| 17896334 |
Spies P, Frohlich R, Kehr G, Erker G, Grimme S: Structural importance of secondary interactions in molecules: origin of unconventional conformations of phosphine-borane adducts. Chemistry. 2008;14(1):333-43.
The series of phosphine-borane adducts, Ph2 (H3C--C [triple chemical bond] C) P--B (C6F5) 3 (8 c), Ph (H3C--C [triple chemical bond] C) 2P--B (C6F5) 3 (8 b) and (H3C--C [triple chemical bond] C) 3P--B (C6F5) 3 (8 a), was prepared. The X-ray crystal structure analyses revealed close to eclipsed conformations for all members of this series with average dihedral angles theta (C-P-B-C) of 8.1 degrees (8 c), 12.3 degrees (8 b) and 20.3 degrees (8 a). Quantum chemical analysis of these compounds revealed the importance of a subtle interplay between competing attractive and repulsive secondary interactions, causing the surprising eclipsed conformational preference for systems of this degree of complexity. Some cyclic phosphine-borane adducts were studied for comparison. |
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