Cleavage of carbon-carbon bonds of diphenylacetylene and its derivatives via photolysis of pt complexes: Tuning the c-c bond formation energy toward selective c-c bond activation
Cleavage of carbon-carbon bonds of diphenylacetylene and its derivatives via photolysis of pt complexes: Tuning the c-c bond formation energy toward selective c-c bond activation
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DOI：
10.1021/ja071698k
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发表时间：
2007-07-18
影响因子：
15
通讯作者：
Jones, William D.
中科院分区：
文献类型：
--
作者：
Gunay, Ahmet;Jones, William D.
本文研究了二苯乙炔及其取代衍生物的碳-碳键活化。合成并表征了炔的eta（2）-配位的Pt-O-乙炔配合物，沿着合成了相应的Pt-II C-C活化光解产物，包括X-射线晶体结构分析。虽然C-C裂解反应在光化学条件下容易发生，但没有观察到C-C键的热活化或Pt-II络合物的形成。然而，逆反应，C-C还原偶联（Pt-II -> Pt-0），在热条件下确实发生，允许测定不同Pt-II络合物形成C-C键的能垒。对于反应（dtbpe）Pt（-Ph）（-CCPh）（2）->（dtbpe）Pt（eta（2）-PhCCPh）（1），Δ G为32.03（3）kcal/mol。作为比较，在缺电子体系中，即（dtbpe）Pt（C6 F5）（CCC 6 F5）（6）->（dtbpe）Pt（η（2）-双（五氟苯基）乙炔）（5）中，C-C键形成的能垒为47.30 kcal/mol。C-C键形成的能垒能够通过用吸电子或供电子基团电子改性基底来调节。在（dtbpe）Pt（eta（2）-（对氟苯基-对甲苯基乙炔）（9）中的C-C键断裂后，获得（dtbpe）Pt（对氟苯基）（对甲苯基乙炔）（10）和（dtbpe）Pt（对甲苯基）（对氟苯基乙炔）（11）。逆反应的动力学研究证实，在两种途径的过渡态能量相同的假设下，10对还原偶联[术语“还原偶联”被定义为从Pt-II络合物形成（dtbpe）Pt（eta（2）-乙炔）络合物]比11更稳定1.22 kcal/mol。10和11的产物比为55：45，表明缺电子C-C键仅轻微优先断裂。
Carbon-carbon bond activation of diphenylacetylene and several substituted derivatives has been achieved via photolysis and studied. Pt-0-acetylene complexes with eta(2)-coordination of the alkyne, along with the corresponding Pt-II C-C activated photolysis products, have been synthesized and characterized, including X-ray crystal structural analysis. While the C-C cleavage reaction occurs readily under photochemical conditions, thermal activation of the C-C bonds or formation of Pt-II complexes was not observed. However, the reverse reaction, C-C reductive coupling (Pt-II -> Pt-0), did occur under thermal conditions, allowing the determination of the energy barriers for C-C bond formation from the different Pt-II complexes. For the reaction (dtbpe)Pt(-Ph)(-CCPh) (2) -> (dtbpe)Pt(eta(2)-PhCCPh) (1), Delta G was 32.03(3) kcal/mol. In comparison, the energy barrier for the C-C bond formation in an electron-deficient system, that is, (dtbpe)Pt(C6F5)(CCC6F5) (6) -> (dtbpe)Pt(eta(2)-bis(pentafluorophenyl)acetylene) (5), was found to be 47.30 kcal/mol. The energy barrier for C-C bond formation was able to be tuned by electronically modifying the substrate with electron-withdrawing or electron-donating groups. Upon cleavage of the C-C bond in (dtbpe)Pt(eta(2)-(p-fluorophenyl-p-tolylacetylene) (9), both (dtbpe)Pt(p-fluorophenyl)(p-tolylacetylide) (10) and (dtbpe)Pt(p-tolyl)(p-fluorophenylacetylide) (11) were obtained. Kinetic studies of the reverse reaction confirmed that 10 was more stable toward the reductive coupling [the term "reductive coupling" is defined as the formation of (dtbpe)Pt(eta(2)-acetylene) complex from the Pt-II complex] than 11 by 1.22 kcal/mol, under the assumption that the transition-state energies are the same for the two pathways. The product ratio for 10 and 11 was 55:45, showing that the electron-deficient C-C bond is only slightly preferentially cleaved.