Samec Joseph S M, Ell Alida H, Aberg Jenny B, Privalov Timofei, Eriksson Lars, Bäckvall Jan-E
Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91 Stockholm, Sweden.
J Am Chem Soc. 2006 Nov 8;128(44):14293-305. doi: 10.1021/ja061494o.
Reaction of [2,3,4,5-Ph(4)(eta(5)-C(4)COH)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)(C(4)Ph(4)COHOCC(4)Ph(4))] (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)-C(4)CO)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)-C(4)CO)]Ru(CO)(2)NH(CH(3))(CHPhCH(3)) (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-BnNH-C(6)H(9)=NPh (18), with an internal amine trap, only afforded 2,3,4,5-Ph(4)(eta(4)-C(4)CO)(2)RuNH(Ph)(C(6)H(10)-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)-C(4)CO)(2)RuNH(Bn)(C(6)H(10)-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.
[2,3,4,5-四苯基(η⁵-环丁烯基羰基)钌(羰基)₂氢] (2) 与不同的亚胺在低温下反应生成钌胺配合物。在较高温度且存在2的情况下，这些配合物分解生成 [Ru₂(羰基)₄(μ-氢)(环丁四苯基羰基氧代环丁四苯基)] (1) 和游离胺。富电子亚胺与2反应生成钌胺配合物的温度低于缺电子亚胺。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)，这表明在速率决定步骤中，氢化物 (RuH) 和质子 (OH) 都没有转移到亚胺上。在通过 [2,3,4,5-四苯基(η⁴-环丁烯基羰基)钌(羰基)₂] (A) 将N-苯基-1-苯乙胺 (4) 脱氢生成相应的亚胺8的反应中，观察到的动力学同位素效应支持逐步氢转移，其中C-H键断裂的同位素效应 (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)。在外部胺捕获剂N-甲基-1-(4-甲氧基苯基)乙胺 (16) 存在下，2对N-甲基(1-苯基亚乙基)胺 (14) 的氢化反应得到90 - 100% 的配合物 [2,3,4,5-四苯基(η⁴-环丁烯基羰基)]钌(羰基)₂NH(CH₃)(CHPhCH₃) (15)，它是钌与从亚胺新生成胺之间的配合物。在 -80℃ 时，氢化物2与带有内部胺捕获剂的4-苄基氨基-C₆H₉=NPh (18) 反应，仅得到 2,3,4,5-四苯基(η⁴-环丁烯基羰基)₂RuNH(Ph)(C₆H₁₀-4-NHBn) (19)，其中钌与源自亚胺的胺结合，这表明既没有形成配合物A也没有形成二胺。在 -8℃ 以上，配合物19重排为热力学上更稳定的 四苯基(η⁴-环丁烯基羰基)₂RuNH(Bn)(C₆H₁₀-4-NHPh) (20)。这些结果与内球机制一致，即底物在氢转移之前与钌配位，并且难以用先前提出的外球途径来解释。
