| Abstract
| - A recent experimental investigation in which a salt containing the unusual charge distributionH+ and Na- was synthesized and characterized prompted us to undertake an ab initio theoreticalinvestigation. In the salt synthesized, the H+ is bound to the nitrogen center of an amine and the Na-alkalide is “blocked” from approaching the protonated amine site by steric constraints of a cage structure.Although one expects that the Na- would deprotonate an unprotected R3N−H+ cation, we decided to furtherexplore this issue. Using extended atomic orbital basis sets and Møller−Plesset and coupled-clustertreatments of electron correlation, we examined the relative stabilities of the prototype (Me)3N + NaH,(Me)3N + Na+ + H-, (Me)3N−H+ + Na- , and (Me)3N−Na+ + H- as well as the ion pair complexes (Me)3N−H+···Na- and (Me)3N−Na+···H-. The primary focus of this effort was to determine whether the high-energy(Me)3N−H+···Na- ion pair, which is the analogue of what the earlier workers termed “inverse sodiumhydride”, might be stable with respect to proton abstraction under any reasonable solvation conditions(which we treated within the polarized continuum model). Indeed, we find that such ion pairs are metastable(i.e., locally geometrically stable with a barrier to dissociation) for solvents having dielectric constants below∼2 but spontaneously decompose into their constituent ions for solvents with higher dielectric constants.We suggest that amines with large proton affinities and/or metals with weaker MH bond strengths shouldbe explored experimentally.
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