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

The 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.