Rearrangement of Iridabenzvalenes to Iridabenzenes and/or η5-Cyclopentadienyliridium(I) Complexes: Experimental and Computational Analysis of the Influence of Silyl Ring Substituents and Phosphine Ligands§

Lithium−halogen exchange of either (Z)-1-phenyl-2-trimethylsilyl- (5a) or (Z)-1,2-bis(trimethylsilyl)-3-(2-iodovinyl)cyclopropene (5b) and addition to either Vaska's or Vaska-type complexes generated iridabenzvalenes (9, 14, 17), iridabenzenes (10, 18), and/or cyclopentadienyl complexes (11, 15, 19), depending on both the substituents on the C5 framework and the phosphine ligands on Ir. Specifically, the reaction of 5a with Vaska's complex afforded a mixture of 9, 10, and 11. Heating this mixture to 75 °C converted 9 and 10 to 11. NMR studies at 75 °C showed that samples of 9 isomerize to 11 in high yield and generate regioisomeric iridabenzene 12 as an intermediate. The reaction of 5b with Vaska's complex produced benzvalene 14 as the sole product. Complex 14 transformed completely to cyclopentadienyliridium complex 15 at 75 °C with no benzene intermediate detectable by NMR spectroscopy. The reaction of cyclopropene 5a with Vaska-type complexes containing alkylphosphines of varying cone angles yielded only benzvalene complexes, which either rearranged or decomposed depending upon the extent of heating. A hybrid-DFT computational study was carried out to investigate reactivity differences between phenyl and trimethylsilyl iridabenzvalenes, regioselective rearrangement of 9, and the unexpected stability/instability of 14/16. These calculations rationalize the sometimes contradictory experimental results.

对(Z)-1-苯基-2-三甲基硅基环丙烯（5a）或(Z)-1,2-双(三甲基硅基)-3-(2-碘乙烯基)环丙烯（5b）进行锂-卤素交换反应后，再与瓦斯克氏配合物（Vaska's complex）或瓦斯克型配合物发生加成反应，可生成铱杂苯并降瓦烯类化合物（9、14、17）、铱杂苯类化合物（10、18）与/或环戊二烯基配合物（11、15、19），产物组成取决于C5骨架上的取代基以及铱中心的膦配体（phosphine ligands）。具体而言，化合物5a与瓦斯克氏配合物的反应可得到9、10与11的混合物。将该混合物加热至75℃，可使9和10完全转化为11。75℃下的核磁共振（NMR）研究显示，化合物9以高收率异构化为11，反应过程中以区域异构体铱杂苯12作为中间体。化合物5b与瓦斯克氏配合物的反应仅生成苯并降瓦烯配合物14作为唯一产物。配合物14在75℃下可完全转化为环戊二烯基铱配合物15，且未通过NMR检测到苯类中间体。环丙烯5a与带有不同锥角烷基膦配体的瓦斯克型配合物反应时，仅生成苯并降瓦烯类配合物，这类配合物会随加热时长发生重排或分解。本研究开展了杂化密度泛函理论（hybrid-DFT）计算，以探究苯基与三甲基硅基取代铱杂苯并降瓦烯之间的反应活性差异、化合物9的区域选择性重排过程，以及14/16出人意料的稳定性差异。这些计算结果对部分看似矛盾的实验结果给出了合理解释。