Synthesis and Characterization of Bis(dithiolene) Tungsten(VI), ‐(V), and ‐(IV) Complexes and Their Reactivities in Coupled Electron–Proton Transfer: A New Series of Active Site Models of Tungstoenzymes

Abstract

AbstractNew tungsten(VI), ‐(V), and ‐(IV) complexes containing 3,6‐dichloro‐1,2‐benzenedithiolate (bdtCl2), (Et4N)2[WVIO2(bdtCl2)2] {(Et4N)2[1]}, (Et4N)[WVO(bdtCl2)2] {(Et4N)[2]}, and (Et4N)2[WIVO(bdtCl2)2] {(Et4N)2[3]} were synthesized and characterized as active site models of tungstoenzymes.(Et4N)2[1] was prepared in high yield by the reaction of WO2Cl2 with 2bdtCl2 at low temperature, and its crystal structure was determined. Isomerization between octahedral structures (Δ and Λ forms) of the tungsten center of(Bu4N)2[1] was characterized by variable‐temperature 1H NMR (VT 1H NMR) spectral analysis, which offers the first example of six‐coordinate bis(dithiolene) tungsten(VI) complexes. The isomerization of the molybdenum center of (Bu4N)2[MoVIO2(bdtCl2)2] {(Bu4N)2[4]} was similarly characterized. A comparison of their activation energies indicated that the tungsten center underwent slower isomerization than that of the molybdenum one. (Et4N)2[1] underwent an irreversible reduction at –2.1 V vs. SCE in CH3CN by a coupled electron–proton transfer (CEPT) process to yield(Et4N)2[3], while (Et4N)2[3] underwent an irreversible oxidation by a CEPT process at –0.27 V in the presence of 2 equiv. of Et4NOH in CH3CN to yield (Et4N)2[1]. (Et4N)[2] disproportionated into 0.5 equiv. of (Et4N)2[1] and 0.5 equiv. of (Et4N)2[3] when treated with 1 equiv. of Et4NOH in CH3CN.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)