B–H functionalization of the monocarba-closo-dodecaborate anion by rhodium and iridium catalysis

We report selective formation of heterobimetallic PtII/CuI complexes that demonstrate how facile bond activation processes can be achieved by altering reactivity of common organoplatinum compounds through their interaction with another metal center. The interaction of the Cu center with Pt center and with a Pt-bound alkyl group increases the stability of PtMe2 towards undesired rollover cyclometalation. The presence of the CuI center also enables facile transmetalation from electron-deficient tetraarylborate [B(ArF)4]- anion and mild C-H bond cleavage of a terminal alkyne, which was not observed in the absence of an electrophilic Cu center. The DFT study indicates that the role of Cu center acts as a binding site for alkyne substrate, while activating its terminal C-H bond.

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Imine as a Linchpin Approach for Distal C(sp2)–H Functionalization

10.26434/chemrxiv.11521827 ◽

2020 ◽

Author(s):

Sukdev Bag ◽

Sadhan Jana ◽

Sukumar Pradhan ◽

Suman Bhowmick ◽

Nupur Goswami ◽

...

Keyword(s):

Organic Molecules ◽

Bond Activation ◽

Bond Formation ◽

Ancillary Ligand ◽

Significant Challenge ◽

Site Selectivity ◽

Directing Group ◽

Covalently Linked ◽

Complex Organic ◽

Post Functionalization

Despite the widespread applications of C–H functionalization, controlling site selectivity remains a significant challenge. Covalently attached directing group (DG) served as an ancillary ligand to ensure proximal ortho-, distal meta- and para-C-H functionalization over the last two decades. These covalently linked DGs necessitate two extra steps for a single C–H functionalization: introduction of DG prior to C–H activation and removal of DG post-functionalization. We introduce here a transient directing group for distal C(sp2)-H functionalization via reversible imine formation. By overruling facile proximal C-H bond activation by imine-N atom, a suitably designed pyrimidine-based transient directing group (TDG) successfully delivered selective distal C-C bond formation. Application of this transient directing group strategy for streamlining the synthesis of complex organic molecules without any necessary pre-functionalization at the distal position has been explored.

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Pt-Pd Nanoalloy for the Unprecedented Activation of Carbon-Fluorine Bond at Low Temperature

10.26434/chemrxiv.11145098 ◽

2019 ◽

Author(s):

Raghu Nath Dhital ◽

keigo nomura ◽

Yoshinori Sato ◽

Setsiri Haesuwannakij ◽

Masahiro Ehara ◽

...

Keyword(s):

Activation Energy ◽

Low Temperature ◽

Dft Calculations ◽

Bond Activation ◽

Mild Conditions ◽

Selective Transformation ◽

Rate Determining Step ◽

Highly Active ◽

Harsh Conditions ◽

Reaction Profile

Carbon-Fluorine (C-F) bonds are considered the most inert organic functionality and their selective transformation under mild conditions remains challenging. Herein, we report a highly active Pt-Pd nanoalloy as a robust catalyst for the transformation of C-F bonds into C-H bonds at low temperature, a reaction that often required harsh conditions. The alloying of Pt with Pd is crucial to activate C-F bond. The reaction profile kinetics revealed that the major source of hydrogen in the defluorinated product is the alcoholic proton of 2-propanol, and the rate-determining step is the reduction of the metal upon transfer of the beta-H from 2-propanol. DFT calculations elucidated that the key step is the selective oxidative addition of the O-H bond of 2-propanol to a Pd center prior to C-F bond activation at a Pt site, which crucially reduces the activation energy of the C-F bond. Therefore, both Pt and Pd work independently but synergistically to promote the overall reaction

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Carbon Dioxide-Mediated C(sp2)–H Arylation of Primary and Secondary Benzylamines

10.26434/chemrxiv.7138088.v2 ◽

2018 ◽

Author(s):

Mohit Kapoor ◽

Pratibha Chand-Thakuri ◽

Michael Young

Keyword(s):

Carbon Dioxide ◽

Transition Metal ◽

Bond Activation ◽

Bond Formation ◽

Carbon Bond ◽

Chelate Effect ◽

Free Amine ◽

Carbon Carbon Bond ◽

New Strategy ◽

Metal Catalyzed

Carbon-carbon bond formation by transition metal-catalyzed C–H activation has become an important strategy to fabricate new bonds in a rapid fashion. Despite the pharmacological importance of ortho-arylbenzylamines, however, effective ortho-C–C bond formation from C–H bond activation of free primary and secondary benzylamines using PdII remains an outstanding challenge. Presented herein is a new strategy for constructing ortho-arylated primary and secondary benzylamines mediated by carbon dioxide (CO2). The use of CO2 is critical to allowing this transformation to proceed under milder conditions than previously reported, and that are necessary to furnish free amine products that can be directly used or elaborated without the need for deprotection. In cases where diarylation is possible, a chelate effect is demonstrated to facilitate selective monoarylation.

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Theoretical and experimental studies of palladium-catalyzed site-selective C(sp3)−H bond functionalization enabled by transient ligands

10.26434/chemrxiv.5717950 ◽

2017 ◽

Author(s):

Haibo Ge ◽

Lei Pan ◽

Piaoping Tang ◽

Ke Yang ◽

Mian Wang ◽

...

Keyword(s):

Bond Activation ◽

Theoretical Calculations ◽

Experimental Studies ◽

Bond Functionalization ◽

Aliphatic Ketones ◽

Site Selectivity ◽

Mechanistic Investigation ◽

Palladium Catalyzed ◽

Metal Catalyzed ◽

Site Selective

Transition metal-catalyzed selective C–H bond functionalization enabled by transient ligands has become an extremely attractive topic due to its economical and greener characteristics. However, catalytic pathways of this reaction process on unactivated sp3 carbons of reactants have not been well studied yet. Herein, detailed mechanistic investigation on Pd-catalyzed C(sp3)–H bond activation with amino acids as transient ligands has been systematically conducted. The theoretical calculations showed that higher angle distortion of C(sp2)-H bond over C(sp3)-H bond and stronger nucleophilicity of benzylic anion over its aromatic counterpart, leading to higher reactivity of corresponding C(sp3)–H bonds; the angle strain of the directing rings of key intermediates determines the site-selectivity of aliphatic ketone substrates; replacement of glycine with β-alanine as the transient ligand can decrease the angle tension of the directing rings. Synthetic experiments have confirmed that β-alanine is indeed a more efficient transient ligand for arylation of β-secondary carbons of linear aliphatic ketones than its glycine counterpart.

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Thioether-Facilitated Iridium-Catalyzed Hydrosilylation of Steric 1,1-Disubstituted Olefins

10.26434/chemrxiv.9859103.v1 ◽

2019 ◽

Author(s):

Shengtao Ding

Keyword(s):

Side Chains ◽

Feasible Method ◽

Iridium Catalysis ◽

Efficient Strategy ◽

Terminal Alkenes ◽

And Control ◽

Sulfur Containing ◽

Organosilicon Polymers

One facile and efficient strategy for the hydrosilylation of steric 1,1-disubstituted terminal alkenes is demonstrated. Investigations on substrate scope and control experiments revealed the necessity of thioether in promoting this process under a simple iridium catalysis system. This convenient and feasible method is expected to be useful in the synthesis of sulfur-containing organosilicon polymers with different side-chains.

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