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

A series of 15 mononuclear complexes [PdBr((i)Pr2-bimy)(L2)]PF6 (1-15) ((i)Pr2-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((i)Pr2-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 (13)Ccarbene signals of the (i)Pr2-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.