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