Sheldon Shore, Small Boranes, and Ammonia

Abstract

Although trimethylamine [(CH3)3N] and ammonia [H3N] are both recognized as classic Lewis bases, their reactions with classic Lewis acid borane [BH3 from diborane] was very different. Trimethylamine gave expected trimethylamine borane [(CH3)3NBH3] while ammonia gave a product called the diammoniate of diborane. Its structure was shown to be [H2B(NH3)2]+[BH4]- in late nineteen fifties. The Compound [H2B(NH3)2]+[BH4]- can be viewed as a classic coordination compound in which four-coordinate boron +3 ions are coordinated to hydride ion and ammonia molecule as ligands. It is noted that CoCl2 reacts with (CH3)3N and with NH3 in different ways. The anomaly is in bases, not borane acid. The paper discusses early studies on the diammoniate of diborane and emphasizes how continuing work done by Sheldon Shore at Ohio State University extended work on boranes and answered here-to-fore vexing structural problems on intermediates in borane and borane-ammonia system. His work made major contributions to synthesis. He worked out techniques to prepare significant quantities of pure [H2B(NH3)2][BH4] and of pure H3NBH3. He also prepared fascinating, theoretically anticipated compounds K2BH3 and K2B2H6. The story, as told, shows how a brilliant, imaginative, and thoughtful person, using superb experimental techniques, has been able to develop a difficult experimental system from black art to sound science. Note: This article was prepared from a talk given by author at a Symposium (8/23/95) honoring Sheldon G. Shore on his sixty-fifth birthday. Dr. Shore is Charles H. Kimberly Professor of Chemistry at Ohio State University.