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

Abstract

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 www.ccdc.cam.ac.uk/structures. Raw research data files supporting this publication are available from Mendeley Data at https://doi.org/10.17632/rzzpcwgkx5.1. Apart from the datasets mentioned, all other data supporting the findings of this study are available within the Article and Supplementary Information.

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Acknowledgements

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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Contributions

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.

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

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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. (2020). https://doi.org/10.1038/s41557-020-00595-w

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