title: Reactions of the terminal Ni(II)-OH group in substitution and electrophilic reactions with carbon dioxide and other substrates: structural definition of binding modes in an intramolecular Ni(II)...Fe(II) bridged site.
abstract: A singular feature of the catalytic C-cluster of carbon monoxide dehydrogenase is a sulfide-bridged Ni...Fe locus where substrate is bound and transformed in the reversible reaction CO + H(2)O right harpoon over left harpoon CO(2) + 2H(+) + 2e(-). A similar structure has been sought in this work. Mononuclear planar Ni(II) complexes [Ni(pyN(2)(Me2))L](1-) (pyN(2)(Me2) = bis(2,6-dimethylphenyl)-2,6-pyridinedicarboxamidate(2-)) derived from a NNN pincer ligand have been prepared including L = OH(-) (1) and CN(-) (7). Complex 1 reacts with ethyl formate and CO(2) to form unidentate L = HCO(2)(-) (5) and HCO(3)(-) (6) products. A binucleating macrocycle was prepared which specifically binds Ni(II) at a NNN pincer site and five-coordinate Fe(II) at a triamine site. The Ni(II) macrocyle forms hydroxo (14) and cyanide complexes (15) analogous to 1 and 7. Reaction of 14 with FeCl(2) alone and with ethyl formate and 15 with FeCl(2) affords molecules with the Ni(II)-L-Fe(II) bridge unit in which L = mu(2):eta(1)-OH(-) (17) and mu(2):eta(2)-HCO(2)(-) (18) and -CN(-) (19). All bridges are nonlinear (17, 140.0 degrees ; 18, M-O-C 135.9 degrees (Ni), 120.2 degrees (Fe); 19, Ni-C-N 170.3 degrees , Fe-N-C 141.8 degrees ) with Ni...Fe separations of 3.7-4.8 A. The Ni(II)Fe(II) complexes, lacking appropriate Ni-Fe-S cluster structures, are not site analogues, but their synthesis and reactivity provide the first demonstration that molecular Ni(II)...Fe(II) sites and bridges can be attained, a necessity in the biomimetic chemistry of C-clusters.
authors.affiliation: Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: Deguang
authors.initials: D
authors.lastname: Huang
authors.forename: R H
authors.initials: RH
authors.lastname: Holm
mesh_terms: D000445:Aldehyde Oxidoreductases / Q000737:chemistry / Q000378:metabolism; D001665:Binding Sites; D002245:Carbon Dioxide / Q000737:chemistry*; D002384:Catalysis; D017665:Hydroxyl Radical / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D009097:Multienzyme Complexes / Q000737:chemistry / Q000378:metabolism; D009532:Nickel / Q000737:chemistry*; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D013440:Sulfides / Q000737:chemistry*
chemical_list: D009097:Multienzyme Complexes; D009942:Organometallic Compounds; D013440:Sulfides; D002245:Carbon Dioxide; D017665:Hydroxyl Radical; D009532:Nickel; D007501:Iron; D000445:Aldehyde Oxidoreductases; C019823:carbon monoxide dehydrogenase