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

Abstract 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 [HOCR 1 R 2 CH 2 (1-HC{NCHCHNR})][X], H 2 L 1 X (X = Br, I), [H 2 NR 1 CHR 2 CHR 2 (1-HC{NCHCHNR})][Br] 2 H 3 L 2 X 2 (X = Cl, Br), and [H 2 N{CH 2 CH 2 (1-HC[NCHCHNMes])} 2 ][X] 3 H 4 L 3 X 3 (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 L 1 ligand precursors, to afford rare examples of silver alkoxide complexes [Ag(L 1 )], stabilised by the soft donor carbene. Another complex of L 1 is characterised as the carbene alcohol adduct [Ag(HL 1 ) 2 I]. The analogous reactions of silver(I) oxide with the amino imidazolium precursors afford silver amino-carbenes [Ag(HL 2 )Br] with the potentially bidentate L 2 ligand, and [Ag(HL 3 )X] (X = Cl, Br) with the potentially tridentate L 3 ligand. A single crystal X-ray diffraction study of the latter complex confirms that the neutral amine of the potentially tridentate L 3 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(L 1a )] and [Ag(HL 2a )Br], affords imidazolium complexes salts [H 2 L 1a ][AgCl 2 ] and [Ag(H 2 L 2a )Br][AgBr 2 ] 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.