Aluminum‐Ligand Cooperative O−H Bond Activation Initiates Catalytic Transfer Hydrogenation
Aluminum‐Ligand Cooperative O−H Bond Activation Initiates Catalytic Transfer Hydrogenation
复制标题
DOI：
10.1002/cctc.202101869
复制
发表时间：
2022-04
期刊：
影响因子：
4.5
通讯作者：
Cody R. Carr;James I. Vesto;Xiujing Xing;J. Fettinger;Louise A. Berben
中科院分区：
文献类型：
--
作者：
Cody R. Carr;James I. Vesto;Xiujing Xing;J. Fettinger;Louise A. Berben
随着时间的推移，分子设计最终提供了性能的改进，这就是目前用于精细化学合成的转移氢化（TH）反应的Rh -和Ir -基分子催化剂的情况。在这篇报道中，我们描述了一种分子钳形配体Al催化剂，（I2P2−）Al(THF)Cl （I2P=二亚氨基吡啶；THF=四氢呋喃）。TH的机制是由两个连续的Al -配体协同键激活两个异丙醇（iPrOH）分子中的O - H键产生六配位（H2I2P）Al(OiPr)2Cl。化学计量化学反应和动力学实验表明，在极性溶剂的支持下，氢化物从iPrO−向底物转移是有序的过渡态。金属-配体在循环过渡态的协同氢键可能是协同氢化物转移事件的支持。现有的数据不支持中间氢化铝参与TH。描述了在1小时内以90%的转化率将异丙醇和二苯酮转化为丙酮和二苯甲醇的原理证明反应。类似的氢化物化合物（I2P2−）Al(THF)H也能在iPrOH中裂解O−H键，生成（HI2P−）Al(OiPr)H和（HI2P−）Al(OiPr)2，但没有观察到催化TH的活性。
Molecular design ultimately furnishes improvements in performance over time, and this has been the case for Rh‐ and Ir‐based molecular catalysts currently used in transfer hydrogenation (TH) reactions for fine chemical synthesis. In this report, we describe a molecular pincer ligand Al catalyst for TH, (I2P2−)Al(THF)Cl (I2P=diiminopyridine; THF=tetrahydrofuran). The mechanism for TH is initiated by two successive Al‐ligand cooperative bond activations of the O−H bonds in two molecules of isopropanol (iPrOH) to afford six‐coordinate (H2I2P)Al(OiPr)2Cl. Stoichiometric chemical reactions and kinetic experiments suggest an ordered transition state, supported by polar solvents, for concerted hydride transfer from iPrO− to substrate. Metal‐ligand cooperative hydrogen bonding in a cyclic transition state is a likely support for the concerted hydride transfer event. The available data does not support involvement of an intermediate Al‐hydride in the TH. Proof‐of‐principle reactions including the conversion of isopropanol and benzophenone to acetone and diphenylmethanol with 90 % conversion in 1 h are described. The analogous hydride compound, (I2P2−)Al(THF)H, also cleaves the O−H bond in iPrOH to afford (HI2P−)Al(OiPr)H and (HI2P−)Al(OiPr)2, but no activity for catalytic TH was observed.