TETRAHYDROPTERIN REACTIONS OF DIOXO-MOLYBDENUM(6- DOES REDOX OCCUR() COMPLEXES )

This report describes out continued investigation of reactions between tetrahydropterins and dioxomolybdenum complexes. We report the result s of structural, reactivity, and theoretical experiments that indicate these reduced molybdenum-pterin complexes are better described as Mo( 6+)-H(4)pterin rather than Mo(4+)-H(2)pterin as previously assigned. B oth Mulliken charges calculated using the extended Huckel molecular or bital method and the bond valence sum method predict a formal molybden um oxidation state midway between 5+ and 6+. The complexes Mo2O4Cl2(te trahydro-6,7-dimethylpterin)(2), MoOCl3(tetrahydro-6,7-dimethylpterin) , and ro-6-(hydroxymethyl)pterin)(diethyldithiocarbaate) have been cha racterized by H-1 NMR, IR, UV/vis, and conductivity measurements. The X-ray crystal structure is reported for Mo2O4Cl2(tetrahydro-6,7-dimeth ylpterin)(2) . 4DMF. Inner coordination sphere bond distances indicate substantial electron density is donated from the pterin N(5) to Mo. T hese complexes undergo solvation and ligand substitution reactions. It is shown that solvation is associated with acid-base reactions at the tetrahydropterin ligands. The molybdenum-tetrahydropterin complexes s how a variety of reactivities toward the oxidants O-2, 2,6-dichloroind ophenol, and dimethyl sulfoxide. This study shows that tetrahydropteri n has a high affinity to chelate Mo(6+) if one of the two oxo ligands is removed and that coordination to molybdenum stabilizes tetrahydropt erins toward oxidation. Results from this study also suggest that diox o-Mo(VI) coordination to tetrahydropterin is unlikely.