The Photoisomerization and Photosubstitution Reactions of the Ruthenium Cluster HRu3(Co)10(μ-Coch3)

Friedman, Alan E.; Ford, Peter C.

doi:10.1007/978-3-642-72666-8_38

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“…This is particularly evident in their photochemical properties where most information has been obtained for simplest tri- and tetrametal clusters. The mechanistic features of photochemical transformations occurring in these polynuclear complexes have been studied either by the matrix isolation technique − or by a photokinetic approach based on the treatment of quantum yield dependence on the concentration of reaction components. − These days, direct information about the chemical behavior of transient species formed after photoexcitation can be obtained by flash photolysis experiments. However, quantitative data of this sort are rarely found in the transition metal cluster literature. ,, To some extent this lack of information about transient species formed after photoexcitation of the polynuclear complexes is due to the fact that the UV−vis probe techniques commonly used in flash photolysis experiments carry minimal structural information.…”

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confidence: 99%

Reaction Intermediates in the Solution Photochemistry of a Tetrarhodium Carbonyl Cluster: FTIR Structural Characterization and Transient Kinetics

et al. 2003

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The photochemistry of the tetranuclear rhodium carbonyl cluster, Rh 4 (CO) 12 , in heptane solution has been studied using pulsed laser photoexcitation coupled to time-resolved step-scan FTIR spectrometry. It was found that excitation of the cluster with 266 nm light results in CO dissociation to form a Rh 4 (CO) 11 (Solv) species, transformations of which were observed in the nanosecond time domain. Monitoring the reaction course revealed the presence of two successive transients, I and II, which eventually reform the parent cluster. The FTIR spectrometric study showed that these transients represent two isomeric forms of the Rh 4 (CO) 11 (Solv) species. The second transient exhibits the structure typical of ground-state substituted Rh 4 (CO) 11 (L) derivatives with the solvent molecule in an axial position of the basal plane of the metal tetrahedron. The first isomer is a "nonequilibrium" form of the same species where the solvent molecule occupies either a radial site at the basal rhodium triangle or a vacancy at the apical rhodium atom. The kinetics of the reaction sequence is consistent with a unimolecular isomerization of I into II and trapping of the latter by CO evolved at earlier stage of reaction. In the presence of excess CO in the reaction mixture the first transient is effectively scavenged to form Rh 4 (CO) 12 . The kinetic parameters of the isomerization process and the trapping of I by CO have been determined.

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