Redox behavior of novel nickel and palladium complexes supported by trianionic non-innocent ligand containing β-diketiminate and phenol groups

Abstract

A new type of nickel and palladium complexes with non-innocent b-diketiminate ligand having redox active phenol groups, 2,4-di-tert-butyl-6-(((1E,2E)-3-((3,5-di-tert-butyl-2-hydroxyphenyl) amino)-2-nitroallylidene)amino)phenol (LH 3 , fully protonated form) have been developed, and the structure, physical properties, and reactivity of their one-electron and two-electron oxidized complexes, [M II (L ·2-)] and [M II (L -)] + (M = Ni II or Pd II ) have been examined in detail. The two-electron oxidized forms of both complexes, [M II (L -)] + , exhibited hydrogen atom abstraction ability from 1,4-cyclohexadiene (CHD) comparable to its copper analog [Cu II (L -)] + (Dalton Trans. 2013; 42: 2438-2444). The oneelectron oxidized form of palladium complex, [Pd II (L ·2-)], was also found to oxidize CHD, whereas the nickel analog, [Ni II (L ·2-)], exhibited photo-induced oxidation ability of CHD.

Hydroxylation of Unactivated C(sp3)–H Bonds with m-Chloroperbenzoic Acid Catalyzed by an Iron(III) Complex Supported by a Trianionic Planar Tetradentate Ligand

“…The first and second oxidation potentials of 1 were determined to be 0.11 and 0.76 V versus ferrocene/ferrocenium ion (Fc/Fc + ) by cyclic voltammetry (CV; Figure S2). The first oxidation potential is close to those of the Cu 2+ , Ni 2+ , Pd 2+ , and Rh 3+ complexes of L 3– (−0.06, 0.04, 0.07, and 0.22 vs Fc/Fc + , respectively), indicating that the redox locus of the first oxidation is on the ligand center irrespective of the metal ion, as previously reported. − Calculation of the one-electron-oxidized complex [Fe III ( L 2•– )­(Cl)] ( 2 ) with DFT indicated that the complex has a quintet spin ground state (Table S3). A significant amount of β-spin density was localized on the ligand in the spin density map of 2 (Figure S3), suggesting that the redox locus is the ligand rather than the metal center, as suggested by the CV data.…”

“…The spectral changes in the titration ended when an equimolar amout of (4-BrC 6 H 4 ) 3 N •+ was added to the solution of 1 (Figure S4b). Complex 2 shows a broad absorption band in the near-IR (NIR) region attributable to the one-electron-oxidized ligand L 2•– , which is a common spectral feature of the one-electron-oxidized complexes of this ligand. − The EPR spectral change observed upon the addition of (4-BrC 6 H 4 ) 3 N •+ was also consistent with formation of the one-electron-oxidized species with an integer spin state (Figure b) …”

“…The reagents and solvents used in this study, except the ligands and complexes, were commercial products of the highest available purity and were further purified by standard methods, if necessary . Ligand L H 3 was prepared according to the reported procedures. , …”

“…We have recently developed a planar trianionic ligand having redox-noninnocent character, L 3– ( L H 3 = 2,4-di- tert -butyl-6-({(1 E ,2 E )-3-[(3,5-di- tert -butyl-2-hydroxyphenyl)­amino]-2-nitroallylidene}­amino)­phenol; Figure a), which was used for the synthesis of late-transition-metal [copper­(II), nickel­(II), palladium­(II), and rhodium­(III)] complexes. − In this study, we have synthesized and characterized an iron complex of L 3– [(NEt 4 )­[Fe III ( L 3 )­(Cl)] ( 1 )] and found its prominent catalyst ability in the hydroxylation of alkanes including those having only primary C–H bonds with m -chloroperbenzoic acid ( m -CPBA) under very mild conditions.…”

On the non-innocence of “Nacnacs”: ligand-based reactivity in β-diketiminate supported coordination compounds

“…[18][19][20] Recently Wolczanski implemented the BDI motif as a component of chelate ligands possessing imino-pyridine moieties (Scheme 1) whose Cr and Fe derivatives featured rich ligand chemistry including redox non-innocent behaviour and multiple rearrangements. For instance, the introduction of phenol substituents (Scheme 1) leads to oxidative non-innocence through the formation of ligand phenoxyl radicals.…”