A coordinatively flexible ligand for carbonyl clusters: bridging and terminal SnCl3 groups in the iridium clusters [Ir4(CO)11(μ-SnCl3)]−, [Ir4(CO)10(SnCl3)(μ-SnCl3)]2− and [Ir6(CO)15(μ3-SnCl3)]−

Abstract

The carbonyl cluster [Ir₄(CO)₁₁(SnX₃)]⁻ [X = Cl, (1a) or Br (1b)] can be formed in good yield by insertion of SnX₂ in the Ir–Br bond of [Ir₄(CO)₁₁Br]⁻ or, much less efficiently, by substitution of bromine with [SnCl₃]⁻, in THF at room temperature. The disubstituted cluster [Ir₄(CO)₁₀(SnCl₃)₂]²⁻ (2) was obtained in 50% yields by double substitution on [Ir₄(CO)₁₁Br]⁻, in THF at 60 °C, whereas [Ir₆(CO)₁₅(SnCl₃)]⁻ (3) can be prepared by carbonyl substitution of the homoleptic complex [Ir₆(CO)₁₆] with an excess of [SnCl₃]⁻ in refluxing THF. In the three compounds, the SnCl₃ units act as a one electron donor, displaying terminal (in 2), edge-bridging (in 1 and 2) and face-bridging (in 3) coordination. In keeping with a reduced bond order, the Ir–Sn bond distances increase in the series, being 2.584(1) Å for a terminal group; 2.72 Å for edge-bringing units and 2.78 Å for the face-bridging SnCl₃. Regardless of the coordination mode, the geometry of the three chlorine atoms is always pyramidal, with Cl–Sn–Cl angles close to 90° and Sn–Cl bond distances close to 2.42 Å. Tin is always symmetrically bridging, with Ir–Sn–Ir close to 60°.