Synthesis of Diiron(I) Dithiolato Carbonyl Complexes

Virtually all organosulfur compounds react with Fe(0) carbonyls to give the title complexes. These reactions are reviewed in light of major advances over the past few decades, spurred by interest in Fe-2(mu-SR)(2)(CO)(x) centers at the active sites of the [FeFe]-hydrogenase enzymes. The most useful synthetic route to Fe-2(mu-SR)(2)(CO)(6) involves the reaction of thiols with Fe-2(CO)(9) and Fe-3(CO)(12). Such reactions can proceed via mono-, di-, and triiron intermediates. The reactivity of Fe(0) carbonyls toward thiols is highly chemoselective, and the resulting dithiolato complexes are fairly rugged. Thus, many complexes tolerate further synthetic elaboration directed at the organic substituents. A second major route involves alkylation of Fe-2(mu-S-2)(CO)(6), Fe-2(mu-SH)(2)(CO)(6), and Li2Fe2(mu-S)(2)(CO)(6). This approach is especially useful for azadithiolates Fe-2[(mu-SCH2)(2)NR](CO)(6). Elaborate complexes arise via addition of the FeSH group to electrophilic alkenes, allcynes, and carbonyls. Although the first example of Fe-2(mu-SR)(2)(CO)(6) was prepared from ferrous reagents, ferrous compounds are infrequently used, although the Fe(II)(SR)(2) + Fe(0) condensation reaction is promising. Almost invariably low-yielding, the reaction of Fe-3(CO)(12), S-8, and a variety of unsaturated substrates results in C-H activation, affording otherwise inaccessible derivatives. Thiones and related C=S containing reagents are highly reactive toward Fe(0), often giving complexes derived from substituted methanedithiolates and C-H activation.