High-Valent Ni and Cu Complexes of a Tetraanionic Bis(amidateanilido) Ligand

High-valent metal species are often invoked as intermediates during enzymatic and synthetic catalytic cycles. Anionic donors are often required to stabilize such high-valent states by forming strong bonds with the Lewis acidic metal centers while decreasing their oxidation potentials. In this report, we discuss the synthesis of two high-valent metal complexes [ML](+) in which the Ni-III and Cu-III centers are ligated by a new tetradentate, tetraanionic bis(amidateanilido) ligand. [ML](+), obtained via chemical oxidation of ML, exhibits UV-vis-NIR, EPR, and XANES spectra characteristic of square planar, high-valent M-III species, suggesting the locus of oxidation for both [ML](+) is predominantly metal-based. This is supported by theoretical analyses, which also support the observed visible transitions as ligand-to-metal charge transfer transitions characteristic of square planar, high-valent M-III species. Notably, [ML](+) can also be obtained via O-2 oxidation of ML due to its remarkably negative oxidation potentials (CuL/[CuL](+): -1.16 V, NiL/[NiL](+): -1.01 V vs Fc/Fc(+) in MeCN). This demonstrates the exceptionally strong donating nature of the tetraanionic bis(amidateanilido) ligation and its ability to stabilize high-valent metal centers..

Automated summary

High-valent metal complexes [ML] (+) were synthesized using a new tetradentate, tetraanionic bis(amidateanilido) ligand. The UV-vis-NIR, EPR, and XANES spectra of [ML] (+) indicate the presence of square planar, high-valent M-III species, with ligand-to-metal charge transfer transitions. The tetraanionic bis(amidateanilido) ligand showed exceptionally strong donating nature, enabling the stabilization of the high-valent metal centers.