The origin of different driving forces between O–H/N–H functional groups in metal ligand cooperation: mechanistic insight into Mn(I) catalysed transfer hydrogenation,Catalysis Science & Technology

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The origin of different driving forces between O–H/N–H functional groups in metal ligand cooperation: mechanistic insight into Mn(I) catalysed transfer hydrogenation
Catalysis Science & Technology ( IF 4.4 ) Pub Date : 2019-11-21 , DOI: 10.1039/c9cy02112d
Li Zhou _{1,

2,

3,

4,

5} , Datai Liu _{1,

2,

3,

4,

5} , Haiyi Lan _{1,

2,

3,

4,

5} , Xiujian Wang _{1,

2,

3,

4,

5} , Cunyuan Zhao _{6,

7,

8,

9,

10} , Zhuofeng Ke _{6,

7,

8,

9,

10} , Cheng Hou _{1,

2,

3,

4,

5}

Affiliation

Metal–ligand cooperation catalysis is currently the prevailing strategy in the field of homogeneous catalyst research, and is widely used in direct catalytic hydrogenation and transfer hydrogenation reactions. Herein, a density functional theory (DFT) study is conducted to clarify the origin of the different activities of Mn(I) bifunctional catalysts bearing similar Lewis base functional ligands, and amine and hydroxyl groups. The results indicate that a Mn(I) catalyst with an OH group as a bifunctional group requires a higher activation free energy barrier relative to the catalyst with amine as an active ligand, which is in line with the experimental observations. By comparing the electronic structures of the key intermediates in the two catalytic systems, it is found that the Mn–O complex catalyst is thermodynamically unstable and may lead to irreversible decomposition, which accounts for its lower catalytic activity. Moreover, the inductive effect between the OH group and the metal hydride increases unfavorable orbital interactions in the Mn–O system. Consequently, the generation of a metal hydride intermediate becomes a thermodynamically uphill process, further leading to a lack in driving force for the dehydrogenation of ⁱPrOH. Further investigation suggests that the driving force of the catalyst can be tuned by changing the different oxidation states of the metal centers, revealing a crucial role for the metal center in M–L bond cooperation mode in MLC catalysis. This study highlights that although the hydroxyl and amine groups are both Lewis base functional ligands, subtle differences in the electronic effects of ligand have a significant impact on the activities of the metal–ligand cooperation (MLC) catalysts.

中文翻译：

金属配体协作中OH / NH功能基之间不同驱动力的起源：Mn（I）催化转移加氢的机理研究

金属-配体协同催化是目前在均相催化剂研究领域的主要策略，并广泛用于直接催化加氢和转移加氢反应中。本文中，进行了密度泛函理论（DFT）研究，以阐明带有相似路易斯碱官能配体以及胺和羟基的Mn（I）双官能催化剂的不同活性的起源。结果表明Mn（I）具有OH基作为双官能团的催化剂相对于以胺为活性配体的催化剂需要更高的活化自由能垒，这与实验观察一致。通过比较两种催化体系中关键中间体的电子结构，发现Mn-O络合物催化剂是热力学不稳定的，可能导致不可逆分解，这是其催化活性较低的原因。此外，OH基团与金属氢化物之间的感应作用增加了Mn-O系统中不利的轨道相互作用。因此，金属氢化物中间体的生成成为热力学上的艰难过程，进一步导致缺乏用于ⁱ脱氢的驱动力。脯氨酸进一步的研究表明，可以通过改变金属中心的不同氧化态来调节催化剂的驱动力，从而揭示了金属中心在MLC催化中M–L键合作模式中的关键作用。这项研究强调，尽管羟基和胺基都是路易斯碱功能性配体，但配体电子效应的细微差别对金属-配体配合（MLC）催化剂的活性有重大影响。

更新日期：2019-11-21

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