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Investigations on Synthesis, Structure, and Properties of New Butterfly [2Fe2Se] Cluster Complexes Relevant to Active Sites of Some Hydrogenases

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posted on 26.10.2009, 00:00 by Li-Cheng Song, Wei Gao, Cui-Ping Feng, De-Fu Wang, Qing-Mei Hu
As a continuation of our studies on biomimetic chemistry and butterfly cluster chemistry, two series of “closed” and “open” butterfly [2Fe2Se] cluster complexes have been prepared in satisfactory yields. Thus, treatment of Fe3(CO)12 with (HSeCH2)2CHOH in toluene at reflux gave the expected “closed” butterfly [2Fe2Se] cluster complex [(μ-SeCH2)2CH(OH)]Fe2(CO)6 (A), whereas the “open” butterfly cluster complex (μ-EtSe)[(μ-SeCH2CH(OH)(CH2Br)]Fe2(CO)6 (B) was unexpectedly produced along with complex A via a sequential reaction of (μ-Se2)Fe2(CO)6 with Et3BHLi, followed by treatment with (BrCH2)2CHOH. The other “closed” and “open” cluster complexes 16 could be further prepared by the hydroxy transformation and CO substitution reactions of complexes A and B. For example, (i) reaction of A with PPh3 and decarbonylating agent Me3NO afforded PPh3-monosubstituted complex [(μ-SeCH2)2CH(OH)]Fe2(CO)5(PPh3) (1), (ii) further reaction of 1 with the acylating agent PhC(O)Cl in the presence of Et3N produced the benzoate-functionalized complex [(μ-SeCH2)2CH(O2CPh)]Fe2(CO)5(PPh3) (2), (iii) treatment of A with the phosphatizing agent Ph2PCl in the presence of Et3N or simply with PhPCl2 yielded the phosphite-functionalized complexes [(μ-SeCH2)2CH(OPPh21)]Fe2(CO)5 (3) and [(μ-SeCH2)2CH(OPPhCl-η1)]Fe2(CO)5 (4), and (iv) treatment of B with 4-pyridinecarboxylic chloride or Ph2PCl in the presence of Et3N resulted in formation of the “open” butterfly cluster complexes (μ-EtSe)[μ-SeCH2CH(CH2Br)(O2CC5H4N-4)]Fe2(CO)6 (5) and (μ-EtSe)[μ-SeCH2CH(CH2Br)(OPPh21)]Fe2(CO)5 (6). All the new complexes have been characterized by elemental analysis and spectroscopy, as well as for A, 14, and 6 by X-ray crystallography. Both 1H and 77Se NMR spectral studies demonstrated that complexes B and 5 consist of three isomers of e-Et/a-R, e-Et/e-R, and a-Et/e-R, whereas complex 6 exists only as one isomer of e-Et/a-R. On the basis of an electrochemical study, it was found that the “closed” and “open” complexes A and B can catalyze the proton reduction of TsOH and HOAc to give hydrogen, respectively.