An investigation of the photochemical properties of transition metal arene complexes: Final report for the period July 1, 1983 to June 30, 1987

Technical Report · Sat Aug 01 00:00:00 EDT 1987

OSTI ID:6286123

Mann, K R

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
• Resource Relation: Other Information: Portions of this document are illegible in microfiche products
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
AROMATICS
COMPLEXES
CYCLOPENTADIENE
IRON COMPLEXES
PHOTOLYSIS
RUTHENIUM COMPLEXES
ACETONITRILE
EXCITED STATES
PHOTOCHEMICAL REACTIONS
SOLUTIONS
ALKENES
CHEMICAL REACTIONS
CYCLOALKENES
DECOMPOSITION
DIENES
DISPERSIONS
ENERGY LEVELS
HYDROCARBONS
MIXTURES
NITRILES
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
POLYENES
TRANSITION ELEMENT COMPLEXES
400500* - Photochemistry