Abstract
Spectroscopic and kinetic studies indicate that oxo-carboxylato-molybdenum(VI) bis-dithiolene complexes, (Mo(VI)O(p-X-OBz)L2), have been generated at low temperature as active site structural models for the type II class of pyranopterin molybdenum DMSOR family enzymes. A DFT analysis of low energy charge transfer bands shows that these complexes possess a Mo-S(dithiolene) π-bonding interaction between the Mo(d(xy)) redox active molecular orbital and a cis S(p(z)) donor orbital located on one of the dithiolene ligands.
Highlights
Oxo-carboxylato-molybdenum(VI) complexes possessing dithiolene ligands related to the active site of type II dimethyl sulfoxide reductase (DMSOR) family molybdoenzymes†
The vast majority of pyranopterin molybdenum enzymes catalyse oxygen atom transfer reactions between the substrate and solvent water coupled with proton and electron transfer.[1]
The dimethyl sulfoxide reductase (DMSOR) family of pyranopterin molybdenum enzymes is unique in that they possess two pyranopterin ene-1,2-dithiolate ligands bound to the Mo ion.[1]
Summary
Spectroscopic and kinetic studies indicate that oxo-carboxylatomolybdenum(VI) bis-dithiolene complexes, (MoVIO( p-X-OBz)L2), have been generated at low temperature as active site structural models for the type II class of pyranopterin molybdenum DMSOR family enzymes. The reduction peak potential is observed to shift in a negative direction (Cl, Epc = −1.08 V; H, Epc = −1.16; OMe, Epc = −1.18 V vs SCE) as the pKa value of the p-substituted benzoic acid increases (3.99 for X = Cl, 4.20 for X = H and 4.50 for X = OMe) This result provides support for the coordination of the p-X-OBz anion to the Mo center of MoVIOL2 since the electron-donating substituent increases the basicity of the benzoate anion and enhances its ability to coordinate to MoVI. Scheme 1 Proposed mechanism for formation of MoVIO( p-X-OBz)L
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