Diazotization of the amino acid [closo-1-CB₉H ₈-1-COOH-6-NH₃] and reactivity of the [closo-1-CB ₉H₈-1-COO-6-N₂]^- anion

A comparative study of the reactivity of dinitrogen acids [c1oso-1-CB ₉H₈-1-COOH-10-N₂](3[l0])and [closo-1-CB ₉H₈-1-COOH-6-N₂](3[6]) was conducted by diazotization of a mixture of amino acids [closo-1-CB₉H ₈-1-COOH-6-NH₃] (l[6])and [closo-1-CB₉H ₈-1-COOH-10-NH₃](l[l0])with NO⁺BF ₄^- in the presence of a heterocyclic base (pyridine, 4-methoxypyridine, 2-picoline, or quinoline). The 10-amino acid l[l0] formed an isolable stable 10-dinitrogen acid 3[l0],while the 6-dinitrogen carboxylate 3[6]^- reacted in situ, giving products of N-substitution at the B6 position with the heterocyclic solvent (4[6]). The molecular and crystal structures for pyridinium acid 4[6]a were determined by X-ray crystallography. The electronic structures and reactivity of the 6-dinitrogen derivatives of the {1-CB₉} cluster were assessed computationally at the B3LYP/6-31G(d,p) and MP2/6-31G(d,p) levels of theory and compared to those of the 10-dinitrogen, 2-dinitrogen, and 1-dinitrogen analogues.