Crystal structures of the Cu(I)/Cu(II) complexes of the pentadentate nitrogen-bonding Schiff-base ligand, $\{$bis-2,6- (1-(2-pyridin-2-ylethylimino)ethyl) pyridine$\}$, (Cu$\sp{\rm I/II}$(py)$\sb2$DAP) $\sp{\rm n+}$, 1, and of the similar ligand, $\{$bis-2,6- (1-(2-imidazol-4yl-ethylimino)ethyl) pyridine$\}$, (Cu$\sp{\rm I}$(imidH)$\sb2$DAP$\sp+$, 2, have been solved as the tetrafluorobrorate salts. The complexes are all pentacoordinate about the copper center. The crystal structure of the tetracoordinate isomer of 1, the Cu(I) complex of $\{$2- (1-(2-imidazol-4yl-ethylimino)ethyl) -6- ((1-tetrahydropyrido (3,4) imidazol)ethyl) pyridine$\}$, (Cu$\sp{\rm I}$(imidH)(imidH)$\sp\prime$DAP) $\sp{\rm n+}$, 4, has also been solved as the tetrafluoroborate salt.
The kinetics of the electron self-exchange for the two couples (Cu$\sp{\rm I/II}$(py)$\sb2$DAP) $\sp{\rm n+}$ and (Cu$\sp{\rm I/II}$(imidH)$\sb2$DAP) $\sp{\rm n+}$ has been studied by dynamic NMR, and the kinetics opf electron cross-exchange has also been investigated by reducing (Cu$\sp{\rm II}$(py)$\sb2$DAP) $\sp{2+}$ with the two similar complexes, 2, (Cu$\sp{\rm I}$(imidH)$\sb2$DAP) $\sp+$, and 3, (Cu$\sp{\rm I}$(imidR)$\sb2$DAP) $\sp+$, where R = p-xylyl, and monitoring the reactions with stopped-flow trechniques. These measured rates have been correlated by Marcus theory, and the good agreement suggests an outer-sphere electron transfer mechanism, although the possibility of an inner sphere electron-transfer mechanism has not been ruled out on the basis of ligand substitution kinetics studies and solution phase structural probes for complexes 1 and 2. These electron exchange results are apparently the first to be reported for synthetic Cu(I)/Cu(II) couples in which the coordination number is likely the same in the two oxidation states.
(Cu$\sp{\rm I}$(imidH)$\sb2$DAP) $\sp+$, 2, has been previously proposed to form a reversibly-bound dioxygen adduct, which, under removal of the dioxygen, regenerates (Cu$\sp{\rm I}$(imidH)$\sb2$ DAP) $\sp+$. This regeneration step has now been determined to proceed by a route not related to reversible coordination of O$\sb2$, but, instead, by a more complicated redox pathway.
| Identifer | oai:union.ndltd.org:RICE/oai:scholarship.rice.edu:1911/16145 |
| Date | January 1987 |
| Creators | Goodwin, John Alan |
| Contributors | Stanbury, David M., Wilson, Lon J. |
| Source Sets | Rice University |
| Language | English |
| Detected Language | English |
| Type | Thesis, Text |
| Format | 275 p., application/pdf |
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