Stable Carbenes, Nitrenes, Phosphinidenes, and Borylenes: Past and Future

The different modes of stabilization for carbenes are briefly discussed in the context of the discovery of their first stable representatives. Largely because a diversity of stable carbenes are available today, their use has spanned across the chemical sciences, including medicinal and material applications. Much less is known about the isolobal group 15 cousins of carbenes, namely nitrenes and phosphinidenes, given that only one example of each has been isolated. The difficulties associated with their applications are discussed, and possible solutions are presented, As for group 13 element carbenoids, two types are considered: (1) mono(Lewis base)-stabilized borylenes that have been recently isolated and (2) borylenes, the only carbenoids discussed in this article that have eluded the synthetic skills of investigators. This Perspective describes potentially attainable targets, such as monocoordinated aminocarbanions, aminocarbynes, and aminocarbocations, which feature a carbon atom with six, five, and four valence electrons, respectively.