Synthesis and characterization of oxygen-functionalized-NHC silver(I) complexes and NHC transmetallation to nickel(II).

Abstract : The new oxygen-functionalized-NHC silver(I) complexes bis(l-{2,6-diisopropylphenyl)-3-(2-hydroxyethyl)-1H-imidazol-2(3H)-ylidene)silver(I) chloride ([Ag{lmDiPP(EtOH)}2]CI, 4), bis(1-(2-hydroxyethyl)-3-mesityl-1H-imidazol-2(3H)-ylidene )silver(I) chloride ([Ag {lmMes(EtOH) }2]CI, 5),bis(l-(2-hydroxyethyl)-3-methyl-1H-imidazol-2(3H)-ylidene )silvet{l) chloride ([Ag { lmMe(EtOH) }2]Cl, 6), bis( l-(2,6-diisopropylphenyl)-3 -(2-hydroxyethyl)-1 H-imidazol-2(3H)-ylidene)silver(I) tetrafluoroborate ([Ag {ImDiPP(EtOH) }2]BF 4, 9) and bis( l-{2,6-diisopropylphenyl)-3-(2-methoxyethyl)IH-imidazol-2(3H)-ylidene)silver(I) chloride ([Ag{ImDiPP(EtOMe)}2]CI, 13), have been synthesized and fully characterized by NMR spectroscopy and single crystal X-ray diffraction. For some complexes, an uncommon heteronuclear coupling of 4J{'071109 Ag-1H) was unveiled. Their transmetallation ability was assessed in presence of different nickel(II) sources and the bis-NHC Ni{Il) complex bis( 1-(2,6-diisopropylphenyl )-3 -(2-methoxyethyl)-1 H-imidazol-2(3H)-ylidene )nickel{ll) chloride ([NiC12{ImDiPP(Et0Me)} 2], 15) was obtained from 13 and shown by X-ray diffraction to have a transarrangement of the two NHC ligands. In contrast, it was found with the other Ag{I) NHC complexes that the acidity of the alcohol OH proton was detrimental for the transmetallation process, and reprotonation of the CNHc carbon to give the corresponding imidazolium salt was observed.