title: Synthesis of a molecular Mo2Fe6S9 cluster with the topology of the PN cluster of nitrogenase by rearrangement of an edge-bridged Mo2Fe6S8 double cubane.
abstract: The structures of the P cluster and cofactor cluster of nitrogenase are well-defined crystallographically. They have been obtained only by biosynthesis; their chemical synthesis remains a challenge. Synthetic routes are sought to the P cluster in the P(N) state in which two cuboidal Fe(3)S(3) units are connected by a mu(6)-S atom and two Fe-(mu(2)-S(Cys))-Fe bridges. A reaction scheme affording a Mo(2)Fe(6)S(9) cluster in molecular form having the topology of the P(N) cluster has been devised. Reaction of the single cubane [(Tp)MoFe(3)S(4)Cl(3)](1)(-) with PEt(3) gives [(Tp)MoFe(3)S(4)(PEt(3))(3)](1+) (2), which upon reduction with BH(4)(-) affords the edge-bridged all-ferrous double cubane [(Tp)(2)Mo(2)Fe(6)S(8)(PEt(3))(4)] (4) (Tp = tris(pyrazolylhydroborate(1-)). Treatment of 4 with 3 equiv of HS(-) produces [(Tp)(2)Mo(2)Fe(6)S(9)(SH)(2)](3)(-) (7) as the Et(4)N(+) salt in 86% yield. The structure of 7 is built of two (Tp)MoFe(3)(mu(3)-S)(3) cuboidal fragments bridged by two mu(2)-S atoms and one mu(6)-S atom in an arrangement of idealized C(2) symmetry. The cluster undergoes three one-electron oxidation reactions and is oxidatively cleaved by p-tolylthiol to [(Tp)MoFe(3)S(4)(S-p-tol)(3)](2)(-) and by weak acids to [(Tp)MoFe(3)S(4)(SH)(3)](2-). The cluster core of 7 has the bridging pattern [Mo(2)Fe(6)(mu(2)-S)(2)(mu(3)-S)(6)(mu(6)-S)](1+) with the probable charge distribution [Mo(3+)(2)Fe(2+)(5)Fe(3+)S(9)](1+). Cluster 7 is a topological analogue of the P(N) cluster but differs in having two heteroatoms and two Fe-(mu(2)-S)-Fe instead of two Fe-(mu(2)-S(Cys))-Fe bridges. A best-fit superposition of the two cluster cores affords a weighted rms deviation in atom positions of 0.38 A. Cluster 7 is the first molecular topological analogue of the P(N) cluster. This structure had been prepared previously only as a fragment of complex high-nuclearity Mo-Fe-S clusters.
authors.affiliation: Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: Yugen
authors.initials: Y
authors.lastname: Zhang
authors.forename: R H
authors.initials: RH
authors.lastname: Holm
mesh_terms: D040761:Biomimetic Materials / Q000138:chemical synthesis* / Q000737:chemistry; D003067:Coenzymes; D018360:Crystallography, X-Ray; D007501:Iron / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008667:Metalloproteins / Q000737:chemistry; D008958:Models, Molecular; D015394:Molecular Structure; D008982:Molybdenum / Q000737:chemistry*; D000090006:Molybdenum Cofactors; D009591:Nitrogenase / Q000737:chemistry*; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry; D011621:Pteridines / Q000737:chemistry; D018036:Selenium Compounds / Q000737:chemistry; D013455:Sulfur / Q000737:chemistry*
chemical_list: D003067:Coenzymes; D007501:Iron; D008667:Metalloproteins; D008982:Molybdenum; D000090006:Molybdenum Cofactors; D009591:Nitrogenase; D009942:Organometallic Compounds; D011621:Pteridines; D018036:Selenium Compounds; D013455:Sulfur; C022261:molybdopterin