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As the active site mimics of [FeFe]-hydrogenases, 14 new butterfly [2Fe2E] (E = Se, S) cluster complexes have been prepared by various synthetic routes. The N-substituted single-butterfly [2Fe2Se] complexes [(μ-SeCH2)2NC(O)R]Fe2(CO)6(1, R = Me; 2, R = Ph; 3, R = PhCH2O) were prepared by reactions of the in situ formed (μ-LiSe)2Fe2(CO)6with RC(O)N(CH2Cl)2, whereas the corresponding [2Fe2S] complexes [(μ-SCH2)2NC6H4R-p]Fe2(CO)6(4, R = CO2Et; 5, R = CH2OH) were produced by reaction of the in situ generated (μ-HS)2Fe2(CO)6with aqueous CH2O followed by treatment with p-RC6H4NH2. The parent single-butterfly [2Fe2Se] complex [(μ-SeCH2)2NH]Fe2(CO)6(6) could be prepared by reaction of the N-substituted complex 3with deprotecting reagent BBr3, BF3·OEt2/EtSH, or BF3·OEt2/Me2S, whereas the N-substituted single-butterfly [2Fe2Se] complexes [(μ-SeCH2)2NC(O)R]Fe2(CO)6(7, R = Et; 8, R = PhCH2) were produced by reactions of 6with acylating agents RC(O)Cl in the presence of Et3N. While the known parent single-butterfly [2Fe2S] complex [(μ-SCH2)2NH]Fe2(CO)6reacted with 2,6-[ClC(O)]2C5H3N to afford double-butterfly [2Fe2S] complex [Fe2(CO)6(μ-SCH2)2NC(O)]2(2,6-C5H3N) (9), the new N-hydroxyethyl-substituted single-butterfly [2Fe2Se] complex [(μ-SeCH2)2N(CH2)2OH]Fe2(CO)6(10) could be obtained by the in situ reaction of (μ-HSe)2Fe2(CO)6with (HOCH2)2N(CH2)2OH. Interestingly, complex 10could react with [ClC(O)]2CH2or 1,3,5-[ClC(O)]3C6H3in the presence of Et3N to give the corresponding double-butterfly [2Fe2Se] complex [Fe2(CO)6(μ-SeCH2)2N(CH2)2O2C]2CH2(11) and triple-butterfly complex [Fe2(CO)6(μ-SeCH2)2N(CH2)2O2C]3(1,3,5-C6H3) (12), whereas the known single-butterfly [2Fe2S] complex [(μ-SCH2)2N(CH2)2OH]Fe2(CO)6could react with 2,6-[ClC(O)]2C5H3N and 1,3,5-[ClC(O)]3C6H3in the presence of Et3N to afford the corresponding double-butterfly [2Fe2S] complex [Fe2(CO)6(μ-SCH2)2N(CH2)2O2C]2(2,6-C5H3N) (13) and triple-butterfly complex [Fe2(CO)6(μ-SCH2)2N(CH2)2O2C]3(1,3,5-C6H3) (14), respectively. All the new complexes 1–14have been characterized by elemental analysis and spectroscopy, as well as by X-ray crystallography for 1–4, 7–9, and 14. In addition, the electrochemical study indicated that complexes 1and 2can catalyze the proton reduction of HOAc to give hydrogen. [ABSTRACT FROM AUTHOR]

Reactions of 2,6-(ArNCH)2C6H3Li with CrCl2(THF)2afford two trinuclear bis(imino)aryl NCN pincer Cr(II) complexes {[2,6-(ArNCH)2C6H3]Cr(μ-Cl)2}2Cr [Ar = 2,6-Me2C6H3(1a), 2,6-Et2C6H3(1b)], and a mononuclear bis(imino)aryl NCN pincer Cr(II) complex [2,6-(ArNCH)2C6H3]Cr(μ-Cl)2Li(THF)2[Ar = 2,6-iPr2C6H3(1c)], respectively. Similar reactions of 2,6-(ArNCH)2C6H3Li with CrCl3(THF)3produce only mononuclear bis(imino)aryl NCN pincer Cr(III) complexes [2,6-(ArNCH)2C6H3]CrCl2(THF) [Ar = 2,6-Me2C6H3(2a), 2,6-Et2C6H3(2b), 2,6-iPr2C6H3(2c)]. X-ray crystallographic analysis reveals that the terminal Cr(II) atoms in 1aand 1band the Cr(II) atom in 1cpossess a distorted trigonal bipyramidal coordination environment with the Cipsoatom of the pincer ligand and two chloride atoms in the equator and the two imine nitrogen atoms in the apical positions, while the Cr(III) complexes 2a, 2b, and 2call adopt a distorted octahedral geometry around the chromium metal. Upon activation with trialkylaluminum and [Ph3C][B(C6F5)4]−, the Cr(III) complexes show high catalytic activity for isoprene polymerization and afford polyisoprene with predominately trans-1,4 units, whereas the Cr(II) complexes are inert under the same conditions. [ABSTRACT FROM AUTHOR]

Reactions of 2,6-(ArNCH)2C6H3Li with AlEt2Cl afford a number of NCN pincer aluminum complexes (2,6-(ArNCH)2C6H3)AlEt2(Ar = Ph (1), 2,6-Me2C6H3(2), 2,6-Et2C6H3(3), 2,6-iPr2C6H3(4)). Similar reactions of 2,6-(ArNCH)2C6H3Li with ZnEtCl produce bisligated zinc complexes (2,6-(ArNCH)2C6H3)2Zn (Ar = Ph (5), 2,6-Me2C6H3(6), 2,6-Et2C6H3(7)) and monoligated NCN pincer zinc complex (2,6-(ArNCH)2C6H3)ZnEt (Ar = 2,6-iPr2C6H3(8)). All complexes were characterized by 1H and 13C NMR spectroscopy, and the molecular structures of complexes 3, 4, 6, 7, and 8were determined by X-ray crystallography. The X-ray diffraction analysis reveals that both complexes 3and 4adopt a distorted trigonal-bipyramidal geometry around the aluminum central metal with three carbon atoms in the equator and the two imine nitrogen atoms in the apical positions. Complexes 6and 7adopt a distorted tetrahedral geometry around their zinc metal centers, while complex 8adopts a square-planar geometry around its metal center. All these Al and Zn complexes are efficient initiators for l-lactide ring-opening polymerization in the presence of benzyl alcohol, and the polymerization reaction takes place in an immortal manner. The productivity of the Zn complexes is generally higher than that of the Al complexes under similar conditions. [ABSTRACT FROM AUTHOR]

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]