Conformational and Configurational Dynamics of a Highly Fluorinated Hydrazone

Ramanathan, S.; Lemal, David M.

doi:10.1021/jo061945n

Cited by 16 publications

(12 citation statements)

References 8 publications

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“…However, the C–N single-bond rotation is restricted only in CDCl 3 , possibly due to its greater steric bulk. Factors such as Lewis basicity, dielectric constant, and steric bulk of the solvent have been shown to affect the relative population of rotamers. , Thus, two rotamers are observed in CDCl 3 , while only one is observed in CD 3 CN and DMSO- d 6 .…”

Section: Resultsmentioning

confidence: 99%

Depalladation of Neutral Monoalkyne- and Dialkyne-Inserted Palladacycles and Alkyne Insertion/Depalladation Reactions of Cationic Palladacycles Derived from N,N′,N″-Triarylguanidines as Facile Routes for Guanidine-Containing Heterocycles/Carbocycles: Synthetic, Structural, and Mechanistic Aspects

2014

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Depalladation of the monoalkyne-inserted cyclopalladated guanidines [κ 2 (C,N)Pd(2,6-Me 2 C 5 H 3 N)Br] (I and II) in PhCl under reflux conditions and that of the dialkyne-inserted cyclopalladated guanidine [κ 2 (C,N):η 2 (CC)PdBr] (III) in pyridine under reflux conditions afforded a guanidine-containing indole (1), imidazoindole (2), and benzazepine (3) in 80%, 67%, and 76%, yields, respectively. trans-[L 2 PdBr 2 ] species (L = 2,6-Me 2 C 5 H 3 N, C 5 H 5 N) were also isolated in the aforementioned reactions in 35%, 42%, and 40% yields. Further, the reaction of the cyclopalladated guanidine [κ 2 (C,N)Pd(μ-Br)] 2 (IV) with AgBF 4 in a CH 2 Cl 2 /MeCN mixture afforded the cationic pincer type cyclopalladated guanidine [κ 3 (C,N,O)Pd(MeCN)][BF 4 ] (4) in 85% yield and this palladacycle upon crystallization in MeCN and the reaction of [κ 2 (C,N)Pd(μ-Br)] 2 (V) with AgBF 4 in a CH 2 Cl 2 /MeCN mixture afforded the cationic palladacycles [{κ 2 (C,N)Pd(MeCN) 2 ][BF 4 ] (5 and 6) in 89% and 91% yields, respectively. The separate reactions of 4 with 2 equiv of methyl phenylpropiolate (MPP) or diphenylacetylene (DPA) and the reaction of 5 with 2 equiv of MPP in PhCl at 110 °C afforded the guanidine-containing quinazolinium tetrafluoroborate 7 in 25−32% yields. The reaction of 6 with 2 equiv of DPA under otherwise identical conditions afforded the unsymmetrically substituted guanidinium tetrafluoroborate 8, containing a highly substituted naphthalene unit, in 82% yield. Compounds 1−8 were characterized by analytical and spectroscopic techniques, and all compounds except 4 were characterized by single-crystal X-ray diffraction. The molecular structures of 2 and 3 are novel, as the framework in the former arises due to the formation of two C−N bonds upon depalladation while the butadienyl unit in the latter revealed cis,cis stereochemistry, a feature unprecedented in alkyne insertion chemistry. Plausible pathways for the formation of heterocycles/carbocycles are proposed. The influence of substituents on the aryl rings of the cyclopalladated guanidine moiety and those on alkynes upon the nature of the products is addressed. Heterocycles 1 and 7 revealed the presence of two rotamers in about a 1.00:0.43 ratio in CDCl 3 and in about a 1.00:0.14 ratio in CD 3 OD, respectively, as detected by 1 H NMR spectroscopy while in CD 3 CN and DMSO-d 6 (1) and CD 3 CN and CDCl 3 (7), these heterocycles revealed the presence of a single rotamer. These spectral features are attributed to the restricted C−N single-bond rotation of the CN 3 unit of the guanidine moiety, which possibly arises from steric constraint due to the formation of a N−H•••Cl hydrogen bond with CDCl 3 (1) and N−H•••O and O−D•••O hydrogen bonds with CD 3 OD (7).

