Introduction of Substituents in the Aromatic Nucleus. Exploration of its Mechanism by means of Isotopic Hydrogen.

Melander, Lars; Willstaedt, Ebba; Lund, L. Koren; Hakala, Maire

doi:10.3891/acta.chem.scand.03-0095

Cited by 22 publications

(10 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…However, when the optimal AcOH concentration is exceeded, the KIE drops to a value of 1.1±0.1. Considering that rate limitation by the reoxidation step can be ruled out and assuming that these electrophilic Pd‐complexes undergo fast reductive elimination, this value could correspond to a S E Ar mechanism . Here, the rate of C−H activation is determined by the formation of the non‐aromatic “Wheland intermediate” rather than by the cleavage of the C−H bond.…”

Section: Methodsmentioning

confidence: 99%

The Dual Effect of the Acetate Ligand on the Mechanism of the Pd‐Catalyzed C−H/C−H Coupling of Benzene

2019

View full text Add to dashboard Cite

Pd(II)carboxylates have emerged as potent catalysts for the direct coupling of (hetero)aromatics, enabling a two‐fold C−H activation with various oxidants. Yet, prior research on the mechanism of the C−H/C−H coupling without directing group(s) has led to contrasting insights. In this work, a direct effect of acetic acid (AcOH) concentration on the mechanism of Pd‐catalyzed benzene coupling to biphenyl is uncovered. The catalytic cycle was investigated via kinetic isotope effects, H/D exchange experiments and by assessing the reactivity of the Pd(aryl)‐intermediates. The study revealed that the catalytic reaction makes a transition between two dissimilar C−H activation steps: a “concerted metalation‐deprotonation” (CMD) mechanism followed by an electrophilic substitution (SEAr). A dual role of the acetate ligand explains the transition between these mechanisms, mediating the deprotonation via CMD and coordinating on the Pd(II) ion to preclude a SEAr mechanism for the first C−H activation.

show abstract

Section: Methodsmentioning

confidence: 99%

The Dual Effect of the Acetate Ligand on the Mechanism of the Pd‐Catalyzed C−H/C−H Coupling of Benzene

2019

View full text Add to dashboard Cite

show abstract

“…It is then desirable to determine whether the initial att'ack or subsequent loss of a proton is the rate-determining step. Melander (148,149,150) has studied this problem using tritium-labeled benzene, nitrobenzene, the three possible monotritiumsubstituted toluenes, and naphthalene-&. In every case nitration gave no appreciable isotope effect, and a similar result was observed in the case of bromination.…”

Section: Aromatic Substitutionmentioning

confidence: 95%

The Deuterium Isotope Effect

Wiberg¹

1955

Chem. Rev.

714

303

View full text Add to dashboard Cite

“…Electrophilic aromatic nitration is one of the most thoroughly studied classes of organic reactions, and its mechanism has been intensely debated over many decades [ 1 – 7 ]. Still it continues to fascinate.…”

Section: Introductionmentioning

confidence: 99%

Mechanism and regioselectivity of electrophilic aromatic nitration in solution: the validity of the transition state approach

2017

View full text Add to dashboard Cite

The potential energy surfaces in gas phase and in aqueous solution for the nitration of benzene, chlorobenzene, and phenol have been elucidated with density functional theory at the M06-2X/6-311G(d,p) level combined with the polarizable continuum solvent model (PCM). Three reaction intermediates have been identified along both surfaces: the unoriented π-complex (I), the oriented reaction complex (II), and the σ-complex (III). In order to obtain quantitatively reliable results for positional selectivity and for modeling the expulsion of the proton, it is crucial to take solvent effects into consideration. The results are in agreement with Olah’s conclusion from over 40 years ago that the transition state leading to (II) is the rate-determining step in activated cases, while it is the one leading to (III) for deactivated cases. The simplified reactivity approach of using the free energy for the formation of (III) as a model of the rate-determining transition state has previously been shown to be very successful for halogenations, but problematic for nitrations. These observations are rationalized with the geometric and energetic resemblance, and lack of resemblance respectively, between (III) and the corresponding rate determining transition state. At this level of theory, neither the σ-complex (III) nor the reaction complex (II) can be used to accurately model the rate-determining transition state for nitrations.

show abstract

Introduction of Substituents in the Aromatic Nucleus. Exploration of its Mechanism by means of Isotopic Hydrogen.

Cited by 22 publications

References 0 publications

The Dual Effect of the Acetate Ligand on the Mechanism of the Pd‐Catalyzed C−H/C−H Coupling of Benzene

The Dual Effect of the Acetate Ligand on the Mechanism of the Pd‐Catalyzed C−H/C−H Coupling of Benzene

The Deuterium Isotope Effect

Mechanism and regioselectivity of electrophilic aromatic nitration in solution: the validity of the transition state approach

Contact Info

Product

Resources

About