N,N-Chelate-control on the regioselectivity in acetate-assisted C–H activation

Cross, Warren B.; Hope, Eric G.; Lin, Ying-Hsi; Macgregor, Stuart A.; Singh, Kuldip; Solan, Gregory A.; Yahya, Nurhusna

doi:10.1039/c3cc38697j

Cited by 35 publications

(31 citation statements)

References 30 publications

(19 reference statements)

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“…The nature of these two-step C-H activations does vary, however, with the higher transition state corresponding to C-H bond cleavage in MeCO 2 H but changing to the formation of the agostic intermediate in F 3 CCO 2 H. Regioselective formation of six-membered palladacycles was also observed with naphthyl moieties fitted with a bidentate N,N-pyridylarylimine directing group (23, DIPP= 2,6-C 6 H 3 i Pr 2 ). BP86-D3(toluene) calculations on the full experimental system defined a two-step C-H activation process that is favored at the C8-position both kinetically (ΔΔG ‡ = 1.8 kcal mol −1 ) and thermodynamically (ΔΔG = 3.5 kcal mol −1 ) over a one-step process at the C2-position [28]. With monodentate 2-naphthylpyridine, both the kinetic and thermodynamic preference swaps to the 2-position, consistent with experimental observations and indicating that the additional imine anchor is indeed responsible for the change in selectivity.…”

Section: Intramolecular C-h Activation Of Heterocyclic Substratesmentioning

confidence: 99%

Computational Studies of Heteroatom‐Assisted CH Activation at Ru, Rh, Ir, and Pd as a Basis for Heterocycle Synthesis and Derivatization

Carr¹,

Macgregor²,

McMullin³

2016

Transition Metal‐Catalyzed Heterocycle Synthesis via CH Activation

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IntroductionModern computational chemistry is a key tool by which insight into organometallic reaction mechanisms can be gained. The ability to characterize short-lived intermediates and transition states provides an ideal complement to experiment, where such information is often extremely difficult, if not impossible, to obtain. Recent years have seen great advances in understanding the mechanisms of C-H bond activation, and this area was the subject of several major reviews toward the end of the last decade [1,2]. More recently, the focus has shifted to how C-H activation can be integrated into catalytic cycles for useful organic transformations. The C-H bond activation event is itself mechanistically diverse, with oxidative addition (OA), σ-bond metathesis (SBM), and electrophilic activation (EA) all potentially available at late transition metal centers, depending on the metal, its oxidation state, and the coordination environment. C-H activation assisted by a heteroatom base (typically a carboxylate or carbonate) falls into the last of these categories and forms the focus of this chapter. More recently, computational studies of catalytic cycles for C-H activation and functionalization have become more common. These reveal the complexity of what are usually multiple-step processes, and calculations are particularly well placed to test different mechanistic possibilities. Such studies are most effectively pursued through a close interaction between experiment and computation, and increasingly this is allowing for a more quantitative assessment of computed reaction mechanisms.As well as progress in mechanistic understanding, the last 10 years have seen important developments in the computational methodologies available to model transition metal reactivity. While density functional theory (DFT) remains the core method of choice, the ability to model larger systems that more closely reflect experiment has highlighted the known shortcomings of DFT in describing dispersion interactions. These long-range, stabilizing interactions are individually weak, but their cumulative effect in large systems can be significant. Methods to incorporate this component include its separate calculation (e.g., Transition Metal-Catalyzed Heterocycle Synthesis via C-H Activation, First Edition. Edited by Xiao-Feng Wu.

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Section: Intramolecular C-h Activation Of Heterocyclic Substratesmentioning

confidence: 99%

Computational Studies of Heteroatom‐Assisted CH Activation at Ru, Rh, Ir, and Pd as a Basis for Heterocycle Synthesis and Derivatization

