| Green plants, blue green algae and cyanobacteria are all capable of carrying out the four electron oxidation of water to dioxygen. This photosynthetic process is responsible for nearly all the O2 in our atmosphere. The water splitting chemistry occurs in photsystem II at the oxygen evolving complex (OEC). The OEC contains a manganese tetramer, made up of di-mu-oxo dimanganese units, a redox active tyrosine, YZ, Ca2+ and Cl--.; The precise nature of the intermediates involved in photosynthetic water oxidation is not known, and this is partly due to the lack of functional inorganic model systems. This thesis outlines the development of di-mu-oxo dimanganese complex that is capable of carrying out a catalytic O-O bond forming reaction that leads to O2 formation, making it a functional model for photosynthetic water oxidation.; We show that the reaction between Mn(II) and Mn(III) complexes and potassium peroxomonosulfate (oxone) produces O2 catalytically, and that this reaction is optimized by the use of the meridionally coordination planar tridentate ligands dipicolinate (dpa) and 2,2':6,2 ''-terpyridine (terpy). The key feature of these ligands is their ability to form complexes of the formula [(H 2O)LMn(O)2MnL(OH2)]n+/--, which have exchangeable solvent coordination sites, a key feature for a catalyst.; The chemistry with oxone, where L = terpy, has been extended with the use of NaOCl as an oxidant, and here O2 evolution is an unambiguous example of a homogeneous catalytic O-O bond formation. This is the first example of such a reaction involving a Mn dimer containing a di-mu-oxo bridge. Mechanistic studies of this reaction are consistent with a pathway involving a formally Mn=O intermediate. This is an important finding, as such species have been proposed as the active species in the OEC.; The thesis ends with a discussion of the chemistry of Mn=O and Ru=O complexes, and ties these findings in with biophysical studies of the OEC in order to propose a mechanism for photosynthetic water oxidation. This discussion includes a proposal for the roles of the Ca2+ and Cl-- co-factors, the function of which is still a matter for debate. |
