Alumazene adducts with acetonitrile: Structure and thermal stability

Abstract

Lewis acid-base adducts of the “inorganic analog of benzene” alumazene [{2,6-(i-Pr)2C6H3NAlMe}3] (1) with acetonitrile (CH3CN, acn) and deuteroacetonitrile (CD3CN, d3-acn) were synthesized, spectroscopically characterized, and their molecular structures were elucidated by the X-ray diffraction analysis as a bis-adduct 1(acn)2 and a tris-adduct 1(d3-acn)3. The thermodynamics of complex formation was investigated experimentally and theoretically. Thermodynamic characteristics of process 1(acn)3·acn (s) = 1(acn)2 (s) + 2 acn (g) in the temperature range 294–370 K have been derived from the vapor pressure–temperature dependence measurements by the static tensimetric method. It is shown that above 435 K in the presence of 1 gaseous acn undergoes irreversible polymerization reaction. Quantum chemical computations at B3LYP/6-311G(d,p) level of theory have been performed for the 1(acn)n and model complexes of [(HAlNH)3] (1m), 1m(acn)n (n = 1–3). Obtained results indicate that for the gas phase adducts upon increasing the number of acn ligands the donor-acceptor Al–N(acn) distances increase in accord with decrease of the donor-acceptor bond dissociation energies.