A New Spin on Cyclooctatetraene (COT) Redox Activity: Low-Spin Iron(I) Complexes That Exhibit Antiferromagnetic Coupling to a Singly Reduced η<sup>4</sup>‑COT Ligand Tufan K. Mukhopadhyay Marco Flores Russell K. Feller Brian L. Scott R. Dean Taylor Moshe Paz-Pasternak Neil J. Henson Francisca N. Rein Nathan C. Smythe Ryan J. Trovitch John C. Gordon 10.1021/om500909h.s002 https://acs.figshare.com/articles/dataset/A_New_Spin_on_Cyclooctatetraene_COT_Redox_Activity_Low_Spin_Iron_I_Complexes_That_Exhibit_Antiferromagnetic_Coupling_to_a_Singly_Reduced_sup_4_sup_COT_Ligand/2223403 Formally zerovalent (κ<sup>3</sup>-phosphine)­Fe­(η<sup>4</sup>-COT) complexes supported by either Triphos (PhP­(CH<sub>2</sub>CH<sub>2</sub>PPh<sub>2</sub>)<sub>2</sub>) or Triphos* (H<sub>3</sub>CC­(CH<sub>2</sub>PPh<sub>2</sub>)<sub>3</sub>) have been prepared following chelate addition to (COT)<sub>2</sub>Fe (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 Mössbauer spectroscopic data collected for both (Triphos)­Fe­(η<sup>4</sup>-COT) complexes with data obtained for two appropriate reference compounds indicated that they possess a low-spin Fe­(I) center that is antiferromagnetically coupled to a COT radical monoanion. Further evidence for this electronic structure determination by EPR spectroscopy and cyclic voltammetry is presented. A comparison of the solid-state metrical parameters determined in this study to those of related first-row transition-metal complexes has provided insight into the electronic structure analysis of related organometallic complexes. 2014-12-22 00:00:00 COT ligand reduction Redox Activity cyclic voltammetry dianionic forms structure investigation EPR spectroscopy Exhibit Antiferromagnetic dibromide complexes structure analysis organometallic complexes New Spin reference compounds coordination geometry chelate addition Tripho monoanion form H 3CC structure determination