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Isolation and electronic structures of derivatized manganocene, ferrocene and cobaltocene anions


The discovery of ferrocene nearly 70 years ago marked the genesis of metallocene chemistry. Although the ferrocenium cation was discovered soon afterwards, a derivatized ferrocenium dication was only isolated in 2016 and the monoanion of ferrocene has only been observed in low-temperature electrochemical studies. Here we report the isolation of a derivatized ferrocene anion in the solid state as part of an isostructural family of 3d metallocenates, which consist of anionic complexes of a metal centre (manganese, iron or cobalt) sandwiched between two bulky Cpttt ligands (where Cpttt is {1,2,4-C5H2 tBu3}). These thermally and air-sensitive complexes decompose rapidly above −30 °C; however, we were able to characterize all metallocenates by a wide range of physical techniques and ab initio calculations. These data have allowed us to map the electronic structures of this metallocenate family, including an unexpected high-spin S = 3/2 ground state for the 19e derivatized ferrocene anion.

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Fig. 1: Electrochemical studies for 1, 2 and 3.
Fig. 2: Synthesis of 4, 5 and 6 and molecular structure of 5.
Fig. 3: Zero-field 57Fe Mössbauer spectra for 2 and 5.
Fig. 4: Continuous-wave Q-band EPR spectra of 3 and 5.
Fig. 5: Orbital ordering, occupation and approximate symmetry labels for the active space of 2–7 from CASSCF-SO.

Data availability

Crystallographic data for the structures reported in this Article have been deposited at the Cambridge Crystallographic Data Centre, under deposition nos. CCDC 1951767 (1), 1951768 (2), 1951769 (3), 1951770 (4), 1951771 (5), 1951772 (6), 1951773 (7) and 1951774 (8). Copies of the data can be obtained free of charge from the CCDC via Raw research data files supporting this publication are available from Mendeley Data at Apart from the datasets mentioned, all other data supporting the findings of this study are available within the Article and Supplementary Information.


  1. Kealy, T. J. & Pauson, P. L. A new type of organo-iron compound. Nature 168, 1039–1040 (1951).

    CAS  Google Scholar 

  2. Miller, S. A., Tebboth, J. A. & Tremaine, J. F. 114. Dicyclopentadienyliron. J. Chem. Soc. 1952, 632–635 (1952).

    Google Scholar 

  3. Wilkinson, G., Rosenblum, M., Whiting, M. C. & Woodward, R. B. The structure of iron bis-cyclopentadienyl. J. Am. Chem. Soc. 74, 2125–2126 (1952).

    CAS  Google Scholar 

  4. Long, N. J. Metallocenes—An Introduction to Sandwich Complexes (Blackwell Science, 1998).

  5. Togni, A. & Halterman, R. L. Metallocenes: Synthesis Reactivity Applications (Wiley, 1998).

  6. Fukino, T. et al. Manipulation of discrete nanostructures by selective modulation of noncovalent forces. Science 344, 499–540 (2014).

    CAS  PubMed  Google Scholar 

  7. Astruc, D. Why is ferrocene so exceptional?. Eur. J. Inorg. Chem. 2017, 6–29 (2017).

    CAS  Google Scholar 

  8. Jumde, R. P., Lanza, F., Veenstra, M. J. & Harutyunyan, S. R. Catalytic asymmetric addition of Grignard reagents to alkenyl-substituted aromatic N-heterocycles. Science 352, 433–437 (2016).

    CAS  PubMed  Google Scholar 

  9. Connelly, N. G. & Geiger, W. E. Jr Chemical redox agents for organometallic chemistry. Chem. Rev. 96, 877–910 (1996).

    CAS  PubMed  Google Scholar 

  10. Malischewski, M., Adelhardt, M., Sutter, J., Meyer, K. & Seppelt, K. Isolation and structural and electronic characterization of salts of the decamethylferrocene dication. Science 353, 678–682 (2016).

    CAS  PubMed  Google Scholar 

  11. Holloway, J. D. L., Bowden, W. L. & Geiger, W. E. Jr Unusual electron-transfer processes involving electron-rich and electron-deficient metallocenes. J. Am. Chem. Soc. 99, 7089–7090 (1997).

    Google Scholar 

  12. Mugnier, Y., Moise, C., Tirouflet, J. & Laviron, E. Reduction electrochimique du ferrocene. J. Organomet. Chem. 186, C49–C52 (1980).

    CAS  Google Scholar 

  13. Ito, N., Saji, T. & Aoyagui, S. Electrochemical formation of stable ferrocene anion and the formal rate constant of the ferrocene0/− electrode. J. Organomet. Chem. 247, 301–305 (1983).

    CAS  Google Scholar 

  14. Geiger, W. E. Jr Electroreduction of cobaltocene. Evidence for a metallocene anion. J. Am. Chem. Soc. 96, 2632–2634 (1974).

