A proton-responsive ligand becomes a dimetal linker for multisubstrate assembly via nitrate deoxygenation

Abstract

A bidentate pyrazolylpyridine ligand (HL) was installed on divalent nickel to give [(HL)₂Ni(NO₃)]NO₃. This compound reacts with a bis-silylated heterocycle, 1,4-bis-(trimethylsilyl)-1,4-diaza-2,5-cyclohexadiene (TMS₂Pz) to simultaneously reduce one of the nitrate ligands and deprotonate one of the HL ligands, giving octahedral (HL)(L⁻)Ni(NO₃). The mononitrate species formed is then further reacted with TMS₂Pz to doubly deoxygenate nitrate and form [(L⁻)Ni(NO)]₂, dimeric via bridging pyrazolate with bent nitrosyl ligands, representing a two-electron reduction of coordinated nitrate. Independent synthesis of a dimeric species [(L⁻)Ni(Br)]₂ is reported and effectively assembles two metals with better atom economy.