scholarly journals Alumination of Aryl Methyl Ethers: Switching Between Sp2 and Sp3 C–O Bond Functionalisation with Pd-Catalysis

2021 ◽  
Author(s):  
Ryan Brown ◽  
Thomas N hooper ◽  
Feriel Rekroukh ◽  
Andrew J. P. White ◽  
Paulo J. Costa ◽  
...  
Keyword(s):  
Dft Calculations ◽  
Oxidative Addition ◽  
Starting Material ◽  
Aromatic Molecules ◽  
Kinetic Isotope ◽  
Mechanistic Insight ◽  
Sn2 Pathway ◽  
Aryl Methyl

The reaction of [{(ArNCMe)2CH}Al] (Ar = 2,6-di-iso-propylphenyl, 1) with aryl methyl ethers proceeded with alumination of the sp3 C–O bond by a presumed SN2 pathway. The selectivity of this reaction could be switched by inclusion of a catalyst. In the presence of [Pd(PCy3)2], chemoselective sp2 C–O bond functionalisation was observed. Kinetic isotope experiments and DFT calculations support a catalytic pathway involving the ligand-assisted oxidative addition of the sp2 C–O bond to a Pd---Al intermetallic complex. The net result of both non-catalysed and catalytic pathways is the generation of polar organoaluminium complexes from aryl methyl ethers with complete atom-efficiency. Switches in selectivity yield isomeric products from a single starting material. The methodology (and mechanistic insight) holds promise as a means to functionalise aromatic molecules derived from lignin depolymerisation and we demonstrate an application to a derivative of vanillin.

scholarly journals Alumination of Aryl Methyl Ethers: Switching Between Sp2 and Sp3 C–O Bond Functionalisation with Pd-Catalysis

2021 ◽  
Author(s):  
Ryan Brown ◽  
Thomas N hooper ◽  
Feriel Rekroukh ◽  
Andrew J. P. White ◽  
Paulo J. Costa ◽  
...  
Keyword(s):  
Dft Calculations ◽  
Oxidative Addition ◽  
Starting Material ◽  
Aromatic Molecules ◽  
Kinetic Isotope ◽  
Mechanistic Insight ◽  
Sn2 Pathway ◽  
Aryl Methyl

The reaction of [{(ArNCMe)2CH}Al] (Ar = 2,6-di-iso-propylphenyl, 1) with aryl methyl ethers proceeded with alumination of the sp3 C–O bond by a presumed SN2 pathway. The selectivity of this reaction could be switched by inclusion of a catalyst. In the presence of [Pd(PCy3)2], chemoselective sp2 C–O bond functionalisation was observed. Kinetic isotope experiments and DFT calculations support a catalytic pathway involving the ligand-assisted oxidative addition of the sp2 C–O bond to a Pd---Al intermetallic complex. The net result of both non-catalysed and catalytic pathways is the generation of polar organoaluminium complexes from aryl methyl ethers with complete atom-efficiency. Switches in selectivity yield isomeric products from a single starting material. The methodology (and mechanistic insight) holds promise as a means to functionalise aromatic molecules derived from lignin depolymerisation and we demonstrate an application to a derivative of vanillin.

Reversible Oxidative-Addition and Reductive-Elimination of Thiophene from a Titanium Complex and Its Thermally-Induced Hydrodesulfurization Chemistry

2019 ◽  
Author(s):  
Alejandra Gomez-Torres ◽  
J. Rolando Aguilar-Calderón ◽  
Carlos Saucedo ◽  
Aldo Jordan ◽  
Alejandro J. Metta-Magaña ◽  
...  
Keyword(s):  
Dft Calculations ◽  
Ring Opening ◽  
Thiophene Ring ◽  
Oxidative Addition ◽  
Reductive Elimination ◽  
Thermally Induced ◽  
Titanium Complex

<p>The masked Ti(II) synthon (<sup>Ket</sup>guan)(<i>η</i><sup>6</sup>-Im<sup>Dipp</sup>N)Ti (<b>1</b>) oxidatively adds across thiophene to give ring-opened (<sup>Ket</sup>guan)(Im<sup>Dipp</sup>N)Ti[<i>κ</i><sup>2</sup>-<i>S</i>(CH)<sub>3</sub><i>C</i>H] (<b>2</b>). Complex <b>2</b> is photosensitive, and upon exposure to light, reductively eliminates thiophene to regenerate <b>1</b> – a rare example of early-metal mediated oxidative-addition/reductive-elimination chemistry. DFT calculations indicate strong titanium π-backdonation to the thiophene π*-orbitals leads to the observed thiophene ring opening across titanium, while a proposed photoinduced LMCT promotes the reverse thiophene elimination from <b>2</b>. Finally, pressurizing solutions of <b>2 </b>with H<sub>2</sub> (150 psi) at 80 °C leads to the hydrodesulfurization of thiophene to give the Ti(IV) sulfide (<sup>Ket</sup>guan)(Im<sup>Dipp</sup>N)Ti(S) (<b>3</b>) and butane. </p>

scholarly journals The role of hypervalent iodine(iii) reagents in promoting alkoxylation of unactivated C(sp3)–H bonds catalyzed by palladium(ii) complexes

