A variable bidentate traceless directing group for nickel-catalyzed regioselective B–H poly-chalcogenation of o-carboranes

A nickel-catalyzed direct cage B–H poly-chalcogenation of icosahedral carborane clusters, enabled by a variable bidentate 8-aminoquinoline traceless directing group (TDG), has been developed under oxidant-free and weakly basic conditions, resulting in poly-thiolated/selenylated o-carboranes present in boron delivery agents for boron neutron capture therapy (BNCT). The controllable selectivity of removal and retention of these TDGs was achieved through simple substrate structure modification (C2-substitution in o-carboranes). A wide range of disulfides, diselenides, thiophenols and benzeneselenols, as well as o-carborane substrates, are compatible, generating diversely functionalized o-carboranes with tetra- and tri-chalcogen substitution. The current protocol opens new avenues for oxidant- and strong base-free, base-metal-catalyzed regioselective iterative B–H chalcogenation of carboranes via a variable bidentate TDG strategy.