Electron transfer reactions of organometallic compounds

Igor S Zavarine, Purdue University

Abstract

The mixed valence states of the twelve ligand bridged hexaruthenium clusters $\rm Ru\sb3(\mu\sb3$-O)($\mu$-$\rm CH\sb3CO\sb2)\sb6(CO)(L\sp\prime)(\mu$-L)$\rm Ru\sb3(\mu\sb3$-O)($\mu$-$\rm CH\sb3CO\sb2)\sb6(CO)(L\sp{\prime\prime})$ (L = 1,4-pyrazine or 4,4$\sp\prime$-bipyridine; L$\sp\prime$ (or L$\sp{\prime\prime})$ = 4-dimethyl-aminopyridine, pyridine, 4-cyanopyridine, undergo rapid intramolecular electron transfer. The splitting of the reduction waves in cyclic voltammetry depends on the electronic coupling H$\rm\sb{AB}$ between the triruthenium centers, and varies from $<$50 mV to 440 mV. The mixed valence states also exhibit intervalence charge transfer (ICT) bands which provide estimates of H$\rm\sb{AB}$ in the range 6050 cm$\sp{-1}$ to 1310 cm$\sp{-1}.$ The magnitude of the electronic coupling H$\rm\sb{AB}$ strongly influences the IR spectra of the mixed valence states in the $\nu$(CO) region. In the case of relatively weak electronic coupling two $\nu$(CO) bands are clearly resolved. In the case of strong electronic coupling these bands broaden to a single $\nu$(CO) absorption band. These data allow the rate constants, k$\rm\sb{e},$ for electron transfer in the mixed valence states of pyrazine bridged compounds to be estimated by simulating dynamical effects (with Bloch equations) on $\nu$(CO) absorption band shape at $\rm9\times10\sp{11}\ s\sp{-1}$ (L$\sp\prime$ = 4-dimethyl-aminopyridine) and $\rm5\times10\sp{11}\ s\sp{-1}$ (L$\sp\prime$ = 4-pyridine). The less strongly coupled 4,4$\sp\prime$-bipyridine bridged complexes also undergo intramolecular electron transfer slower than the IR vibrational time scale. Asymmetric compounds with different pyridine ligands on two sides show asymmetric spectra. The IR intensity between the peaks for neutral and doubly reduced states correlates well with the rate of electron transfer. The spectra of compounds in which CO was substituted by an isocyanide ligand as well as compounds with L = p-phenylene diisocyanide bridge were shown to exhibit Fermi resonance. The superreducing ability of photogenerated 19e- radicals of the type W(CO)$\rm\sb5(THF)\sp{\cdot-}$ was shown to be attenuated by large reorganizational energies associated with the electron transfer step.

Degree

Ph.D.

Advisors

Kubiak, Purdue University.

Subject Area

Chemistry|Chemistry

COinS