The reaction of NiBr (EtOH) with a 1:2-3 mixture of FeBr (CO) and Na(SPh) generated a linear trinuclear Fe-Ni-Fe cluster (CO) Fe(μ-SPh) Ni(μ-SPh) Fe(CO) , 1, whereas the analogous reaction system FeBr (CO) /Na(S Bu)/NiBr (EtOH) (1:2-3:1) gave rise to a linear tetranuclear Fe-Ni-Ni-Fe cluster [(CO) Fe(μ-S Bu) Ni(μ-Br)] , 2. By using this tetranuclear cluster 2 as the precursor, we have developed a new synthetic route to a series of thiolate-bridged dinuclear Fe(CO) -Ni complexes, the structures of which mimic [NiFe] hydrogenase active sites. The reactions of 2 with SC(NMe ) (tmtu), Na{S(CH ) SMe} and ortho-NaS(C H )SR (R = Me, Bu) led to isolation of (CO) Fe(μ-S Bu) NiBr(tmtu), 3, (CO) Fe(S Bu)(μ-S Bu) Ni{S(CH ) SMe}, 4, and (CO) Fe(S Bu)(μ-S Bu) Ni{S(C H )SR}, 5a (R = Me) and 5b (R = Bu), respectively. On the other hand, treatment of 2 with 2-methylthiophenolate (ortho-O(C H )SMe) in methanol resulted in (CO) Fe(μ-S Bu) Ni(MeOH) {O(C H )SMe}, 6a. The methanol molecule bound to Ni is labile and is readily released under reduced pressure to afford (CO) Fe(S Bu)(μ-S Bu) Ni{O(C H )SMe}, 6b, and the coordination geometry of nickel changes from octahedral to square planar. Likewise, the reaction of 2 with NaOAc in methanol followed by crystallization from THF gave (CO) Fe(μ- S Bu) Ni(THF)(OAc), 7. The dinuclear complexes, 3-7, are thermally unstable, and a key to their successful isolation is to carry out the reactions and manipulations at -40° C. © 2008 by The National Academy of Sciences of the USA. 2 4 2 4 3 3 3 3 2 4 2 4 3 3 2 3 2 2 2 2 6 4 3 3 3 2 2 2 3 2 6 4 6 4 3 3 6 4 3 2 6 4 3 3 t t t t t t t t t t t t t