Suggested Mechanisms of 0-0 Bond Formation

There is a large number of proposed mechanisms for 0-0 bond formation by the WOC (for reviews, see references [53, 54]). Essentially, a proposed mechanism has to address two questions  

What is the chemical mechanism by which these adjacent substrate oxygens couple  

4 Molecular Concepts of Water Splitting Nature s Approach 

The experimental evidence already described limits the scope of question (1). At least one substrate site, presumably the slow substrate Ws bound in the early, S states (S0-S2), must be either a ligand to the Ca (W3 or W4) or a ligand to the MnA4 (terminal H20/ OH (W1 or W2) or a (r2-oxo bridge (05). From these restrictions, the subsequent mechanism by which the two substrates couple is grouped into two classes  

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