Bis(functionalized NHC) Palladium(II) Complexes via a Postmodification Approach

A series of 20 bis­(functionalized
NHC) Pd­(II) complexes have been
conveniently synthesized through postmodification reactions of the
common parent NHC complexes trans-[PdBr2(C3Br-bimy)2] (1a) and trans-[PdBr2(C3Br-imy)2] (1b) (C3Br-bimy = 1-benzyl-3-(3-bromopropyl)­benzimidazolin-2-ylidene
and C3Br-imy = 1-benzyl-3-(3-bromopropyl)­imidazolin-2-ylidene)
with an N-C3Br tether. Depending on the
nature of the nucleophiles added, competing bromido ligand displacements
also occurred. In comparison to the conventional access to functionalized
NHC complexes, which involves metalation of individually prefunctionalized
azolium salts, this highly modular method proves more effective in
cost and time savings. The tetraalkylammonium-functionalized complex trans-[PdBr2(C3NEt3-bimy)2]­Br2 (14) as a product of the second-generation
postmodification of complex 1a was also tested for its
catalytic activity in Mizoroki–Heck coupling reactions to study
and model the effect of a catalytic amount of ammonium salt additive
in Pd-catalyzed C–C coupling reactions. The ammonium functionalities
in this complex exhibit a positive effect on the catalysis in comparison
to its parent complexes.

一系列20个功能化的NHC（氮杂环卡宾）钯（II）配合物，通过常见母体NHC配合物trans-[PdBr2(C3Br-bimy)2]（1a）和trans-[PdBr2(C3Br-imy)2]（1b）（其中C3Br-bimy为1-苄基-3-（3-溴丙基）-苯并咪唑啉-2-亚胺基，C3Br-imy为1-苄基-3-（3-溴丙基）-咪唑啉-2-亚胺基）与N-C3Br键合物的后修饰反应而方便地合成。根据加入的亲核试剂的性质，还发生了竞争性的溴化配位体取代反应。与传统的通过金属化预先功能化的唑盐获得功能化NHC配合物的方法相比，这种方法在成本和时间上具有更高的模块化效率。作为1a的第二代后修饰产物，四甲基铵功能化的配合物trans-[PdBr2(C3NEt3-bimy)2]Br2（14）也被测试其在Mizoroki-Heck偶联反应中的催化活性，以研究和模拟在钯催化的C-C偶联反应中，催化量的铵盐添加剂的影响。与母体配合物相比，该配合物中的铵功能团对催化具有积极的影响。