Aromatic and aliphatic hydrocarbon hydroxylation via a formally NiIVO oxidant

Abstract

The reaction of (NMe₄)₂[Ni^II(L^Ph)(OAc)] (1[OAc], L^Ph = 2,2′,2′′-nitrilo-tris-(N-phenylacetamide); OAc = acetate) with 3-chloroperoxybenzoic acid (m-CPBA) resulted in the formation of a self-hydroxylated Ni^III-phenolate complex, 2, where one of the phenyl groups of L^Ph underwent hydroxylation. 2 was characterised by UV-Vis, EPR, and XAS spectroscopies and ESI-MS. 2 decayed to yield a previously characterised Ni^II-phenolate complex, 3. We postulate that self-hydroxylation was mediated by a formally Ni^IVO oxidant, formed from the reaction of 1[OAc] with m-CPBA, which undergoes electrophilic aromatic substitution to yield 2. This is supported by an analysis of the kinetic and thermodynamic properties of the reaction of 1[OAc] with m-CPBA. Addition of exogenous hydrocarbon substrates intercepted the self-hydroxylation process, producing hydroxylated products, providing further support for the formally Ni^IVO entity. This study demonstrates that the reaction between Ni^II salts and m-CPBA can lead to potent metal-based oxidants, in contrast to recent studies demonstrating carboxyl radical is a radical free-chain reaction initiator in Ni^II/m-CPBA hydrocarbon oxidation catalysis.