Silver alkoxide and amino N-heterocyclic carbenes; syntheses and crystal structures

Silver(I) complexes of heterobidentate ligands that incorporate one or two N-heterocyclic carbene moieties coupled with an alcohol or amine group have been made by direct deprotonation of ligands of the form [HOCR1R2CH2(1-HC{NCHCHNR})][X], H2L1X (X = Br, I), [H2NR1CHR2CHR2(1-HC{NCHCHNR})][Br]2 H3L2X2 (X = Cl, Br), and [H2N{CH2CH2(1-HC[NCHCHNMes])}2][X]3 H4L3X3 (X = Cl, Br). Silver(I) oxide is sufficiently basic to deprotonate both the imidazolium and the alcohol functional groups of all but one of the L1 ligand precursors, to afford rare examples of silver alkoxide complexes [Ag(L1)], stabilised by the soft donor carbene. Another complex of L1 is characterised as the carbene alcohol adduct [Ag(HL1)2I]. The analogous reactions of silver(I) oxide with the amino imidazolium precursors afford silver amino-carbenes [Ag(HL2)Br] with the potentially bidentate L2 ligand, and [Ag(HL3)X] (X = Cl, Br) with the potentially tridentate L3 ligand. A single crystal X-ray diffraction study of the latter complex confirms that the neutral amine of the potentially tridentate L3 ligand is unco-ordinated; instead the structure contains discrete chains of T-shaped silver bis(carbene) halide moieties that bridge to form a zig-zag 2-connected polymer. Protonolysis of two of the silver alkoxide and amino adducts, [Ag(L1a)] and [Ag(HL2a)Br], affords imidazolium complexes salts [H2L1a][AgCl2] and [Ag(H2L2a)Br][AgBr2] that retain the Ag(I) centre as complex counterions. The single crystal X-ray structures of these salts have been determined and show the silver(I) cations are now incorporated into ladders or chains as silver(I) halo-anions, and a silver amine dative bond is present in the latter complex.