺-脒基稀土二烷基化合物[NNN]Ln(CH2SiMe3)2{[NNN]=[2-C(H)NDippC6H3NHC(Ph)NDipp],Dipp=2,6-i-Pr2C6H3,Ln=Y(2),Sm(3)},2和3通过了1H NMR,13C NMR,IR和元素分析测试,通过X-ray确定了化合物2的晶体结构.加入[Ph3C][B(C6F5)4]和烷基铝,两个化合物均能高效催化异戊二烯聚合,具有较好的3,4-选择性(88%),中等的立体选择性(rr=50%),较高的分子量(Mn=6.8×104)和较窄的分子量分布(Mw/Mn=1.15).同时发现,烷基铝和[Ph3C][B(C6F5)4]的比例影响催化聚合的区域选择性.

Reaction of the arylimine-amidinate ligand [NNN]H （1） （[NNN] = [2-C（H）NDippC6H3NHC（Ph）NDipp], Dipp= 2,6-i-Pr2C6H3） with Ln（CH2SiMe3）3（THF）2 （Ln=Y, Sm） in n-hexane at -78 ℃ followed by stirring the mixture for 3 h at room temperature afforded [NNN]Ln（CH2SiMe3）2 （Ln=Y, 2; Ln：Sm, 3） in 75% and 50% yields after work up. 2 and 3 have been characterized by 1H NMR, 13C NMR, IR spectroscopy, elemental analysis. The molecular structure of 2 has been confirmed by X-ray analysis. Complexes 2 and 3 catalyzed the polymerization of isoprene in the presence of [Ph3C][B（C6Fs）4] （1 equiv.） and A1Et3 （10 equiv.） at 25 ℃. 2 converted 250 equivalents of isoprene into polyisoprene with a narrow molecular weight distribution （Mw/Mn： 1.20） and a 3,4-rich microstructure （3,4-selectivity： 78%, rr=50%） in 12 h. A significant increase of 3,4-selectivity was observed in the presence of one equivalent of A1Et3 （3,4-selectivity： 87%）. When i-Bu2A1H （10 equiv.） was used instead of A1Et3, the catalytic activity and selectivity did not change noticeably while the re- suiting polyisoprenes feature a broad molecular weight distribution （Mw/Mn=2.45）. When the amounts of i-Bu2A1H de- creased from 5 to 1 equivalent, a significant increase of 3,4-selectivity and number-average molecular weight have been ob- served while the molecular distributions became small. The catalyst is active within a wide range of temperatures from low temperature to 40 ℃. At 40 ℃, a similar selectivity （3,4-selectivity： 78%, Mw/Mn= 1.43） to that found at 25 ℃ but the increased reaction rate has been observed. High stereo- and regioselectivity and narrow molecular weight distributions were obtained at -20 ℃ （3,4-selectivity： 88%, rr： 52%, Mw/Mn= 1.15）. The samarium alkyl 3 exhibited a high activity but low selectivity （25 ℃, 3 h, 3,4-selectivity： 67%, Mw/Mn： 1.71） compared to the yttrium alkyl 2.