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

• Published in: Nature chemistry 2021-03, Vol.13 (3), p.243-248
• Main Authors: Goodwin, Conrad A. P., Giansiracusa, Marcus J., Greer, Samuel M., Nicholas, Hannah M., Evans, Peter, Vonci, Michele, Hill, Stephen, Chilton, Nicholas F., Mills, David P.
• Format: Article
• Language: English
• Subjects: 639/638/263; 639/638/263/406; 639/638/563/606; 639/638/563/979; 639/638/911; Analytical Chemistry; Anions; Biochemistry; Cations; Chemistry; Chemistry and Materials Science; Chemistry/Food Science; Cobalt; Coordination compounds; Electrochemistry; Inorganic and Physical Chemistry; Inorganic Chemistry; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Ligands; Low temperature; Manganese; Organic Chemistry; Physical Chemistry
• ISSN: 1755-4330; 1755-4349
• DOI: 10.1038/s41557-020-00595-w

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 3 d metallocenates, which consist of anionic complexes of a metal centre (manganese, iron or cobalt) sandwiched between two bulky Cp ttt ligands (where Cp ttt is {1,2,4-C 5 H 2 t Bu 3 }). 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 19 e − derivatized ferrocene anion. Unlike ferrocene and its cationic counterpart ferrocenium, the ferrocene monoanion is an unusual species that has been observed through low-temperature electrochemical studies. Now, a family of isostructural 3 d metallocenates has been isolated that consists of a manganocene, a cobaltocene and a high-spin ferrocene anion stabilized by cyclopentadienyl ligands bearing bulky aliphatic groups.