The first example of a structurally characterized octahedral hydrotris(pyrazolyl)borate iron methyl complex

The one-step synthesis of the known acetyl complex κ3-TpFe(CO)(PMe3)(COMe) (1, 78% yield) is achieved by reaction of cis,trans-Fe(CO)2(PMe3)2MeI with potassium hydrotris(pyrazolyl)borate (KTp), in CH2Cl2 at room temperature. This reaction is specific to the parent Tp ligand. Visible light irradiation of 1 in toluene for 1 h afforded the first octahedral methyl–iron complex featuring the hydrotris(pyrazolyl)borate ligand TpFe(CO)(PMe3)Me (2) in 80% yield. Compound 2 has been fully characterized by elemental analysis, IR, NMR spectroscopies, cyclic voltammetry and by an X-ray diffraction analysis. A comparison of steric and electronic properties is made with those of related cyclopentadienyl (Cp, Cp*, C5Ph5) complexes, and suggests that relative donating abilities follow the trend Cp, Cp*, C5Ph5>Tp, and structural comparisons indicate that Tp is the most sterically demanding ligand.