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17 Dec 17:25

Spin‐Forbidden Reactivity of Transition Metal Oxo Species: Exploring the Potential Energy Surfaces

by Damiano Ricciarelli, Leonardo Belpassi, Jeremy N. Harvey, Paola Belanzoni
Chemistry – A European Journal Spin‐Forbidden Reactivity of Transition Metal Oxo Species: Exploring the Potential Energy Surfaces

Spin‐forbidden reactivity of first row transition metal‐oxo species is computationally investigated through both the MECP between the two diabatic reactants and products PESs, and the TS SOC approach which allows to explore a single adiabatic PES by inclusion of spin‐orbit coupling. Both approaches provide qualitatively and quantitatively similar reactivity pictures. The TS SOC straightforward exploration of a single adiabatic PES can avoid possible pitfalls when tricky diabatic PESs are involved.


Abstract

Spin‐forbidden reactions are frequently encountered when transition metal oxo species are involved, particularly in oxygen transfer reactivity. The computational study of such reactions is challenging, because reactants and products are located on different spin potential energy surfaces (PESs). One possible approach to describe these reactions is the so‐called minimum energy crossing point (MECP) between the diabatic reactants and products PESs. Alternatively, inclusion of spin‐orbit coupling (SOC) effects allows to locate a saddle point on a single adiabatic PES (TS SOC). The TS SOC approach is rarely applied because of its high computational cost. Recently evidence for a TS SOC impact on significantly lowering the activation barrier in dioxygen addition to a carbene‐gold(I)‐hydride complex reaction (Chem. Sci. 2016, 7, 7034–7039) or even on predicting a qualitatively different reaction mechanism in mercury methylation by cobalt corrinoid (Angew. Chem. Int. Ed. 2016, 55, 11503–11506) has been put forward. Using MECP and TS SOC approaches a systematic analysis is provided here of three prototypical transition metal oxo spin‐forbidden processes to investigate their implications on reactivity. Cycloaddition of ethylene to chromyl chloride (CrO2Cl2+C2H4), iron oxide cation insertion into the hydrogen molecule (FeO++H2) and H‐abstraction from toluene by a MnV‐oxo‐porphyrin cation (MnOP(H2O)++C6H5CH3) are case studies. For all these processes the MECP and TS SOC results are compared, which show that the spin‐forbidden reactivity of transition metal oxo species can be safely described by a MECP approach, at least for the first‐row transition metals investigated here, where the spin‐orbit coupling is relatively weak. However, for the Mn‐oxo reactivity, the MECP and TS SOC have been found to be crucial for a correct description of the reaction mechanism. In particular, the TS SOC approach allows to straightforwardly explore detailed features of the adiabatic potential energy surface which in principle could affect the overall reaction rate in cases where the involved diabatic PESs are tricky.

09 Dec 14:33

Blocking the Hype‐Hypocrisy‐Falsification‐Fakery Pathway is Needed to Safeguard Science

by Henning Hopf, Stephen A. Matlin, Goverdhan Mehta, Alain Krief
Angewandte Chemie International Edition Blocking the Hype‐Hypocrisy‐Falsification‐Fakery Pathway is Needed to Safeguard Science

Hype in science is commonplace, compounded by the hypocrisy of those who engage in or tolerate it while disapproving of the consequences. These are first steps along a slippery slope of hype, hypocrisy, data falsification, and dissemination of fake science, encouraged by systemic drivers in the contemporary structure of the science establishment. Collective, concerted intervention is required to discourage entry to this dangerous pathway; chemists must play and active role.


Abstract

In chemistry and other sciences, hype has become commonplace, compounded by the hypocrisy of those who tolerate or encourage it while disapproving of the consequences. This reduces the credibility and trust upon which all science depends for support. Hype and hypocrisy are but first steps down a slippery slope towards falsification of results and dissemination of fake science. Systemic drivers in the contemporary structure of the science establishment encourage exaggeration and may lure the individual into further steps along the hype‐hypocrisy‐falsification‐fakery continuum. Collective, concerted intervention is required to effectively discourage entry to this dangerous pathway and to restore and protect the probity and reputation of the science system. Chemists must play and active role in this effort.

11 Sep 08:41

Highly Enantioselective Catalytic Addition of Grignard Reagents to N‐Heterocyclic Acceptors

by Yafei Guo, Syuzanna R. Harutyunyan
Angewandte Chemie International Edition Highly Enantioselective Catalytic Addition of Grignard Reagents to N‐Heterocyclic Acceptors

General access: A general catalytic protocol to access various derivatives of chiral 2‐ and 4‐substituted tetrahydroquinolones, dihydro‐4‐pyridones, and 2,6‐substituted piperidones has been developed. The reactions all proceed with the same copper catalyst system.


