: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

The development of new methods for the direct functionalization of unactivated C–H bonds is ushering in a paradigm shift in the field of retrosynthetic analysis. In particular, the catalytic enantioselective functionalization of C–H bonds represents a highly atom- and step-economic approach toward the generation of structural complexity. However, as a result of their ubiquity and low reactivity, controlling both the chemo- and stereoselectivity of such processes constitutes a significant challenge. Herein we comprehensively review all asymmetric transition-metal-catalyzed methodologies that are believed to proceed via an inner-sphere-type mechanism, with an emphasis on the nature of stereochemistry generation. Our analysis serves to document the considerable and rapid progress within in the field, while also highlighting limitations of current methods.

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

Site Heterogeneous Catalysts: Strategies, Methods, Structures, and Activities Christophe Copeŕet,*,† Aleix Comas-Vives,† Matthew P. Conley,† Deven P. Estes,† Alexey Fedorov,† Victor Mougel,† Haruki Nagae,†,‡ Francisco Nuñ́ez-Zarur,† and Pavel A. Zhizhko†,§ †Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir Prelog Weg 1−5, CH-8093 Zürich, Switzerland ‡Department of Chemistry, Graduate School of Engineering Science, Osaka University, CREST, Toyonaka, Osaka 560-8531, Japan A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Vavilov str. 28, 119991 Moscow, Russia

Surface Organometallic and Coordination Chemistry toward Single-Site Heterogeneous Catalysts: Strategies, Methods, Structures, and Activities

The engineering of catalysts with desirable properties can be accelerated by computer-aided design. To achieve this aim, features of molecular catalysts can be condensed into numerical descriptors that can then be used to correlate reactivity and structure. Based on such descriptors, we have introduced topographic steric maps that provide a three-dimensional image of the catalytic pocket-the region of the catalyst where the substrate binds and reacts-enabling it to be visualized and also reshaped by changing various parameters. These topographic steric maps, especially when used in conjunction with density functional theory calculations, enable catalyst structural modifications to be explored quickly, making the online design of new catalysts accessible to the wide chemical community. In this Perspective, we discuss the application of topographic steric maps either to rationalize the behaviour of known catalysts-from synthetic molecular species to metalloenzymes-or to design improved catalysts.

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Towards the online computer-aided design of catalytic pockets

N-Heterocyclic carbenes (NHCs) have become without doubt one of the most exciting and popular species in chemical science due to the ease of their preparation and modularity in stereoelectronic properties. Numerous types of NHCs have been prepared, and various experimental methodologies have been proposed for the study of their electronic properties in order to rationalize reactivities observed. The objective of this article is to provide a comprehensive overview of the most common and popular ones among them. In particular, these include the nickel(0)-based TEP, its rhodium(I) and iridium(I) variants, LEP and related electrochemical methods, the palladium(II)-based HEP, phosphinidene- and selenourea-based methods, as well as the use of direct 1J(C–H) coupling constants of the precarbene carbon in azolium salts. Each individual method and the underlying principle of detection it utilizes will be critically discussed in terms of strength and weakness. In addition, comprehensive amounts of data from various...

Electronic Properties of N-Heterocyclic Carbenes and Their Experimental Determination

Multivariate Linear Regression (MLR) models utilizing computationally-derived and empirically-derived physical organic molecular descriptors are described in this review. Several reports demonstrating the effectiveness of this methodological approach towards reaction optimization and mechanistic interrogation are discussed. A detailed protocol to access quantitative and predictive MLR models is provided as a guide for model development and parameter analysis.

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Predictive and mechanistic multivariate linear regression models for reaction development

An enantioselective, intermolecular dehydrogenative Heck arylation of trisubstituted alkenes to construct remote quaternary stereocenters has been developed. Using a new chiral pyridine oxazoline ligand, good to high enantioselectivity is achieved for various combinations of indole derivatives and trisubstituted alkenes. However, some combinations of substrates led to lower enantioselectivity, which provided the impetus to use structure enantioselectivity correlations to design a better performing ligand.

