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

New tungsten(VI), ‐(V), and ‐(IV) complexes containing 3,6‐dichloro‐1,2‐benzenedithiolate (bdtCl 2 ), (Et 4 N) 2 [W VI O 2 (bdtCl 2 ) 2 ] {(Et 4 N) 2 [ 1 ]}, (Et 4 N)[W V O(bdtCl 2 ) 2 ] {(Et 4 N)[ 2 ]}, and (Et 4 N) 2 [W IV O(bdtCl 2 ) 2 ] {(Et 4 N) 2 [ 3 ]} were synthesized and characterized as active site models of tungstoenzymes.(Et 4 N) 2 [ 1 ] was prepared in high yield by the reaction of WO 2 Cl 2 with 2bdtCl 2 at low temperature, and its crystal structure was determined. Isomerization between octahedral structures (Δ and Λ forms) of the tungsten center of(Bu 4 N) 2 [ 1 ] was characterized by variable‐temperature 1 H NMR (VT 1 H NMR) spectral analysis, which offers the first example of six‐coordinate bis(dithiolene) tungsten(VI) complexes. The isomerization of the molybdenum center of (Bu 4 N) 2 [Mo VI O 2 (bdtCl 2 ) 2 ] {(Bu 4 N) 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. (Et 4 N) 2 [ 1 ] underwent an irreversible reduction at –2.1 V vs. SCE in CH 3 CN by a coupled electron–proton transfer (CEPT) process to yield(Et 4 N) 2 [ 3 ], while (Et 4 N) 2 [ 3 ] underwent an irreversible oxidation by a CEPT process at –0.27 V in the presence of 2 equiv. of Et 4 NOH in CH 3 CN to yield (Et 4 N) 2 [ 1 ]. (Et 4 N)[ 2 ] disproportionated into 0.5 equiv. of (Et 4 N) 2 [ 1 ] and 0.5 equiv. of (Et 4 N) 2 [ 3 ] when treated with 1 equiv. of Et 4 NOH in CH 3 CN.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)