Solid state and solution characterization of chiral, conformationally mobile tripodal ligands

The synthesis of the ligands N,N-bis[(2-pyridyl)methyl]-1-(2-pyridyl)ethana mine (1, alpha-MeTPA), N,N-bisl[6-phenyl-2-pyridyl)methyl]-1-(2-pyridyl)eth anamine (2, alpha-MePh(2)TPA), N,N-bis[(2-quinolyl)methyl]-1-(2-pyridyl)eth anamine, (3, alpha-MeBQPA), and N,N-bis[(2-pyridyl)]methyl(phenyl)(2-pyridy l)methanamine (4, alpha-PhTPA) is described. The ligands form chiral, pseud o C-3-symmetric complexes with Zn-II and Cu-II salts that possess an availa ble electrophilic coordination site. X-ray crystallographic structures of t he complexes [Zn(alpha-MeTPA)Cl] (ClO4), [Zn(alpha-MeBQPA)Cl](ClO4), and [Z n(alpha-PhTPA)Cl](ClO4) show that the spatial arrangement of the three pyri dyl groups resembles a propeller whose directional sense is controlled by a substituent on one methylene arm. Chiroptical measurements provide support ing information that the complexes maintain similar structures in solution. Monte Carlo/stochastic dynamics (MC/SD) simulations of the [Zn(L)Cl](+) co mplexes indicate that only two conformers are populated at normal temperatu res, suggest the presence of a synchronicity in the movement of the heteroa romatic rings during conformer interconversions, and provide an estimate of the energy difference between the conformers.