Ligand metathesis as rational strategy for the synthesis of cubane-type heteroleptic iron-sulfur clusters relevant to the FeMo cofactor
Xu, G (Xu, Gan)[ 1 ] ; Wang, Z (Wang, Zheng)[ 1 ] ; Ling, R (Ling, Rong)[ 1 ] ; Zhou, J (Zhou, Jie)[ 1 ] ; Chen, XD (Chen, Xu-Dong)[ 1,2 ]*（陈旭东）; Holm, RH (Holm, Richard H.)[ 2 ]*
[ 1 ] Nanjing Normal Univ, Sch Chem & Mat Sci, Jiangsu Collaborat Innovat Ctr Biomed Funct Mat, Jiangsu Key Lab Biofunct Mat, Nanjing 210023, Jiangsu, Peoples R China
[ 2 ] Harvard Univ, Dept Chem & Chem Biol, Cambridge, MA 02138 USA
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA，201805,115(20),5089-5092
Molybdenum-dependent nitrogenases catalyze the transformation of dinitrogen into ammonia under ambient conditions. The active site (FeMo cofactor) is the structurally and electronically complex weak-field metal cluster [MoFe7S9C] built of Fe4S3 and MoFe3S3C portions connected by three sulfur bridges and containing an interstitial carbon atom centered in an Fe-6 trigonal prism. Chemical synthesis of this cluster is a major challenge in biomimetic inorganic chemistry. One synthetic approach of core ligand metathesis has been developed based on the design and synthesis of unprecedented incomplete ([(Tp*)WFe(2)S(3)Q(3)](-)) and complete ([(Tp*)WFe(3)S(3)Q(4)](2-)) cubane-type clusters containing bridging halide (Q = halide). These clusters are achieved by template-assisted assembly in the presence of sodium benzophenone ketyl reductant; products are controlled by reaction stoichiometry. Incomplete cubane clusters are subject to a variety of metathesis reactions resulting in substitution of a mu(2)-bridging ligand with other bridges such as N-3(-), MeO-, and EtS-. Reactions of complete cubanes with Me3SiN3 and S-8 undergo a redox metathesis process and lead to core ligand displacement and formation of [(Tp*)WFe3S3(mu(3)-Q)Cl-3](-) (Q = Me3SiN2-, S-2(-)). This work affords entry to a wide variety of heteroleptic clusters derivable from incomplete and complete cubanes; examples are provided. Among these is the cluster [(Tp*)WFe3S3(mu(3)-NSiMe3)Cl-3](-), one of the very few instances of a synthetic Fe-S cluster containing a light atom (C, N, O) in the core, which constitutes a close mimic of the [MoFe3S3C] fragment in FeMo cofactor. Superposition of them and comparison of metric information disclose a clear structural relationship [Tp* = tris(3,5-dimethyl-1-pyrazolyl) hydroborate(1-)].