Construction Of Thiolate-bridged Dimetallic Complexes And Their Application In The Biomimetic Chemical Simulation Of Metalloenzymes

For the purpose of biomimetic chemical simulation of the belt diiron active sites of the FeMo-co in nitrogenase and the second coordination spheres of metalloenzymes,a series of thiolate-bridged dimetallic complexes were designed and synthesized by introducing new cyclic(alkyl)(amino)carbene ligand Me2-cAAC,pendent amine functionalized Cp*ligand Cp*N and N,P hybrid multidentate ligand P2N2.These complexes can serve as platforms to get deep insight into the active sites of metalloenzymes and the function of second coordination spheres in small molecule activation.Firstly,thiolate-bridged diiron nitrogenase model complexes were constructed by using complex[(Me2-cAAC)Fe(?-Br)(Br)]2 as precusor.When complex[(Me2-cAAC)Fe(?-Br)(Br)]2 reacted with the flexible monodentate thiolate ligands,two thiolate-bridged diiron complexes[(Me2-cAAC)Fe(?-SR)(Br)]2(R = Me,Et)with Me2-cAAC ligand were obtained.These two complexes successfully simulate the diiron centers in the belt region of the FeMo-co in terms of the S/C coordination environment and the coordination geometry.Moreover,complex[(Me2-cAAC)Fe(?-Br)(Br)]2 reacted with NaSCPh3 to form a[3:1]site-differentiated cubane-type cluster[(Me2-cAAC)Fe4(?-S)4(Br)3][Me2-cAACH],in which the[Fe4S4]geometric configuration and the formal valence are similar to the[Fe4S4]2+cluster in Fe-protein of nitrogenase.Secondly,the construction of diiron complexes with azido ligands was achieved by using[(Me2-cAAC)Fe(?-Br)(Br)]2 as precursor.Reaction of complex[(Me2-cAAC)Fe(?-Br)(Br)]2 with 2 equivalent of NaN3 afforded an one-dimensional infinite chain of polymer[(Me2-cAAC)Fe(?-N3)(Br)]n featuring end-to-end azido groups.In contrast,when complex[(Me2-cAAC)Fe(?-Br)(Br)]2 reacted with 4 equivalent of NaN3.a diiron complex[(Met-cAAC)Fe(?-N3)(N3))2 with four azido ligands was obtained.In addition,the reaction of complex[(Me2-cAAC)Fe(?-SMe)(Br)]2 with 2 equivalent of NaN3 resulted in the corresponding azide complex[(Me2-cAAC)Fe(?-SMe)(N3)]2,in which the two terminal azide are in a trans arrangement.These iron complexes possessing azido ligands in different coordination modes provide new molecular systems for developing single molecular magnet based on azido ligands.Thirdly,using complex[Cp*NFe(?-CO)(CO)]2 and its protonated derivative as starting complexes,a series of mono-and diiron complexes possessing pendent amine functionalized side chain were synthesized.The protonation of the amino group in the side chain of a piano-stool type mono-iron complex[{?5,?1-C5Me4(CH2)2NMe2}Fe(MeCN)2][PF6]with MeCN ligands led to reversible dissociation of the nitrogen atom from the iron center.In addition,the bridged CO ligands of[Cp*NFe(?-CO)(CO)]2 can be replaced by monodentate thiolate ligands,leading to thiolate-bridged diiron complexes[Cp*NFe(?-SR)(CO)]2(R = Me,Et)with second coordination spheres.Different stretch directions of the side chains were presented when different substituent groups were adopted.When the N atom of the side chain was protonated,the stretch directions of the side chain and the stretch states were changed.Finally,thiolate-bridged heteronuclear complexes[Cp*M(?-bdt)Ni(P2N2R)][PF6](R = Br,MeO)were synthesized by self-assembly reactions of mono-nickel complexes[(P2N2R)Ni(bdt)]with mono-iron or mono-ruthenium complexes[Cp*M(MeCN)3][PF6].When these heteronuclear complexes reacted with CO,complexes[Cp*Fe(?-bdt)(?-CO)Ni(P2N2Br)][PF6]and[Cp*Ru(?-bdt)(?-CO)Ni(P2N2MeO)][PF6]with rare semi-bridging CO ligand were obained,which mimic the coordination mode of CO to the active site of the[Ni-Fe]-hydrogenase.