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. 2022 Jan 18;13(7):2094-2104.
doi: 10.1039/d1sc05473b. eCollection 2022 Feb 16.

Combining metal-metal cooperativity, metal-ligand cooperativity and chemical non-innocence in diiron carbonyl complexes

Cody B van Beek  1 , Nicolaas P van Leest  2 , Martin Lutz  3 , Sander D de Vos  1 , Robertus J M Klein Gebbink  1 , Bas de Bruin  2 , Daniël L J Broere  1
Affiliations

Combining metal-metal cooperativity, metal-ligand cooperativity and chemical non-innocence in diiron carbonyl complexes

Cody B van Beek et al. Chem Sci. .

Abstract

Several metalloenzymes, including [FeFe]-hydrogenase, employ cofactors wherein multiple metal atoms work together with surrounding ligands that mediate heterolytic and concerted proton-electron transfer (CPET) bond activation steps. Herein, we report a new dinucleating PNNP expanded pincer ligand, which can bind two low-valent iron atoms in close proximity to enable metal-metal cooperativity (MMC). In addition, reversible partial dearomatization of the ligand's naphthyridine core enables both heterolytic metal-ligand cooperativity (MLC) and chemical non-innocence through CPET steps. Thermochemical and computational studies show how a change in ligand binding mode can lower the bond dissociation free energy of ligand C(sp3)-H bonds by ∼25 kcal mol-1. H-atom abstraction enabled trapping of an unstable intermediate, which undergoes facile loss of two carbonyl ligands to form an unusual paramagnetic (S = ) complex containing a mixed-valent iron(0)-iron(i) core bound within a partially dearomatized PNNP ligand. Finally, cyclic voltammetry experiments showed that these diiron complexes show catalytic activity for the electrochemical hydrogen evolution reaction. This work presents the first example of a ligand system that enables MMC, heterolytic MLC and chemical non-innocence, thereby providing important insights and opportunities for the development of bimetallic systems that exploit these features to enable new (catalytic) reactivity.

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Conflict of interest statement

There are no conflicts to declare.

Figures

Fig. 1
Fig. 1. Different methods of metal–ligand cooperativity in bimetallic complexes.
Scheme 1
Scheme 1. Synthesis of complexes 1 and 2 by reaction of iPrPNNP with Fe2(CO)9.
Scheme 2
Scheme 2. Synthesis of 3 by deprotonation of 1.
Scheme 3
Scheme 3. The photochemical synthesis of complexes 1 and 4.
Fig. 2
Fig. 2. Experimental (black) and simulated (red) X-band EPR spectrum of 4 in toluene at room temperature (A) or in a toluene glass at 30 K (B). (A): microwave freq. 9.650747 GHz, mod. amp. 4.000 G, power 0.6325 mW. Simulation parameters: giso = 2.0475, Gaussian line broadening 1.284 mT. (B): microwave freq. 9.641384 GHz, mod. amp. 4.000 G, power 0.6325 mW. Simulation parameters: g [2.0081, 2.0282, 2.1028], Gaussian line broadening 1.153 mT. (C): the DFT optimized structure of 4 (B3LYP/def2-TZVP) and its spin density plot (isosurface value of 0.02 e Bohr−3).
Scheme 4
Scheme 4. The reduction of complex 4 to complex 5 and its protonation to 6.
Fig. 3
Fig. 3. Displacement ellipsoid plots (50% probability) of the asymmetric units of complex 1, 3, 5 and 6. Most hydrogen atoms and the benzene molecules in 6 are omitted and iPr groups on P and the THF molecules in 3 and 5 are depicted as wireframe for clarity. For 5 and 6 only the major disorder component is shown.
Scheme 5
Scheme 5. Light induced conversion of 7 to 4.
Fig. 4
Fig. 4. Experimental (black) and simulated (red) X-band EPR spectrum of 7 in toluene at room temperature (A) or in a toluene glass at 30 K (B). (A) Microwave freq. 9.649849 GHz, mod. amp. 4.000 G, power 0.6325 mW. Simulation parameters component 1 (7): giso = 2.0418, A31P = 58.279 MHz, Gaussian line broadening 0.68 mT, weight = 99.9%. Simulation parameters component 2 (TBP): giso = 2.005, Gaussian line broadening 0.3 mT, weight = 0.1%. (B) Microwave freq. 9.650852 GHz, mod. amp. 2.000 G, power 0.2000 mW. Simulation parameters: g [2.0027, 2.0478, 2.0684], A31P [40.15, 71.2293, 62.89], g-strain [0, 0, 0.013007], g-frame [−1.21, 2.34, 3.02], A-frame [1.06, 1.02, −1.53]. (C) The structure of 7 and its spin density plot (isosurface value of 0.02 e Bohr−3).
Scheme 6
Scheme 6. Partial thermochemical square scheme of complex 1 to determine the BDFEC–H.
Fig. 5
Fig. 5. Cyclic voltammograms of complex 6 (1 mM) in THF/[Bu4N]PF6 (scan rate = 0.1 V s−1); the arrow indicates the scan direction.
Fig. 6
Fig. 6. Cyclic voltammograms of complex 4 and 6 (1 mM) with the addition 1 mM of phenol in THF/[Bu4N]PF6 (scan rate = 0.1 V s−1); the arrow indicates the scan direction.
Fig. 7
Fig. 7. Cyclic voltammograms of complex 6 (1 mM) with the addition of 1–10 mM of TEA in THF/[Bu4N]PF6 (scan rate = 0.1 V s−1); the arrow indicates the scan direction.
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References

