This review covers all aspects of 9-borafluorene chemistry, from the first attempted synthesis in 1960 to the present. This class of molecules consists of a tricyclic system featuring a central antiaromatic BC 4 ring with two fused arene groups. The synthetic routes to all 9-borafluorenes and their adducts are presented. The Lewis acidity and photophysical properties outlined demonstrate potential utility as sensors and in electronic materials. The reactivity of borafluorenes reveals their prospects as reagents for the synthesis of other boron-containing molecules. The appealing traits of 9-borafluorenes have stimulated investigations into analogues that bear different aromatic groups fused to the central BC 4 ring. Finally, we offer our views on the challenges and future of borafluorene chemistry.
The synthesis of tris(ortho-carboranyl)borane (BoCb 3 ), a single site neutral Lewis superacid, in one pot from commercially available materials is achieved. The high fluoride ion affinity (FIA) confirms its classification as a Lewis superacid and the Gutmann-Beckett method as well as adducts with Lewis bases indicate stronger Lewis acidity over the widely used fluorinated aryl boranes. The electron withdrawing effect of ortho-carborane and lack of pi-delocalization of the LUMO rationalize the unusually high Lewis acidity. Catalytic studies indicate that BoCb 3 is a superior catalyst for promoting CÀ F bond functionalization reactions than tris(pentafluorophenyl)borane [B(C 6 F 5 ) 3 ].
The stoichiometric reactions of antimony trichloride, trimethylsilyl trifluoromethanesulfonate, and diiminopyridine ligands lead to the formation of N,N′,N″-chelated SbCl2 cationic complexes. Methyl, phenyl substituents on the imine carbons of the ligand...
The reactions of bismuth(III) chloride, a diiminopyridine ligand, and various stoichiometries of trimethylsilyl trifluoromethanesulfonate (TMSOTf) generated the first bismuth complexes with this ubiquitous ligand. The reaction with 0.5 equivalents of TMSOTf furnished a chloride bridged Bi 2 Cl 5 + complex, with each bismuth center complexed by a ligand; 1 equivalent yielded a BiCl 2 + chelated species; and 2 equivalents provided a ligated BiCl 2+ cation.
The Lewis superacid, bis(1‐methyl‐ortho‐carboranyl)borane, is rapidly accessed in two steps. It is a very effective hydroboration reagent capable of B−H addition to alkenes, alkynes, and cyclopropanes. To date, this is the first identified Lewis superacidic secondary borane and most reactive neutral hydroboration reagent.
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