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首页> 外文期刊>Chemistry: A European journal >The Ever-Surprising Chemistry of Boron: Enhanced Acidity of Phosphine center dot Boranes
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The Ever-Surprising Chemistry of Boron: Enhanced Acidity of Phosphine center dot Boranes

机译：硼的不断惊奇的化学反应：提高膦中心点硼烷的酸度

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摘要

The gas-phase acidity of a series of phosphines and their corresponding phosphine center dot borane derivatives was measured by FT-ICR techniques. BH3 attachment leads to a substantial increase of the intrinsic acidity of the system (from 80 to 110 kJ mol(-1)). This acidity-enhancing effect of BH3 is enormous, between 13 and 18 orders of magnitude in terms of ionization constants. This indicates that the enhancement of the acidity of protic acids by Lewis acids usually observed in solution also occurs in the gas phase. High-level DFT calculations reveal that this acidity enhancement is essentially due to stronger stabilization of the anion with respect to the neutral species on BH3 association, due to a stronger electron donor ability of P in the anion and better dispersion of the negative charge in the system when the BH3 group is present. Our study also shows that deprotonation of ClCH2PH2 and ClCH2PH2 center dot BH3 is followed by chloride departure. For the latter compound deprotonation at the BH3 group is found to be more favorable than PH2 deprotonation, and the subsequent loss of Cl- is kinetically favored with respect to loss of Cl- in a typical S(N)2 process. Hence, ClCH2PH2 center dot BH3 is the only phosphine-borane adduct included in this study which behaves as a boron acid rather than as a phosphorus acid.
机译：通过FT-ICR技术测量了一系列膦及其相应的膦中心点硼烷衍生物的气相酸性。 BH3附着导致系统的固有酸度大幅增加（从80到110 kJ mol（-1））。 BH3的这种提高酸度的作用是巨大的，就电离常数而言，介于13到18个数量级之间。这表明通常在溶液中观察到的路易斯酸对质子酸酸性的增强也发生在气相中。高水平DFT计算表明，这种酸性增强主要是由于阴离子相对于BH3缔合的中性物质具有更强的稳定性，这是由于P在阴离子中的电子供体能力较强，而负电荷在BH3离子中的分散性更好。 BH3组存在时的系统。我们的研究还表明，ClCH2PH2和ClCH2PH2中心点BH3的去质子化之后是氯化物离开。对于后者，发现BH3基团的去质子化比PH2去质子化更有利，并且相对于典型S（N）2过程中Cl-的损失，动力学上有利于随后的Cl-的损失。因此，ClCH2PH2中心点BH3是这项研究中唯一的膦-硼烷加合物，其表现为硼酸而不是磷酸。

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