Mono- and Dinuclear Ag(I), Au(I), and Au(III) Metallamacrocycles Containing N-Heterocyclic Dicarbene Ligands

Ag(I) dicarbene complexes [Ag-m(L-n)(m)]X-m (L-n = Im(Me)(CH2)(n)Im(Me), Im(Me) = N-methylimidazol-N-yl-2-ylidene; n = 3, X = PF6, m = 2; n = 6-8, 10, X = AgBr2, m = 1, 2) were prepared by reacting Ag2O with 1 equiv of the corresponding bisimidazolium salt [H2Ln]A(2) (A = PF6, Br). The dibromoargentates react with 1 equiv of AgTfO to afford [Ag-m(L-n)(m)](TfO)(m) (m = 1, 2). The room temperature transmetalation reaction of [Ag-m(L-n)(m)][AgBr2](m) (n = 3, 5, 6-8, 10) with [AuCl(SMe2)] and AgTfO (L-n:Au:TfO = 1:1:1) affords [Au-2(mu-L-n)(2)](TfO)(2) (n = 3, 5, 10), or mixtures of [Au(kappa(2)-L-n)]TfO (main product for n = 7) and [Au-2(mu-L-n)(2)](TfO)(2) (main product for n = 6, 8). At room temperature, the equilibrium between [M-2(mu-L-n)(2)](TfO)(2) and [M(kappa(2)-L-n)]TfO is fast for M = Ag, but slow for M = Au, in the NMR time scale. When n >= 7 and M = Ag or Au, the equilibrium is shifted toward the mononuclear complexes in the order 8 > 10 > 7, which proves that the (CH2)(8) linker has the optimal length for trans chelation. Correspondingly, the high-temperature metalation of [H2Ln]Br-2 (n = 8, 10) with 1 equiv of [AuCl(SMe2)] and excess of NaAcO, affords [Au(kappa(2)-L-n)]Br with a small amount of [Au-2(mu-L-n)(2)]Br-2. If AgTfO is added to the reaction mixture, [Au(kappa(2)-L-8)](2)[AgBr3] is isolated instead of the desired triflate, which can be obtained by reacting the mixture of [Au(kappa(2)-L-8)]Br and [Au-2(mu-L-8)(2)]Br-2 with AgTfO. [Au(kappa(2)-L-10)]TfO was isolated after thermal conversion of [Au-2(mu-L-10)(2)](TfO)(2). [Au(kappa(2)-L-8)]TfO reacts with I-2 to give trans-[AuI2(kappa(2)-L-8)]TfO, which is the first Au(III) complex containing a trans-spanning bidentate ligand. We have determined the crystal structures of complexes [Ag-2(mu-L-3)(2))(PF6)(2), [Ag(kappa(2)-L-7)]TfO, [Au-2(mu-L-3)(2)](TfO)(2), [Au(kappa(2)-L-8)](2)[Au(kappa(2)-L-8)](2)[AgBr3], and trans-[AuI2(kappa(2)-L-8)]TfO.