New types of Cu and Ag clusters supported by the pyrrole-based NNN-pincer type ligand

Abstract

2,5-Bis(3,5-dimethylpyrazolylmethyl)pyrrole LH becomes the monoanionic NNN pincer ligand upon deprotonation of the pyrrolic NH proton. It not only gives typical pincer type complexes but also supports multinuclear complexes via its bridging mode of coordination. This was demonstrated by the synthesis and characterization of a series of copper(I) and silver(I) complexes. The reaction between LH and CuX, where X = Cl, Br and I, gave binuclear complexes of the type [Cu₂(μ-X)₂(μ-C₄H₃N-2,5-(CH₂Me₂pz)₂-N,N)₂] (1a–c). Conversely, when the reaction was carried out with the lithium salt of LH and CuI, a novel tetranuclear copper(I) complex [Cu₄(μ-I)₂(μ-C₄H₂N-2,5-(CH₂Me₂pz)₂-N,N,N)₂] 2 was obtained and its core structure resembled an ‘hourglass’. The analogous reaction with CuCl or CuBr yielded the neutral copper(II) complex [Cu(μ-C₄H₂N-2,5-(CH₂Me₂pz)₂-N,N,N)₂] 3 upon oxidation in air, in which L displayed the chelating bonding mode. The analogous reaction between LH and AgOTf or AgBF₄ afforded the 1D coordination polymer of the type [Ag(μ-C₄H₃N-2,5-(CH₂Me₂pz)₂-N,N)(X)]_n where X = CF₃SO₃⁻4a or BF₄⁻4b. Conversely, a new trinuclear silver(I) complex [Ag₃(μ-C₄H₂N-2,5-(CH₂Me₂pz)₂-N,N,N)₃] 5 was obtained when the reaction was carried out with the lithium salt of LH and AgBF₄. The structures of 1b, 1c, 3, 4a and 5 were confirmed by single crystal X-ray diffraction studies and supported by NMR, FTIR, HRMS and CHN analyses. The Cu–Cu distance of 2.6127(8) Å in 2 and the Ag–Ag distance of 2.8514(8) Å in 5 indicate the presence of d¹⁰–d¹⁰ interactions.