Conformational behavior of 3-borabicyclo[3.3.1]nonanes. Intramolecular p–σ and p–π interactions in 3,7-endo-disubstituted 3-borabicyclo[3.3.1]nonanes

Intramolecular interactions between the unoccupied p-orbital of the boron atom and the σ- (Me) or π-orbital (Ph) of the 7-endo-substituent lead to an unusual stability of the chair–chair conformation in 3-borabicyclo[3.3.1]nonanes. X-ray analysis of 3,7α-dimethyl-3-borabicyclo[3.3.1]nonane (7) and 3-methyl-7α-phenyl-3-borabicyclo[3.3.1]nonane (8), and single point ab initio calculation (B3LYP/6-31G*) of 8 have confirmed the existence of this specific attractive interaction.