Photochemical organic oxidations and dechlorinations with a mu-oxo bridged heme/non-heme diiron complex.
Steady state and laser flash photolysis studies of the heme/non-heme mu-oxo diiron complex [((6)L)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 [((6)L)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 (approximately 28) 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 (approximately 15%) for the reaction in THF and benzaldehyde (approximately 23%) 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 = tetraaryl 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 [[((6)L)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 (approximately 70%). A brief discussion of the dehalogenation chemistry, along with relevant environmental perspectives, is included.
Wasser
Ian M
IM
Department of Chemistry, Johns Hopkins University, Charles and 34th Streets, Baltimore, Maryland 21218, USA.
Fry
H Christopher
HC
Hoertz
Paul G
PG
Meyer
Gerald J
GJ
Karlin
Kenneth D
KD
D004578:Electron Spin Resonance Spectroscopy; D005290:Ferric Compounds / Q000737:chemistry*; D005296:Ferrous Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D006418:Heme / Q000737:chemistry*; D006843:Hydrocarbons, Chlorinated / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010782:Photolysis; D013056:Spectrophotometry, Ultraviolet
D005290:Ferric Compounds; D005296:Ferrous Compounds; D006843:Hydrocarbons, Chlorinated; D006418:Heme; D007501:Iron