The nature and role of bridged carbonyl intermediates in theultrafast photo-induced rearrangement of Ru3(CO)12. Page: 4 of 41
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not able to stabilize the intermediate, such as alkanes, it is observed that the starting material is
eventually reformed.6'16 In the presence of 7-backbonding ligands, for example CO and phosphines,
fragmentation of the photoexcited cluster and formation of three identical monomer units each
containing a 7-backbonding molecule is observed.6-''16 Interestingly, in the presence of molecules, such
as THF, that can only donate electron density to the metal in a 6-bonding fashion, photofragmentation is
blocked and the starting material is regenerated; the reasons for this behavior remain unclear.68
The short wavelength, high energy peak at 238 nm in the UV-vis absorption spectrum of Ru3(CO)12
has been characterized as a metal to ligand charge transfer (MLCT) excitation that ultimately results in
loss of one carbonyl group in solution or in a matrix. '14 Again, the solvent molecules play a key role in
determining the final photoproducts. Non-coordinating solvents such as alkanes cannot stabilize the
coordinatively unsaturated cluster so the complex is internally stabilized by a bridging carbonyl
between two of the metal atoms (Figure 1, complex II). The bridged carbonyl has been observed in a 90
K matrix and in solution in the 1830-1850 cm1 region.3'10 In coordinating solvents, both 6-donating and
7-backbonding, the solvent molecule binds and forms the photo-substituted product Ru3(CO)iiS (S =
solvent molecule). The lifetime of this product depends on its thermodynamic stability with respect to
the starting material and the availability of CO to replace the solvent S and reform the original
Despite the wealth of information provided by previous studies, some particularly important details of
the photochemistry of Ru3(CO)12 are unresolved. First, the timescales of formation and decay for the CO
loss transient have not been determined and the structures of both bridged carbonyl complexes
discussed above are uncertain. Second, a clear picture of the structure and dynamics of the cluster in 6-
donating solvents does not exist. Finally, a careful perusal of the literature exposes an inconsistency
concerning the number and type of photoproducts formed with disparate wavelengths of excitation as is
discussed below. Photofragmentation products are formed upon excitation with both visible and
ultraviolet light (in the presence of 7-backbonding ligands) and a constant quantum yield between 313
and 436 nm was observed.''g'16 In contrast, the quantum yields for photosubstitution products resulting
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Glascoe, Elizabeth A.; Kling, Matthias F.; Shanoski, Jennifer E. & Harris, Charles B. The nature and role of bridged carbonyl intermediates in theultrafast photo-induced rearrangement of Ru3(CO)12., article, September 18, 2005; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc874121/m1/4/: accessed October 17, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.