Studies in Solution and the Solid State of Coordination Compounds Derived from LiBH4, NaBH4, and Bidentate Aromatic Amines

Abstract

AbstractThe mixture of 2,2′‐bipyridylamine, 2,2′‐bipyridine, 1,10‐phenanthroline, 1,2‐phenylendiamine, and 1,4‐phenylendiamine each with LiBH4 and NaBH4 in a 1:1 molar ratio in THF yields seven new complexes of the type MBH4·L‐THF and one complex of the type MBH4·L. These compounds were characterized by IR and NMR spectroscopy and X‐ray single‐crystal structure determinations. In the solid state, the [BH4]– group is bidentate, as deduced from the stretching patterns observed in IR spectra and confirmed by X‐ray single‐crystal structure analysis. NMR spectroscopy showed that all amines act as bidentate ligands and are symmetrically coordinated to the metal cation. Complexes LiBH4‐2,2′‐bipyridine‐THF (1), NaBH4‐2,2′‐bipyridine‐THF (2), LiBH4‐1,10‐phenanthroline‐THF (3), and NaBH4‐1,10‐phenanthroline‐THF (4) have a discrete molecular structure, whereas the complexes LiBH4‐1,2‐phenylendiamine‐THF (5), NaBH4‐1,2‐phenylendiamine‐THF (6), LiBH4‐2,2′‐dipyridilamine (7), and LiBH4‐1,4‐phenylendiamine‐THF (8) have polymeric structures in the solid state. N‐borane‐dipyridylamine adduct 9 was isolated from an aged solution of 7. IR spectroscopy of the new complexes showed that the structures of complexes 1, 3, 4, and 6 are maintained in the solid state and in solution. A rotational barrier for the [BH4]– group of less than 38 KJ mol–1 was estimated for some of the new complexes.