2021 ◽  
Author(s):  
Payam Abdolalian ◽  
Samaneh K. Tizhoush ◽  
Kaveh Farshadfar ◽  
Alireza Ariafard
Keyword(s):  
Dft Calculations ◽  
Oxidative Addition ◽  
Hypervalent Iodine

This work uses DFT calculations to explore Pd(ii)-catalysed iodine(iii)-mediated alkoxylation of unactivated C(sp3)–H bonds and reveals how important the isomerization is in triggering the oxidative addition of ArIX2 to Pd(ii).

scholarly journals Palladium-Catalysed C–F Alumination of Fluorobenzenes: Mechanistic Diversity and Origin of Selectivity

2020 ◽  
Author(s):  
Feriel Rekhroukh ◽  
Wenyi Chen ◽  
Ryan Brown ◽  
Andrew J. P. White ◽  
Mark Crimmin
Keyword(s):  
Dft Calculations ◽  
Bond Activation ◽  
Oxidative Addition ◽  
Fluorine Content ◽  
Model Potential ◽  
Heterometallic Complex ◽  
Experimental Support ◽  
Highly Active ◽  
Reaction Proceeds ◽  
Directing Group

A palladium pre-catalyst, [Pd(PCy<sub>3</sub>)<sub>2</sub>] is reported for the efficient and selective C–F alumination of fluorobenzenes with the aluminium(I) reagent [{(ArNCMe)<sub>2</sub>CH}Al] (<b>1</b>, Ar = 2,6-di-iso-propylphenyl). The catalytic protocol results in the transformation of sp<sup>2</sup> C–F bonds to sp<sup>2</sup> C–Al bonds and provides a route into reactive organoaluminium complexes (<b>2a-h</b>) from fluorocarbons. The catalyst is highly active. Reactions proceed within 5 minutes at 25 ºC (and at appreciable rates at even –50 ºC) and the scope includes low-fluorine-content substrates such as fluorobenzene, difluorobenzenes and trifluorobenzenes. The reaction proceeds with complete chemoselectivity (C–F vs C–H) and high regioselectivities ( >90% for C–F bonds adjacent to the most acidic C–H sites). The heterometallic complex [Pd(PCy<sub>3</sub>)(<b>1</b>)<sub>2</sub>] was shown to be catalytically competent. Catalytic C–F alumination proceeds with a KIE of 1.1–1.3. DFT calculations have been used to model potential mechanisms for C–F bond activation. These calculations suggest that two competing mechanisms may be in operation. Pathway 1 involves a ligand-assisted oxidative addition to [Pd(<b>1</b>)<sub>2</sub>] and leads directly to the product. Pathway 2 involves a stepwise C–H to C–F functionalisation mechanism in which the C–H bond is broken and reformed along the reaction coordinate, allowing it to act as a directing group for the adjacent C–F site. This second mechanism explains the experimentally observed regioselectivity. Experimental support for this C–H activation playing a key role in C–F alumination was obtained by employing [{(MesNCMe)<sub>2</sub>CH}AlH<sub>2</sub>] (<b>3</b>, Mes = 2,4,6-trimethylphenyl) as a reagent in place of 1. In this instance, the kinetic C–H alumination intermediate could be isolated. Under catalytic conditions this intermediate converts to the thermodynamic C–F alumination product.

scholarly journals Synergistic catalysis: enantioselective cyclopropanation of alkylidene benzoxazoles by Pd(ii) and secondary amine catalysis. Scope, limitations and mechanistic insight

2018 ◽  
Vol 5 (5) ◽  
pp. 806-812 ◽  
Author(s):  
Marta Meazza ◽  
Victor Polo ◽  
Pedro Merino ◽  
Ramon Rios
Keyword(s):  
Dft Calculations ◽  
Secondary Amine ◽  
Ring Opening ◽  
Synergistic Catalysis ◽  
Mechanistic Insight ◽  
Amine Catalysis

An enantioselective synergistic cascade cyclopropanation/NHC catalyzed ring opening has been reported. DFT calculations have been performed to confirm the mechanism.

scholarly journals Palladium-Catalysed C–F Alumination of Fluorobenzenes: Mechanistic Diversity and Origin of Selectivity

2020 ◽  
Author(s):  
Feriel Rekhroukh ◽  
Wenyi Chen ◽  
Ryan Brown ◽  
Andrew J. P. White ◽  
Mark Crimmin
Keyword(s):  
Dft Calculations ◽  
Bond Activation ◽  
Oxidative Addition ◽  
Fluorine Content ◽  
Model Potential ◽  
Heterometallic Complex ◽  
Experimental Support ◽  
Highly Active ◽  
Reaction Proceeds ◽  
Directing Group

