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

Silver(l) 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 [(HOCRR2)-R-1 CH2(1HC{NCHCHNR})][X], (H2LX)-X-1 (X=Br, I), [(H2NRCHR2)-C-1 CHR2(1-HC{NCHCHNR})][Br](2) (H3LX2)-X-2 (X=Cl, Br), and [H2N{CH2CH2(1-HC[NCHCHNMes])}(2)][X](3) (H4LX3X3)-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(HL1)(2)I]. The analogous reactions of silver(I) oxide with the amino imidazolium. precursors afford silver aminocarbenes [Ag(HL2)Br] with the potentially bidentate L-2 ligand, and [Ag(HL3)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(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. (c) 2005 Elsevier B.V. All rights reserved.