Syntheses and electrochemistry of imidochromium(V) compounds. Crystal structure of [PPh4][Cr(NBut)Cl4(OH2)]

Abstract

Reactions of [Cr(NBu^t)Cl₃(dme)](dme = 1,2-dimethoxyethane) or [PPh₄][Cr(NBu^t)Cl₄] with TI(C₅H₅) and NaL′{L′=(η-C₅H₅)Co[PO(OEt)₂]₃} gave respective paramagnetic (µ_effca. 1.7 µ_B) half-sandwich imidochromium(V) compounds [CrL(NBu^t)Cl₂](L =η-C₅H₅1 or L′2). The structure of [PPh₄][Cr-(NBu^t)Cl₄(OH₂)] has been established by X-ray crystallography. The [Cr(NBu^t)Cl₄(OH₂)]^– anion has an octahedral geometry with Cr–N (imido) 1.619(3)Å. Treatment of [Cr(NBu^t)(L)Cl][H₂L =N,N′-bis(salicylidene)ethane-1,2-diamine or its 3,5-Bu^t₂ derivative] with AgBF₄ afforded cationic imidochromium(V) Schiff-base compounds [Cr(NBu^t)L]BF₄. Reactions of the imidochromium(V) compounds with PPh₃ at reflux or on irradiation with UV light gave Ph₃PNBu^t and Cr^III. Cyclic voltammetry of the imidochromium(V) compounds showed in most cases irreversible oxidation and reduction waves, which are attributed to oxidation and reduction of Cr^V.