Noyori氢化催化剂之[RuCl2(BINAP)(diamine)]
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[RuCl2(BINAP)(diamine)]催化剂
[RuCl2(BINAP)(diamine)]催化剂的制备一般分为两步:首先BINAP与[RuCl2(benzene)]2在DMF溶液中配位,然后在加入手性双胺(diamine)得到相应的催化剂。此催化剂是Noyori在1995年发现的一种新型催化剂,它对简单酮化合物的不对称氢化非常有效。它在苯乙酮的氢化中,转化数(底物与催化剂的物质的量之比)可达到2400000。在碱(如叔丁醇钾)存在下,以异丙醇为溶剂,各种芳酮、杂环芳酮、不饱和酮等均可以被高效、高对映选择性地氢化,产物的ee值高达99%。
BINAP与手性胺必须构型匹配:BINAP类配体中,磷原子所连苯基上有3,5-二甲基取代时(Xyl-BINAP),手性诱导效果最佳。手性二胺配体主要是环己二胺(DACH),1,2-二苯基乙二胺(DPEN)和1,1-二(4-甲氧基苯)-2-异丙基-1,2-乙二胺(DaiPEN)。(R)-Xyl-BINAP与(R)-DaiPEN或者(S)-Xyl-BINAP与(S)-DaiPEN组合的催化剂的效果最佳。
此类催化剂的反应中通常要加入强碱,因此不能用于对碱敏感的酮的氢化。但最近Noyori发展了一类不需要加碱的手性钌-双膦双胺催化剂[RuH(BH4)(BINAP)(diamine)]。该催化剂可以在中性条件下实现简单酮的不对称氢化,但反应速度较慢。
反应机理
产物的构型和对映选择性由双氢配位化合物J将氢通过六元过渡态L转移到酮羰基这一过程决定的。
反应实例
【J. Am. Chem. Soc., 1995, 117 (9), pp 2675–2676】
【Angew. Chem. Int. Ed. 2001, 40,40-73】
Air present in a 1-L stainless steel autoclave1,2 equipped with a mechanical stirringblade, a pressure gauge, and a gas inlet tube attached to a hydrogen source was replaced byargon.3 Acetophenone (3) (102.1 g, 0.85 mol)4 in 2-propanol (160 mL)5 which had beendegassed by three freeze–thaw cycles and trans-RuH(η1-BH4)[(S)-xylbinap][(S,S)-dpen][(S,SS)-2] (9.0 mg, 0.0085 mmol) in benzene (3 mL) were added under a stream of argonby cannula to the autoclave which had been heated at 45 °C.6 Air present in the gas inlettube was removed by flushing with a stream of hydrogen.7 The vessel was pressurized to 8atm and then the reaction mixture was vigorously stirred at 45 °C6 for 7 h. After cooling toroom temperature, the hydrogen gas was carefully vented. The yield and enantiomericexcess (ee) of (R)-1-phenylethanol were determined by GC analysis to be 100 and 99%,respectively.
【J. Am. Chem. Soc., 2002, 124 (23), pp 6508–6509】
【J. Am. Chem. Soc., 2005, 127 (23), pp 8288–8289】
编辑自: 《有机人名反应、试剂与规则》,黄培强等编,P254-260。
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