Synthesis, characterization, and spectroscopy of model molybdopterin complexes

Abstract

The preparation and characterization of new model complexes for the molybdenum cofactor are reported. The new models are distinctive for the inclusion of pterin-substituted dithiolene chelates and have the formulation Tp∗MoX(pterin-R-dithiolene) (Tp∗=tris(3,5,-dimethylpyrazolyl)borate), X=O, S, R=aryl. Syntheses of Mo(4+) and (5+) complexes of two pterin-dithiolene derivatives as both oxo and sulfido compounds, and improved syntheses for pterinyl alkynes and [Et4N][Tp∗MoIV(S)S4] reagents are described. Characterization methods include electrospray ionization mass spectrometry, electrochemistry, infrared spectroscopy, electron paramagnetic resonance and magnetic circular dichroism. Cyclic voltammetry reveals that the Mo(5+/4+) reduction potential is intermediate between that for dithiolenes with electron-withdrawing substituents and simple dithiolates chelates. Electron paramagnetic resonance and magnetic circular dichroism of Mo(5+) complexes where X=O, R=aryl indicates that the molybdenum environment in the new models is electronically similar to that in Tp∗MoO(benzenedithiolate).