Crystal structures of two new six-coordinate iron(III) complexes with 1,2-bis(diphenyl-phosphane) ligands

Abstract

Structural characterization of the ionic complexes [FeCl₂(C₂₆H₂₂P₂)₂][FeCl₄]·0.59CH₂Cl₂ or [(dppen)₂FeCl₂][FeCl₄]·0.59CH₂Cl₂ (dppen = cis-1,2-bis-(di-phenyl-phosphane)ethyl-ene, P₂C₂₆H₂₂) and [FeCl₂(C₃₀H₂₄P₂)₂][FeCl₄]·CH₂Cl₂ or [(dpbz)₂FeCl₂][FeCl₄]·CH₂Cl₂ (dpbz = 1,2-bis-(di-phenyl-phosphane)benzene, P₂C₃₀H₂₄) demonstrates trans coordination of two bidentate phosphane ligands (bis-phosphanes) to a single iron(III) center, resulting in six-coordinate cationic complexes that are balanced in charge by tetra-chlorido-ferrate(III) monoanions. The trans bis-phosphane coordination is consistent will all previously reported mol-ecular structures of six coordinate iron(III) complex cations with a (PP)₂X₂ (X = halido) donor set. The complex with dppen crystallizes in the centrosymmetric space group C2/c as a partial-occupancy [0.592 (4)] di-chloro-methane solvate, while the dpbz-ligated complex crystallizes in the triclinic space group P1 as a full di-chloro-methane monosolvate. Furthermore, the crystal studied of [(dpbz)₂FeCl₂][FeCl₄]·CH₂Cl₂ was an inversion twin, whose component mass ratio refined to 0.76 (3):0.24 (3). Beyond a few very weak C-H⋯Cl and C-H⋯π inter-actions, there are no significant supra-molecular features in either structure.

Keywords: bidentate phosphane; crystal structure; inversion twin; iron; iron-catalysed cross-coupling.