Synthesis And Study Of 1,2,4-Diazaarsole Ligands And Radical Complexes

1,2,4-diazaphosphole are five-membered aromatic heterocycles,which provide very special properties due to the synergistic effect of nitrogen and phosphorus(σ2λ3)atoms orbitals assisted with different substituents to change the chemical environment of diazaphosphole ring,and then affected its physicochemical properties,showing significantly different redox properties and special radical stability from other five membered heterocycles containing nitrogen or phosphorus atoms,such as triazole,pyrazole and phosphole.As far as we know,the basic redox properties and coordination diversity of diazaphosphole ligands and their metal complexes were explored in great detail,and have achieved fruitful results.Based on the extensive research of 1,2,4-diazaphosphole complexes and radicals,our group decided to replace the phosphorus atom of diazaphosphole ring with the heavier arsenic atom,so as to provide a more valuable 1,2,4-diazaarsole(da)ligand.The specific work list as follows:1.Synthesis of diazaarsole ligands.Two ligands containing 3,5-di-tert-butyl-1,2,4diazaarsole(H[3,5-tBu2da](1))and 3,5-di-phenyl-1,2,4-diazaarsole(H[3,5-Ph2da](2))were synthesized through three-step reaction,which could be sublimated by vacuum to provide pure and stable products as pale yellow solids.The structure and properties of the ligands 1 and 2 were characterized by X-ray single crystal diffraction,nuclear magnetic resonance(NMR),infrared spectrum(IR)and melting point.This study enriched the species of diazaarsole ligands.2.Synthesis of potassium diazaarsolide and holmium complexe.The potassium diazaarsolide of K[3,5-tBu2da](3)and[(η2-3,5-Ph2da)K(η6-[18]crown-6)](4)were synthesized by the reaction of ligands 1 and 2 with KH in anhydrous tetrahydrofuran(THF),respectively.The holmium complex[η2-(N,N)-3,5-tBu2da]3Ho(THF)2(5)was prepared by the metathesis reacton K[3,5-tBu2da](3)with HoCl3 in anhydrous THF,which has a slightly distorted trigonal bipyramidal geometry.The structure and properties of the complexes 3,4 and 5 were recorded on X-ray single crystal diffraction,NMR,IR and melting point.Among the three crystal structures,potassium and holmium ions were coordinated with the two nitrogen atoms of the diazaarsole rings in η2-coordination mode,which enriches the coordination mode of diazaarsole.3.Study on the diazaarsole radicals.Using 5,5-dimethyl-1-dihydropyrrole-N-oxide(DMPO)as radical trapping agent,K[3,5-tBu2da]was oxidized by Bi3+to provide the related radical[3,5-tBu2da]· in anhydrous THF,which was characterized by electron paramagnetic resonance(EPR)spectroscopy.The EPR spectrum shows a superfine structure,high resolution coupling 12-fold peaks.In order to verify the oxidation property of the potassium diazaarsole(3),cyclic voltammetry analysis of complex 3 was performed and a irreversible oxidation wave was found at Eox=+0.95V,which indicates that the diazaarsole anion[3,5-tBu2da]-could be oxidized by Bi3+.The radical dimer of diazaarsole[3,5-tBu2da](N)[3,5-tBu2da](As)(6)was successfully synthesized by the oxidation reaction of[K(3,5-tBu2da)]with Bi3+in anhydrous THE.The single crystal structure was successfully obtained.In order to explore the reduction property of K[3,5-Ph2da](4),metallic potassium was used as reducing agent to provide the black radical[K(η6-18-Cr-6)]+[(η75,η5-3,5-Ph2da)·2-][K(η6-18-Cr-6)]+(7)in anhydrous THF.The reaction solution quickly turned black,which proved that the radical(3,5-Ph2da)·2-complex was formed.The black solid and the reaction solution were tested by EPR.The line of black solid shows a set of four peaks,and the g factor was 2.0017.The spectrum of the reaction solution shows a group of peaks with basic symmetry up and down,which was not completely split,and the g factor was 2.005.This work laid the foundation for the discovery of more diazaarsole radicals.