Synthesis and structural characterisation of unprecedented primary N-nitrosamines coordinated to iridium(iv)

Abstract

The redox chemistry of the N-nitrosamine complexes [IrCl₅(RN(H)NO)]^2– (R = benzyl or n-butyl) was studied in detail. One-electron oxidations at around 200 mV vs. ferrocene/ferrocenium were reversible in cyclic voltammograms. UV-vis spectroelectrochemistry reveals spectra characteristic of Ir^IV species but also partial decomposition of the oxidised species [Ir^IVCl₅(RN(H)NO)]˙⁻ on this timescale (minutes). Detailed studies on chemically oxidised solutions of the parent Ir^III complexes gave evidence for paramagnetic Ir^IV from NMR spectra. Final products of the decomposition were the corresponding alcohols and presumably [Ir^IIICl₅(L)]^2– (L = N₂, solvent, amine) complexes. Similar decomposition reactions of acidic DMSO solutions of [IrCl₅(RN(H)NO)]^2–revealed that this combination produces the so-called “activated” DMSO (Me₂S⁺–O⁻ or Me₂S⁺–OE, with “E” being an electrophile) which oxidises the parent Ir^III complexes. Finally, with the very reactive purple Ir^IV compound (PPh₄)[IrCl₅(BnN(H)NO)], the first primary N-nitrosamine coordinated to [Ir^IVCl₅]⁻ was isolated and characterised by UV-vis absorption, FTIR, NMR spectroscopy, ultra-high resolution electrospray mass spectrometry (UHR-ESI-MS) and iridium L₃ X-ray absorption near-edge spectroscopy (XANES).