This invention relates to compositions and methods for achieving the efficient aziridination of organic molecules, especially olefins. More specifically, the invention is directed to a mild, selective, and efficient aziridination protocol that involves catalysis by a mixed-valent dirhodium(II,III) catalyst (Rh25+). Especially preferred sources for forming such mixed-valent dirhodium(II,III) catalyst (Rh25+) are dirhodium(II) carboxamidates, such as dirhodium(II) caprolactamate, and their derivatives and analogues.