A palladium pre-catalyst, [Pd(PCy<sub>3</sub>)<sub>2</sub>] is reported for the efficient and selective C–F alumination of fluorobenzenes with the aluminium(I) reagent [{(ArNCMe)<sub>2</sub>CH}Al] (<b>1</b>, Ar = 2,6-di-iso-propylphenyl). The catalytic protocol results in the transformation of sp<sup>2</sup> C–F bonds to sp<sup>2</sup> C–Al bonds and provides a route into reactive organoaluminium complexes (<b>2a-h</b>) from fluorocarbons. The catalyst is highly active. Reactions proceed within 5 minutes at 25 ºC (and at appreciable rates at even –50 ºC) and the scope includes low-fluorine-content substrates such as fluorobenzene, difluorobenzenes and trifluorobenzenes. The reaction proceeds with complete chemoselectivity (C–F vs C–H) and high regioselectivities ( >90% for C–F bonds adjacent to the most acidic C–H sites). The heterometallic complex [Pd(PCy<sub>3</sub>)(<b>1</b>)<sub>2</sub>] was shown to be catalytically competent. Catalytic C–F alumination proceeds with a KIE of 1.1–1.3. DFT calculations have been used to model potential mechanisms for C–F bond activation. These calculations suggest that two competing mechanisms may be in operation. Pathway 1 involves a ligand-assisted oxidative addition to [Pd(<b>1</b>)<sub>2</sub>] and leads directly to the product. Pathway 2 involves a stepwise C–H to C–F functionalisation mechanism in which the C–H bond is broken and reformed along the reaction coordinate, allowing it to act as a directing group for the adjacent C–F site. This second mechanism explains the experimentally observed regioselectivity. Experimental support for this C–H activation playing a key role in C–F alumination was obtained by employing [{(MesNCMe)<sub>2</sub>CH}AlH<sub>2</sub>] (<b>3</b>, Mes = 2,4,6-trimethylphenyl) as a reagent in place of 1. In this instance, the kinetic C–H alumination intermediate could be isolated. Under catalytic conditions this intermediate converts to the thermodynamic C–F alumination product.

scholarly journals Formation of Enamines via Catalytic Dehydrogenation by Pincer-Iridium Complexes

2019 ◽  
Author(s):  
Xiawei Zhang ◽  
Santanu Malakar ◽  
Karsten Krogh-Jespersen ◽  
Faraj Hasanayn ◽  
Alan Goldman
Keyword(s):  
Isotope Effects ◽  
Oxidative Addition ◽  
Kinetic Isotope Effects ◽  
Catalytic Dehydrogenation ◽  
Iridium Complexes ◽  
Tertiary Amines ◽  
Iridium Catalysts ◽  
Kinetic Isotope ◽  
Dehydrogenation Mechanism

Efficient pincer-ligated iridium catalysts are reported for the dehydrogenation of simple tertiary amines to give enamines, and for the dehydrogenation of β-functionalized amines to give the corresponding 1,2-difunctionalized olefins. Experimentally determined kinetic isotope effects in conjunction with DFT-based analysis support a dehydrogenation mechanism involving initial pre-equilibrium oxidative addition of the amine α C-H bond followed by rate-determining elimination of the β-C-H bond.<br>

scholarly journals On the N-Arylation of Acetamide Using 2-, 3- and 1’-Substituted Iodoferrocenes

2020 ◽  
Author(s):  
Lingaswamy Kadari ◽  
William Erb ◽  
Yury S. Halauko ◽  
Oleg A. Ivashkevich ◽  
Vadim E. Matulis ◽  
...  
Keyword(s):  
Dft Calculations ◽  
Large Range ◽  
Activation Barrier ◽  
Oxidative Addition ◽  
Structure Property ◽  
Structure Property Relationships

Various 2-, 3- and 1’-substituted iodoferrocenes were<br>reacted with acetamide in the presence of copper(I) iodide (1<br>equiv), N,N’-dimethylethylenediamine (1 equiv), tripotassium<br>phosphate (2 equiv) in dioxane at 90 °C for 14 h, and allowed a large range of original 1,2-, 1,3- and 1,1’-disubstituted ferrocenes to be obtained. The results were compared as a function of the substituent and its position on the ring. DFT calculations revealed higher activation barrier for the oxidative addition in the ferrocene series when compared with classical planar aromatics. Structure–property relationships were applied to rationalize the reactivity of the different iodoferrocenes.

Mechanistic insight into the silver-catalyzed cycloaddition synthesis of 1,4-disubstituted-1,2,3-triazoles: the key role of silver

2019 ◽  
Vol 43 (22) ◽  
pp. 8634-8643 ◽  
Author(s):  
Feiyun Jia ◽  
Bo Zhang
Keyword(s):  
Dft Calculations ◽  
Mechanistic Insight ◽  
Insight Into

By using DFT calculations, we disclose the reason why silver(i) catalytically promotes the activity and regioselectivity of the cycloaddition of 1,4-disubstituted-1,2,3-triazoles.

Sign in / Sign up

Export Citation Format

Share Document