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A new ambient-temperature, catalyst-free reaction between ammonia borane and tetrahydrofuran borane produces aminodiborane via the formation of a dihydrogen bond and subsequent molecular hydrogen elimination. The facile synthesis of aminodiborane will make this long-sought active chemical reagent readily available for both inorganic and organic reactions. From aminodiborane, an inorganic butane analogue, NH(3)BH(2)NH(2)BH(3), was prepared, and its single-crystal structure displayed a gauche rather than an anti form conformation.

The mechanism of formation of ammonia borane (NH(3)BH(3), AB) and the diammoniate of diborane ([H(2)B(NH(3))(2)][BH(4)], DADB) in the reaction between NH(3) and THF·BH(3) was explored experimentally and computationally. Ammonia diborane (NH(3)BH(2)(μ-H)BH(3), AaDB), a long-sought intermediate proposed for the formation of DADB, was directly observed in the reaction using (11)B NMR spectroscopy. The results indicate that dihydrogen bonds between the initially formed AB and AaDB accelerate the formation of DADB in competition with the formation of AB.

New lanthanide-transition-metal (Ln-M) compounds were prepared and the structural relationships of the metal combinations were discerned. Numerous compounds derived from divalent or trivalent lanthanides and from transition metals in groups 7-11 were isolated. Three different types of interactions were observed: (1). Ln-M direct bonds, (2). ionic associations, and (3). carbonyl or cyanide linkers between the metals. These assorted Ln-M interactions influence the assembly of the compounds, and discrete molecules or polymeric arrays were encountered. The extended arrays spanning one, two, and three dimensions can function as heterogeneous catalyst precursors. Two classes of systems, Ln-M carbonyls and cyanides, are described.

A dihydrogen bond (DHB) is an electrostatic interaction between a protonic hydrogen and a hydridic hydrogen. Over the past two decades, researchers have made significant progress in the identification and characterization of DHBs and their properties. In comparison with conventional hydrogen bonds (HBs), which have been widely used in catalysis, molecular recognition, crystal engineering, and supramolecular synthesis, chemists have only applied DHBs in very limited ways. Considering that DHBs and conventional HBs have comparable strength, DHBs could be more widely applied in chemistry. Over the past several years, we have explored the impact of DHBs on amine borane chemistry and the syntheses and characterization of amine boranes and ammoniated metal borohydrides for hydrogen storage. Through systematic computational and experimental investigations, we found that DHBs play a dominant role in dictating the reaction pathways (and thus different products) of amine boranes where oppositely charged hydrogens coexist for DHB formation. Through careful experiments, we observed, for the first time, a long-postulated reaction intermediate, ammonia diborane (AaDB), whose behavior is essential to mechanistic understanding of the formation of the diammoniate of diborane (DADB) in the reaction of ammonia (NH3) with tetrahydrofuran borane (THF·BH3). The formation of DADB has puzzled the boron chemistry community for decades. Mechanistic insight enabled us to develop facile syntheses of aminodiborane (ADB), ammonia borane (AB), DADB, and an inorganic butane analog NH3BH2NH2BH3 (DDAB). Our examples, together with those in the literature, reinforce the fact that DHB formation and subsequent molecular hydrogen elimination are a viable approach for creating new covalent bonds and synthesizing new materials. We also review the strong effects of DHBs on the stability of conformers and the hydrogen desorption temperatures of boron-nitrogen compounds. We hope that this Account will encourage further applications of DHBs in molecular recognition, host-guest chemistry, crystal engineering, supramolecular chemistry, molecular self-assembly, chemical kinetics, and the syntheses of new advanced materials.