Synthesis of MFe3S4 Clusters Containing a Planar MIISite (M = Ni Pd Pt) a Structural Element in the C-Cluster of Carbon Monoxide Dehydrogenase

摘要

Synthesis of an analogue of the C-cluster of C. hydrogenoformans carbon monoxide dehydrogenase requires formation of a planar Ni^II site and attachment of an exo iron atom in the core unit NiFe4S5. The first objective has been achieved by two reactions: (i) displacement of Ph3P or Bu^tNC at tetrahedral Ni^II sites of cubane-type [NiFe3S4]¹⁺ clusters with chelating diphosphines, and (ii) metal atom incorporation into a cuboidal [Fe3S4]⁰ cluster with a M⁰ reactant in the presence of dmpe. The isolated product clusters [(dmpe)MFe3S4(LS3)]²⁻ (M = Ni^II (>9), Pd^II (>12), Pt^II (>13)) contain the cores [MFe3(μ2-S*)(μ3-S)3]¹⁻ having planar M^IIP2S2 sites and variable non-bonding M···S* distances of 2.6–3.4 Å. Reaction (i) involves a tetrahedral → planar Ni^II structural change between isomeric cubane and cubanoid [NiFe₃S₄]¹⁺ cores. Based on the magnetic properties of >12 and earlier considerations, the S = 5/2 ground state of the cubanoid cluster arises from the [Fe₃S₄]¹⁻ fragment, whereas the S = 3/2 ground state of the cubane cluster is a consequence of antiferromagnetic coupling between the spins of Ni²⁺ (S = 1) and [Fe₃S₄]¹⁻. Other substitution reactions of [NiFe₃S₄]¹⁺clusters and 1:3 site-differentiated [Fe₄S₄]²⁺clusters are described, as are the structures of >12, 13, [(Me₃P)NiFe₃S₄(LS₃)]²⁻, and [Fe₄S₄(LS₃)L′]²⁻ (L′ = Me₂NC₂H₄S⁻, Ph₂P(O)C₂H₄S⁻). This work significantly expands our initial report of cluster >9 (Panda et al., J. Am. Chem. Soc. >2004, 126, 6448–6459) and further demonstrates that a planar M^II site can be stabilized within a cubanoid [NiFe₃S₄]¹⁺ core. (dmpe = bis(1,2-dimethylphosphino)ethane; 1,3,5-tris((4,6-dimethyl-3-mercaptophenyl)thio)-2,4,6-tris(p-tolylthio)benzene(3-)).