| Research Abstract |
1. Rational Assemblage of Iron and Nickel Ions by Thiolate/thioether Hybrid Ligands Thiolate-sulfurs are coordinated at transition metal atoms strongly, while thioether-type sulfurs form weak M-S bonds, often exhibiting a facile association/dissociation equilibration. We have utilized the thiolate/thioether hybrid ligands RSCH_2CH_2S(-) (R=Et (etet), R=^iPr (ptet), R=Ph (ptet)) to assemble iron(II) and Ni(II) metal ions. For instance, the reaction of NiCl_2 with 2 equiv of Li(etet) produced a linear polymer [Ni(etet)_2]n, while the analogous 1 : 2 NiCl_/Li(ptet) reaction resulted in formation of a cyclic hexa-nuclear [Ni_6(ptet)_<12>]. In these mezzozcopic-size clusters/polymers, thiolate-sulfur atoms bridge Ni centers, leaving thioether sufurs uncoordinated. When the 1 : 1 mixture of NaSCH_2CH_2SR (R=Me (mtet), R=Et (etet), or R=^iPr (^iptet)) and NaS^tBu was treated with 1 equiv of NiCl_2, unusual cyclic deca-nuclear clusters [Ni(SCH_2CH_2SR)(S^tBu)_<10> were formed, where a solvent
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benzene/THF molecule was incorporated in the cavity of the ring for R=Et, ^iPr.
2. Toward Better Iron-Sulfur Clusters Modeling the Nitrogenase Active Sites : The unusual [8Fe-7S] inorganic core structure of the reduced form of P-cluster (P^N) was self-assembled by the reaction of Fe{N(SiMe_3)_2}_2, tetramethylthiourea (tmtu), 2, 4, 6-triiso-propylbenzenethiol(HS-tip), and elemental sulfur in the ratio of 8(Fe) : 3(tmtu) : 12(HS-tip) : 7(S). The complex RN(SiMe_3)_2}(tmtu)Fe_4S_3]_2(μ_6-S){μ-N(SiMe_3)}_2 (1), obtained therefrom, consists of irons with a 6Fe(II)+2Fe(III) oxidation state, while PN consists of 8 Fe(II) ions. We have also isolated yet another type of [8Fe-7S] clusters, RSDmp)Fe4S312(μ_6-S)(μ-SDmP)_2 (μ-STip)} (2) (major) and [(STip)Fe_4S_3]_2(μ_6-S)(μ-SDmP)_2{μ-N(SiMe3)} (3) (minor), from the reaction of Fe{N(SiMe_3)_2}_2, HSDmp, HSTip, and elemental sulfur (8 : 6 : 10 : 7), which are topologically analogous to FeMo-co and have an intriguing 5Fe(II)+3Fe(III) oxidation state with a doublet ground state. Cluster 2 was also generated in 34% yield from the reaction of the di-iron complex [Fe(Stip)]_2(μ-SDmp)_2 with Sg.
3. Dinuclear Fe-Ni complexes modelling the active site of [Ni-Fe] Hydrogenase : A tetranuclear Fe2Ni_2 complex, [(CO)_3Fe(μ-S^tBu)_3NiBr]_2, obtained from the reaction of FeBr_2(CO)_4, NaS^tBu, and NiBr_2(EtOH)_4 at 40℃, was found to serve as a convenient entry into a series of dinuclear Fe(CO)_3-Ni complexes. They include (CO)_3Fe(μ-S^tBu)_3NiBr(S=C(NMe_2)_2), [(CO)_3Fe(S^tBu)(R-S^tBu)_2Ni{S_2(C_6H_4)}], (CO)_3Fe(S^tBu) (R-S^tBu)_2Ni{S(CH_2)_2SMe}, (CO)_3Fe(μ-S^Bu)_3Ni(MeOH)(ortho-OC6_H4_SMe) (4), (CO)_3Fe(S^TBu)(μ-S^tBu)_2Ni (ortho-OC_6H_4SMe) (5), (CO)_3Fe(μ-S`tBu)_3Ni(THF)(OAc), (CO)_3Fe(μ-S`tBu)_3Ni(SDmp), and (CO)_3Fe (S`tBu)(μ-S`tBu)_2Ni(SDmp)(CO). Furthermore, we isolated (PPh_4)[(CO)_2(CN)_2Fe(μ-pdt)Ni(S_2CNR_2) (7) from the reaction of (PPh_4)[Fe(CO)_2(CN)_2(pdt)K] (6) with (PPh_3)NiBr(S_2CNR_2), which is the best structural model of [NiFe] hydrogenase reported so far. Less
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