Synthesis and Structure of Palladium 1,2,3-Triazol-5-ylidene Mesoionic Carbene PEPPSI Complexes and Their Catalytic Applications in the Mizoroki–Heck Reaction

New mono- and bimetallic 1,2,3-triazol-5-ylidene mesoionic
carbene
(MIC) complexes of Pd have been synthesized, isolated, and characterized.
We have described the synthesis of a bis­(MIC) complex via transmetalation
from a Ag-MIC complex and two PEPPSI-type complexes which are directly
available from their respective triazolium salts by treatment with
PdCl2 in pyridine. The X-ray structures are reported for
all complexes described herein. Interestingly, each complex described
exhibits various secondary noncovalent interactions in the solid state
of the general type C–H···Cl, which appear to
be important for the stabilization of the solid-state structure of
the complexes. We further demonstrated the utility of the new PEPPSI
complexes in the Mizoroki–Heck reaction. In the case of aryl
iodides and electron-deficient bromides, high conversion is observed
with methyl acrylate. Hg poisoning tests suggest that, even with an
easily dissociated ligand, the reaction likely proceeds via Pd nanoparticles.

我们成功合成、分离并表征了一类新型钯基单金属与双金属1,2,3-三唑-5-亚基介离子卡宾（mesoionic carbene, MIC）配合物。我们通过银-MIC配合物与两种PEPPSI型配合物的转金属化反应制备了双(MIC)配合物；其中两种PEPPSI型配合物可直接由相应三唑鎓盐在吡啶中与氯化钯（PdCl₂）反应制得。本文报道了上述所有配合物的X射线晶体结构。值得注意的是，所有配合物在固态下均存在多种典型的C–H···Cl型次级非共价相互作用，这类相互作用对稳定配合物的固态结构至关重要。我们进一步验证了新型PEPPSI配合物在沟吕木-赫克（Mizoroki–Heck）反应中的应用价值。对于芳基碘化物与缺电子溴代芳烃，该催化剂与丙烯酸甲酯反应可获得较高的转化率。汞中毒实验结果表明，即使配体易于解离，该反应仍大概率通过钯纳米颗粒介导进行。