Photochemical organic oxidations and dechlorinations with a μ-oxo bridged heme/non-heme dilron complex

Steady state and laser flash photolysis studies of the heme/non-heme mu-oxo diron complex [(L-6)Fe-III-O-Fe-III-Cl](+) (1) have been undertaken. The anaerobic photolysis of benzene solutions of 1 did not result in the buildup of any photoproduct. However, the addition of excess triphenylphosphine resulted in the quantitative photoreduction of 1 to [(L-6)Fe-II...Fe-II-Cl](+) (2), with concomitant production by oxo-transfer of 1 equiv of triphenylphosphine oxide. Under aerobic conditions and excess triphenylphosphine, the reaction produces multiple turnovers (similar to28) before the diiron complex is degraded. The anaerobic photolysis of tetrahydrofuran (THF) or toluene solutions of 1 likewise results in the buildup of 2. The oxidation products from these reactions included gamma-butyrolactone (similar to15%) for the reaction in THF and benzaldehyde (similar to23%) from the reaction in toluene. In either case, the O-atom which is incorporated into the carbonyl product is derived from dioxygen present under workup or under aerobic photolysis conditions. Transient absorption measurements of low-temperature THF solutions of 1 revealed the presence of an (P)Fe-II-like {P = tetraayl porphyrinate dianion} species suggesting that the reactive species is a formal (heme)-Fe-II/Fe-IV=O(non-heme) pair. The non-heme Fe-IV=O is thus most likely responsible for C-H bond cleavage and subsequent radical chemistry. The photolysis of 1 in chlorobenzene or 1,2-dichlorobenzene resulted in C-Cl cleavage reactions and the formation of {[(L-6)Fe-III-Cl...Fe-III-Cl](2)O}(2+) (3), with chloride ligands that are derived from solvent dehalogenation chemistry. The resulting organic products are biphenyl trichlorides or biphenyl monochlorides, derived from dichlorobenzene and chlorobenzene, respectively. Similarly, product 3 is obtained by the photolysis of benzene-benzyl chloride solutions of 1; the organic product is benzaldehyde (similar to70%). A brief discussion of the dehalogenation chemistry, along with relevant environmental perspectives, is included.