Monocarbaborane Chemistry: Cage Opening of nido ‐1‐CB 8 H 12 by Tertiary Bases − an Example of a Straightforward nido → arachno Transformation; Isolation of a New Series of 4‐L‐ arachno ‐5‐CB 8 H 12 Compounds (L = NMe 3 , NEt 3 , and Quinoline)

Room‐temperature reactions between the carborane nido ‐1‐CB 8 H 12 ( 1 ) and selected tertiary Lewis bases [L = NMe 3 , NEt 3 , and quinoline (quin)] in CH 2 Cl 2 at room temperature for 24 h resulted in the isolation of a series of 4‐L‐ arachno ‐5‐CB 8 H 12 compounds ( 2 ; L = NMe 3 , 2a , L = NEt 3 , 2b and L = quin, 2c ). This main reaction mode can be classified as a straightforward nido → arachno transformation and was characterized by a cage opening of the original pentagonal face in 1 by L at the bridging site adjacent to the carbon apex with the formation of a hexagonal open face. The formation of 2a was clean, whereas that of 2c was accompanied by formation of the closo ‐[4‐CB 8 H 9 ] − ( 3 ) anion as a side‐product. The first representative of the zwitterionic 1‐L‐ closo ‐4‐CB 8 H 8 ( 4 ) series, 1‐quin‐ closo ‐4‐CB 8 H 8 ( 4c ), was isolated as another side product from the quinoline reaction. The structure of compound 2b was determined by an X‐ray diffraction analysis and the constitution of all compounds is consistent with the results of mass spectrometry. Multinuclear ( 1 H, 11 B, and 13 C), two‐dimensional [ 11 B‐ 11 B]‐COSY, and 1 H{ 11 B(selective)} magnetic resonance measurements lead to complete assignments of all resonances and are in excellent agreement with the structures proposed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)