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Interplay between Terminal and Bridging Diiron Hydrides in Neutral and Oxidized States

Journal Article · · Organometallics
 [1];  [1];  [1];  [2];  [2];  [2];  [2]
  1. Shandong Univ., Jinan (China). School of Chemistry and Chemical Engineering
  2. Univ. of Illinois at Urbana-Champaign, IL (United States). School of Chemical Sciences
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This study describes the structural, spectroscopic, and electrochemical properties of electronically unsymmetrical diiron hydrides. The terminal hydride Cp*Fe(pdt)Fe(dppe)(CO)H ([$$1$$($$t$$-H)]$^0$, Cp$$^{*–}$$ = Me5C5–, pdt2– = CH2(CH2S–)2, dppe = Ph2PC2H4PPh2) was prepared by hydride reduction of [Cp*Fe(pdt)Fe(dppe)(CO)(NCMe)]+. As established by X-ray crystallography, [$$1$$($$t$$-H)]$^0$ features a terminal hydride ligand. Unlike previous examples of terminal diiron hydrides, [$$1$$($$t$$-H)]$^0$ does not isomerize to the bridging hydride [$$1$$($$μ$$-H)]$^0$. Oxidation of [$$1$$($$t$$-H)]$^0$ gives [$$1$$($$t$$-H)]$^+$, which was also characterized crystallographically as its BF$$_4^–$$ salt. Density functional theory (DFT) calculations indicate that [$$1$$($$t$$-H)]$^+$ is best described as containing an Cp*FeIII center. In solution, [$$1$$($$t$$-H)]$^+$ isomerizes to [$$1$$($$μ$$-H)]$^+$, as anticipated by DFT. Reduction of [$$1$$($$μ$$-H)]$^+$ by Cp2Co afforded the diferrous bridging hydride [$$1$$($$μ$$-H)]$^0$. Electrochemical measurements and DFT calculations indicate that the couples [$$1$$($$t$$-H)]+/0 and [$$1$$($$μ$$-H)]+/0 differ by 210 mV. Qualitative measurements indicate that [$$1$$($$t$$-H)]0 and [$$1$$($$μ$$-H)]0 are close in free energy. Protonation of [$$1$$($$t$$-H)]0 in MeCN solution affords H2 even with weak acids via hydride transfer. In contrast, protonation of [$$1$$($$μ$$-H)]0 yields 0.5 equiv of H2 by a proposed protonation-induced electron transfer process. Isotopic labeling indicates that μ-H/D ligands are inert.
Research Organization:
Energy Frontier Research Centers (EFRC) (United States). Center for Molecular Electrocatalysis (CME)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Grant/Contract Number:
AC05-76RL01830
OSTI ID:
1469825
Alternate ID(s):
OSTI ID: 1572656
Journal Information:
Organometallics, Journal Name: Organometallics Journal Issue: 11 Vol. 36; ISSN 0276-7333
Publisher:
American Chemical SocietyCopyright Statement
Country of Publication:
United States
Language:
English

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Cited By (7)

Reactions of Fe 2 ( μ ‐odt)(CO) 6 (odt = 1, 3‐oxadithiolate) with small bite‐angle diphosphines to afford the monodentate, chelate, and bridge diiron complexes: Selective substitution, structures, protonation, and electrocatalytic proton reduction journal April 2019
Electrochemical Proton Reduction Catalyzed by [Fe 2 (CO) 6 {μ-(TeCH 2 Te)}] Model that Mimics the Structure of the Active Site of [FeFe]-Hydrogenase : Electrochemical Proton Reduction Catalyzed by [Fe journal May 2018
Synthetic [NiFe] models with a fluxional CO ligand journal January 2017
Reactant or reagent? Oxidation of H 2 at electronically distinct nickel-thiolate sites [Ni 2 (μ-SR) 2 ] + and [Ni–SR] + journal January 2018
Protonation and electrochemical properties of a bisphosphide diiron hexacarbonyl complex bearing amino groups on the phosphide bridge journal January 2019
The effect of a pendant amine in phosphine ligand on the structure and electrochemical property of diiron dithiolate complexes journal September 2018
The effect of a pendant amine in phosphine ligand on the structure and electrochemical property of diiron dithiolate complexes text January 2018

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