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Enantioselective Dehydrogenative Heck Arylations of Trisubstituted Alkenes with Indoles to Construct Quaternary Stereocenters

A highly enantioselective and site-selective Pd-catalyzed arylation of alkenes linked to carbonyl derivatives to yield α,β-unsaturated systems is reported. The high site selectivity is attributed to both a solvent effect and the polarized nature of the carbonyl group, both of which have been analyzed through multidimensional analysis tools. The reaction can be performed in an iterative fashion allowing for a diastereoselective installation of two aryl groups along an alkyl chain.

/pdf/alkenyl-carbonyl-derivatives-in-enantioselective-redox-relay-32esy2wush.pdf

Alkenyl Carbonyl Derivatives in Enantioselective Redox Relay Heck Reactions: Accessing α,β-Unsaturated Systems

A broad series of fully characterized, well-defined silica-supported W metathesis catalysts with the general formula [(≡SiO)W(═NAr)(═CHCMe2R)(X)] (Ar = 2,6-iPr2C6H3 (AriPr), 2,6-Cl2C6H3 (ArCl), 2-CF3C6H4 (ArCF3), and C6F5 (ArF5); X = OC(CF3)3 (OtBuF9), OCMe(CF3)2 (OtBuF6), OtBu, OSi(OtBu)3, 2,5-dimethylpyrrolyl (Me2Pyr) and R = Me or Ph) was prepared by grafting bis-X substituted complexes [W(NAr)(═CHCMe2R)(X)2] on silica partially dehydroxylated at 700 °C (SiO2-(700)), and their activity was evaluated with the goal to obtain detailed structure-activity relationships. Quantitative influence of the ligand set on the activity (turnover frequency, TOF) in self-metathesis of cis-4-nonene was investigated using multivariate linear regression analysis tools. The TOF of these catalysts (activity) can be well predicted from simple steric and electronic parameters of the parent protonated ligands; it is described by the mutual contribution of the NBO charge of the nitrogen or the IR intensity of the symmetric N-H stretch of the ArNH2, corresponding to the imido ligand, together with the Sterimol B5 and pKa of HX, representing the X ligand. This quantitative and predictive structure-activity relationship analysis of well-defined heterogeneous catalysts shows that high activity is associated with the combination of X and NAr ligands of opposite electronic character and paves the way toward rational development of metathesis catalysts.

Quantitatively Analyzing Metathesis Catalyst Activity and Structural Features in Silica-Supported Tungsten Imido–Alkylidene Complexes

The effects of aryl ring ortho-, meta-, and para-substitution on site selectivity and enantioselectivity were investigated in the following reactions: (1) enantioselective Pd-catalyzed redox-relay Heck reaction of arylboronic acids, (2) Pd-catalyzed β-aryl elimination of triarylmethanols, and (3) benzoylformate decarboxylase-catalyzed enantioselective benzoin condensation of benzaldehydes. Through these studies, it is demonstrated that the electronic and steric effects of various substituents on selectivities obtained in these reactions can be described by NBO charges, the IR carbonyl stretching frequency, and Sterimol values of various substituted benzoic acids. An extended compilation of NBO charges and IR carbonyl stretching frequencies of various substituted benzoic acids was used as an alternative to Hammett values. These parameters provide a correlative tool that allows for the analysis of a much greater range of substituent effects because they can also account for proximal and remote steric effects.

Celine B. Santiago

Papers

Predictive and mechanistic multivariate linear regression models for reaction development

Enantioselective Dehydrogenative Heck Arylations of Trisubstituted Alkenes with Indoles to Construct Quaternary Stereocenters

Alkenyl Carbonyl Derivatives in Enantioselective Redox Relay Heck Reactions: Accessing α,β-Unsaturated Systems

Quantitatively Analyzing Metathesis Catalyst Activity and Structural Features in Silica-Supported Tungsten Imido–Alkylidene Complexes

Developing a Modern Approach To Account for Steric Effects in Hammett-Type Correlations.