Isomerization and deuterium scrambling evidence for a change in the rate-limiting step during imine hydrogenation by Shvo's hydroxycyclopentadienyl ruthenium hydride
Isomerization and deuterium scrambling evidence for a change in the rate-limiting step during imine hydrogenation by Shvo's hydroxycyclopentadienyl ruthenium hydride
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DOI：
10.1021/ja044450t
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发表时间：
2005-02-16
影响因子：
15
通讯作者：
Johnson, JB
中科院分区：
文献类型：
--
作者：
Casey, CP;Johnson, JB
羟基氢化钌5在室温以下有效地还原亚胺。氮上更好的供体取代基引起更快的速率和从氢转移到胺配位的速率决定步骤的转变。在11 ℃下还原缺电子N-二苯甲酰基五氟苯胺（8）导致游离胺和动力学同位素效应，k（OH）/k（OD）= 1.61 +/- 0.08，k（RuH）= 2.05 +/- 0.08，和k（RuHOH）/k（RuDOD）= 3.32 +/- 0.14，指示限速协同氢转移，该机制类似于针对醛和酮还原提出的机制。富电子的N-烷基取代的亚胺，N-异丙基-（4-甲基）亚苄基胺（9）的还原伴随着容易的亚胺异构化和来自用5-RuDOH还原的氘标记物到胺络合物的N-烷基取代基和回收的亚胺中的混乱。在-48 ℃还原N-二亚苄基-叔丁胺（11）时观察到逆平衡同位素效应（k（OH）/k（OD）= 0.89 +/- 0.06，k（RUH）/k（RUD）= 0.64 +/- 0.05，和k（RuHOH）/k（RuDOD）= 0.56 +/- 0.05）。这些结果是一致的机制，涉及可逆的氢转移，然后通过限速胺协调。
Hydroxycyclopentadienyl ruthenium hydride 5 efficiently reduces imines below room temperature. Better donor substituents on nitrogen give rise to faster rates and a shift of the rate-determining step from hydrogen transfer to amine coordination. Reduction of electron-deficient N-benzilidenepentafluoroaniline (8) at 11 degreesC resulted in free amine and kinetic isotope effects of k(OH)/k(OD) = 1.61 +/- 0.08, k(RuH) = 2.05 +/- 0.08, and k(RuHOH)/k(RuDOD) = 3.32 +/- 0.14, indicative of rate-limiting concerted hydrogen transfer, a mechanism analogous to that proposed for aldehyde and ketone reduction. Reduction of electron-rich N-alkyl-substituted imine, N-isopropyl-(4-methyl)benzilidene amine (9), was accompanied by facile imine isomerization and scrambling of deuterium labels from reduction with 5-RuDOH into the N-alkyl substituent of both the amine complex and into the recovered imine. Inverse equilibrium isotope effects were observed in the reduction of N-benzilidene-tert-butylamine (11) at -48 degreesC (k(OH)/k(OD) = 0.89 +/- 0.06, k(RUH)/k(RUD) = 0.64 +/- 0.05, and k(RuHOH)/k(RuDOD) = 0.56 +/- 0.05). These results are consistent with a mechanism involving reversible hydrogen transfer followed by rate-limiting amine coordination.