Binuclear Iron(I) Complex Containing Bridging Phenanthrene-4,5-dithiolate Ligand: Preparation, Spectroscopy, Crystal Structure, and Electrochemistry

• Published in: ZAAC - Journal of Inorganic and General Chemistry 2010-12, Vol.636 (15), p.2550-2554
• Main Authors: Mebi, Charles A., Noll, Bruce C., Gao, Ruixiao, Karr, Derek
• Format: Article
• Language: English
• Subjects: 5-dithiolate; Cluster compounds; Electrochemistry; Hydrogenase model; Phenanthrene-4; Phenanthrene‐4,5‐dithiolate; Solid-state structures
• ISSN: 0044-2313; 1521-3749
• DOI: 10.1002/zaac.201000236

A diiron hexacarbonyl complex containing bridging phenanthrene‐4,5‐dithiolate ligand is prepared by oxidative addition of Phenanthro[4,5‐cde][1,2]dithiin to Fe2(CO)9. The complex is investigated as a model for the active site of the [Fe–Fe] hydrogenase enzyme. The compound, [(μ‐PNT)Fe2(CO)6]; (PNT = phenanthrene‐4,5‐dithiolate), was characterized by spectroscopic methods (IR, UV/Vis and NMR) and X‐ray crystallography. The IR and proton NMR spectra of [(μ‐PNT)Fe2(CO)6] (4) are in agreement with a PNT ligand attached to a Fe2(CO)6 core. The infrared spectrum of 4 recorded in dichloromethane contains three peaks at 2001, 2040, and 2075 cm–1 corresponding to the stretching frequency of terminal metal carbonyls. X‐ray crystallographic study unequivocally confirms the structure of the complex having a butterfly shape with an Fe–Fe bond length of 2.5365 Å close to that of the enzyme (2.6 Å). Electrochemical properties of [(μ‐PNT)Fe2(CO)6] have been investigated by cyclic voltammetry. The cyclic voltammogram of [(μ‐PNT)Fe2(CO)6] recorded in acetonitrile contains one quasi‐irreversible reduction (E1/2 = –0.84 V vs. Ag/AgCl, Ipc/Ipa = 0.6, ΔEp = 131 V at 0.1 V·s–1) and one irreversible oxidation (Epa = 0.86 V vs. Ag/AgCl). The redox of [(μ‐PNT)Fe2(CO)6] at E1/2 = –0.84 V can be assigned to the one‐electron transfer processes; [FeI–FeI] → [FeI–Fe0] and [FeI–Fe0] → [FeI–FeI].