Carr¹,

Macgregor²,

McMullin³

2016

Transition Metal‐Catalyzed Heterocycle Synthesis via CH Activation

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“…The structures are similar with a central pyridine ring substituted at its 6-position by a 1-naphthyl group and at the 2-position by an imine unit [C (6) Reaction of ketimine-containing L1dipp-L1Brdipp with two equivalents of trimethylaluminum in toluene at refluxing temperatures overnight results in complexation and methylation of the ketimine carbon moiety to afford the air sensitive 2-(amido-prop-2-yl)-6-(1-naphthyl)pyridine aluminum dimethyl complexes, [2-{CMe2N(Ar)}-6-(1-C10H7)C5H3N]AlMe2 [Ar = 2,6-i-Pr2C6H3 (1a), 2,4,6-i-Pr3C6H2 (1b), 4-Br-2,6-i-Pr2C6H2 (1c)], in good yield (Scheme 1). Leaving the reaction longer at the same temperature or increasing the ratio of trimethylaluminum gave no evidence for an ortho-nor peri-C-H activated naphthyl species [53]. Complexes 1 have been both characterized by NMR and IR spectroscopy, mass spectrometry and gave satisfactory microanalytical data (see Experimental section).…”

Section: Synthetic and Structural Aspectsmentioning

confidence: 89%

“…The precursor ketone is not commercially available and has been synthesized using a variation of the previously reported Suzuki cross-coupling reaction of 1-naphthyl boronic acid with 2-bromo-6-acetylpyridine [61]. Compound L1dipp has been reported before [53,62], although no characterization data were disclosed. Hence, L1dipp and its substituted counterparts, L1tripp and L1Brdipp, have been characterized by a combination of 1 H, 13 In addition, single-crystal X-ray diffraction studies have been performed on L1dipp and L1tripp.…”

Section: Synthetic and Structural Aspectsmentioning

confidence: 99%

“…Indeed, the thermally-induced migration of an Al-alkyl to the imino carbon of a coordinated N,N-pyridylimine represents a powerful tool for transforming a pyridylimine into a pyridyl-alkylamide (and pyridyl-alkylamine on hydrolysis [45,52]). Moreover, functionalizing the 6-position of the pyridine moiety of the pyridylimine with an aryl or 1-naphthyl group presents a versatile set of substrates for studying ortho vs. peri-palladation reactions during the formation of N,N,C-chelates [53,54]. Likewise, N,N-pyridyl-alkylamides and their 6-aryl and -naphthyl derivatives have also been attracting attention due, in large measure, to their emergence as supports for exceptionally active N,N- [45,55,56] and N,N,C-bound group 4 olefin polymerization catalysts [57][58][59][60].…”

Section: Introductionmentioning

confidence: 99%

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Dimethyl-Aluminium Complexes Bearing Naphthyl-Substituted Pyridine-Alkylamides as Pro-Initiators for the Efficient ROP of ε-Caprolactone

et al. 2015

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Three sterically-enhanced 2-imino-6-(1-naphthyl)pyridines, 2-{CMe=N(Ar)}-6-(1-C10H7)C5H3N [Ar = 2,6-i-Pr2C6H3 (L1dipp), 2,4,6-i-Pr3C6H2 (L1tripp), 4-Br-2,6-i-Pr2C6H2 (L1Brdipp)], differing only in the electronic properties of the N-aryl group, have been prepared in high yield by the condensation reaction of 2-{CMe=O}-6-(1-C10H7)C5H3N with the corresponding aniline. Treatment of L1dipp, L1tripp and L1Brdipp with two equivalents of AlMe3 at elevated temperature affords the distorted tetrahedral 2-(amido-prop-2-yl)-6-(1-naphthyl)pyridine aluminum dimethyl complexes, [2-{CMe2N(Ar)}-6-(1-C10H7)C5H3N]AlMe2 [Ar = 2,6-i-Pr2C6H3 (1a), 2,4,6-i-Pr3C6H2 (1b), 4-Br-2,6-i-Pr2C6H2 (1c)], in good yield. The X-ray structures of 1a-1c reveal that complexation has resulted in concomitant C-C bond formation via methyl migration from aluminum to the corresponding imino carbon in L1aryl; in solution, the restricted rotation of the pendant naphthyl group in 1 confers inequivalent methyl ligand environments. The ring opening polymerization of ε-caprolactone employing 1, in the presence of benzyl alcohol, proceeded efficiently at 30 °C producing polymers of narrow molecular weight distribution with the catalytic activities dependent on the nature of the substituent located at the > 1c); at 50 °C 1b mediates 100% conversion of the monomer to polycaprolactone (poly(CL)) in one hour. In addition to 1a, 1b and 1c, the single crystal X-ray structures are reported for L1dipp and L1tripp.

