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

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)12with (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 Avia a sequential reaction of (μ-Se2)Fe2(CO)6with Et3BHLi, followed by treatment with (BrCH2)2CHOH. The other “closed” and “open” cluster complexes 1−6could be further prepared by the hydroxy transformation and CO substitution reactions of complexes Aand B. For example, (i) reaction of Awith PPh3and decarbonylating agent Me3NO afforded PPh3-monosubstituted complex [(μ-SeCH2)2CH(OH)]Fe2(CO)5(PPh3) (1), (ii) further reaction of 1with 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 Awith the phosphatizing agent Ph2PCl in the presence of Et3N or simply with PhPCl2yielded the phosphite-functionalized complexes [(μ-SeCH2)2CH(OPPh2-η1)]Fe2(CO)5(3) and [(μ-SeCH2)2CH(OPPhCl-η1)]Fe2(CO)5(4), and (iv) treatment of Bwith 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)(OPPh2-η1)]Fe2(CO)5(6). All the new complexes have been characterized by elemental analysis and spectroscopy, as well as for A, 1−4, and 6by X-ray crystallography. Both 1H and 77Se NMR spectral studies demonstrated that complexes Band 5consist of three isomers of e-Et/a-R, e-Et/e-R, and a-Et/e-R, whereas complex 6exists 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 Aand Bcan catalyze the proton reduction of TsOH and HOAc to give hydrogen, respectively. [ABSTRACT FROM AUTHOR]