Sepulchrate: Four decades on

The report of the synthesis of the complex [(1,3,6,8,10,13,16,19-octaazabicyclo[6.6.6]icosane)cobalt(III)] chloride ([Co(sep)]Cl3) in 1977 was innocuously titled “A macrobicyclic nitrogen cage for metal ions”. The short, two page, manuscript reported the assembly of an encapsulating ligand through a series of small ring closures around the ubiquitous [Co(en)3]3+ ion, resulting in the ready isolation of the complex of the octaazacryptate termed « sepulchrate » (sep). The scope of this seemingly simple chemistry, and the extension of it over the past four decades, was prophesied in this first paper. Herein, we review the extensions of this chemistry, from the basic coordination chemistry to practical applications, and illustrate the fact that apparently simple chemistry can lead to diverse and in many ways revolutionary outcomes.

Graphical abstractThe synthesis of the macrobicyclic nitrogen cage complex sepulchrate ([(1,3,6,8,10,13,16,19-octaazabicyclo[6.6.6]icosane)cobalt(III)] chloride, [Co(sep)]Cl3), through a series of small ring closures around the ubiquitous [Co(en)3]3+ ion, was the forerunner to an expansive range of chemistry. The scope of this discovery, and the extension of it over the past four decades, from basic coordination chemistry to practical applications, has illustrated the potential for apparently simple chemistry to lead to potentially revolutionary outcomes.Figure optionsDownload full-size imageDownload as PowerPoint slide