Unconventional Ionic Hydrogen Bonds. 1. Complexes of Quaternary Ions with n- and ?-Donors

Article abstract of DOI:10.1021/ja00288a033

interaction energies are obtained from the clustering of quaternary onium ions with n-donor solvent molecules.The dissociation energies (ΔH^o_D) of Me4N(1+) clustered with the n-donor H2O, MeOH, MeNH2, and Me3N and with the ?-donors benzene and toluene range between 8 and 10 kcal mol^-1.With the weak, bulky n-donor MeCl the interaction is weaker (6.5 kcal mol^-1) while the more polar ligands Me2CO and MeCONMe2 attach strongly (14.6 and 18.0 kcal mol^-1, respectively) to Me4N(1+).Strong interactions, 20-23 kcal mol^-1, are also observed with polyethers and CH3CO-gly-OCH3, indicating polydentate complexing.The attachment energies of ligands to Et4N(1+) are smaller by 2 kcal mol^-1 than those to Me4N(1+).Ab initio calculations show that in the Me4N(1+)*H2O, MeOH, MeNH2, and MeCl complexes the ligands attach electrostatically to a cavity created by protons of three CH3 gropus rather than hydrogen bonding to one proton or to one CH3 group.Both experiment and theory indicate that a second solvent molecule (H2O or CH3OH) attaches preferentially to the first solvent molecule rather than to Me4N(1+).