Cu3(µ2-Cl)3 and Ag3(μ2-Cl)3 Complexes Supported by Tetradentate Trisphosphino-stibine and -bismuthine Ligands: Structural Evidence for Triply Bridging Heavy Pnictines

Abstract

The tetradentate stibine and bismuthine ligands (o-(iPr2P)C6H4)3Sb (LSbP3) and (o-(iPr2P)C6H4)3Bi (LBiP3) react with CuCl and AgCl in THF at room temperature to afford (o-(iPr2P)C6H4)3SbCu3(μ2-Cl)3 (1), (o-(iPr2P)C6H4)3SbAg3(μ2-Cl)3 (2), (o-(iPr2P)C6H4)3BiCu3(μ2-Cl)3 (3), and (o-(iPr2P)C6H4)3BiAg3(μ2-Cl)3 (4), respectively. These complexes, which have been fully characterised, feature a central M3(μ2-Cl)3 cluster (M = Cu or Ag) supported by coordination of a LSbP3- or LBiP3-phosphino group to each group 11 metal ion. The heavy pnictogen atom (Pn) interacts simultaneously with the three group 11 metal ions of the M3(μ2-Cl)3 cluster leading to formation of a tetrahedral PnM3 core. Bonding analysis using the Natural Bond Orbital method indicates the presence of a four-centre two-electron Pn→M3 interaction whose strength is the highest in 1 and the lowest in 4. The triply bridging bonding mode of the stibine and bismuthine ligands observed in these complexes is, to our knowledge, unprecedented. We also note that the central M3(μ2-Cl)3 clusters found in these complexes are related to the cyclo-trimers observed in vapours of CuCl and AgCl.