Diaminoguanidinium And Triaminoguanidinium Schiff Bases And Their Complexation With Cis-MoO₂ Units

Coordination complexes with cis-MoO₂ units of Schiff bases have attracted much attention due to their application and dinitrogenases used as catalysts and structural and functional models of molybdenum enzymes.Syntheses of such complexes and catalyses of more organic transformation reactions have been active research interests of bioinorganic chemists.The diversity of the formation of molybdenum（VI） complexes could depand upon variations of different reaction conditions.Interactions of bis[（3,5-di-tert-butyl-2-hydroxyphenyl）amino]diaminoguanidiniumchloride（[H₆^tBu₄L]Cl）and ammonium heptamolybdate tetrahydrate(（NH₄）₆Mo₇O₂₄·4H₂O)in different mole ratios afforded new mononuclear and dinuclear cis-MoO₂diaminoguanidinium Schiff base complexes[（MoO₂）（OHMe）（H₃^tBu₄L）]（1）,[（MoO₂）₂（OHMe）₂（H^tBu₄L）]·2DMF（2）,[（MoO₂）₂（H^tBu₄L）]（3a）and[（MoO₂）₂（OH）₂（H^tBu₄L）]（3b）,respectively.Novel mononuclear,dinuclear and tetranuclear cis-MoO₂ triaminoguanidinium Schiff base complexes[（MoO₂）（OHMe）（H₃^tBu₆L’）]·CH₃OH·H₂O（4）,[（MoO₂）（OH₂）（H₃^tBu₆L’）]（5）,[（MoO₂）₂（OH₂）（DMF）（H^tBu₆L’）]·3DMF（6）and[（MoO₂）₄（DMF）₂（H^tBu₆L’）₂]·H₂O（7）wereobtainedbyreactionsof tris[（3,5-di-tert-butyl-2-hydroxyphenyl）triamino]tri-aminoguanidiniumchloride（[H₆^tBu₆L’]Cl） with （NH₄）₆Mo₇O₂₄·4H₂O under different reaction conditions,in the presence of triethylamine.Their molecular structures were determined by single-crystal X-ray diffraction.Structral analyses show that stable five-and six-membered rings based on cis-MoO₂ units were formed from NNO-donors of the aminoguanidinium Schiff-base ligands.The central molybdenum（VI） atoms are in the MoO₂N₂O₄ distorted octahedral coordination environment in the present complexes except for complex（3a）.All complexes were well characterized by ¹H NMR,FI-IR,UV-vis,fluorescence spectroscopies along with cyclic volammetries of electrochemical properties.Their catalytic activities involving in oxidative cyclization of cyclohexene were also investigated,indicating that the present cis-MoO₂ Schiff base complexes are promising catalysis for cyclohexene olefins.