ja0110832_si_001.pdf (1.04 MB)

Synthesis and Characterization of Sulfur-Voided Cubanes. Structural Analogues for the MoFe3S3 Subunit in the Nitrogenase Cofactor

Download (1.04 MB)
journal contribution
posted on 14.12.2001, 00:00 by Dimitri Coucouvanis, Jaehong Han, Namdoo Moon
A new class of Mo/Fe/S clusters with the MoFe3S3 core has been synthesized in attempts to model the FeMo-cofactor in nitrogenase. These clusters are obtained in reactions of the (Cl4-cat)2Mo2Fe6S8(PR3)6 [R = Et (I), nPr (II)] clusters with CO. The new clusters include those preliminarily reported:  (Cl4-cat)MoFe3S3(PEt3)2(CO)6 (III), (Cl4-cat)(O)MoFe3S3(PEt3)3(CO)5 (IV), (Cl4-cat)(Pyr)MoFe3S3(PEt3)2(CO)6 (VI), and (Cl4-cat)(Pyr)MoFe3S3(PnPr3)3(CO)4 (VIII). In addition the new (Cl4-cat)(O)MoFe3S3(PnPr3)3(CO)5 cluster (IVa), the (Cl4-cat)(O)MoFe3S3(PEt3)2(CO)6cluster (V), the (Cl4-cat)(O)MoFe3S3(PnPr3)2(CO)6 cluster (Va), the (Cl4-cat)(Pyr)MoFe3S3(PnPr3)2(CO)6 cluster (VIa), and the (Cl4-cat)(PnPr3)MoFe3S3(PnPr3)2(CO)6 cluster (VII) also are reported. Clusters IIIVIII have been structurally and spectroscopically characterized. EPR, zero-field 57Fe-Mössbauer spectroscopic characterizations, and magnetic susceptibility measurements have been used for a tentative assignment of the electronic and oxidation states of the MoFe3S3 sulfur-voided cuboidal clusters. A structural comparison of the clusters with the MoFe3S3 subunit of the FeMo-cofactor has led to the suggestion that the storage of reducing equivalents into M−M bonds, and their use in the reduction of substrates, may occur with the FeMo-cofactor, which also appears to have M−M bonding. On the basis of this argument, a possible N2-binding and reduction mechanism on the FeMoco-cofactor is proposed.