Rao P Venkateswara, Bhaduri Sumit, Jiang Jianfeng, Hong Daewon, Holm R H
Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, USA.
J Am Chem Soc. 2005 Feb 16;127(6):1933-45. doi: 10.1021/ja040222n.
The construction of a synthetic analogue of the A-cluster of carbon monoxide dehydrogenase/acetylcoenzyme synthase, the site of acetylcoenzyme A formation, requires as a final step the formation of an unsupported [Fe(4)S(4)]-(mu(2)-SR)-Ni(II) bridge to a preformed cluster. Our previous results (Rao, P. V.; Bhaduri, S.; Jiang, J.; Holm, R. H. Inorg. Chem. 2004, 43, 5833) and the work of others have addressed synthesis of dinuclear complexes relevant to the A-cluster. This investigation concentrates on reactions pertinent to bridge formation by examining systems containing dinuclear and mononuclear Ni(II) complexes and the 3:1 site-differentiated clusters Fe(4)S(4)(LS(3))L' (L' = TfO(-) (14), SEt (15)). The system 14/{Ni(L(O)-S(2)N(2))}M(SCH(2)CH(2)PPh(2)) results in cleavage of the dinuclear complex and formation of [{Ni(L(O)-S(2)N(2))}Fe(4)S(4)(LS(3))]- (18), in which the Ni(II) complex binds at the unique cluster site with formation of a Ni(mu(2)-SR)(2)Fe bridge rhomb. Cluster 18 and the related species {Ni(phma)}Fe(4)S(4)(LS(3))- (19) are obtainable by direct reaction of the corresponding cis-planar Ni(II)-S(2)N(2) complexes with 14. The mononuclear complexes [M(pdmt)(SEt)]- (M = Ni(II), Pd(II)) with 14 in acetonitrile or Me(2)SO solution react by thiolate transfer to give 15 and [M(2)(pdmt)(2)]. However, in dichloromethane the Ni(II) reaction product is interpreted as {Ni(pdmt)(mu(2)-SEt)}Fe(4)S(4)(LS(3)) (20). Reaction of Et(3)NH(+) and 15 affords the double cubane {Fe(4)S(4)(LS(3))}(2)(mu(2)-SEt) (21). Cluster 18 contains two mutually supportive Fe-(mu(2)-SR)-Ni(II) bridges, 19 exhibits one strong and one weaker bridge, 20 has one unsupported bridge (inferred from the (1)H NMR spectrum), and 21 has one unsupported Fe-(mu(2)-SR)-Fe bridge. Bridges in 18, 19, and 21 were established by X-ray structures. This work demonstrates that a bridge of the type found in the enzyme A-clusters is achievable by synthesis and implies that more stable, unsupported single thiolate bridges may require reinforcement by an additional covalent linkage between the Fe(4)S(4) and nickel-containing components. (LS(3) = 1,3,5-tris((4,6-dimethyl-3-mercaptophenyl)thio)-2,4,6-tris(p-tolylthio)benzene(3-); L(O)-S(2)N(2) = N,N'-diethyl-3,7-diazanonane-1,9-dithiolate(2-); pdmt = pyridine-2,6-methanedithiolate(2-); phma = N,N'-1,2-phenylenebis(2-acetylthio)acetamidate(4-); TfO = triflate.).
一氧化碳脱氢酶/乙酰辅酶合成酶A簇的合成类似物的构建是乙酰辅酶A形成的位点，其最后一步需要形成一个无支撑的[Fe(4)S(4)]-(μ(2)-SR)-Ni(II)桥连接到预先形成的簇上。我们之前的结果（Rao, P. V.; Bhaduri, S.; Jiang, J.; Holm, R. H. Inorg. Chem. 2004, 43, 5833）以及其他人的工作已经涉及到与A簇相关的双核配合物的合成。本研究通过研究含有双核和单核Ni(II)配合物以及3:1位点分化簇Fe(4)S(4)(LS(3))L'（L' = TfO(-) (14)，SEt (15)）的体系，集中关注与桥形成相关的反应。体系14/{Ni(L(O)-S(2)N(2))}M(SCH(2)CH(2)PPh(2))导致双核配合物的裂解并形成[{Ni(L(O)-S(2)N(2))}Fe(4)S(4)(LS(3))]-(18)，其中Ni(II)配合物在独特的簇位点结合并形成一个Ni(μ(2)-SR)(2)Fe桥菱形。簇18和相关物种{Ni(phma)}Fe(4)S(4)(LS(3))- (19)可通过相应的顺式平面Ni(II)-S(2)N(2)配合物与14直接反应得到。单核配合物[M(pdmt)(SEt)]-（M = Ni(II)，Pd(II)）与14在乙腈或Me(2)SO溶液中通过硫醇盐转移反应生成15和[M(2)(pdmt)(2)]。然而，在二氯甲烷中，Ni(II)反应产物被解释为{Ni(pdmt)(μ(2)-SEt)}Fe(4)S(4)(LS(3)) (20)。Et(3)NH(+)与15反应得到双立方烷{Fe(4)S(4)(LS(3))}(2)(μ(2)-SEt) (21)。簇18包含两个相互支撑的Fe-(μ(2)-SR)-Ni(II)桥，19呈现一个强桥和一个弱桥，20有一个无支撑桥（从(1)H NMR光谱推断），21有一个无支撑的Fe-(μ(2)-SR)-Fe桥。18、19和21中的桥通过X射线结构得以确定。这项工作表明，通过合成可以实现酶A簇中发现的那种类型的桥，并且意味着更稳定的、无支撑的单硫醇盐桥可能需要通过Fe(4)S(4)和含镍组分之间的额外共价连接来加强。（LS(3) = 1,3,5-三((4,6-二甲基-3-巯基苯基)硫代)-2,4,6-三(对甲苯硫代)苯(3-); L(O)-S(2)N(2) = N,N'-二乙基-3,7-二氮杂壬烷-1,9-二硫醇盐(2-); pdmt = 吡啶-2,6-二甲硫醇盐(2-); phma = N,N'-1,2-亚苯基双(2-乙酰硫代)乙酰胺酸盐(4-); TfO = 三氟甲磺酸盐。）
