Über Pterinchemie. 90. Mitteilung. Synthese und Kristallstruktur des ersten chinoiden Dihydropterinmolybdän (IV)‐Komplexes

Synthesis and Crystal Structure of the First Quinoid Dihydropterinmolybdenum (IV) Complex The first molybdenum(IV) complex with a quinoid dihydropterin, i.e. 2, was isolated and characterized by IR, UV and NMR data and single‐crystal X‐ray diffraction. The reaction of MoVIO2Cl2 with the biologically important 6β‐5,6,7,8‐tetrahydro‐L‐biopterin(2) (7) in MeOH gave almost quantitatively trichloro(1,5‐quinoid‐7,8‐dihydro‐6H‐L‐biopterin)oxomolybdenLim(IV) (2). The complex crystallizes with one molecule of MeOH in the noncentrosymmetric orthorhombic space group P212121 (No. 19) with unit cell dimensions a = 1009.3(3), b = 1104.7(3), and c = 1484.5(4) pm and Z = 4. The Mo‐atom has a distorted octahedral geometry (Fig.1). It is coordinated by N(5) and O(4) of the pterin ligand. The distance of the Mo–N(5) bond (202 pm) is unusually short compared to similar complexes. O(4) is located trans to a terminal oxo ligand. The octahedral coordination is completed by three Cl‐atoms in a meridional arrangement. Complex 2, with the Mo‐atom in the enzyme‐relevant oxidation state +IV and the pterin in the intermediate quinoid dihydro form, should lead to an extension of the proposed ‘common molybdenum cofactor’ model.