Spectroscopic Elucidation of a Peroxo Ni₂(μ‐O₂) Intermediate Derived from a Nickel(I) Complex and Dioxygen

Abstract

The preparative chemistry and reactivity of NiÀO x intermediates has advanced significantly in the past few years with the identification of a number of new structure types. The most common synthetic approach, reaction of a nickel(ii) precursor with H 2 O 2 , has yielded bis-m-oxo [1][2][3][4] and bis-msuperoxo complexes.[4] An attractive alternate route utilizes the reaction of nickel(i) complexes with O 2 . This strategy relies on, and is limited by, the ability to prepare suitable nickel(i) species. We have utilized this latter approach to[5] (PhTt tBu = phenyltris((tertbutylthio)methyl)borate) and the related side-on bound superoxo complex, [{PhTt Ad }Ni(O 2 )] (PhTt Ad = phenyltris((1-adamantylthio)methyl)borate).[6] During the course of these studies, we considered whether a m-peroxo Ni 2 species was a possible intermediate along the reaction trajectory leading to the bis-m-oxo dimer. Lacking experimental evidence, a m-h 2 ,h 2 -peroxo bridged Ni 2 dimer supported by the tris(thioether) borato ligand was evaluated by density functional methods. [7] This hypothetical species was deemed to be of high energy, significantly destabilized (DH8 = 32 kcalmol À1 ) relative to the bis-m-oxo dimer and, therefore, an unlikely intermediate. Consequently, we turned our attention to macrocyclic tetradentate ligands that coordinate in a planar array, reasoning that such an attribute would render access to the m-h 2 ,h 2 -peroxo coordination more difficult. Herein, we report on the successful pursuit of this strategy, which led to the discovery of a Ni 2 (m-O 2 ) complex in which the peroxo moiety spans the metals in the m-1,2 mode.Addition of dry O 2 to [Ni(tmc)]OTf [8,9] (1; tmc = 1, 4,8,4,8, OTf = [CF 3 SO 3 ] À ) in THF or acetonitrile at room temperature resulted in a color change from pale blue to clover green. The FT-IR spectrum of the paramagnetic product (m eff = 2.7(1) m B ) included a prominent new feature at 3628 cm À1 assigned to the ñ(OÀH) mode

Terminal NiII−OH/−OH2 complexes in trigonal bipyramidal geometries derived from H2O

“…Riordan was the first report such a species but this Ni II –OH complex has a square planar primary coordination sphere coordination with a τ 5 value of 0.0 [22]. Levy’s nickel-hydroxido complex has a τ 5 value of 0.86, and is thus the only other Ni II –OH complex with tbp geometry [23].…”

“…To the best of our knowledge, there are only two examples of crystallographically characterized monometallic 5-coordinate Ni II –OH complexes. Riordan has prepared a square pyramidal complex with a 1,4,8,11-tetramethyl-1,4,8,11-tetraazadodecane ligand in which the exogenous hydroxido ligand is derived from dioxygen [22], and Levy has prepared a trigonal bipyramidal complex with a bulky Schiff base ligand where the exogenous hydroxido ligand is derived from adventitious water [23]. The earliest structurally characterized 5-coordinate terminal Ni II –OH 2 complex was reported by Stuky in 1969 [24], and since then many other structurally characterized terminal Ni II –OH 2 complexes have been prepared [25–27].…”

Synthesis and Spectroscopic Identification of a μ-1,2-Disulfidodinickel Complex

“…A qualitative comparison between 2 and the isostructural trans -1,2-peroxo bridged dinickel complex, {[Ni(tmc)] 2 ( μ -O 2 )} 2+ ( 4 ),13 is instructive. Because the disulfide π * orbitals in 2 are higher in energy than the peroxo π * orbitals in 4 , the former are closer in energy to the nickel 3d orbitals and, thus, interact more strongly to produce more covalent Ni–S bonds in 2 compared to the Ni–O bonds in 4 .…”

Ultrafast selected energy x-ray absorption spectroscopy investigations of Ni and Zn species

“…1-3 Ni͑tmc͒ + ͑tmc= 1,4,8,11-tetramethyl-1, 4,8,11-tetrazadodecane͒ has been investigated for their potential use in forming various Ni-O intermediates in many applications. 4 Ni compounds such as Ni 2 S 3 have been known to be carcinogenic. 5,6 Although a molecular level understanding of carcinogenesis of Ni is lacking, one of the mechanisms suggested that a square-planar binding of Ni ͑II͒ to a peptide motif in the C-tail region of histone H2A helped the hydrolysis of peptides.…”