Heteroatom-Based Diradical(oid)s

Heteroatom-centered diradical(oid)s have been in thefocus of molecularmain group chemistry for nearly 30 years. During this time, the diradicalconcept has evolved and the focus has shifted to the rational designof diradical(oid)s for specific applications. This review articlebegins with some important theoretical considerations of the diradicaland tetraradical concept. Based on these theoretical considerations,the design of diradical(oid)s in terms of ligand choice, steric, symmetry,electronic situation, element choice, and reactivity is highlightedwith examples. In particular, heteroatom-centered diradical reactionsare discussed and compared with closed-shell reactions such as pericyclicadditions. The comparison between closed-shell reactivity, which proceedsin a concerted manner, and open-shell reactivity, which proceeds ina stepwise fashion, along with considerations of diradical(oid) design,provides a rational understanding of this interesting and unusualclass of compounds. The application of diradical(oid)s, for examplein small molecule activation or as molecular switches, is also highlighted.The final part of this review begins with application-related detailsof the spectroscopy of diradical(oid)s, followed by an update of theheteroatom-centered diradical(oid)s and tetraradical(oid)s publishedin the last 10 years since 2013.

Automated summary

Heteroatom-centered diradical(oid)s have been the focus of molecular main group chemistry for the past 30 years, with a shift towards rational design for specific applications. Theoretical considerations and examples are presented to highlight the design of diradical(oid)s, including ligand choice, steric, symmetry, electronic situation, element choice, and reactivity. The review also discusses heteroatom-centered diradical reactions, their comparison with closed-shell reactions, and the application of diradical(oid)s in small molecule activation and molecular switches. Lastly, recent developments in spectroscopy and the study of heteroatom-centered diradical(oid)s and tetraradical(oid)s published since 2013 are summarized.