    1. Can M. Armstrong F. A. Ragsdale S. W. Chem. Rev. 2014;114:4149–4174. doi: 10.1021/cr400461p. - DOI - PMC - PubMed
    2. Lubitz W. Ogata H. Rüdiger O. Reijerse E. Chem. Rev. 2014;114:4081–4148. doi: 10.1021/cr4005814. - DOI - PubMed
    3. Wodrich M. D. Hu X. Nat. Rev. Chem. 2017;2:0099. doi: 10.1038/s41570-017-0099. - DOI
    4. Sippel D. Rohde M. Netzer J. Trncik C. Gies J. Grunau K. Djurdjevic I. Decamps L. Andrade S. L. A. Einsle O. Science. 2018;359:1484–1489. doi: 10.1126/science.aar2765. - DOI - PubMed
    1. Li Y. Rauchfuss T. B. Chem. Rev. 2016;116:7043–7077. doi: 10.1021/acs.chemrev.5b00669. - DOI - PMC - PubMed
    2. Birrell J. A. Pelmenschikov V. Mishra N. Wang H. Yoda Y. Tamasaku K. Rauchfuss T. B. Cramer S. P. Lubitz W. DeBeer S. J. Am. Chem. Soc. 2020;142:222–232. doi: 10.1021/jacs.9b09745. - DOI - PMC - PubMed
    1. Land H. Senger M. Berggren G. Stripp S. T. ACS Catal. 2020;10:7069–7086. doi: 10.1021/acscatal.0c01614. - DOI
    2. Kleinhaus J. T. Wittkamp F. Yadav S. Siegmund D. Apfel U.-P. Chem. Soc. Rev. 2021;50:1668–1784. doi: 10.1039/D0CS01089H. - DOI - PubMed
    1. Tai H. Hirota S. Stripp S. T. Acc. Chem. Res. 2021;54:232–241. doi: 10.1021/acs.accounts.0c00651. - DOI - PubMed
    1. Duan J. Senger M. Esselborn J. Engelbrecht V. Wittkamp F. Apfel U.-P. Hofmann E. Stripp S. T. Happe T. Winkler M. Nat. Commun. 2018;9:4726. doi: 10.1038/s41467-018-07140-x. - DOI - PMC - PubMed