Scrutinizing the redox chemistry of group 10 complexes supported by a redox-active bis-phenolate mesoionic carbene

Abstract

We present the synthesis of an isostructural series of group 10 mesoionic carbene complexes with the general formula [M(MIC)Py] (with M = Ni (1), Pd (2) and Pt (3), Py = pyridine and MIC = bis-phenolate triazolylidene). Their electrochemical properties are investigated, revealing two quasi-reversible oxidations for all compounds, while no reductions are observed. Isolation of the oxidized species has been achieved using either silver triflate or nitrosonium tetrafluoroborate for the nickel and the platinum complex yielding the corresponding mono-cationic complexes [1]X and [3]X (X = OTf or BF4). For the palladium complex, oxidation reactions yielded different products 4 and 5 in which the pyridine and/or the phenol(oxy) donors were found to be labile compared to Ni and Pt. Additionally, for Pt the electron transfer reaction was found to be quite slow and short reaction times led to the isolation of an unusual heterobimetallic silver-platinum complex 6. The location of the redox event has been investigated using EPR spectroscopy and computational methods, which suggest, that the oxidation is mostly centered on one of the phenolate anchors.