Paramagnetic aluminium β-diketiminate

Moilanen, Jani O.; Borau‐Garcia, Javier; Roesler, Roland; Tuononen, Heikki M.

doi:10.1039/c2cc34051h

Cited by 17 publications

(12 citation statements)

References 32 publications

(12 reference statements)

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“…The observation of two distinct ligand redox states is likely related to electrostatic interactions with the cation, which localizes the additional negative charge. A similar situation is observed in related bis(ligand) complexes: in the case of neutral radical species [{PhB(m-NtBu) 2 } 2 M] (M = Al, Ga) [16] and [(b-diketiminate) 2 Al], [17] the unpaired electron is fully delocalized over the spirocyclic structure, while for the radical anions [{PhB(m-NtBu) 2 } 2 M À ] (M = Mg, Zn), localized spin density is observed owing to interaction with the cation. [18] As suggested by the CV measurements, compounds 3 react with an additional equivalent of Na amalgam to give the dianionic complexes [Na(THF) 3 ] 2 [(PhNNC(R)NNPh) 2 Zn] (R = p-tolyl, 4 a; R = tBu, 4 b), of which 4 b was crystallographically characterized (Figure 4; pertinent bond distances in Table 2).…”

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confidence: 68%

The Formazanate Ligand as an Electron Reservoir: Bis(Formazanate) Zinc Complexes Isolated in Three Redox States

et al. 2014

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The synthesis of bis(formazanate) zinc complexes is described. These complexes have well-behaved redox-chemistry, with the ligands functioning as a reversible electron reservoir. This allows the synthesis of bis(formazanate) zinc compounds in three redox states in which the formazanate ligands are reduced to "metallaverdazyl" radicals. The stability of these ligand-based radicals is a result of the delocalization of the unpaired electron over four nitrogen atoms in the ligand backbone. The neutral, anionic, and dianionic compounds (L2 Zn(0/-1/-2)) were fully characterized by single-crystal X-ray crystallography, spectroscopic methods, and DFT calculations. In these complexes, the structural features of the formazanate ligands are very similar to well-known β-diketiminates, but the nitrogen-rich (NNCNN) backbone of formazanates opens the door to redox-chemistry that is otherwise not easily accessible.

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confidence: 68%

The Formazanate Ligand as an Electron Reservoir: Bis(Formazanate) Zinc Complexes Isolated in Three Redox States

et al. 2014

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“…The molecular structure of 1 reveals that the Al–N1 and Al–N8 bond vectors lie along the axial directions and the Al–Cl1, Al–N4, and Al–N5 bonds form the equatorial plane in 1 (Figure 1). The axial Al–N bonds are elongated as compared to equatorial Al–N bonds by about 0.081 Å, similar to related pentacoordinated Al(III) compounds in the literature, 47,48 and both are significantly longer than the Al–N bonds in four-coordinate β-diketiminate aluminum dichlorides. 11 The Al–Cl bond length in 1 (2.143(1) Å) is somewhat shorter than that in Berben’s pentacoordinated aluminum chloride complex with two bidentate nitrogen ligands (2.191(1) Å).…”

Section: Resultssupporting

confidence: 82%

Aluminum Complexes with Redox-Active Formazanate Ligand: Synthesis, Characterization, and Reduction Chemistry

Mondol

Otten

2019

Inorg. Chem.

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The synthesis of aluminum complexes with redox-active formazanate ligands is described. Salt metathesis using AlCl3 was shown to form a five-coordinate complex with two formazanate ligands, whereas organometallic aluminum starting materials yield tetrahedral mono(formazanate) aluminum compounds. The aluminum diphenyl derivative was successfully converted to the iodide complex (formazanate)AlI2, and a comparison of spectroscopic/structural data for these new complexes is provided. Characterization by cyclic voltammetry is supplemented by chemical reduction to demonstrate that ligand-based redox reactions are accessible in these compounds. The possibility to obtain a formazanate aluminum(I) carbenoid species by two-electron reduction was examined by experimental and computational studies, which highlight the potential impact of the nitrogen-rich formazanate ligand on the electronic structure of compounds with this ligand.

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“…The observation of two distinct ligand redox states is likely related to electrostatic interactions with the cation, which localizes the additional negative charge. A similar situation is observed in related bis(ligand) complexes: in the case of neutral radical species [PhB(μ-N t Bu) 2 ] 2 M (M = Al, Ga) [16] and (β-diketiminate) 2 Al [17] the unpaired electron is fully delocalized over the spirocyclic structure, while for the radical anions [PhB(μ-N t Bu) 2 ] 2 M -(M = Mg, Zn) localized spin density is observed due to interaction with the cation. [18] As suggested by the CV measurements, compounds 3 react with an additional equivalent of Na amalgam to give the dianionic complexes [Na(THF) 3 ] 2 [(PhNNC(R)NNPh) 2 Zn] (R = p-tolyl, 4a; R = t Bu, 4b), of which 4b was crystallographically characterized (Figure 4, pertinent bond distances in Table 2).…”

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confidence: 79%

The Formazanate Ligand as an Electron Reservoir: Bis(Formazanate) Zinc Complexes Isolated in Three Redox States

et al. 2014

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Metal-mediated redox processes are of fundamental importance in a wide variety of bond formation and cleavage reactions. The utility of transition metal catalysts in this type of reactions stems from their ability to switch between two (or more) oxidation states. Recently, there has been increased interest in redox processes that do not occur at the metal centre, but instead take place within the ancillary ligand framework (so-called 'redox-active' or 'non-innocent' ligands). [1] The use of organic ligands as redox equivalents is of key importance in biological (enzymatic) transformations, [2] and has been shown to open new reactivity pathways in catalysis. [1c] The most studied ligands of this class are dithiolenes and dioxolenes, while recent work has focussed on α-diimines [3] and bis(imino)pyridines. [4] A class of ligands that has found widespread utility in the synthesis of metal complexes across the periodic table are the monoanionic β-diketiminates. [5] These are generally considered as stable ligand scaffolds without involvement in redox-chemistry. Recently, examples of β-diketiminate metal complexes were reported in which the ligand was either reduced to a metal-bound di-or trianion, [6] or oxidized to a neutral radical species. [7] However, the limited stability of β-diketiminate complexes upon changing oxidation state prevents widespread application. [8] Formazanates (1,2,4,5-tetraazapentadienyls), [9] which are close analogues of β-diketiminates, have received comparatively little attention as ligands in coordination chemistry. [10] The stability of organic 6-membered heterocyclic radicals (verdazyls) that are derived from formazans prompted us to explore the use of formazanates as potential redox-active ligands (Chart 1). Here we show that zinc complexes with formazanate ligands engage in remarkably facile and reversible redox-chemistry which allows the full characterization of bis(formazanate) L 2 Zn complexes in charge neutral, anionic or dianionic redox states.

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Paramagnetic aluminium β-diketiminate

Cited by 17 publications

References 32 publications

The Formazanate Ligand as an Electron Reservoir: Bis(Formazanate) Zinc Complexes Isolated in Three Redox States

The Formazanate Ligand as an Electron Reservoir: Bis(Formazanate) Zinc Complexes Isolated in Three Redox States

Aluminum Complexes with Redox-Active Formazanate Ligand: Synthesis, Characterization, and Reduction Chemistry

The Formazanate Ligand as an Electron Reservoir: Bis(Formazanate) Zinc Complexes Isolated in Three Redox States

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