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“…11 For example, reaction of the pyridylimine-containing 1-substituted naphthalene, 2-(1-C 10 H 7 )-6-{CMe=N(2,6-i-Pr 2 C 6 H 3 )}C 5 H 3 N (HL Me ), with Pd(OAc) 2 led exclusively to peri-C-H activation of the naphthyl group, while for the pyridylalcohol analogue 2-(1-C 10 H 7 )-6-(CMe 2 OH)C 5 H 3 N solely the ortho-C-H activation product was observed (Scheme 1). DFT calculations were performed on the peri-pathway which revealed: (i) that the reaction proceeded by a mechanism commonly referred to as a concerted metalation deprotonation (CMD) or ambiphilic metal-ligand activation (AMLA), involving an acetate ligand as an intramolecular base; 12 (ii) that the peri-C-H activation was both kinetically and thermodynamically favoured; and (iii) that the site-selectivity of the C-H activation was controlled, in some measure, by the N,N-Given this subtle balance between ortho-and peri-activation of a naphthalene ring, we decided to explore the reactivity of HL Me and its aldimine analogue, 2-(1-C 10 H 7 )-6-{CH=N(2,6-i-Pr 2 C 6 H 3 )}C 5 H 3 N (HL H ), towards acetate-free palladium(II) sources and in particular the palladium(II) chlorides, (MeCN) 2 PdCl 2 and Na 2 [PdCl 4 ]. In these cases, the intramolecular base is now a chloride ligand rather than an κ 1 -acetate and as such a conventional CMD (or AMLA-6) type mechanism will be prevented.…”

Section: Introductionmentioning

confidence: 99%

Ligand and solvent control of selectivity in the C–H activation of a pyridylimine-substituted 1-naphthalene; a combined synthetic and computational study

et al. 2018

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The pyridylimine-substituted 1-naphthalenes, 2-(1-C10H7)-6-{CR[double bond, length as m-dash]N(2,6-i-Pr2C6H3)}C5H3N (R = Me HLMe, H HLH), react with Na2[PdCl4] in acetic acid at elevated temperature to afford either ortho-C-Hnaphthyl activated (LMe)PdCl (2ortho) or the unactivated adduct (HLH)PdCl2 (1b). Alternatively, 1b and its ketimine analogue (HLMe)PdCl2 (1a), can be prepared by treating (MeCN)2PdCl2 with either HLMe or HLH in chloroform at room temperature. Regio-selective ortho-C-H activation to form 2ortho can also be initiated by the thermolysis of 1a in acetic acid, while no reaction occurs under similar conditions with 1b. Interestingly, the C-H activation of HLMe to give 2ortho is found to be reversible with 100% deuteration of the peri-site occurring on reacting Na2[PdCl4] with HLMe in acetic acid-d4. By contrast, heating 1a in toluene gives a 55 : 45 mixture of 2ortho and its peri-activated isomer 2peri. Pure 2peri can, however, be obtained either from (LMe)PdOAc (3peri) by OAc/Cl exchange or by the sequential reactions of 1a with firstly silver acetate then with aqueous sodium chloride. Intriguingly, a peri to ortho interconversion occurs on heating 2peri in acetic acid to give 2ortho. DFT calculations have been used to investigate the C-H activation steps and it is found that in acetic acid ortho-C-H activation is kinetically and thermodynamically favoured but peri-CH activation is kinetically accessible (ΔΔG‡ = 2.4 kcal mol-1). By contrast in toluene, the reaction appears to be irreversible with the difference in barrier height for ortho- and peri-C-H activation being very small within the error of the method (ΔΔG‡ = 0.7 kcal mol-1), findings that are in agreement with the empirically observed product distribution for 2ortho and 2peri. Single crystal X-ray structures are reported for 1a, 1b, 2ortho and 2peri.

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N,N-Chelate-control on the regioselectivity in acetate-assisted C–H activation

Cited by 35 publications

References 30 publications

Computational Studies of Heteroatom‐Assisted CH Activation at Ru, Rh, Ir, and Pd as a Basis for Heterocycle Synthesis and Derivatization

Computational Studies of Heteroatom‐Assisted CH Activation at Ru, Rh, Ir, and Pd as a Basis for Heterocycle Synthesis and Derivatization

Dimethyl-Aluminium Complexes Bearing Naphthyl-Substituted Pyridine-Alkylamides as Pro-Initiators for the Efficient ROP of ε-Caprolactone

Ligand and solvent control of selectivity in the C–H activation of a pyridylimine-substituted 1-naphthalene; a combined synthetic and computational study

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