Metal-Induced C–N Bond Cleavage in the Decomposition of Alkali (<i>R</i>,<i>R</i>)-Bis(α-methylbenzyl)amide Complexes

Border, Emily Chantelle; Maguire, Melissa; MacLellan, Jonathan G.; Andrews, Philip C.

doi:10.1021/acs.organomet.7b00074

Cited by 6 publications

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“…The 1 H and 13 C NMR spectra of the PMDETA-coordinated complex i share characteristic features of the aza-enolate structure with those seen in previously reported examples. ,,, In particular, the disappearance of the distinctive quartet and doublet in the 1 H NMR spectra corresponding to the α-methylbenzyl moiety and appearance of a pair of signals at 3.81 and 3.44 ppm show that a rearrangement to the aza-enolate form has occurred (see Figure ).…”

Section: Results and Discussionmentioning

confidence: 99%

“…In the course of our research of unsaturated alkali metal amides, the persistent occurrence of sigmatropic rearrangements (often accompanied by decomposition pathways and frequently with a loss of chirality where present) has sparked our interest. − In particular, the structural chemistry and the driving forces behind these rearranged products have not been well understood.…”

Section: Introductionmentioning

confidence: 99%

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Isomers of Alkali Metal (Methylbenzyl)allylamides: A Theoretical Perspective

et al. 2020

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Recent studies of alkali metal N-(α-methylbenzyl)allylamides containing lithium, sodium, and potassium have shown unique rearrangements in NMR experiments. It was found that lithium isomers favored the formation of aza-allyl and aza-enolate complexes that could exist in a solution for a substantial amount of time. As the radius of the metal ion increases going from lithium to potassium, so does the preference for the formation of the imine structure. For sodium, the aza-allyl complex could still be isolated, whereas the imine structure was only found to be stable on the scale of several hours for potassium. In this work, ab initio calculations were used to shed light on this phenomenon. Decomposition of intermolecular interaction energies of the aza-allyl, aza-enolate, and imine complexes showed that for lithium, the formation of aza-allyl and aza-enolate complexes was driven by electrostatic interactions. For potassium, the dispersion component of the metal interaction with the ligand proved to be more important for the stability of the imine structure. The presence of the imine formation in potassium and partially in sodium was found to be due to the reduced electrostatic nature of these larger metals. The assignment of the experimental NMR spectra was further confirmed with the natural bond order (NBO) analysis as well as the partial charge calculations. Analysis of orbital energies, specifically those of the highest occupied molecular orbitals (HOMOs), as well as the deformation energies of each of the ligands, were also considered. Through these procedures, an understanding of the tendency for each metal to have a unique isomerization pathway was gained.

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Section: Results and Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Isomers of Alkali Metal (Methylbenzyl)allylamides: A Theoretical Perspective

et al. 2020

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“…[15] Based on these reports and our experiments the coordination behavior of N-(2-pyridylethyl)-substituted amidinates and triazenides attracted our attention. [15] Based on these reports and our experiments the coordination behavior of N-(2-pyridylethyl)-substituted amidinates and triazenides attracted our attention.…”

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Coordination Chemistry of N‐(2‐Pyridylethyl)‐Substituted Bulky Amidinates and Triazenides of Magnesium

et al. 2018

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The amidines Dipp-N=C(R)-NH(C 2 H 4 R′) [R = tBu, R′ = Ph (1a); R = Ph, R′ = Py (1b)] as well as 1-(2,4,6-triisopropylphenyl)-3-(2-pyridylethyl)triazene (1c) are magnesiated with commercially available dibutylmagnesium yielding the complexes [(thf )Mg{Dipp-N=C(tBu)-solvent. [15] Based on these reports and our experiments the coordination behavior of N-(2-pyridylethyl)-substituted amidinates and triazenides attracted our attention. Starting N-(2-pyridylethyl)triazenes are rarely reported [16] and the coordination chemistry has been totally neglected. In contrast to the missing knowledge on the coordination chemistry of 2-pyridylethyltriazenides, there exist very few magnesium complexes of N-aryl-N′-(2-pyridylethyl)amidinates [12,17] that were structurally authenticated.For comparison reasons we included amidinate complexes of the type [Mg{Dipp-NC(R)N(C 2 H 4 R′)} 2 ] (R = tBu, Ph; R′ = Ph, Py) in our investigations. Results and DiscussionSynthesis. The preparation of the amidines followed a previously published protocol. [12] Dipp-N=C(R)Cl was added at room temperature to a toluene solution of phenylethylamine or 2-pyridylethylamine yielding the amidines Dipp-N=C(R)-NH(C 2 H 4 R′) [R = tBu, R′ = Ph (1a); R = Ph, R′ = Py (1b)] according to Scheme 2. Scheme 2. Syntheses of the amidines Dipp-N=C(R)-NH(C 2 H 4 R′) [R = tBu, R′ = Ph (1a); R = Ph, R′ = Py (1b)] in toluene at room temperature.The reaction of 2-pyridylethyl azide with 2,4,6-triisopropylphenylmagnesium bromide (Tripp-MgBr) in tetrahydrofuran (THF) and subsequent aqueous work-up yielded the corresponding 1-(2,4,6-triisopropylphenyl)-3-(2-pyridylethyl)triazene (1c) as depicted in Scheme 3. This triazene easily lost dinitrogen already in boiling n-pentane solution leading to the formation of 2-pyridylethyl-(2,4,6-triisopropylphenyl)amine (2). Therefore, during synthesis and recrystallization of 1c from aliphatic hydrocarbons, temperatures may not exceed room temperature.Scheme 3. Synthesis of Tripp-N=N-NH(C 2 H 4 Py) (1c) in tetrahydrofuran at room temperature and degradation in hot pentane yielding Tripp-NH(C 2 H 4 Py) (2). General Considerations:All manipulations were carried out in a nitrogen atmosphere using standard Schlenk techniques. The sol-Eur.

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“…Variabletemperature NMR studies at −60 and 25 °C also failed to shed any light on what was happening in solution. A single signal in the 7 Li NMR in d 8 -toluene with a line width of 210 Hz at 25 °C, which broadens to 269 Hz at −60 °C, suggests that there are at least two lithium environments in rapid exchange.…”

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confidence: 99%

“…In our studies on commonly used chiral benzylic and allylic amides we have discovered and reported on decomposition and rearrangement processes which are dependent on the metal (Li, Na, or K), reaction temperature, and the nature of any Lewis base(s) and/or solvents present. − Since our initial discovery of facile anion rearrangements in metalated N -(α-methylbenzyl)allylamide systems, we have been exploring the chemistry of related amines in an attempt to understand better the factors which drive these rearrangements and which ultimately result in the relocation of the π bond within the molecule. These processes can have a significant effect, changing completely the nature of the amido moiety and often negating the chiral nature of the α-methylbenzyl moiety, resulting in aza-allylic and aza-enolate systems. , …”

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