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

Qiaoqiao Teng and Han Vinh Huynh*

Synopsis

The net donating ability of 15 bidentate ligands including aromatic and aliphatic diimines as well as alkyl-bridged di-N-heterocyclic carbenes was determined using a 13C NMR-based electronic parameter. Differences in the substituents and the backbones affect the donating ability of the bidentate ligands according to their inductive and mesomeric effects. The methodology allows for the evaluation of classical Werner-type and organometallic ligands on a unified scale.

Abstract

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 the13Ccarbene 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.

http://pubs.acs.org/doi/abs/10.1021/ic501325j?journalCode=inocaj&quickLinkVolume=53&quickLinkPage=10964&selectedTab=citation&volume=53