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 WIVS
(4), WIV(O2CPh) (5), and WIV(2-AdQ)(CO) (Q = S (6), Se (7); Ad = adamantyl). Those obtained by oxidation
reactions contain the groups WVO (9), WV(QPh)2 (Q = S (10), Se (11)), WVIS(OPh) (12), and WVIO2 (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 WVS complex results in the formation of binuclear [W2(μ2-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.