An investigation of the photochemical properties of transition metal arene complexes: Final report for the period July 1, 1983 to June 30, 1987
The photochemical removal of the arene from CpM(eta/sup 6/-arene)/sup +/ was studied for complexes of Fe(II) and Ru(II); (Fe, arene = p-dichlorobenzene, benzene, toluene, d/sub 8/-toluene, p-xylene, mesitylene, durene, pentamethylbenzene, hexamethylbenzene, hexaethylbenzene, and tri-t-butylbenzene; Ru, p-dichlorobenzene, benzene, toluene, mesitylene, pentamethylbenzene, hexamethylbenzene, and tri-t-butylbenzene). Quantum yields were determined. The photoactive state was identified as the distorted a/sup 3/E/sub 1/ ligand field excited state. The excited state energy of the Fe complexes lies about 14,000 cm/sup -1/ above ground state. A theoretical photophysical model was developed to relate the quantum yield for arene release to the rate of arene release. This model predicts a linear correlation between log((phi/1-phi)) and sigma/sub p/, the Hammett parameter if electronic effects at the arene influence the rate of arene substitution. For chloro and methyl substituted arenes (up to 5 substituents for Fe and 6 substituents for Ru), the linear correlation was verified. The Hammett rho parameter is +1.03 and +0.53 for the Fe complexes in CH/sub 2/Cl/sub 2/ and CH/sub 3/CN solution respectively; for the Ru complexes in CH/sub 3/CN solution rho = +1.38. These data indicate a small negative charge builds up at the arene in the transition state for the arene release reaction. Deviations from the linear correlation of log(phi/(1-phi)) with sigma/sub p/ were found for the sterically hindered CpFe(eta/sup 6/-HMB)/sup +/, CpFe(eta/sup 6/-HEB)/sup +/ and CpFe(eta/sup 6/-1,3,5-tri-t-butylbenzene)/sup +/ complexes (HMB = hexamethylbenzene; HEB = hexaethylbenzene). These deviations result from steric interactions that hinder the interaction of nucleophiles in the transition state and ultimately control the quantum yield of arene release for a given complex.
- Research Organization:
- Minnesota Univ., Minneapolis (USA). Dept. of Chemistry
- DOE Contract Number:
- AC02-83ER13103
- OSTI ID:
- 6286123
- Report Number(s):
- DOE/ER/13103-2; ON: DE87014161
- Country of Publication:
- United States
- Language:
- English
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400500* -- Photochemistry
ACETONITRILE
ALKENES
AROMATICS
CHEMICAL REACTIONS
COMPLEXES
CYCLOALKENES
CYCLOPENTADIENE
DECOMPOSITION
DIENES
DISPERSIONS
ENERGY LEVELS
EXCITED STATES
HYDROCARBONS
IRON COMPLEXES
MIXTURES
NITRILES
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
POLYENES
RUTHENIUM COMPLEXES
SOLUTIONS
TRANSITION ELEMENT COMPLEXES