Photodynamics of [FeFe]-Hydrogenase Model Compounds with Bidentate Heterocyclic Ligands.

Two asymmetrically structured model compounds for the hydrogen-generating [Fe-Fe]-hydrogenase active site were investigated to determine the ultrafast photodynamics, structural intermediates, and photoproducts compared to more common symmetric di-iron species. The bidentate-ligand-containing compounds studied were Fe(μ-SCH)(CO)(bipy), , and Fe(μ-SCH)(CO)(phen), , in dilute room temperature acetonitrile solution and low-temperature 2Me-THF matrix isolation using static FTIR difference and time-resolved infrared spectroscopic methods (TRIR). Ultraviolet-visible spectra were also compared to time-dependent density functional theory (TD-DFT) to ascertain the orbital origins of long wavelength electronic absorption features.

Intramolecular CH Activation and Metallacycle Aromaticity in the Photochemistry of [FeFe]-Hydrogenase Model Compounds in Low-Temperature Frozen Matrices.

The [FeFe]-hydrogenase model complexes [(μ-pdt){Fe(CO)3 }2 ], [(μ-edt){Fe(CO)3 }2 ], and [(μ-mdt){Fe(CO)3 }2 ], where pdt=1,3-propanedithiolate, edt=1,2-ethanedithiolate, and mdt=methanedithiolate, undergo wavelength dependent photodecarbonylation in hydrocarbon matrices at 85 K resulting in multiple decarbonylation isomers. As previously reported in time-resolved solution photolysis experiments, the major photoproduct is attributed to a basal carbonyl-loss species. Apical carbonyl-loss isomers are also generated and may undergo secondary photolysis, resulting in β-hydride activation of the alkyldithiolate bridge, as well as formation of bridging carbonyl isomers.

Rotameric transformations in the photochemistry of TpM(CO)2(η(3)-C3H4R), where Tp = tris(pyrazolyl)borate, M = Mo or W, and R = H or Me.

Low energy photolysis of TpM(CO)2(η(3)-C3H4R), where Tp = tris(pyrazolyl)borate, M = Mo or W, and R = 2-H or 2-Me in PVC matrices at 85 K results in exo/gauche isomerism of the allyl ligand. This transformation comes in contrast to the behaviour observed in cyclopentadienyl analogues which undergo exo/endo isomerism. DFT computations reveal an η(3) → η(1)* → η(3) mechanism for the allyl rotameric interconversion where the η(1)*-allyl intermediate is generated upon MLCT excitation.

Photochemistry of the permanganate ion in low-temperature frozen matrices.

Photolysis of the permanganate anion, MnO4(-), in tetralkylammonium tetrafluoroborate matrices at 85 K results in formation of a single product, the metastable manganese(V) peroxo complex MnO2(η(2)-O2)(-). Although previously unobserved, this peroxo species has been postulated to be an intermediate in the photodecomposition of permanganate, yielding O2 and MnO2(-). Results from variable-temperature and intensity-dependence photolysis experiments in solution, however, suggest that MnO2(η(2)-O2)(-) does not lose O2 thermally or photochemically and is not an intermediate in the photodecomposition reaction.

Photochemically induced intramolecular six-electron reductive elimination and oxidative addition of nitric oxide by the nitridoosmate(VIII) anion.

UV photolysis of the nitridoosmate(VIII) anion, OsO3 N(-) , in low-temperature frozen matrices results in nitrogen-oxygen bond formation to give the Os(II) nitrosyl complex OsO2 (NO)(-) . Photolysis of the Os(II) nitrosyl product with visible wavelengths results in reversion to the parent Os(VIII) complex. Formally a six-electron reductive elimination and oxidative addition, respectively, this represents the first reported example of such an intramolecular transformation.