Syntheses and electrochemistry of imidochromium(v) compounds. Crystal structure of [PPh₄][Cr(NBu^t)Cl₄(OH₂)]

Reactions of [Cr(NBut)Cl3(dme)] (dme = 1,2-dimethoxyethane) or [PPh4][Cr(NBut)Cl4] with Tl(C5H5) and NaL′ {L′ = (η-C5H5)Co[PO(OEt)2]3} gave respective paramagnetic (μeffca. 1.7 μB) half-sandwich imidochromium(V) compounds [CrL(NBut)Cl2] (L = η-C5H51 or L′ 2). The structure of [PPh4][Cr-(NBut)Cl4(OH2)] has been established by X-ray crystallography. The [Cr(NBut)Cl4(OH2)]-anion has an octahedral geometry with Cr-N (imido) 1.619(3) Å. Treatment of [Cr(NBut)(L)Cl] [H2L = N,N′-bis(salicylidene)ethane-1,2-diamine or its 3,5-But2derivative] with AgBF4afforded cationic imidochromium(V) Schiff-base compounds [Cr(NBut)L]BF4. Reactions of the imidochromium(V) compounds with PPh3at reflux or on irradiation with UV light gave Ph3P=NButand CrIII. Cyclic voltammetry of the imidochromium(V) compounds showed in most cases irreversible oxidation and reduction waves, which are attributed to oxidation and reduction of CrV.