    CAS  Google Scholar 

  15. Bard, A. J., Garcia, E., Kukharenko, S. & Strelets, V. V. Electrochemistry of metallocenes at very negative and very positive potentials. Electrogeneration of 17-electron Cp2Co2+, 21-electron Cp2Co2−, and 22-electron Cp2Ni2− species. Inorg. Chem. 32, 3528–3531 (1993).

    CAS  Google Scholar 

  16. Smart, J. C. & Robbins, J. L. A low spin manganocene and its novel anionic derivative. Synthesis and characterization of decamethylmanganocene complexes. J. Am. Chem. Soc. 100, 3936–3937 (1978).

    CAS  Google Scholar 

  17. Robbins, J. L., Edelstein, N. M., Cooper, S. R. & Smart, J. C. Syntheses and electronic structures of decamethylmanganocenes. J. Am. Chem. Soc. 101, 3853–3857 (1979).

    CAS  Google Scholar 

  18. Baudry, D. & Ephritikhine, M. Reactions de (η5-C5H5)2reh et de ses derives. Preparation de nouveaux complexes biscyclopentadienyles du rhenium. J. Organomet. Chem. 195, 213–222 (1980).

    CAS  Google Scholar 

  19. Gardner, B. M., McMaster, J., Lewis, W. & Liddle, S. T. Synthesis and structure of [{N(CH2CH2NSiMe3)3}URe(η5-C5H5)2]: a heterobimetallic complex with an unsupported uranium-rhenium bond. Chem. Commun. 2009, 2851–2853 (2009).

    Google Scholar 

  20. Hung-Low, F. & Bradley, C. A. Synthesis of a bis(indenyl) Co(i) anion: a reactive source of a 14 electron indenyl Co(i) equivalent. Inorg. Chem. 52, 2446–2457 (2013).

    CAS  PubMed  Google Scholar 

  21. Malischewski, M. & Seppelt, K. Structural characterization of potassium salts of the decamethylmanganocene anion Cp*2Mn. Dalton Trans. 48, 17078–17082 (2019).

    CAS  PubMed  Google Scholar 

  22. Astruc, D., Román, E., Hamon, E., Batail, J. R. & Novel, P. Reactions of dioxygen in organometallic chemistry. Hydrogen atom abstraction vs. dimerization of the 19-electron complexes η5-cyclopentadienyliron(i) η6-arene. J. Am. Chem. Soc. 101, 2240–2242 (1979).

    CAS  Google Scholar 

  23. Hamon, J. R., Astruc, D. & Michaud, P. Syntheses, characterizations, and stereoelectronic stabilization of organometallic electron reservoirs: the 19-electron d7 redox catalysts η5-C5R5Fe-η6-C6R′6. J. Am. Chem. Soc. 103, 758–766 (1981).

    CAS  Google Scholar 

  24. Saito, M. et al. Anionic stannaferrocene and its unique electronic state. Chem. Lett. 48, 163–165 (2019).

    CAS  Google Scholar 

  25. Sitzmann, H., Schär, M., Dormann, E. & Kelemen, M. High spin-manganocenes with bulky, alkylated cyclopentadienyl ligands. Z. Anorg. Allg. Chem. 623, 1609–1613 (1997).

    CAS  Google Scholar 

  26. Walter, M. D., Sofield, C. D., Booth, C. H. & Andersen, R. A. Spin equilibria in monomeric manganocenes: solid-state magnetic and EXAFS studies. Organometallics 28, 2005–2019 (2009).

    CAS  Google Scholar 

  27. Walter, M. D. & White, P. S. [Cp′FeI]2 as convenient entry into iron-modified pincer complexes: bimetallic η61-POCOP-pincer iron iridium compounds. New J. Chem. 35, 1842–1854 (2011).

    CAS  Google Scholar 

  28. Schneider, J. J. et al. Synthesis, structure and spectroelectrochemistry of bis(η6-1,4-tri-tert-butyl-benzene)chromium(0) and bis(η5-1,2,4-tri-tert-butyl-cyclopentadienyl)cobalt(ii). Dia- and paramagnetic sandwich complexes derived from sterically highly demanding π-ligands. J. Organomet. Chem. 590, 7–14 (1999).

    CAS  Google Scholar 

  29. Peters, M. et al. Pogo-stick iron and cobalt complexes: synthesis, structures, and magnetic properties. Inorg. Chem. 58, 16475–16486 (2019).

    CAS  PubMed  Google Scholar 

  30. Jaroschik, F., Nief, F., Le Goff, X.-F. & Ricard, L. Synthesis and reactivity of organometallic complexes of divalent thulium with cyclopentadienyl and phospholyl ligands. Organometallics 26, 3552–3558 (2007).

