OXO-TUNGSTEN BIS-DITHIOLENE COMPLEXES RELEVANT TO TUNGSTEN CENTERS INENZYMES

The reaction of [WO2(CN)(4)](4-) with a series of dimethylamino- or th ione-protected asymmetric dithiolenes (ene-1,2-dithiolates) has been u sed 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 quin oxalin-2-yl), which have been characterised by elemental analysis, spe ctroscopy 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 squ are-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 geo metry of the phenyl groups, although H-1 NMR studies indicate that bot h cis and trans isomers are present in the isolated solid. The physica l properties of all of the [WO(dithiolene)(2)](2-) complexes are consi stent with a retention of the (WOS4)-O-IV centre and each system under goes a reversible electrochemical one-electron oxidation to the corres ponding 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 c onsideration of the nature of the aryl substituent. These data are com pared to those of the analogous Mo-IV complexes and to those of the ca talytic centres of the tungstoenzymes and their oxomolybdoenzyme count erparts.