Structural Mimics of Acetylene Hydratase: Tungsten Complexes Capable of Intramolecular Nucleophilic Attack on Acetylene

摘要

Bioinspired complexes employing the ligands 6-tert-butylpyridazine-3-thione (SPn) and pyridine-2-thione (SPy) were synthesized and fully characterized to mimic the tungstoenzyme acetylene hydratase (AH). The complexes [W(CO)(C_2H_2)(CHCH-SPy)(SPy)] (4) and [W(CO)(C_2H_2)(CHCH-SPn)(SPn)] (5) were formed by intramolecular nucleophilic attack of the nitrogen donors of the ligand on the coordinated C_2H_2 molecule. Labelling experiments using C2D2 with the SPy system revealed the insertion reaction proceeding via a bis-acetylene intermediate. The starting complex [W(CO)(C_2H_2)(SPy)_2] (6) for these studies was accessed by the new acetylene precursor mixture [W(CO)(C_2H_2)_n(MeCN)_3-nBr_2] (n=1 and 2; 7). All complexes represent rare examples in the field of W-C_2H_2 chemistry with 4 and 5 being the first of their kind. In the ongoing debate on the enzymatic mechanism, the findings support activation of acetylene by the tungsten center.