Aluminum–Ligand Cooperative N–H Bond Activation and an Example of Dehydrogenative Coupling

Myers, Thomas W.; Berben, Louise A.

doi:10.1021/ja4032874

Cited by 130 publications

(102 citation statements)

References 31 publications

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“…We have previously reported that aluminum complexes of Ph I 2 P are able to adopt both symmetric and asymmetric electronic structures upon two-electron reduction and this result was observed crystallographically. 9,33 However, in that previous instance with asymmetric complexes of Al(III), the 1 H-NMR spectra displayed only an average signal that could have been consistent with the symmetric electronic structure of Ph I 2 P (B Chart 1).…”

Section: Synthesis Of Complexesmentioning

confidence: 74%

Synthesis and characterization of bis(imino)pyridine complexes of divalent Mg and Zn

et al. 2016

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Phenyl-bis(imino)pyridine (PhI2P) complexes, (PhI2P)ZnCl2 (1), (PhI2P−)ZnCl (2) and (PhI2P−)Zn(py)Cl (3) were obtained with the I2P ligand in both the neutral and the one-electron reduced state. In all examples, the metal ion is Zn(II). Metrical parameters obtained from solid state structures of 2 and 3 indicate that the PhI2P− ligand exists as a radical which is supported at the carbon atom of the imino donor, and this electronic state is also apparent in the analogous one-electron reduced ligand Al(III) complex, (PhI2P−)AlCl2 (4), that we prepared for comparison. We were unable to obtain PhI2P Mg complexes, and so the more electron rich methyl-substituted bis(imino)pyridine ligand, MeI2P, was investigated. Reaction of two-electron reduced MeI2P with MgCl2 and Mg(OTf)2 did afford the two-electron reduced ligand complexes [(MeI2P2−)Mg(THF)]2(μ-MgCl2) (5) and (MeI2P2−)Mg(THF)2 (6), respectively (MeI2P = 2,6-bis(1-methylethyl)-N-(2-pyridinylmethylene)phenylamine). Complex 5 crystallizes as a trinuclear Mg complex consisting of two (MeI2P2−)Mg moieties bridged by MgCl2 and the (MeI2P2−) ligand is symmetric across the pyridine ring, but is not planar. In contrast, the (MeI2P2−) ligand in 6 is asymmetric across the pyridine ring and all atoms in the ligand are coplanar. Cyclic voltammetry measurements reveal that in complexes, 1, 4, 5, 6, the I2P0, I2P−, and I2P2− ligand charge states are accessible electrochemically.

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Section: Synthesis Of Complexesmentioning

confidence: 74%

Synthesis and characterization of bis(imino)pyridine complexes of divalent Mg and Zn

et al. 2016

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“…Complexes with general formulation ( Ph I 2 P n− )AlX 2 were isolated in two oxidation states, where n =1, 2 24. The most notable feature of the electronic structure of complexes of the two‐electron reduced tridentate I 2 P ligand, ( Ph I 2 P 2− )AlX, is the ability of the 2− oxidation state to support multiple resonance forms of I 2 P. The most commonly observed resonance form is asymmetric with reduction localized at the pyridyl and one of the imino donor ligands (Scheme ).…”

Section: Reduced‐ligand Complexes Of Aluminummentioning

confidence: 99%

Catalysis by Aluminum(III) Complexes of Non‐Innocent Ligands

Berben

2014

Chemistry A European J

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Non-Innocent ligand complexes of aluminum are described in this Concept article, beginning with a discussion of their synthesis, and then structural and electronic characterization. The main focus concerns the ability of the ligands in these complexes to mediate proton transfer reactions. As examples, aluminum-ligand cooperation in the activation of polar bonds is described, as is the importance of hydrogen bonding to stabilization of a transition state for β-hydride abstraction. Taken together these reactions enable catalytic processes such as the dehydrogenation of formic acid.

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“…12 We have previously reported that ( Ph I 2 P 2− )AlH (1; Ph I 2 P = 2,6-(2,6-i Pr 2 -C 6 H 3 NCPh) 2 C 5 H 3 N) activated the N−H bonds in anilines and benzylamine. 4 We now report the synthesis of [( Ph HI 2 …”

Section: T He Addition Of O−h Bonds Across the Metal−ligand Bondsmentioning

confidence: 99%

Aluminum–Amido-Mediated Heterolytic Addition of Water Affords an Alumoxane

Myers

Berben

2013

Organometallics

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Addition of the O−H bonds in water across the aluminum− nitrogen bond of a molecular aluminum−amido complex affords an alumoxane. The reaction of ( Ph I 2 P 2− )AlH (1) with water forms dimeric [( Ph HI 2 P − )AlH](μ-O) (2) under mild conditions. Upon reaction of 2 with excess water [( Ph HI 2 P − )Al(OH)](μ-O) (3) is formed with liberation of H 2 . T he addition of O−H bonds across the metal−ligand bonds of a metal complex, essentially an acid−base process, represents an alternative to oxidative addition of OH bonds at a single metal center. This elementary step has been shown to initiate the activation of alcohols toward reactions such as dehydrogenative coupling and amide formation. 1 The activation of water, via addition of the O−H bond across a metal− ligand bond, has also been reported by Milstein and co-workers, who showed formation of a ruthenium hydroxide complex. 2 Examples of heterolytic bond activation by group 13 metal complexes include activation of weak C−H bonds and of the N−H bonds in amines, 3,4 but we are not aware of examples of O−H cleavage.The bis(imino)pyridine (I 2 P) ligand system has been employed for its redox noninnocence in a variety of transition-metal complexes. 5 Reports of the chemical noninnocence of this ligand are rarer and include radical coupling to form new C−C bonds between ligands and the transfer of alkyl or hydride groups to various positions on the ligand backbone. 6 Budzelaar and co-workers showed that alkylation of a variety of I 2 P ligands by main-group-metal alkyls can occur at any site on the pyridine ring in addition to the imine carbons and that the selectivity is influenced by both the identity of the metal and the alkyl used. 7 In order to access the potential of metal−ligand cooperative pathways observed in other pincer ligand systems, it is necessary to design (I 2 P)M complexes that preferentially access two-electron acid−base reactions over radical or redox processes. 8 Due to their tendency of discrete complexes containing the Al−O−Al moiety (alumoxanes) to form oligomers, their formation is a synthetic challenge. 9 Most commonly, alumoxanes are formed through the interaction of water with Al−H, Al−R, or Al−X bonds (R = alkyl, X = halide), 10

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Aluminum–Ligand Cooperative N–H Bond Activation and an Example of Dehydrogenative Coupling

Cited by 130 publications

References 31 publications

Synthesis and characterization of bis(imino)pyridine complexes of divalent Mg and Zn

Synthesis and characterization of bis(imino)pyridine complexes of divalent Mg and Zn

Catalysis by Aluminum(III) Complexes of Non‐Innocent Ligands

Aluminum–Amido-Mediated Heterolytic Addition of Water Affords an Alumoxane

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