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.
reflects the promising applications of magnetoelectrics including magnetic field sensors, transducers, microwave devices, oscillators, phase shifters, heterogeneous read/write devices, spintronic devices, and so on. [4][5][6] Among various multiferroics, BiFeO 3 has attracted great attention in the last two decades, being the unique materials to have ferroelectric and magnetic transition temperatures well above room temperature. [7,8] These properties make BiFeO 3 very appealing for the above mentioned applications. In addition, doping BiFeO 3 thin films with rare-earth [9][10][11] represents one of the possible ways to obtain magnetoelectric systems. Recently, an electrical control of magnetic order by manipulating chemical pressure within the material has been achieved by lanthanum substitution in the antiferromagnetic ferroelectric BiFeO 3 . [12] BiFeO 3 oxide system has a slightly distorted perovskite structure. Perovskite structures of general formula ABO 3 play an important role due to their appealing and variegate functional properties. [13] In fact, a wide variety of substitutions at both A and B sites is responsible for the great flexibility of the perovskite structure giving rise to a very large number of derivatives with subtle variations in structure.Great efforts have focused on optimizing undoped BiFeO 3 to enhance the room temperature ferromagnetism. Among the various methods, ion substitution is the most useful and widely applied method to improve the multiferroic properties of BiFeO 3.[14] In particular, a lot of attention has been dedicated on doping of various elements like rare-earth, alkaline-earth metals and transition metals at the A or B site of bismuth ferrite to improve its magnetoelectric properties. [15][16][17] Considerable efforts have been devoted to the synthesis of BiFeO 3 at the nanoscale level [18] and to the study of its ferroelectric properties, but for the above mentioned applications BiFeO 3 is required in thin film forms. Up to date, BiFeO 3 films have been deposited on various substrates using physical vapor deposition techniques such as pulsed laser deposition (PLD), [19][20][21][22] molecular beam epitaxy [23,24] and sputtering. [25][26][27] Atomic layer deposition has been recently applied to the deposition of thin or ultrathin films of BiFeO 3 using a laminar layer approach, alternating Bismuth ferrite (BiFeO 3 ) materials have been the subject of intense research activity in the last two decades. The great interest arises from the BiFeO 3 being one of the rare multiferroic compounds in which ferroelectricity and magnetism coexist at room temperature. To improve these properties several studies have been reported on the doping at the A and/or B sites of the BiFeO 3 perovskite structure. In this short review, the attention is focused to the synthesis of BiFeO 3 and BiFeO 3 doped with Ba or Dy at the A site and Ti at the B site through Metal Organic Chemical Vapor Deposition (MOCVD). The applied MOCVD process consists of an in situ one step approach using a multi-metal s...
Despite their potential role in enzymatic systems, there is a dearth of hydroxide-bridged high-valent oxidants. We recently reported the synthesis and characterization of Ni II Ni III (μ-OH) 2 (2) and Ni 2 III (μ-OH) 2 (3) species supported by a dicarboxamidate ligand (N,N′-bis(2,6-dimethylphenyl)-2,2-dimethylmalonamide). Herein, we explore the oxidative reactivity of these species using a series of para-substituted 2,6-di-tertbutyl-phenols (4-X-2,6-DTBP, X = −OCH 3 , −CH 2 CH 3 , −CH 3 , −C-(CH 3 ) 3 , −H, −Br, −CN, and −NO 2 ) as a mechanistic probe. Interestingly, upon reaction of 3 with the substrates, the formation of a new transient species, 2′, was observed. 2′ is postulated to be a protic congener of 2. All three species were demonstrated to react with the substituted phenols through a hydrogen atom transfer reaction mechanism, which was elucidated further by analysis of the postreaction mixtures. Critically, 3 was demonstrated to react at far superior rates to 2 and 2′, and oxidized substrates more efficiently than any bis-μ-oxo-Ni 2 III reported to date. The kinetic superiority of 3 with respect to 2 and 2′ was attributed to a stronger bond in the product of oxidation by 3 when compared to those calculated for 2 and 2′.
Hydroxide‐bridged high‐valent oxidants have been implicated as the active oxidants in methane monooxygenases and other oxidases that employ bimetallic clusters in their active site. To understand the properties of such species, bis‐μ‐hydroxo‐NiII2 complex (1) supported by a new dicarboxamidate ligand (N,N′‐bis(2,6‐dimethyl‐phenyl)‐2,2‐dimethylmalonamide) was prepared. Complex 1 contained a diamond core made up of two NiII ions and two bridging hydroxide ligands. Titration of the 1 e− oxidant (NH4)2[CeIV(NO3)6] with 1 at −45 °C showed the formation of the high‐valent species 2 and 3, containing NiIINiIII and NiIII2 diamond cores, respectively, maintaining the bis‐μ‐hydroxide core. Both complexes were characterised using electron paramagnetic resonance, X‐ray absorption, and electronic absorption spectroscopies. Density functional theory computations supported the spectroscopic assignments. Oxidation reactivity studies showed that bis‐μ‐hydroxide‐NiIII2 3 was capable of oxidizing substrates at −45 °C at rates greater than that of the most reactive bis‐μ‐oxo‐NiIII complexes reported to date.
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