In exploring terminal nickel‐oxo complexes, postulated to be the active oxidant in natural and non‐natural oxidation reactions, we report the synthesis of the pseudo‐trigonal bipyramidal NiII complexes (K)[NiII(LPh)(DMF)] (1[DMF]) and (NMe4)2[NiII(LPh)(OAc)] (1[OAc]) (LPh=2,2’,2’’‐nitrilo‐tris‐(N‐phenylacetamide); DMF=N,N‐dimethylformamide; −OAc=acetate). Both complexes were characterized using NMR, FTIR, ESI‐MS, and X‐ray crystallography, showing the LPh ligand to bind in a tetradentate fashion, together with an ancillary donor. The reaction of 1[OAc] with peroxyphenyl acetic acid (PPAA) resulted in the formation of [(LPh)NiIII−O−H⋅⋅⋅OAc]2−, 2, that displays many of the characteristics of a terminal Ni=O species. 2 was characterized by UV‐Vis, EPR, and XAS spectroscopies and ESI‐MS. 2 decayed to yield a NiII‐phenolate complex 3 (through aromatic electrophilic substitution) that was characterized by NMR, FTIR, ESI‐MS, and X‐ray crystallography. 2 was capable of hydroxylation of hydrocarbons and epoxidation of olefins, as well as oxygen atom transfer oxidation of phosphines at exceptional rates. While the oxo‐wall remains standing, this complex represents an excellent example of a masked metal‐oxide that displays all of the properties expected of the ever elusive terminal M=O beyond the oxo‐wall.

The reaction of (NMe4)2[NiII(LPh)(OAc)] (1[OAc], LPh = 2,2',2''-nitrilo-tris-(N-phenylacetamide); –OAc = acetate) with 3-chloroperoxybenzoic acid (m-CPBA) resulted in the formation of a self-hydroxylate NiIII-phenolate complex, 2, where one of the phenyl...

The synthesis of tripodal carboxamide ligands using one-pot phosphite coupling reactions with nitrilotriacetic acid (NTA) and 4-substituted anilines is well established. Generation of such tripodal ligands using ortho-substituted anilines ( 2,6À R ArNH 2 , R = F, Me, i Pr) has proven to be challenging. The reaction between NTA and 2,6À R ArNH 2 using triphenylphosphite as a coupling reagent did not yield the desired tripodal carboxamide. Rather, the formation of 3,5-dioxo-1-piperazine intramolecular coupling products 3) was observed. All three compounds have been extensively characterized using nuclear magnetic resonance, Fourier-transform infra-red and mass spectrometry. X-ray diffraction analysis yielded solid state structures of 2 and 3. Substituents at the ortho position of aniline thus favours intramolecular cyclization over the formation of tripodal carboxamide ligands, preventing preparation of the desired bulky ligand.