Synthesis of bipyridine‐linked dimers of azanonaborane: electronic absorption and molecular‐orbital calculations

A new class of azanonaborane–bipyridine derivatives was synthesized from the reaction of bidentate nitrogen ligands with the azanonaborane cluster [(RNH 2 )B 8 H 11 NHR] in benzene under reflux. The exchange of the exo ‐amino ligand by bipyridine derivatives is a convenient route to yield a dimer of the azanonaborane cluster in good yield. Thus, 4,4′‐bipyridine (PyPy) and trans ‐1,2‐di‐(4‐pyridyl)‐ethene (PyPy) replace the exo ‐NH 2 R unit to give [(PyPy)B 8 H 11 NHR] or [RHNH 11 B 8 PyPyB 8 H 11 NHR] and [(PyPy)B 8 H 11 NHR] or [RHNH 11 B 8 PyPyB 8 H 11 NHR] respectively as colored products due to electronic interaction between the {B 8 N} unit and the bonded bipyridine units. This interaction has been investigated by UV–vis spectroscopy and by AM‐1 molecular‐orbital calculations. In the case of [(PyPy)B 8 H 11 NHR], the 1 H and 13 C NMR analysis of the products revealed two isomeric forms ( cis and trans ). This is attributed to thermal cis–trans isomerization. Copyright © 2003 John Wiley & Sons, Ltd.