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Section: Resultsmentioning

confidence: 99%

Depalladation of Neutral Monoalkyne- and Dialkyne-Inserted Palladacycles and Alkyne Insertion/Depalladation Reactions of Cationic Palladacycles Derived from N,N′,N″-Triarylguanidines as Facile Routes for Guanidine-Containing Heterocycles/Carbocycles: Synthetic, Structural, and Mechanistic Aspects

2014

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“…The hydrazone 2 has a value of D { G 0 about 24-25 kcal/mol. 9 The considerable difference in Z/E interconversion barriers between hydrazones 1 and 2 is probably attributable primarily to greater equilibrium state steric hindrance in hydrazone 2. Considering the steric factor among CH 3 CH¼ ¼NNH 2 and hydrazones 1 and 2, we estimated the D { G 0 of (1Z)-CH 3 CH¼ ¼NNH 2 for thermal isomerization should be about 32 kcal/mol.…”

Section: Resultsmentioning

confidence: 99%

“…The experimental observations [7][8][9] proposed an inversional mechansim in which hydrazones were isomerized by following an in-plane inversion of the imine nitrogen atom rather than by using a rotational process around the C¼ ¼N bond. The inversional mechanism was accompanied by rehybridization of the sp 2 nitrogen atom in proceeding from the equilibrium to the linear transition state (TS) reserving more part of a double bond characteristic than did the rotational mechanism.…”

Section: Introductionmentioning

confidence: 99%

Gibbs energy of activation for thermal isomerization of (1Z)‐acetaldehyde hydrazone and (1Z)‐acetaldehyde N,N‐dimethylhydrazone by Gaussian‐4 theory and CCSD(T)/CBS computations

2009

J Comput Chem

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In this article, we examined the Gibbs energy of activation for the Z/E thermal isomerization reaction of (1Z)-acetaldehyde hydrazone and (1Z)-acetaldehyde N,N-dimethylhydrazone, at 298.15 K in the solvent of cyclohexane. We carried out computations employing both the Gaussian-4 (G4) theory and the coupled cluster method using both single and double substitutions and triple excitations noniteratively, CCSD(T). The CCSD(T) energy is extrapolated to the complete basis set (CBS). We compared the calculated results to the available experimental observation. It appeared that both G4 and CCSD(T)/CBS computations overestimated the experimental value by as much as about 6 and 12 kcal/mol in the present two cases. We discussed possible sources of error and proposed the experimental kinetic data could be questionable.

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“…Going back to both mechanisms of isomerization for hydrazones mentioned before, [21,62,70] the inversion mechanism is considered to be the common mechanistic pathway. [71][72][73] However, in some cases the studies focus on the rates of isomerization (evaluate the type of transition state through dependence on solvent polarity) and do not consider the thermodynamic contributions to the activation barrier, which can lead to misleading conclusions. [21,74] In recent years, Aprahamian et al proposed a mechanistic process involving the participation of the NÀ H group.…”

Section: Configurational Dynamicsmentioning

confidence: 99%

Versatility of the Amino Group in Hydrazone‐Based Molecular and Supramolecular Systems

et al. 2022

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Hydrazone‐based systems have been, and continue to be, widely studied in the field of supramolecular chemistry due to the chemical versatility of their triatomic C=N‐N structure, whose amino nitrogen commonly bears a methyl group or a hydrogen atom. Herein we review the conformational, configurational, and constitutional dynamics of these systems, focusing on the particularly important role of the N−H group of the hydrazone framework in each of those processes observed in molecular and supramolecular systems published in recent decades. Due to the enormous diversity of supramolecular architectures and molecular entities, the most representative synthetic methodologies to obtain them are described.

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Conformational and Configurational Dynamics of a Highly Fluorinated Hydrazone

Cited by 16 publications

References 8 publications

Gibbs energy of activation for thermal isomerization of (1Z)‐acetaldehyde hydrazone and (1Z)‐acetaldehyde N,N‐dimethylhydrazone by Gaussian‐4 theory and CCSD(T)/CBS computations

Versatility of the Amino Group in Hydrazone‐Based Molecular and Supramolecular Systems

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