REGIOSELECTION AND ENANTIOSELECTION IN ORGANOLANTHANIDE-CATALYZED OLEFIN HYDROSILYLATION - A KINETIC AND MECHANISTIC STUDY
REGIOSELECTION AND ENANTIOSELECTION IN ORGANOLANTHANIDE-CATALYZED OLEFIN HYDROSILYLATION - A KINETIC AND MECHANISTIC STUDY
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DOI：
10.1021/ja00132a015
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发表时间：
1995-07-12
影响因子：
15
通讯作者：
MARKS, TJ
中科院分区：
文献类型：
--
作者：
FU, PF;BRARD, L;MARKS, TJ
本文研究了有机稀土预催化剂Cp‘(2)-Inch(SiMe(3))(2)、Me(2)SiCp’‘(2)Innch(SIME(3))2和Me(2)SiCp’‘(R*C5H4)Lnch(SIME(3))2(Cp’=ETA(5)-Me(5)C(5)；Cp‘=ETA(5)-Me(4)C(5)；R*=手性辅助剂)。首先通过Ln-CH(SIME(3))(2)官能团的氢解来绕过缓慢的催化剂引发过程。对于α-烯烃，金属连接球(Cp‘(2)Ln->；Me(2)SiCp’(2)，Me(2)-SiCp‘’(R*C5H4))的开放和Ln(3+)离子半径的增大提高了2，1加成区域化学的硅氢化周转频率和选择性。对于苯乙烯烯烃，观察到了完全的2，1区域选择性(硅被转移到苄基位置)，通过对电子释放的取代基提高了反应速度，以及高达400h(-1)(60℃)的翻转频率。对于1-己烯，观察到高达76%的2，1加成区域选择性和>；1000h(-1)(90℃)的翻转频率。对于2-苯基-1-丁烯，(R)-Me(2)SiCp‘’[(-)-薄荷基CP]SmCH(SiMe(3))2和(S)-Me(2)SiCp‘’[(-)-menthylCp]SmCH(SiMe(3))(2)发生了不对称硅氢化反应，ee分别为68%和65%(25℃)。前者遵循速率定律v=k[Sm](1)[烯烃](0)[PhSiH(3)](1)。反应的D2O猝灭产生PhCd(CH3)(CH2CH3)和PhSiH(2)D作为机理信息产物。在Cp‘2SmCH(SIME(3))(2)作用下，1，5-己二烯的硅氢化反应主要生成环戊基CH(2)SiH(2)Ph，而Me(2)SiCp’2SmCH(SIME(3))a和(R)-Me2SiCp‘’[(-)-薄荷基Cp]SmCH(SIME(3))(2)也生成1，5-己二烯骨架重排的硅氢化产物。通过氢化物/烷基循环讨论了硅氢化反应的机理，氢化物/烷基循环包括快速、放热的烯烃插入Ln-H键，然后是限制周转的Si-H/Ln-烷基转位(烷基传递到Si)。
This contribution describes a study of scope, regioselection, enantioselection, metal and ancillary ligand effects, and kinetics in the catalytic PhSiH(3) hydrosilylation of olefins using the organolanthanide precatalysts Cp'(2)-LnCH(SiMe(3))(2), Me(2)SiCp''(2)LnCH(SiMe(3))2, and Me(2)SiCp''(R*C5H4)LnCH(SiMe(3))2 (Cp' = eta(5) - Me(5)C(5); Cp'' = eta(5)-Me(4)C(5); Ln = lanthanide; R* = chiral auxillary). Sluggish catalyst initiation processes were first circumvented by hydrogenolysis of the Ln-CH(SiMe(3))(2) functionality. For alpha-olefins, hydrosilylation turnover frequency and selectivity for 2,1 addition regiochemistry are enhanced by openness of the metal ligation sphere (Cp'(2)Ln --> Me(2)SiCp''(2), Me(2)-SiCp''(R*C5H4)) and increasing Ln(3+) ion radius. For styrenic olefins, complete 2,1 regioselectivity (Si delivery to the benzylic position), rate enhancement by para electron-releasing substituents, and turnover frequencies as high as 400 h(-1) (60 degrees C) are observed. For 1-hexene, 2,1 addition regioselectivities as high as 76% and turnover frequencies > 1000 h(-1) (90 degrees C) are observed. For 2-phenyl-1-butene, (R)-Me(2)SiCp''[(-)-menthyl Cp]SmCH(SiMe(3))2 and (S)-Me(2)SiCp''[(-)-menthylCp]SmCH(SiMe(3))(2) effect asymmetric hydrosilylation with ee values of 68% and 65%, respectively (25 degrees C). The former reaction obeys the rate law v = k[Sm](1) [olefin](0)[PhSiH(3)](1). D2O quenching of the reaction yields PhCD(CH3)(CH2CH3) and PhSiH(2)D as mechanistically informative products. The hydrosilylation of 1,5-hexadiene effected by Cp'2SmCH(SiMe(3))(2) affords predominantly cyclopentylCH(2)SiH(2)Ph, while Me(2)SiCp''2SmCH(SiMe(3))a and (R)-Me2SiCp''[(-)-menthylCp]SmCH(SiMe(3))(2) also yield hydrosilylation products derived from 1,5-hexadiene skeletal rearrangement. The hydrosilylation mechanism is discussed in terms of a hydride/alkyl cycle involving rapid, exothermic olefin insertion into an Ln-H bond followed by turnover-limiting Si-H/Ln-alkyl transposition (delivery of the alkyl group to Si).