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

Abstract

Reactions of [Cr(NBut)Cl3(dme)](dme = 1,2-dimethoxyethane) or [PPh4][Cr(NBut)Cl4] with TI(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-But2 derivative] with AgBF4 afforded cationic imidochromium(V) Schiff-base compounds [Cr(NBut)L]BF4. Reactions of the imidochromium(V) compounds with PPh3 at reflux or on irradiation with UV light gave Ph3PNBut and 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.