17 Dec 17:25
by Damiano Ricciarelli,
Leonardo Belpassi,
Jeremy N. Harvey,
Paola Belanzoni
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
by Henning Hopf,
Stephen A. Matlin,
Goverdhan Mehta,
Alain Krief
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
by Yafei Guo,
Syuzanna R. Harutyunyan
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
by Andrew M. R. Hall, Peilong Dong, Anna Codina, John P. Lowe, Ulrich Hintermair
ACS Catalysis
DOI: 10.1021/acscatal.8b03530
03 Aug 10:27
by Ryan Chung, Anh Vo, Valery V. Fokin, Jason E. Hein
ACS Catalysis
DOI: 10.1021/acscatal.8b01342
18 Mar 07:29
by Jérémy Merad, Claudia Lalli, Guillaume Bernadat, Julien Maury, Géraldine Masson
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
by Christopher G. Newton, Shou-Guo Wang, Caio C. Oliveira and Nicolai Cramer
Chemical Reviews
DOI: 10.1021/acs.chemrev.6b00692