Exceptional Sensitivity of Metal-Aryl Bond Energies to ortho-Fluorine Substituents: Influence of the Metal, the Coordination Sphere, and the Spectator Ligands on M-C/H-C Bond Energy Correlations
Exceptional Sensitivity of Metal-Aryl Bond Energies to ortho-Fluorine Substituents: Influence of the Metal, the Coordination Sphere, and the Spectator Ligands on M-C/H-C Bond Energy Correlations
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DOI：
10.1021/ja901640m
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发表时间：
2009-06-10
影响因子：
15
通讯作者：
Perutz, Robin N.
中科院分区：
文献类型：
--
作者：
Clot, Eric;Megret, Claire;Perutz, Robin N.
本文报道了苯和氟苯的C-H氧化加成反应(ARH)-H-F(Ar-F=C6FnH5-n，n=0-5)在ZrCp2(Cp=ETA(5)-C5H5)、TaCp2H、TaCp2Cl、WCp2、RECP(CO)(2)、RECP(PH3)(2)、RHCP(PH3)(2)、RHCP(PH3)、RHCP(CO)、IrCP(PH3)、IrCp(CO)、Ni(H_2PCCH_2PH2)、Pt(H_2PCCH_2PH2)上的密度泛函理论计算。产物的M-C键能的变化符合氟取代基数的线性函数，邻位、间位和对位氟对应的系数不同。正交系数的取值范围为20~32kJ·mol~(-1)，大大超过偏系数和准系数的取值(2.0~4.5kJ·mol~(-1))。同样，(ArH)-H-F的H-C键能分别产生10.4和3.4kJ·mol(-1)的正、对系数，以及一个可以忽略的元系数。这些结果表明，芳环上的邻氟取代大大增加了M-C键能。D(M-C)与D(H-C)的斜率Rm-C/H-C的变化范围为1.93-3.05(含金属碎片)，均高于报道的其他烷基的1.1-1.3的值。CO取代PH3显著降低了Rm-C/H-C。对于给定的配位体和元素周期表中同一基团的金属，Rm-C/H-C的值不随M-C键的强度而增加。对芳环上电荷的计算表明，M-C键的电离性的变化与M-C键的能量的变化有关。这种金属-芳基键的加强解释了大量的实验结果，这些结果表明了邻氟取代基的偏好。
DFT calculations are reported of the energetics of C-H oxidative addition of benzene and fluorinated benzenes, (ArH)-H-F (Ar-F = C6FnH5-n, n = 0-5) at ZrCp2 (Cp = eta(5)-C5H5), TaCp2H, TaCp2Cl, WCp2, ReCp(CO)(2), ReCp(CO)(PH3), ReCp(PH3)(2), RhCp(PH3), RhCp(CO), IrCp(PH3), IrCp(CO), Ni(H2PCH2CH2PH2), Pt(H2PCH2CH2PH2). The change in M-C bond energy of the products fits a linear function of the number of fluorine substituents, with different coefficients corresponding to ortho-, meta-, and para-fluorine. The values of the ortho-coefficient range from 20 to 32 kJ mol(-1), greatly exceeding the values for the meta- and para-coefficients (2.0-4.5 kJ mol(-1)). Similarly, the H-C bond energies of (ArH)-H-F yield ortho- and para-coefficients of 10.4 and 3.4 kJ mol(-1), respectively, and a negligible meta-coefficient. These results indicate a large increase in the M-C bond energy with ortho-fluorine substitution on the aryl ring. Plots of D(M-C) vs D(H-C) yield slopes RM-C/H-C that vary from 1.93 to 3.05 with metal fragment, all in excess of values of 1.1-1.3 reported with other hydrocarbyl groups. Replacement of PH3 by CO decreases RM-C/H-C significantly. For a given ligand set and metals in the same group of the periodic table, the value of RM-C/H-C does not increase with the strength of the M-C bond. Calculations of the charge on the aryl ring show that variations in ionicity of the M-C bonds correlate with variations in M-C bond energy. This strengthening of metal-aryl bonds accounts for numerous experimental results that indicate a preference for ortho-fluorine substituents.