Mono- and polynuclear Ag(i) complexes of N-functionalized bis(diphenylphosphino)amine DPPA-type ligands: synthesis, solid-state structures and reactivity

Abstract

The reactivity of the N-functionalized DPPA-type ligands (Ph₂P)₂N(p-Z)C₆H₄ [Z = H (1a), SMe (1b), OMe (1c)] with AgBF₄ was investigated and revealed an unexpected influence of the para substituent Z of the N-aryl ligand. In acetone, the mononuclear bis-chelated [Ag{(1a–1c)-P,P}₂]BF₄ (2a·BF₄–2c·BF₄) and dinuclear bridged [Ag₂{μ₂-(1a–1c)-P,P}₂](BF₄)₂ [3a·(BF₄)₂–3c·(BF₄)₂] complexes were obtained with a 1 : 2 and 1 : 1 AgBF₄/ligand molar ratio, respectively. While the molecular structures of 2a·BF₄ and 2b·BF₄ determined in the solid-state by X-ray diffraction revealed their mononuclear nature and the absence of cation/anion interaction, complexes 3b·(BF₄)₂ and 3c·(BF₄)₂ form 2D coordination polymers through intermolecular Ag–S or Ag–O interactions, respectively, involving the N-function of the respective DPPA-type ligand, and display direct interactions between one BF₄ anion and both Ag(I) cations. Surprisingly, the equimolar reaction between ligands 1a–1c and AgBF₄ in CH₂Cl₂ led to different proportions of the dinuclear complexes 3a·(BF₄)₂–3c·(BF₄)₂ and clusters [Ag₃(μ₃-Cl)₂{μ₂-(1b–1c)-P,P}₃]BF₄ (4b·BF₄–4c·BF₄), depending on the nature of the para substituent Z of the N-aryl ligand. The trinuclear complexes resulted from C–Cl bond activation of the chlorinated solvent and were characterized by NMR spectroscopy and X-ray diffraction, and could be selectively produced by addition of 2/3 equiv. of [NMe₄]Cl to the corresponding dinuclear complexes or by a one-pot procedure involving the correct amount of each reagent. A series of experiments and kinetic NMR investigations were performed to gain further insight into the formation of the trinuclear Ag₃Cl₂ core clusters.