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New J. Chem., 2005, 29, 1147 - 1151, DOI: 10.1039/b509050d
Conformational dynamics of Cu(I) complexes of tripodal ligands: steric control of molecular motion
Jing Zhang, Kam Siu, Chin H. Lin and James W. Canary
The dynamics of molecular conformational changes for Cu(I) complexes of two tripodal ligands were studied. Variable-temperature NMR and circular dichroism in combination with two-dimensional NMR experiments were employed to determine the structural and energetic details of a dynamic process in which one of three arms dissociates from coordination to Cu(I). Dissociation was triggered by addition of a strongly coordinating anion (SCN–). One-electron oxidation to the Cu(II) complex returned coordination of all three ligand arms. The observed phenomena were dependent upon steric crowding; addition of a single methyl group to one arm resulted in marked differences in behavior. The CuSCN and CuPF6 complexes of tris(2-quinolylmethyl)amine (TQA) and the CuPF6 complex of 1-(quinolin-2-yl)-N,N-bis(quinolin-2-ylmethyl)ethanamine (MeTQA) did not give any evidence for differences in coordination over the temperature range 0–35 °C, while CuI(MeTQA)NCS demonstrated marked differences in NMR but not CD spectra over this temperature range. In the latter complex, two diastereotopic arms displace each other with a transition energy of 14.0 kcal mol–1. The structure of the arm-dissociated complex contains a higher degree of stereochemical complexity than the tetradentate complexes.
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