Mononuclear structures oxygen atom transfer

Cw-dioxomolybdenum(Vl) complexes of sterically bulky (thiolato)pyridine (41) and bi(thiolato)pyridine (42) ligands were designed to prevent comproportionation and maintain mononuclearity during oxygen-atom transfer reactions. The complex with (41) had a distorted octahedral structure and achieved its designed objective, whereas that with (42) did not, having trigonal bipyramidal structure with axial thiolate donors. 

There are several demonstrations that cytochrome cdi catalyzes the reduction of molecular oxygen to water. Exactly how the enzyme catalyzes this reaction is of some interest, because the crystal structure shows that the catalytic center is mononuclear and expected to handle one electron at a time. If we assume that electron transfer between subimits cannot occur, then only two of the four electrons required for reduction of one oxygen atom can obviously be stored on one subimit of the enz5une before reduction of oxygen commences. Thus, it might be anticipated that some intermediates of oxygen reduction are relatively long-lived. 

The formal transfer of an oxygen atom is one way of describing the function of the Mo site in molybdoenzymes.5 The formation of dinuclear reduction products is a complication that causes difficulty in trying to model the mononuclear site.5,165 This difficulty can be overcome by the use of sterically demanding ligands that prevent the formation of the dinuclear complex,73 79,125 176 177 For example, the cycle shown in Scheme 3 can be effected without dimerization. Further, in this case DMSO and the enzyme substrate biotin sulfoxide, can serve as the oxo donor to form the Movl dioxo complex during the catalytic cycle.79,177 The Movl complex involved is discussed structurally above (Figure 7). 

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