Determining the Electron-Donating Properties of Bidentate Ligands by 13C NMR Spectroscopy

A series of 15 mononuclear complexes [PdBr­(iPr2-bimy)­(L2)]­PF6 (1–15) (iPr2-bimy = 1,3-diisopropylbenzimidazolin-2-ylidene, L2 = aromatic 1,2-diimines, diazabutadienes, or methylene-, ethylene- and propylene-bridged di-N-heterocyclic carbenes) and two dicarbene-bridged, dinuclear complexes [Pd2Br4(iPr2-bimy)2(diNHC)] (16 and 17) were synthesized and characterized by multinuclear NMR spectroscopy, electrospray ionization mass spectrometry, and in some cases X-ray diffraction analysis. The influence of the 15 bidentate ligands L2 on the 13Ccarbene signals of the iPr2-bimy reporter ligand in the chelate complexes was studied, on the basis of which a facile methodology for the donor strength determination of bidentate ligands was developed.本研究合成了15种单核配合物[PdBr(iPr2-bimy)(L2)]PF6（编号1~15，其中iPr2-bimy为1,3-二异丙基苯并咪唑啉-2-亚基，英文全称为1,3-diisopropylbenzimidazolin-2-ylidene；L2为芳香族1,2-二亚胺、二氮杂丁二烯，或是亚甲基、乙烯基、亚丙基桥联的二氮杂环卡宾）以及2种双卡宾桥联双核配合物[Pd2Br4(iPr2-bimy)2(diNHC)]（编号16和17）；所有产物均通过多核核磁共振波谱、电喷雾电离质谱进行了表征，部分产物还通过X射线衍射分析完成了结构表征。本研究考察了15种双齿配体L2对螯合配合物中作为报告配体的iPr2-bimy的13C卡宾信号的影响，并基于此建立了一种简便的双齿配体给体强度测定方法。