RhIII-Catalyzed Functionalization of closo-Dodecaborates by Selective B-H Activation: Bypassing Competitive C-H Activation

The closo-dodecaborate dianion is a fundamental icosahedral boron cage with 12 identical B-H vertices. The chemistry and applications of boron clusters have inspired researchers ever since their discovery several decades ago, and the selective modification of the cage positions has remained a major synthetic challenge. A rhodium(III)-catalyzed B-H functionalization-cyclization cascade of closo-dodecaborate amides is reported. The transformations occur chemoselectively at B-H positions in the presence of C-H bonds prone to competitive cyclometalation. Previously inaccessible cage derivatives with B-C(sp(2)) and B-C(sp(3)) bonds as well as a fused diboraoxazole ring are obtained in a one-pot process. The reactions proceed under mild conditions and exhibit complete cage regioselectivity with broad functional group tolerance. These cluster derivatives enable a largely extended investigation of the application of anionic boron clusters in research areas such as photoluminescent materials and medicinal chemistry.