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)ethanamine ( 1, α-MeTPA), N, N -bis[(6-phenyl-2-pyridyl)methyl]-1-(2-pyridyl)ethanamine ( 2, α-MePh 2 TPA), N, N -bis[(2-quinolyl)methyl]-1-(2-pyridyl)ethanamine, ( 3, α-MeBQPA), and N, N -bis[(2-pyridyl)]methyl(phenyl)(2-pyridyl)methanamine ( 4, α-PhTPA) is described. The ligands form chiral, pseudo C 3 -symmetric complexes with Zn II and Cu II salts that possess an available electrophilic coordination site. X-ray crystallographic structures of the complexes [Zn(α-MeTPA)Cl](ClO 4 ), [Zn(α-MeBQPA)Cl](ClO 4 ), and [Zn(α-PhTPA)Cl](ClO 4 ) show that the spatial arrangement of the three pyridyl groups resembles a propeller whose directional sense is controlled by a substituent on one methylene arm. Chiroptical measurements provide supporting information that the complexes maintain similar structures in solution. Monte Carlo/stochastic dynamics (MC/SD) simulations of the [Zn(L)Cl] + complexes indicate that only two conformers are populated at normal temperatures, suggest the presence of a synchronicity in the movement of the heteroaromatic rings during conformer interconversions, and provide an estimate of the energy difference between the conformers.