A comparative study of the coordination behavior of cyclo-P(5) and cyclo-As(5) ligand complexes towards the trinuclear Lewis acid complex (perfluoro-ortho-phenylene)mercury

Reactions of the cyclo-E(5) sandwich complexes [Cp*Fe(η(5)-P(5))] (1) and [Cp*Fe(η(5)-As(5))] (2) with the planar Lewis acid trimeric (perfluoro-ortho-phenylene)mercury [(o-C(6)F(4)Hg)(3)] (3) afford compounds that show distinctly different assemblies in the solid state. The phosphorus containing ligand 1 forms dimeric coordination units with two molecules of 3, with one P atom of each cyclo-P(5) ligand positioned in close proximity to the center of a molecule of 3. In contrast to the coordination behavior of 1, the arsenic analog 2 shows simultaneous interaction of three As atoms with the Hg atoms of 3. A DFT study and subsequent AIM analyses of the products suggest that electrostatic forces are prevalent over donor–acceptor interactions in these adducts, and may play a role in the differences in the observed coordination behavior. Subsequently, a series of [Cp(R)Fe(η(5)-P(5))] (Cp(R) = C(5)H(5–n) tBu(n), n = 1–3, 6a–c) sandwich complexes was prepared and also reacted with [(o-C(6)F(4)Hg)(3)]. In the solid state the obtained products 7a–c with increasing steric demand of the Cp(R) ligands show no significant change in their assembly compared to the Cp* analog 4. All of the products were characterized by single crystal X-ray structure analysis, mass spectrometry and elemental analysis as well as NMR spectroscopy and IR spectrometry.