Synthesis and Reactivity of a Bioinspired Molybdenum(IV) Acetylene Complex.

The isolation of a molybdenum(IV) acetylene (C2H2) complex containing two bioinspired 6-methylpyridine-2-thiolate ligands is reported. The synthesis can be performed either by oxidation of a molybdenum(II) C2H2 complex or by substitution of a coordinated PMe3 by C2H2 on a molybdenum(IV) center. Both C2H2 complexes were characterized by spectroscopic means as well as by single-crystal X-ray diffraction. Furthermore, the reactivity of the coordinated C2H2 was investigated with regard to acetylene hydratase, one of two enzymes that accept C2H2 as a substrate. While the reaction with water resulted in the vinylation of the pyridine-2-thiolate ligands, an intermolecular nucleophilic attack on the coordinated C2H2 with the soft nucleophile PMe3 was observed to give a cationic ethenyl complex. A comparison with the tungsten analogues revealed less tightly bound C2H2 in the molybdenum variant, which, however, shows a higher reactivity toward nucleophiles.