Thiolate-bridged dinuclear iron(tris-carbonyl)-nickel complexes relevant to the active site of [NiFe] hydrogenase

Abstract

The reaction of NiBr2(EtOH)4 with a 1:2-3 mixture of FeBr2(CO)4 and Na(SPh) generated a linear trinuclear Fe-Ni-Fe cluster (CO)3Fe(μ-SPh)3Ni(μ-SPh) 3Fe(CO)3, 1, whereas the analogous reaction system FeBr2(CO)4/Na(StBu)/NiBr2(EtOH) 4 (1:2-3:1) gave rise to a linear tetranuclear Fe-Ni-Ni-Fe cluster [(CO)3Fe(μ-StBu)3Ni(μ-Br)]2, 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) 3-Ni complexes, the structures of which mimic [NiFe] hydrogenase active sites. The reactions of 2 with SC(NMe2)2 (tmtu), Na{S(CH2)2SMe} and ortho-NaS(C6H4)SR (R = Me, tBu) led to isolation of (CO)3Fe(μ-S tBu)3NiBr(tmtu), 3, (CO)3Fe(S tBu)(μ-StBu)2Ni{S(CH2) 2SMe}, 4, and (CO)3Fe(StBu)(μ-S tBu)2Ni{S(C6H4)SR}, 5a (R = Me) and 5b (R = tBu), respectively. On the other hand, treatment of 2 with 2-methylthiophenolate (ortho-O(C6H4)SMe) in methanol resulted in (CO)3Fe(μ-StBu)3Ni(MeOH) {O(C6H4)SMe}, 6a. The methanol molecule bound to Ni is labile and is readily released under reduced pressure to afford (CO) 3Fe(StBu)(μ-StBu)2Ni{O(C 6H4)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)3Fe(μ- StBu)3Ni(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.