The Mechanism of Efficient Asymmetric Transfer Hydrogenation of Acetophenone Using an Iron(II) Complex Containing an (S,S)-Ph2PCH2CH=NCHPhCHPhN=CHCH2PPh2 Ligand: Partial Ligand Reduction Is the Key
The Mechanism of Efficient Asymmetric Transfer Hydrogenation of Acetophenone Using an Iron(II) Complex Containing an (S,S)-Ph2PCH2CH=NCHPhCHPhN=CHCH2PPh2 Ligand: Partial Ligand Reduction Is the Key
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DOI：
10.1021/ja304814s
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发表时间：
2012-07-25
影响因子：
15
通讯作者：
Morris, Robert H.
中科院分区：
文献类型：
--
作者：
Mikhailine, Alexandre A.;Maishan, Mazharul I.;Morris, Robert H.
在动力学研究和其他证据的基础上，我们提出了一个由前催化剂trans-Fe（CO）（Br）（Ph_2PCH_2CH =N-（（S，S）-C（Ph）H-C（Ph）H）-N= CHCH_2PPh_2）][BPh_4]（2）生成的苯乙酮在碱性异丙醇中不对称转移氢化的高活性体系的活化和操作机理。在催化生产1-苯乙醇之前观察到催化剂活化的诱导期。活化步骤包括2与过量碱快速反应生成烯-酰胺络合物[Fe（CO）]（Ph 2 PCH 2CH =N-（（S，S）-C（Ph）H-C（Ph）H）-NCH= CHPPh 2）]（+）（Fe-p）和双（烯酰胺基）络合物Fe（CO）（Ph 2 PCH =CH-N-（S，S-CH-（Ph）CH（Ph））-N-CH= CHPPh 2）（5）; 5部分表征：催化剂活化中的缓慢步骤被认为是Fe-p与异丙醇的反应，得到具有催化活性的酰氨基-（邻-酰氨基）配合物。Fe-a具有半还原、脱质子的PNNP配体这可以通过与HCl在乙醚中反应来捕获，在与NaBPh 4分离后得到[Fe（CO）（Cl）（Ph 2 PCH 2CH 2N（H）-（（S，S）-CH（Ph）CH（Ph）-N= CHCH 2 PPh 2）][BPh 4]。(7)其特征在于：使用多核MAR和高分辨质谱。当化合物7用碱处理时，它直接进入催化循环而没有诱导期。制备并表征了具有完全还原的P-NH-NH-P配体的预催化剂。通过单晶X射线衍射。发现其活性远低于2或7。通过改变苯乙酮，预催化剂，碱和丙酮的初始浓度，并通过改变温度得到的反应曲线进行拟合的动力学模型对应于所提出的机制，通过数值模拟，以获得一组独特的速率常数和热力学参数。
On the basis of a kinetic study and other evidence, we propose a mechanism of activation and operation of a highly, active system generated from the precatalyst trans-[Fe(CO)(Br)(Ph2PCH2CH=N-((S,S)-C(Ph)H-C(Ph)H)-N=CHCH2PPh2)][BPh4] (2) for the asymmetric transfer hydrogenation of acetophenone in basic isopropanol. An induction period for catalyst activation is observed before the catalytic production of 1-phenethanol. The activation step is proposed to involve a rapid reaction of 2 with excess base to give an ene-amido complex [Fe(CO)(Ph2PCH2CH=N-((S,S)-C(Ph)H-C(Ph)H)-NCH=CHPPh2)](+) (Fe-p) and a bis(enamido) complex Fe(CO)(Ph2PCH=CH-N-(S,S-CH-(Ph)CH(Ph))-N-CH=CHPPh2) (5); 5 was partially Characterized: The slow step in,the catalyst activation is thought to be the reaction of Fe-p with isopropoxide to give the catalytically active amido-(erie-amido) Complex. Fe-a With a half reduced, deprotoriated PNNP ligand This can be trapped by reaction with HCl m ether to give, after isolation With NaBPh4, [Fe(CO)(Cl)(Ph2PCH2CH2N(H)-((S,S)-CH(Ph)CH(Ph))-N=CHCH2PPh2)][BPh4]. (7) Which was characterized: using multinuclear MAR and high resolution mass spectrometry. When compound 7 is treated with base,. it directly enters the catalytic cycle with no induction period. A precatalyst with the fully reduced P-NH-NH-P ligand was prepared and characterized.. by single crystal X-ray diffraction. It was found to be much less active than 2 or 7. Reaction profiles obtained by varying the initial concentrations of acetophenone, precatalyst, base, and acetone and by varying the temperature were fit to the kinetic model corresponding to the proposed mechanism by numerical simulation to obtain a unique set of rate constants and thermodynamic parameters.