Abstract

General methods to prepare chiral N‐heterocyclic molecular scaffolds are greatly sought after because of their significance in medicinal chemistry. Described here is the first general catalytic methodology to access a wide variety of chiral 2‐ and 4‐substituted tetrahydro‐quinolones, dihydro‐4‐pyridones, and piperidones with excellent yields and enantioselectivities, utilizing a single catalyst system.

07 Feb 08:07

[ASAP] Kinetics of Asymmetric Transfer Hydrogenation, Catalyst Deactivation, and Inhibition with Noyori Complexes As Revealed by Real-Time High-Resolution FlowNMR Spectroscopy

by Andrew M. R. Hall, Peilong Dong, Anna Codina, John P. Lowe, Ulrich Hintermair

TOC Graphic

ACS Catalysis
DOI: 10.1021/acscatal.8b03530
27 Nov 23:13

An efficient and highly diastereoselective synthesis of carbocyclic spiropyrazolones via one-pot sequential dual organo-silver catalyzed Michael-hydroalkylation reactions

Publication date: 3 January 2019

Source: Tetrahedron Letters, Volume 60, Issue 1

Author(s): Khyati Shukla, Sadhna Shah, Nirmal K. Rana, Vinod K. Singh

Abstract

An economical approach for the diastereoselective synthesis of highly functionalized carbocyclic spiropyrazolone derivatives having one quaternary and two tertiary stereocenters along with one exocyclic double bond exploiting dual organo-silver sequential catalysis has been developed. The unified method to both cyclohexyl and cyclopentyl spirocompounds involves the reaction of γ- and β-nitroalkynes with alkylidene pyrazolones catalyzed by Hünig’s base followed by carbophilic activation of the triple bond with a Ag(I) salt leading to cyclization via hydroalkylation.

Graphical abstract

Graphical abstract for this article

03 Aug 10:27

[ASAP] Catalyst Activation, Chemoselectivity, and Reaction Rate Controlled by the Counterion in the Cu(I)-Catalyzed Cycloaddition between Azide and Terminal or 1-Iodoalkynes

by Ryan Chung, Anh Vo, Valery V. Fokin, Jason E. Hein

TOC Graphic

ACS Catalysis
DOI: 10.1021/acscatal.8b01342
19 Mar 19:26

Electrophilic Aromatic Formylation with Difluoro(phenylsulfanyl) methane

by Betterley, Nolan M.

Synthesis
DOI: 10.1055/s-0036-1591545



Difluoro(phenylsulfanyl)methane (PhSCF2H) was found to undergo a reaction with aromatic compounds mediated by SnCl4, through a thionium intermediate characterized by NMR and TD-DFT analyses, leading to the formation of a mixture of S,S′-diphenyl dithioacetal and aromatic aldehyde which, after oxidative hydrolysis, provides the aromatic aldehyde in good to excellent yields. The salient feature of the present work is the reaction of activated aromatic compounds containing a deactivating ester functional group, leading to the formylated products in good yields.
[...]

© Georg Thieme Verlag Stuttgart · New York

Article in Thieme eJournals:
Table of contents  |  Abstract  |  Full text

18 Mar 07:29

Frontispiece: Enantioselective Brønsted Acid Catalysis as a Tool for the Synthesis of Natural Products and Pharmaceuticals

by Jérémy Merad, Claudia Lalli, Guillaume Bernadat, Julien Maury, Géraldine Masson
Thumbnail image of graphical abstract

Chiral Brønsted acids are capable of promoting plenty of enantioselective transformations. From simple substrates, chiral protons build complex enantioenriched scaffolds that are subsequently involved in the total synthesis of bioactive moieties. This review aims to describe the value of such asymmetric catalysis to the synthesis of natural products and pharmaceuticals. The target structures, and the potential disconnections are particularly emphasized. For more information see the Minireview by G. Masson and co-workers on page 3925 ff.

01 Mar 09:43

Catalytic Enantioselective Transformations Involving C–H Bond Cleavage by Transition-Metal Complexes

by Christopher G. Newton, Shou-Guo Wang, Caio C. Oliveira and Nicolai Cramer
Maximevitale

Nice !

TOC Graphic

Chemical Reviews
DOI: 10.1021/acs.chemrev.6b00692