Using a diverse array of thermally robust phosphine enediyne ligands (dxpeb, X = Ph, Ph-pOCH3, Ph-pCF3, Ph-m2CH3, Ph-m2CF3, iPr, Cy, and tBu) a novel suite of cisplatin-like Pt(II) metalloenediynes (3, Pt(dxpeb)Cl2) has been synthesized and represents unique electronic perturbations on thermal Bergman cyclization kinetics. Complexes 3e (Ph-m2CF3) and 3f (iPr) are the first of this structure type to be crystallographically characterized with interalkynyl distances (3e: 3.13 Å; 3f: 3.10 Å) at the lower end of the widely accepted critical distance range within which enediynes should demonstrate spontaneous ambient temperature cyclization. Despite different electronic profiles, these metalloenediynes adopt a rigid, uniform structure suggesting complexes of the form Pt(dxpeb)Cl2 have orthogonalized geometric and electronic contributions to thermal Bergman cyclization. Kinetic activation parameters determined using 31P NMR spectroscopy highlight the dramatic reactivity and thermal tunability of these complexes. At room temperature, the half-life (t1/2) of cyclization spans a range of ~35 hours and for the aryl phosphine derivatives, cycloaromatization rates are 10-30 times faster for complexes with electron donating substituents (3b: Ph-pOCH3; 3d: Ph-m2CH3) compared to those with electron withdrawing substituents (3c: Ph-pCF3; 3e: Ph-m2CF3). Computational interrogation of the aryl phosphine metalloenediynes 3a–3e reveals that the origin of this precise electronic control derives from electronic withdrawing group-mediated alkyne carbon polarization that amplifies Coulombic repulsion increasing the cyclization barrier height. Additionally, mixing between the in-plane -orbitals and the phosphine aryl ring system is pronounced for complexes with electron donating substituents which stabilizes the developing C–C bond and lowers the activation barrier. This -orbital mixing is negligible however, for complexes with electron withdrawing substituents due to an energetic mismatch of the orbital systems. Overall, this work demonstrates that for geometrically rigid frameworks, even remote enediyne functionalization can have pronounced effects on activation barrier.

中文翻译：

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几何调控的 Metalloenediyne 环化的显著电子调制


使用多种热稳定型膦二炔配体（dxpeb、X = Ph、Ph-pOCH3、Ph-pCF3、Ph-m2CH3、Ph-m2CF3、iPr、Cy 和 tBu）合成了一套新型的顺铂样 Pt（II） 金属二炔 （3， Pt（dxpeb）Cl2），代表了热 Bergman 环化动力学的独特电子扰动。配合物 3e （Ph-m2CF3） 和 3f （iPr） 是这种结构类型中第一个以炔基间距离（3e：3.13 Å;3f：3.10 Å）在广泛接受的临界距离范围的下限进行晶体学表征的化合物，在该临界距离范围内，烯二炔应表现出自发的环境温度环化。尽管电子分布不同，但这些金属二炔采用刚性、均匀的结构，表明 Pt（dxpeb）Cl2 形式的配合物对热伯格曼环化具有正交的几何和电子贡献。使用 31P NMR 波谱确定的动力学激活参数突出了这些复合物的巨大反应性和热可调性。在室温下，环化的半衰期 （t1/2） 跨越 ~35 小时，对于芳基膦衍生物，与具有吸电子取代基的络合物（3c：Ph-pCF3;3e：Ph-m2CF3）相比，具有电子供体取代基的络合物（3b：Ph-pOCH3;3d：Ph-m2CH3）的环芳构化速率快 10-30 倍。对芳基膦金属二炔 3a-3e 的计算询问表明，这种精确电子控制的起源来自电子撤基团介导的炔烃碳极化，该极化放大了库仑排斥，增加了环化势垒高度。 此外，对于具有电子馈送取代基的复合物，面内  轨道和膦芳基环系统之间的混合很明显，从而稳定了发育中的 C-C 键并降低了活化势垒。然而，由于轨道系统的能量失配，对于具有吸电子取代基的复合物，这种 -轨道混合可以忽略不计。总的来说，这项工作表明，对于几何刚性框架，即使是远程的 enediyne 功能化也会对激活屏障产生显着影响。