Oxo-tungsten bis-dithiolene complexes relevant to tungsten centres in enzymes

The reaction of [WO2(CN)(4)](4-) with a series of dimethylamino- or thione-protected asymmetric dithiolenes (ene-1,2-dithiolates) has been used to synthesise [WO(dithiolene)(2)](2-) complexes (dithiolene = -SC(H)C(R)S-, R = phenyl, pyridin-2-yl, pyridin-3-yl, pyridin-4-yl or quinoxalin-2-yl), which have been characterised by elemental analysis, spectroscopy and electrochemistry. The prototypical compound [PPh4](2)[WO(sdt)(2)]. EtOH [sdt = styrenedithiolate, -SC(H)C(Ph)S-], crystallises in space group P2(1)/c with a = 13.242(4), b = 31.894(8), c = 14.589(5) Angstrom, beta= 113.80(2)degrees, and Z = 4. The WOS4 moiety is square-based pyramidal with the O atom at the apex [W=O 1.724(7) Angstrom, W-S-av 2.37 Angstrom, O-W-S-av 108.7 degrees] and contains a cis geometry of the phenyl groups, although H-1 NMR studies indicate that both cis and trans isomers are present in the isolated solid. The physical properties of all of the [WO(dithiolene)(2)](2-) complexes are consistent with a retention of the (WOS4)-O-IV centre and each system undergoes a reversible electrochemical one-electron oxidation to the corresponding W-V system. The Variation in the dithiolene H-1 NMR resonances, upsilon(W=O) and upsilon(C-C) (dithiolene) IR stretching frequencies, and the Et values for the W-V-W-IV couple can be rationalised by a consideration of the nature of the aryl substituent. These data are compared to those of the analogous Mo-IV complexes and to those of the catalytic centres of the tungstoenzymes and their oxomolybdoenzyme counterparts.