    CAS  Google Scholar 

  31. Woen, D. H. & Evans, W. J. in Handbook on the Physics and Chemistry of Rare Earths Vol. 50 (eds Bünzli, J.-C. G. & Pecharsky, V. K.) Ch. 293, 337–394 (Elsevier, 2016).

  32. Fischer, E. O. & Leipfinger, H. Weitere magnetische Untersuchungen zur Struktur der cyclopentadien- und inden-Verbindungen der Übergangsmetalle. Z. Naturforsch. 10b, 353–355 (1955).

    CAS  Google Scholar 

  33. Wilkinson, G., Cotton, F. A. & Birmingham, J. M. On manganese cyclopentadienide and some chemical reactions of neutral bis-cyclopentadienyl metal compounds. J. Inorg. Nucl. Chem. 2, 95–113 (1956).

    CAS  Google Scholar 

  34. Walter, M. D., Sofield, C. D. & Andersen, R. A. Spin equilibria and thermodynamic constants for (C5H4R)2Mn, R = H or Me, in solid solutions of diamagnetic diluents. J. Organomet. Chem. 776, 17–22 (2015).

    CAS  Google Scholar 

  35. Switzer, M. E., Wang, R., Rettig, M. F. & Maki, A. H. Electronic ground states of manganocene and 1,1′-dimethylmanganocene. J. Am. Chem. Soc. 96, 7669–7674 (1974).

    CAS  Google Scholar 

  36. Fdez. Galván, I. et al. OpenMolcas: from source code to insight. J. Chem. Theory Comput. 15, 5925–5964 (2019).

    PubMed  Google Scholar 

  37. Wickman, H. H., Klein, M. P. & Shirley, D. A. Paramagnetic hyperfine structure and relaxation effects in Mössbauer spectra: Fe57 in ferrichrome A. Phys. Rev. 152, 345 (1966).

    CAS  Google Scholar 

  38. Stoian, S. A. et al. Mössbauer, electron paramagnetic resonance, and crystallographic characterization of a high-spin Fe(i) diketiminate complex with orbital degeneracy. Inorg. Chem. 44, 4915–4922 (2005).

    CAS  PubMed  Google Scholar 

  39. Wertheim, G. K. & Herber, R. H. Fe57 Mössbauer effect in ferrocene derivatives. J. Chem. Phys. 38, 2106–2111 (1963).

    CAS  Google Scholar 

  40. Stukan, R. A., Gubin, S. P., Nesmeyanov, A. N., Gol’danskii, V. I. & Makarov, E. F. A Mössbauer study of some ferrocene derivatives. Theor. Exper. Chem. 2, 581–584 (1966).

    Google Scholar 

  41. Reiners, M. et al. Study on spin–lattice relaxation processes in tert-butyl substituted ferrocenium derivatives. Eur. J. Inorg. Chem. 388–400 (2017).

  42. Mariot, J. P. et al. Mössbauer study and molecular orbital calculations on the organo-iron(i, ii) electron reservoir sandwiches CpFen+ (η6-C6(CH3)6) (n = 0,1) and related CpFe (cyclohexadienyl) complexes. J. Physique 44, 1377–1385 (1983).

    CAS  Google Scholar 

  43. Stoll, S. & Schweiger, A. EasySpin, a comprehensive software package for spectral simulation and analysis in EPR. J. Magn. Reson. 178, 42–55 (2006).

    CAS  PubMed  Google Scholar 

  44. Chilton, N. F., Anderson, R. P., Turner, L. D., Soncini, A. & Murray, K. S. PHI: a powerful new program for the analysis of anisotropic monomeric and exchange-coupled polynuclear d- and f-block complexes. J. Comput. Chem. 34, 1164–1175 (2013).

    CAS  PubMed  Google Scholar 

  45. Rajasekharan, M. V. et al. EPR studies of the electronic structure and dynamic Jahn–Teller effect in iron(i) sandwich compounds. J. Am. Chem. Soc. 104, 2400–2407 (1982).

    CAS  Google Scholar 

  46. Chang, H.-C. et al. Electron paramagnetic resonance signature of tetragonal low spin iron(v)–nitrido and –oxo complexes derived from the electronic structure analysis of heme and non-heme archetypes. J. Am. Chem. Soc. 141, 2421–2434 (2019).

    CAS  PubMed  PubMed Central  Google Scholar 

  47. Gomez-Coca, S., Cremades, E., Aliaga-Alcalde, N. & Ruiz, E. Mononuclear single-molecule magnets: tailoring the magnetic anisotropy of first-row transition–metal complexes. J. Am. Chem. Soc. 135, 7010–7018 (2013).

    CAS  PubMed  Google Scholar 

  48. Molloy, K. C. (ed.) in Group Theory for Chemists 2nd edn, Ch. 10, 109–118 (Woodhead Publishing, 2013);

  49. Cirera, J. & Ruiz, E. Electronic and steric control of the spin-crossover behavior in [(CpR)2Mn] manganocenes. Inorg. Chem. 57, 702–709 (2018).

