A new spin on cyclooctatetraene (COT) redox activity: Low-spin iron(I) complexes that exhibit antiferromagnetic coupling to a singly reduced η4-COT ligand

Formally zerovalent (κ3-phosphine)Fe(η4-COT) complexes supported by either Triphos (PhP(CH2CH2PPh2)2) or Triphos* (H3CC(CH2PPh2)3) have been prepared following chelate addition to (COT)2Fe (COT = 1,3,5,7-cyclooctatetraene) and by reduction of the respective dibromide complexes in the presence of excess COT. The solid-state structure of each complex was determined by single-crystal X-ray diffraction, and close inspection of the metrical parameters revealed significant COT ligand reduction, independent of the coordination geometry about iron. While the neutral and dianionic forms of the redox-active COT ligand have historically received a great deal of attention, a dearth of information regarding the often-evoked radical monoanion form of this ligand prompted the full electronic structure investigation of these complexes using a range of techniques. Comparison of the Mossbauer spectroscopic data collected for both (Triphos)Fe(η4-COT) complexes with data obtained for two appropriate reference compounds indic...