Electrophilic Halogenation of closo-1,2-C 2 B 8 H 10 .

Initial studies on electrophilic halogenation of the dicarbaborane closo-1,2-C2 B8 H10 (1) have been carried out to reveal that the substitution takes place at B7 and B10 vertexes, which are the most removed from the CH positions. The course of the halogenation is strongly dependent on the nature of the halogenation agent and reaction conditions. Individual reactions led to the isolation of the monosubstituted compounds 1,2-C2 B8 H9 -10-X (2) (where X = F, I) and 1,2-C2 B8 H9 -7-X (3) (where X = Cl, I). Disubstituted carboranes 1,2-C2 B8 H8 -7,10-X2 (4) (where X = Cl, Br, I) were obtained under more forcing conditions. Individual halo derivatives were characterized by mass spectrometry and high-field NMR (11 B,1 H,13 C) spectroscopy combined with two-dimensional [11 B-11 B]-COSY,1 H{11 B(selective)}, and [11 B-1 H]-correlation NMR techniques. All of the derivatives bearing a halogen substituent in the B10 position exhibit a remarkable antipodal13 C and1 H NMR shielding at the CH1 vertex, increasing in the order H < I < Br < Cl < F. The structures of 1,2-C2 B8 H8 -7,10-X2 derivatives (where X = Cl, I, 4b,d) were established by X-ray diffraction analyses.