    CAS  PubMed  Google Scholar 

  50. Ishimura, K., Hada, M. & Nakatsuji, H. Ionized and excited states of ferrocene: symmetry adapted cluster–configuration–interaction study. J. Chem. Phys. 117, 6533–6537 (2002).

    CAS  Google Scholar 

  51. Watt, G. W. & Baye, L. J. Reactions of metallocenes with potassium and potassium amide in liquid ammonia. J. Inorg. Nucl. Chem. 26, 2099–2102 (1964).

    CAS  Google Scholar 

  52. Bergbreiter, D. E. & Killough, J. M. Reactions of potassium-graphite. J. Am. Chem. Soc. 100, 2126–2134 (1978).

    CAS  Google Scholar 

  53. Roos, B. O., Lindh, R., Malmqvist, P.-Å., Veryazov, V. & Widmark, P.-O. Main group atoms and dimers studied with a new relativistic ANO basis set. J. Phys. Chem. A 108, 2851–2858 (2004).

    CAS  Google Scholar 

  54. Roos, B. O., Lindh, R., Malmqvist, P.-Å., Veryazov, V. & Widmark, P.-O. New relativistic ANO basis sets for transition metal atoms. J. Phys. Chem. A 109, 6575–6579 (2005).

    CAS  PubMed  Google Scholar 

  55. Veryazov, V., Malmqvist, P. Å. & Roos, B. O. How to select active space for multiconfigurational quantum chemistry? Int. J. Quant. Chem. 111, 3329–3338 (2011).

    CAS  Google Scholar 

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We acknowledge funding from the Engineering and Physical Sciences Research Council (Doctoral Prize Fellowship to C.A.P.G., EP/N007034/1 for M.V., EP/R002605X/1 for P.E., studentship for H.M.N. and EP/K039547/1 for a single-crystal X-ray diffractometer), the Royal Society (University Research Fellowship to N.F.C.), European Research Council CoG-816268 (D.P.M. and M.J.G.) and StG-851504 (N.F.C.) and the University of Manchester (Presidential Doctoral Prize to M.J.G.). C.A.P.G. and S.M.G. thank the Laboratory Directed Research and Development (LDRD) programme at Los Alamos National Laboratory (an affirmative action/equal opportunity employer, managed by Triad National Security, LLC, for the NNSA of the US Department of Energy) (contract no. 89233218CNA000001) for a distinguished J. Robert Oppenheimer Postdoctoral Fellowship and Directors Fellowship, respectively. S.H. acknowledges support from the National Science Foundation (DMR-1610226). We thank the EPSRC UK National Electron Paramagnetic Resonance Service for access to the EPR Facility, and the University of Manchester for access to the Computational Shared Facility. A portion of this work was performed at the National High Magnetic Field Laboratory, which is supported by the National Science Foundation Cooperative agreement no. DMR-1644779 and the State of Florida. We also thank F. Ortu for assistance with the collection of Raman spectra. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreements nos. 816268 and 851504).

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Authors and Affiliations



C.A.P.G. and D.P.M. provided the original concept. C.A.P.G. synthesized and characterized the compounds. H.M.N. and P.E. carried out supporting synthetic and characterization work. D.P.M. supervised the synthetic component. M.J.G., M.V. and N.F.C. collected and interpreted EPR data. M.V. and N.F.C. performed CASSCF calculations. N.F.C. supervised the EPR and CASSCF components. S.M.G. collected and interpreted Mössbauer spectra and performed DFT calculations. S.H. supervised S.M.G. and provided additional EPR/Mössbauer interpretation. D.P.M. and N.F.C. wrote the manuscript, with contributions from all authors.

Corresponding authors

Correspondence to Nicholas F. Chilton or David P. Mills.

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The authors declare no competing interests.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–80, Discussion and Tables 1–20.

Supplementary Data 1

Crystallographic data for compound 1; CCDC 1951767

Supplementary Data 2

Crystallographic data for compound 2; CCDC 1951768

Supplementary Data 3

Crystallographic data for compound 3; CCDC 1951769

Supplementary Data 4

Crystallographic data for compound 4; CCDC 1951770

Supplementary Data 5

Crystallographic data for compound 5; CCDC 1951771

Supplementary Data 6

Crystallographic data for compound 6; CCDC 1951772

Supplementary Data 7

Crystallographic data for compound 7; CCDC 1951773

Supplementary Data 8

Crystallographic data for compound 8; CCDC 1951774

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Goodwin, C.A.P., Giansiracusa, M.J., Greer, S.M. et al. Isolation and electronic structures of derivatized manganocene, ferrocene and cobaltocene anions. Nat. Chem. 13, 243–248 (2021).

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