Copper(I) complexes of 1,4-diisopropyl-7-R"-1,4,7-triazacyclononane (R"=2-pyridylmethyl, LPy; 6-methyl-2-pyridylmethyl, L6MePy; 5-methyl-2-pyridylmethyl, L5MePy; 6-phenyl-2-pyridylmethyl, L6PhPy; 2-quinolylmethyl, LQuin were prepared and characterized by CHN analysis, NMR and FTIR spectroscopy, cyclic voltammetry, and mass spectrometry. An X-ray crystal structure of [L6PhPyCu]SbF6 was determined and compared to that previously reported for [LPyCu]O3SCF3; similar distorted trigonal bipyramidal geometries are adopted with the ligands coordinated in η4 fashion. The complexes [LCu]+ (L = L(Py) or L(Quin)) form adducts with CO(g) in which the heterocyclic appendage is displaced. With NO(g), [L(Py)Cu]O3SCF3 reacts in a disproportionation process to yield N2O and [L(Py)Cu(ONO)]O3SCF3, which was structurally defined by X-ray crystallography. Upon reaction with O2(g) at-75°C the Cu (I) complexes of LPy and L5MePy yield trans-1,2-peroxo species [LCuOOCuL]2+ as determined by UV-Vis and resonance Raman spectroscopy. In contrast, spectroscopy indicates that low temperature oxygenation of [L(6PhPy)Cu]SbF6 yields a bis(μ-oxo)dicopper core, postulated to be capped by η3-L6PhPy (pyridyl appendage not coordinated). Decomposition of the trans-1,2-peroxo compounds results in hydroxylation of the ligand at the benzylic position of the heterocyclic appendage, but the bis(μ-oxo) complexes decay to give products resulting from N-dealkylation of the heterocycle arm. The different fates of the Cu(I) complexes of L(Py) and L(5MePy) versus that of L(6PhPy) upon oxygenation may be traced to the coordination of the heterocycle; in the former cases, the pyridyl unit remains coordinated, favoring trans-1,2-peroxo generation, whereas pyridyl dissociation facilitated (6PhPy) by the sterically bulky 6-phenyl group on L yields a [η3-L(6PhPy)Cu]+ fragment amenable to bis(μ-oxo) core formation. The steric properties of the heterocyclic components of the ligands used in this study thus are important determinants of the reactivity of their Cu(I) complexes with small molecules.
Bibliographical noteFunding Information:
We thank the National Institutes of Health (GM47365 to W.B.T. and a postdoctoral fellowship to L.M.B.), the National Science Foundation (National Young Investigator Award to W.B.T.), and the Alfred P. Sloan and Camille & Henry Dreyfus Foundations for financial support. We also thank Dr Carole Toia for assistance.
- Copper complexes
- Dioxygen activation
- Macrocyclic complexes
- Vitric oxide