Complexes of manganese, iron and cobalt with sterically demanding indenyl ligands

Abstract

A series of manganese, iron and cobalt complexes bearing sterically demanding 1,3-disubstituted indenyl ligands, 1,3-(Me₃C)₂C₉H₅ (Ind^tBu) (1) and 1,3-(C₆H₁₁)₂C₉H₅ (Ind^cHexyl) (2), has been prepared. These complexes have been fully characterised by various spectroscopic techniques, elemental analysis, and X-ray diffraction experiments. In addition the electronic and steric properties of these ligands have been evaluated. Although the cone angles and electronic properties are similar to 1,2,4-(Me₃C)₃C₅H₂ (Cp′), indenyl iron half-sandwich complexes are only stable at low temperature. This has been demonstrated for 1-FeI using suitable trapping experiments such as CO or NaCp′ addition to yield 1-Fe(CO)₂I and 1-FeCp′, respectively. Overall the metal–ligand bonds in these indenyl compounds are weaker than in the corresponding cyclopentadienyl derivatives. In addition, the bis(indenyl)manganese complexes, 1-Mn and 2-Mn, are high-spin, as established by solid state magnetic susceptibility studies in the temperature range 2–300 K.