Substitution and oxidation reactions of bis(dithiolene)tungsten complexes of potential relevance to enzyme sites

Structurally characterized tungstoenzymes contain mononuclear active sites in which tungsten is coordinated by two pterin-dithiolene ligands and one or two additional ligands that have not been identified. In this and prior investigations (Sung, K.-M.; Holm, R. H. Inorg. Chem. 2000, 39, 1275; J. Am. Chem. Soc. 2001, 123, 1931), stable coordination units of bis(dithiolene.)tungsten(IV,V,VI) complexes potentially related to enzyme sites have been sought by exploratory synthesis. In this work, additional members of the sets [WL(S2C2Me2)(2)]2(-,-) and. [WLL ' (S2C2Me2)(2)](2-,-) have been prepared and structurally characterized. Tungsten(IV) complexes obtained by substitution are carbonyl displacement products Of [W(CO)(2)(S2C2Me2)(2)] and include those with the groups (WS)-S-IV (4), W-IV(O2CPh) (5), and W-IV(2-AdQ)(CO) (Q = S (6), Se (7); Ad = adamantyl). Those obtained by oxidation reactions contain the groups (WO)-O-V (9), W-V(QPh)(2) (Q = S (10), Se (11)), (WS)-S-IV(OPh) (12), and (WTO2)-T-VI (14). The latter two complexes were obtained from W(IV) precursors using sulfur and oxygen atom transfer reactions, respectively. Complexes 4 and 9 are square pyramidal; 6, 7, 10, and 11 are distorted trigonal prismatic with cis ligands LL '; and 12 and 14 are distorted octahedral. Complexes 4, 10, and 11 support three-membered electron transfer series. Attempts to oxidize 4 to the (WS)-S-V complex results in the formation of binuclear [W-2(mu (2)-S)(2)(S2C2Me2)(4)](2-) having distorted octahedral coordination. The 21 known functional groups WL and WLL ' in mononuclear bis(dithiolene) complexes prepared in this and prior investigations are tabulated. Of those with physiological-type ligands, it remains to be seen which (if any) of these ligation modes are displayed by enzyme sites.