DFT Mechanistic Investigation into BF3-Catalyzed Alcohol Oxidation by a Hypervalent Iodine(III) Compound,ACS Catalysis

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DFT Mechanistic Investigation into BF3-Catalyzed Alcohol Oxidation by a Hypervalent Iodine(III) Compound
ACS Catalysis ( IF 11.3 ) Pub Date : 2019-06-06 00:00:00 , DOI: 10.1021/acscatal.9b01599
Kaveh Farshadfar ₁ , Antony Chipman ₂ , Brian F. Yates ₂ , Alireza Ariafard _{1,

2}

Affiliation

Density functional theory (DFT) at the SMD/M06-2X/def2-TZVP//SMD/M06-2X/LANL2DZ,6-31G(d) level was employed to explore mechanistic aspects of BF₃-catalyzed alcohol oxidation using a hypervalent iodine(III) compound, [ArI(OAc)₂], to yield aldehydes/ketones as the final products. The reaction is composed of two main processes: (i) ligand exchange and (ii) the redox reaction. Our study for 1-propanol discovered that ligand exchange is preferentially accelerated if BF₃ first coordinates to the alcohol. This coordination increases the acidity of the alcohol hydroxyl proton, resulting in ligand exchange between the iodane and the alcohol proceeding via a concerted interchange associative mechanism with an activation free energy of ∼10 kcal/mol. For the redox process, the calculations rule out the feasibility of the conventional mechanism (alkoxy C^α deprotonation) and introduce a replacement for it. This alternative route commences with α-hydride elimination of the alkoxy group promoted by BF₃ coordination, which yields a BF₃-stabilized aldehyde/ketone product and the iodane [ArI(OAc)(H)]. The ensuing iodane is extremely reactive toward reductive elimination to give ArI + HOAc in a highly exergonic fashion (ΔG = −62.1 kcal/mol). The reductive elimination reaction is the thermodynamic driving force for the alcohol oxidation to be irreversible. Consistent with the kinetic isotope effect reported experimentally, the α-hydride elimination is calculated to be the rate-determining step with an overall activation free energy of ∼24 kcal/mol.

中文翻译：

DFT机制研究高价碘（III）化合物对BF ₃催化的醇氧化

使用SMD / M06-2X / def2-TZVP // SMD / M06-2X / LANL2DZ，6-31G（d）级的密度泛函理论（DFT）来研究高价BF ₃催化醇氧化的机理碘（III）化合物[ArI（OAc）₂ ]，生成醛/酮作为最终产物。该反应由两个主要过程组成：（i）配体交换和（ii）氧化还原反应。我们对1-丙醇的研究发现，如果BF ₃可以优先促进配体交换首先要调整酒精度。这种配位增加了醇羟基质子的酸度，导致碘与醇之间的配体交换通过协同的交换缔合机理进行，活化能约为10 kcal / mol。对于氧化还原过程，计算排除常规机构（烷氧基C的可行性^α去质子化），并引入一个为它置换。该替代途径以α-氢化物消除由BF ₃配位促进的烷氧基开始，产生BF ₃稳定的醛/酮产物和碘[ArI（OAc）（H）]。随之而来的碘对还原消除反应具有极强的反应性，从而以高强度的方式赋予ArI + HOAc（ΔG＝ -62.1kcal / mol）。还原消除反应是使醇氧化不可逆的热力学驱动力。与实验报道的动力学同位素效应一致，计算得出α-氢化物消除是速率确定步骤，总活化自由能约为24 kcal / mol。

更新日期：2019-06-06

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