Synthesis and characterization of chiral bidentate bis(N-heterocyclic carbene)-carboxylate palladium and nickel complexes

Complexes [Pd{(S)-NHCMes,R}2] (R = Me, 2a; iPr, 2b; iBu, 2c) and [Pd{(R)-NHCMes,Me}2] (2a’) were prepared by reaction of the corresponding imidazolium precursor [ImMes,R] (namely (S)–2-alkyl(3-mesityl-1H-imidazol-3-ium-1-yl)acetate, 1a-c, (R)-2-methyl(3-mesityl-1H-imidazol-3-ium-1-yl)acetate, 1a’), with Ag2O subsequent interaction Pd(OAc)2, under appropriate conditions. Alternatively, complexes 2 also obtained treating compounds [ImMes,R], 1, an in-situ lithium diisopropylamide solution then [Pd(OAc)2]. On other hand, nickel complex [Ni{(S)-NHCMes,iPr}2], 3b, was synthesized [NiCp2] (Cp η5-C5H5) [ImMes,iPr], 1b, in THF. If this carried out acetonitrile, a mixture 3b cyclopentadienyl monocarbene [NiCp{(S)-NHCMes,iPr}], 4b, obtained. Similarly to 2b, compound formation carbene [(S)–NHCMes,iPr]- [NiBr2(dme)] (dme 1,2-dimethoxyethane). 2, 3 4 good yields fully characterized analytical (HR-ESI microanalysis), spectroscopic (IR, 1H 13C NMR polarimetry) X-ray methods (2c). In solid state, 2c is square planar containing two [(S)-NHCMes,iBu]- ligands coordinated κ2-C,O fashion, where carboxylate donors have expected trans configuration. The existence possible conformers analyzed using DFT methods.