Alcohol and Aldehyde Adducts of Zinc Thiolates:  Structural Modeling of Alcoholdehydrogenase

Bis(pentafluorothiophenolato)zinc (1) and bis(2,4,6-triisopropylthiophenolato)zinc (2) can be combined with nitrogen-containing derivatives of benzyl alcohol and benzaldehyde to form (N,O-chelate) zinc thiolates. 2-Pyridylmethanol as well as 2-quinolylmethanol (HetMeOH) yield [(HetMeO)Zn(SR)]₄ (3, 4) having a cyclo-Zn₄(μ-O)₄ backbone and only terminal SR. Likewise, thiolate 1 and 2-(dimethylamino)benzyl alcohol form zwitterionic [(dimethylammoniobenzylato)Zn(SR)₂]₂ (5) with bridging alkoxide and terminal thiolate. In contrast, 6-picolylmethanol (PicMeOH) and thiolate 1 result in [(PicMeOH)Zn(SC₆F₅)₂] (6) containing zinc in a tetrahedral ZnNS₂O, environment. Simple aromatic aldehydes form polymeric complexes [(RCHO)Zn(SC₆F₅)₂] (7:  R = p-tolyl, 8:  R = mesityl) with a [Zn−S]_∞ backbone. Chelating aldehydes (CA) yield mononuclear complexes with tetrahedral ZnNS₂O coordination [(CA)Zn(SC₆F₅)₂] (9, CA = pyridine-2-carbaldehyde; 10, CA = 6-methylpyridine-2-carbaldehyde; 11, CA = 6-methoxypyridine-2-carbaldehyde; 12, CA = quinoline-2-carbaldehyde; 13, CA = 2-(dimethylamino)benzaldehyde). In contrast, N-methylimidazole-2-carbaldehyde (ImA) is coordinated twice in tetrahedral [(ImA)₂Zn(SC₆F₅)₂] (14) lacking any Zn−O interactions. Pyridine-2,6-dicarbaldehyde (PDA) forms trigonal bipyramidal [(PDA)Zn(SC₆F₅)₂] (15) with ZnNO₂S₂ ligation. The structures of 3, 4, 6, 8, 10, 11, 13, and 14 were determined crystallographically, and the structures of 5 and 15 were deduced from those of the corresponding ZnBr₂ complexes. The ZnNS₂O coordination pattern observed for the enzyme has been reproduced to a very good approximation. In complexes 6 and 10, which are almost superimposable, it is realized for both the corresponding alcohol and aldehyde.