Unusual interaction of alkynes with nine-vertex arachno-monocarbaboranes 4-CB8H14 and [4-CB8H13]-

Alkynes R1R2C2 react with the neutral monocarbaborane arachno-4-CB8H14 (1) at elevated temperatures (115-120 °C) under the formation of the derivatives of the ten-vertex dicarbaborane nido-5,6-C2B8H12 (2) of general formula 9-Me-5,6-R1,R2-nido-5,6-C 2B8H9 (where R1,R2 = H,H 2a; Me,Me 2b; Et,Et 2c, H,Ph 2d, and Ph,Ph 2e) in moderate yields (26-52%). Side reaction with PhC2H also yields 1-Ph-6-Me-closo-1,2-C 2B8H8 (3d). In contrast, the reaction between [arachno-4-CB8H13]- anion (1-) and PhC2H produces a mixture of the closo anions [1-CB7H 8]- (4-) and [1-CB6H 7]- (5-) (yields 32 and 24%, respectively). Individual compounds were isolated and purified by liquid chromatography and characterized by NMR spectroscopy (11B, 1H and 13C) combined with two-dimensional [11B- 11B]-COSY and 1H-{11B(selective)}NMR techniques. © The Royal Society of Chemistry 2007.