Abstract
Tri-1-naphthylborane (TNB) has been reduced to the anion radical (TNB •−) by 1.55% sodium amalgam in dimethoxyethane (DME). The ESR spectrum consists of 14 poorly-resolved lines based on an 11B quartet of 7.2 G. TNB •− is stable in DME but not in hexamethylphosphoramide. Reduction of TNB by 40% amalgam and sodium metal proceeds to the dianion, and the dianion decomposes to produce, ultimately, the naphthalene anion radical. Reduction of TNB may be complicated by reactions of TNB with water and oxygen. TNB forms a complex with water, and the complex is not reduced by 1.5% amalgam. Therefore, attempts to prepare TNB •− in dilute solutions with this amalgam may be unsuccessful if the solvent is not well dried. TNB undergoes light-catalyzed reaction with oxygen and two of the products are 1,1′-binaphthyl and naphthalene. Consequently, reduction of TNB solutions which have been left standing in air may give the anion radical of 1,1′-binaphthyl (BN •−) instead of TNB •−. BN •− is stable in DME solution, except in the presence of excess sodium, in which case decomposition (presumably via the dianion) occurs and the naphthalene anion radical is formed.
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