Mechanistic study of hydrogen transfer to imines from a hydroxycyclopentadienyl ruthenium hydride.: Experimental support for a mechanism involving coordination of imine to ruthenium prior to hydrogen transfer
Mechanistic study of hydrogen transfer to imines from a hydroxycyclopentadienyl ruthenium hydride.: Experimental support for a mechanism involving coordination of imine to ruthenium prior to hydrogen transfer
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DOI：
10.1021/ja061494o
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发表时间：
2006-11-08
影响因子：
15
通讯作者：
Backvall, Jan-E.
中科院分区：
文献类型：
--
作者：
Samec, Joseph S. M.;Ell, Alida H.;Backvall, Jan-E.
[2,3,4,5-Ph-4(eta(5)-C4COH) Ru(CO)(2)H] (2) 与不同的亚胺在低温下反应得到钌胺络合物。在较高温度下，在 2 存在下，配合物分解生成 [Ru-2(CO)(4)(mu-H)(C4Ph4COHOCC4Ph4)] (1) 和游离胺。与缺电子亚胺相比，富电子亚胺在较低温度下与 2 形成钌胺络合物。在 2 与 N-苯基[1-(4-甲氧基苯基)亚乙基]胺 (12) 的反应中观察到可忽略不计的氘同位素效应 (k(RuHOH)/k(RuDOD) = 1.05），表明在速率决定步骤中氢化物 (RuH) 和质子 (OH) 均未转移至亚胺。在 N-苯基-1-苯乙胺 (4) 通过 [2,3,4,5-Ph-4(eta(4)-C4CO) Ru(CO)(2)] (A) 脱氢成相应的亚胺 8 时，观察到的动力学同位素效应支持逐步氢转移，其中 C-H 裂解的同位素效应 (k(CHNH)/k(CDNH) = 3.24）等于组合的 (C-H, N-H) 同位素效应 (k(CHNH)/k(CDND) = 3.26)。在外部胺捕集器 N-甲基-1-(4-甲氧基苯基)乙胺 (16) 存在下，N-甲基(1-苯基亚乙基)胺 (14) 被 2 氢化，得到 90-100% 的络合物 [2,3,4,5-Ph-4(eta(4)-C4CO)] Ru(CO)(2)NH(CH3)(CHPhCH3) (15)，它是钌和由亚胺新生成的胺。在 -80 摄氏度下，氢化物 2 与 4-BnNHsC(6)H(9)=NPh (18) 的反应，通过内部胺阱，仅产生 [2,3,4,5-Ph-4(eta(4)-C4CO)](CO)(2)RuNH(Ph)(C6H10-4-NHBn) (19)，其中钌与源自亚胺，表明复合物 A 和二胺均未形成。高于 -8 摄氏度时，配合物 19 重新排列成热力学上更稳定的 [Ph-4(eta(4)-C4CO)](CO)(2)RuNH(Bn)(C6H10-4-NHPh) (20)。这些结果与内球机制一致，其中底物在氢转移之前与钌配位，并且很难用先前提出的外球路径来解释。
Reaction of [2,3,4,5-Ph-4(eta(5)-C4COH) Ru(CO)(2)H] (2) with different imines afforded ruthenium amine complexes at low temperatures. At higher temperatures in the presence of 2, the complexes decomposed to give [Ru-2(CO)(4)(mu-H)(C4Ph4COHOCC4Ph4)] (1) and free amine. Electron-rich imines gave ruthenium amine complexes with 2 at a lower temperature than did electron-deficient imines. The negligible deuterium isotope effect (k(RuHOH)/k(RuDOD) = 1.05) observed in the reaction of 2 with N-phenyl[1-(4-methoxyphenyl) ethylidene]amine (12) shows that neither hydride (RuH) nor proton (OH) is transferred to the imine in the rate-determining step. In the dehydrogenation of N-phenyl-1-phenylethylamine (4) to the corresponding imine 8 by [2,3,4,5-Ph-4(eta(4)-C4CO) Ru(CO)(2)] (A), the kinetic isotope effects observed support a stepwise hydrogen transfer where the isotope effect for C-H cleavage (k(CHNH)/k(CDNH) = 3.24) is equal to the combined (C-H, N-H) isotope effect (k(CHNH)/k(CDND) = 3.26). Hydrogenation of N-methyl(1-phenylethylidene) amine (14) by 2 in the presence of the external amine trap N-methyl-1-(4-methoxyphenyl) ethylamine (16) afforded 90-100% of complex [2,3,4,5-Ph-4(eta(4)-C4CO)] Ru(CO)(2)NH(CH3)(CHPhCH3) (15), which is the complex between ruthenium and the amine newly generated from the imine. At -80 degrees C the reaction of hydride 2 with 4-BnNHsC(6)H(9)=NPh (18), with an internal amine trap, only afforded [2,3,4,5-Ph-4(eta(4)-C4CO)](CO)(2)RuNH(Ph)(C6H10-4-NHBn) (19), where the ruthenium binds to the amine originating from the imine, showing that neither complex A nor the diamine is formed. Above -8 degrees C complex 19 rearranged to the thermodynamically more stable [Ph-4(eta(4)-C4CO)](CO)(2)RuNH(Bn)(C6H10-4-NHPh) (20). These results are consistent with an inner sphere mechanism in which the substrate coordinates to ruthenium prior to hydrogen transfer and are difficult to explain with the outer sphere pathway previously proposed.