Tuning Inner-Sphere Electron Transfer in a Series of Copper/Nitrosoarene Adducts

Mohammad Amin Askari (1) , Farshid Effaty (1) , Federica Gennarini (2) , Maylis Orio (3) , Nicolas Le Poul (2) , Xavier Ottenwaelder (1)

1 Concordia - Department of Chemistry and Biochemistry - Concordia University - 7141 Sherbrooke W., Montreal, Canada H4B 1R6
2 CEMCA - Chimie, Electrochimie Moléculaires et Chimie Analytique
3 ISM2 - Institut des Sciences Moléculaires de Marseille

A series of copper/nitrosoarene complexes was created that mimics several steps in biomimetic O2 activation by copper(I). The reaction of the copper(I) complex of N,N,N′,N′-tetramethypropylenediamine with a series of para-substituted nitrosobenzene derivatives leads to adducts in which the nitrosoarene (ArNO) is reduced by zero, one, or two electrons, akin to the isovalent species dioxygen, superoxide, and peroxide, respectively. The geometric and electronic structures of these adducts were characterized by means of X-ray diffraction, vibrational analysis, ultraviolet–visible spectroscopy, NMR, electrochemistry, and density functional theory (DFT) calculations. The bonding mode of the NO moiety depends on the oxidation state of the ArNO moiety: κN for ArNO, mononuclear η2-NO and dinuclear μ-η2:η1 for ArNO•–, and dinuclear μ-η2:η2 for ArNO2–. 15N isotopic labeling confirms the reduction state by measuring the NO stretching frequency (1392 cm–1 for κN-ArNO, 1226 cm–1 for η2-ArNO•–, 1133 cm–1 for dinuclear μ-η2:η1-ArNO•–, and 875 cm–1 for dinuclear μ-η2:η2 for ArNO2–). The 15N NMR signal disappears for the ArNO•– species, establishing a unique diagnostic for the radical state. Electrochemical studies indicate reduction waves that are consistent with one-electron reduction of the adducts and are compared with studies performed on Cu-O2 analogues. DFT calculations were undertaken to confirm our experimental findings, notably to establish the nature of the charge-transfer transitions responsible for the intense green color of the complexes. In fine, this family of complexes is unique in that it walks through three redox states of the ArNO moiety while keeping the metal and its supporting ligand the same. This work provides snapshots of the reactivity of the toxic nitrosoarene molecules with the biologically relevant Cu(I) ion.

Mots clés: Redox reactions; Adducts; Metals; Electronic structure; Electrochemical reduction

Domaines: Chimie; Chimie inorganique

Mohammad Amin Askari, Farshid Effaty, Federica Gennarini, Maylis Orio, Nicolas Le Poul, et al.. Tuning Inner-Sphere Electron Transfer in a Series of Copper/Nitrosoarene Adducts. Inorganic Chemistry, 2020, 59, pp.8678 - 8689. ⟨10.1021/acs.inorgchem.9b03175⟩. ⟨hal-02490219⟩