Metal complexes water cleavage

For the [Pdltriphosphinejlsolvent)] " " complexes, the metallocarboxylic acid formed in step 3 of Sch. 2 is not ready to undergo C—O bond cleavage. In order for this reaction to occur, an additional electron transfer, solvent loss, and a second protonation have to occur. Of particular interest in this sequence is the loss of a weakly coordinated solvent molecule (step 5), to produce a vacant site on the metal for water to occupy as the C—O bond of CO2 is broken to form coordinated CO and coordinated water [34, 35]. This C—O bond cleavage reaction is the slow step in the catalytic cycle for these catalysts at low acid concentrations, and a vacant coordination site is required for this reaction to occur. C—O bond cleavage is also the slow step for Fe(porphyrin) catalysts at low acid concentrations (H+, Mg +, or CO2) [37-39]. In this case, a vacant coordination site is not required. However, the potentials at which catalysis occurs in this case (approximately —2.0 V vs. ferrocene/ferrocen-ium) is much more negative than those... 

WATER CLEAVAGE USING METAL COMPLEXES AS CATALYSTS 495... 

Several metal complexes were prepared with the new products such complexes were evaluated for their efficiencies as DNA cleavers upon exposure to visible light. The attained results enlighten the role played by the water-solubilizing carbohydrate moieties attached to the lipophilic porphyrin macrocycle during the cleavage of the DNA target [145,146]. 

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