Guest-Incorporation in Ternary Clathrate Formation Is Random but Shows Site-Selectivity

1998 ◽  
Vol 120 (15) ◽  
pp. 3799-3800 ◽  
Author(s):  
Naoto Hayashi ◽  
Koji Kuruma ◽  
Yasuhiro Mazaki ◽  
Tatsuro Imakubo ◽  
Keiji Kobayashi
Keyword(s):  
Clathrate Formation ◽  
Site Selectivity

Chelation-assisted transition metal-catalysed C–H chalcogenylations

2020 ◽  
Vol 7 (8) ◽  
pp. 1022-1060 ◽  
Author(s):  
Wenbo Ma ◽  
Nikolaos Kaplaneris ◽  
Xinyue Fang ◽  
Linghui Gu ◽  
Ruhuai Mei ◽  
...  
Keyword(s):  
Transition Metal ◽  
Recent Advances ◽  
Site Selectivity ◽  
Transition Metal Catalyzed ◽  
Metal Catalyzed

This review summarizes recent advances in C–S and C–Se formations via transition metal-catalyzed C–H functionalization utilizing directing groups to control the site-selectivity.

Cobalt/Lewis Acid Catalysis for Hydrocarbofunctionalization of Alkynes via Cooperative C–H Activation

2020 ◽  
Author(s):  
Chang-Sheng Wang ◽  
Sabrina Monaco ◽  
Anh Ngoc Thai ◽  
Md. Shafiqur Rahman ◽  
Chen Wang ◽  
...  
Keyword(s):  
Catalytic System ◽  
Lewis Acid ◽  
Hydrogen Transfer ◽  
Acid Catalysis ◽  
Rate Limiting Step ◽  
Site Selectivity ◽  
Set Up ◽  
Site Selective ◽  
First Time ◽  
Rate Limiting

A catalytic system comprised of a cobalt-diphosphine complex and a Lewis acid (LA) such as AlMe3 has been found to promote hydrocarbofunctionalization reactions of alkynes with Lewis basic and electron-deficient substrates such as formamides, pyridones, pyridines, and azole derivatives through site-selective C-H activation. Compared with known Ni/LA catalytic system for analogous transformations, the present catalytic system not only feature convenient set up using inexpensive and bench-stable precatalyst and ligand such as Co(acac)3 and 1,3-bis(diphenylphosphino)propane (dppp), but also display distinct site-selectivity toward C-H activation of pyridone and pyridine derivatives. In particular, a completely C4-selective alkenylation of pyridine has been achieved for the first time. Mechanistic stidies including DFT calculations on the Co/Al-catalyzed addition of formamide to alkyne have suggested that the reaction involves cleavage of the carbamoyl C-H bond as the rate-limiting step, which proceeds through a ligand-to-ligand hydrogen transfer (LLHT) mechanism leading to an alkyl(carbamoyl)cobalt intermediate.

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

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

<p>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 <i>ortho</i>-, distal <i>meta</i>- and <i>para</i>-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(<i>sp<sup>2</sup></i>)-H functionalization <i>via</i> reversible imine formation. By overruling facile proximal C-H bond activation by imine-<i>N</i> 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.</p>

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

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 sp<sup>3</sup> carbons of reactants have not been well studied yet. Herein, detailed mechanistic investigation on Pd-catalyzed C(sp<sup>3</sup>)–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(sp<sup>3</sup>)–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.<br><br>

Methane Clathrate Formation is Catalyzed and Kinetically Inhibited by the Same Molecule: Two Facets of Methanol

2021 ◽  
Author(s):  
Zhaoqian Su ◽  
Saman Alavi ◽  
John A. Ripmeester ◽  
Gedaliah Wolosh ◽  
Cristiano L. Dias
Keyword(s):  
Clathrate Formation ◽  
Methane Clathrate

Hydroquinone clathrates and the theory of clathrate formation

1985 ◽  
Vol 3 (3) ◽  
pp. 243-260 ◽  
Author(s):  
V. R. Belosludov ◽  
Yu. A. Dyadin ◽  
G. N. Chekhova ◽  
B. A. Kolesov ◽  
S. I. Fadeev
Keyword(s):  
Clathrate Formation

Crossover Site-Selectivity in the Adsorption of the Fullerene Derivative PCBM on Au(111)

2007 ◽  
Vol 46 (41) ◽  
pp. 7874-7877 ◽  
Author(s):  
David Écija ◽  
Roberto Otero ◽  
Luis Sánchez ◽  
José María Gallego ◽  
Yang Wang ◽  
...  
Keyword(s):  
Fullerene Derivative ◽  
Site Selectivity ◽  
Crossover Site

A new synthetic analogue of the bracken ultimate carcinogen: Elevation of stability and alteration of DNA alkylation site selectivity

1997 ◽  
Vol 38 (18) ◽  
pp. 3235-3238 ◽  
Author(s):  
Hideo Kigoshi ◽  
Yuusi Kitamura ◽  
Tatsuya Fujita ◽  
Hidekazu Ohashi ◽  
Toshiyuki Atsumi ◽  
...  
Keyword(s):  
Dna Alkylation ◽  
Synthetic Analogue ◽  
Site Selectivity

Remote C–H Functionalizations by Ruthenium Catalysis

Synthesis ◽  
2021 ◽  
Author(s):  
Korkit Korvorapun ◽  
Ramesh C. Samanta ◽  
Torben Rogge ◽  
Lutz Ackermann
Keyword(s):  
Steric Hindrance ◽  
Late Stage ◽  
Crop Protection ◽  
Full Control ◽  
Site Selectivity ◽  
Important Approach ◽  
Distinct Character ◽  
Ruthenium Catalysis ◽  
Material Sciences ◽  
Site Selective

Synthetic transformations of otherwise inert C–H bonds have emerged as a powerful tool for molecular modifications during the last decades, with broad applications towards pharmaceuticals, material sciences and crop protection. Consistently, a key challenge in C–H activation chemistry is the full control of site-selectivity. In addition to substrate control through steric hindrance or kinetic acidity of C–H bonds, one important approach for the site-selective C–H transformation of arenes is the use of chelation-assistance through directing groups, therefore leading to proximity-induced ortho-C–H metalation. In contrast, more challenging remote C–H activations at the meta- or para-positions continue to be scarce. Within this review, we demonstrate the distinct character of ruthenium catalysis for remote C–H activations until March 2021, highlighting among others late-stage modifications of bio-relevant molecules. Moreover, we highlight important mechanistic insights by experiments and computation, highlighting the key importance of carboxylate-assisted C–H activation with ruthenium(II) complexes.

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