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

Abstract

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-C₂B₈H₉ (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-C₂B₈H₈ (3d). In contrast, the reaction between [arachno-4-CB₈H₁₃]⁻ anion (1⁻) and PhC₂H produces a mixture of the closo anions [1-CB₇H₈]⁻ (4⁻) and [1-CB₆H₇]⁻ (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.