Diazotization of the Amino Acid [closo-1-CB9H8-1-COOH-6-NH3] and Reactivity of the [closo-1-CB9H8-1-COO-6-N2]- Anion

A comparative study of the reactivity of dinitrogen acids [closo-1-CB9H8-1-COOH-10-N-2] (3[10]) and [closo-1-CB9H8-1-COOH-6-N-2] (3[6]) was conducted by diazotization of a mixture of amino acids [closo-1-CB9H8-1-COOH-6-NH3] (1 [6]) and [closo-1-CB9H8-1-COOH-10-NH3] (1[10]) with NO+BF4- in the presence of a heterocyclic base (pyridine,. 4-methoxypyridine, 2-picoline, or quinoline). The 10-amino acid 1[10] formed an isolable stable 10-dinitrogen acid 3[10], 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.