http://pubs.acs.org/doi/abs/10.1021/acscatal.5b02201

Mechanism and Origins of Ligand-Controlled Linear Versus Branched Selectivity of Iridium-Catalyzed Hydroarylation of Alkenes

Genping Huang^*† and Peng Liu^*‡

^† Department of Chemistry, School of Science, Tianjin University, and Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin 300072, People’s Republic of China

^‡ Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States

ACS Catal., 2016, 6, pp 809–820

DOI: 10.1021/acscatal.5b02201

Publication Date (Web): December 21, 2015

Copyright © 2015 American Chemical Society

*E-mail: gphuang@tju.edu.cn. Web: http://genpinghuang.weebly.com., *E-mail: pengliu@pitt.edu.

Abstract

The iridium-catalyzed carbonyl-directed hydroarylation of monosubstituted alkenes developed by Bower and co-workers [Crisenza, G. E. M.; McCreanor, N. G.; Bower, J. F. J. Am. Chem. Soc. 2014, 136, 10258–10261] provides an efficient strategy for highly branched-selective hydroarylation of both aryl- and alkyl-substituted alkenes. Density functional theory calculations in the present study revealed that the unique regiochemical control in this reaction is due to an unconventional modified Chalk–Harrod-type mechanism. Instead of the commonly accepted Chalk–Harrod-type mechanism of transition metal-catalyzed hydroarylation that involves C–H oxidative addition, olefin migratory insertion into the Ir–H bond, and C–C reductive elimination, the Ir-catalyzed reaction occurs via migratory insertion of the olefin into the Ir–aryl bond and C–H reductive elimination. The experimentally observed ligand-controlled selectivity is attributed to a combination of electronic and steric effects in the selectivity-determining olefin migratory insertion step. Ligand steric contour maps show that, in reactions with large-bite-angle bisphosphine ligands, such as d^Fppb, the steric repulsions between the substrate and the aryl substituents on the ligand lead to complete branched selectivity, and the linear selectivity in reactions with small-bite-angle ligands is due to electronic effects that favor 2,1-olefin migratory insertions.

http://pubs.acs.org/doi/abs/10.1021/acscatal.5b02624

Platinum Catalysis Revisited—Unraveling Principles of Catalytic Olefin Hydrosilylation

Teresa K. Meister†‡, Korbinian Riener‡§, Peter Gigler^∥, Jürgen Stohrer^∥, Wolfgang A. Herrmann§, and Fritz E. Kühn^*†§

^†Molecular Catalysis, ^‡Institut für Siliciumchemie, ^§Chair of Inorganic Chemistry, Department of Chemistry, Technische Universität München, Lichtenbergstrasse 4, 85747 Garching b. München, Germany

^∥ Wacker Chemie AG, Consortium für elektrochemische Industrie, Zielstattstraße 20, 81379 München, Germany

ACS Catal., 2016, 6, pp 1274–1284

DOI: 10.1021/acscatal.5b02624

Publication Date (Web): January 7, 2016

Copyright © 2016 American Chemical Society

*E-mail: fritz.kuehn@ch.tum.de.

Abstract

Hydrosilylation of C–C multiple bonds is one of the most important applications of homogeneous catalysis in industry. The reaction is characterized by its atom-efficiency, broad substrate scope, and widespread application. To date, industry still relies on highly active platinum-based systems that were developed over half a century ago. Despite the rapid evolution of vast synthetic applications, the development of a fundamental understanding of the catalytic reaction pathway has been difficult and slow, particularly for the industrially highly relevant Karstedt’s catalyst. A detailed mechanistic study unraveling several new aspects of platinum-catalyzed hydrosilylation using Karstedt’s catalyst as platinum source is presented in this work. A combination of ²H-labeling experiments, ¹⁹⁵Pt NMR studies, and an in-depth kinetic study provides the basis for a further development of the well-established Chalk–Harrod mechanism. It is concluded that the coordination strength of the olefin exerts a decisive effect on the kinetics of the reaction. In addition, it is demonstrated how distinct structural features of the active catalyst species can be derived from kinetic data. A primary kinetic isotope effect as well as a characteristic product distribution in deuterium-labeling experiments lead to the conclusion that the rate-limiting step of platinum-catalyzed hydrosilylation is in fact the insertion of the olefin into the Pt–H bond rather than reductive elimination of the product in the olefin/silane combinations studied.

http://pubs.acs.org/doi/abs/10.1021/acscatal.5b02414

Rhodium(III)-Catalyzed Coupling of Arenes with Cyclopropanols via C–H Activation and Ring Opening

Xukai Zhou, Songjie Yu, Lingheng Kong, and Xingwei Li^*

Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China

ACS Catal., 2016, 6, pp 647–651

DOI: 10.1021/acscatal.5b02414

Publication Date (Web): December 21, 2015

Copyright © 2015 American Chemical Society

*E-mail: xwli@dicp.ac.cn.

Abstract

Rhodium-catalyzed C–H activation of arenes has been established as an important strategy for the rapid construction of new bonds. On the other hand, ring-opening of readily available cyclopropanols has served as a driving force for the coupling with various nucleophiles and electrophiles. Nevertheless, these two important areas evolved separately, and coupling of arenes with cyclopropanols via C–H activation has been rarely explored. In this work, the oxidative coupling between arenes and cyclopropanols has been realized with high efficiency and selectivity under Rh(III)-catalysis, providing an efficient route to access β-aryl ketones. Moreover, the C–H bond has been extended to benzylic C–H bonds.

Determining the Electron-Donating Properties of Bidentate Ligands by 13C NMR Spectroscopy

Qiaoqiao Teng and Han Vinh Huynh*

Synopsis

The net donating ability of 15 bidentate ligands including aromatic and aliphatic diimines as well as alkyl-bridged di-N-heterocyclic carbenes was determined using a 13C NMR-based electronic parameter. Differences in the substituents and the backbones affect the donating ability of the bidentate ligands according to their inductive and mesomeric effects. The methodology allows for the evaluation of classical Werner-type and organometallic ligands on a unified scale.

Abstract

A series of 15 mononuclear complexes [PdBr(iPr2-bimy)(L2)]PF6 (1–15) (iPr2-bimy = 1,3-diisopropylbenzimidazolin-2-ylidene, L2 = aromatic 1,2-diimines, diazabutadienes, or methylene-, ethylene- and propylene-bridged di-N-heterocyclic carbenes) and two dicarbene-bridged, dinuclear complexes [Pd2Br4(iPr2-bimy)2(diNHC)] (16 and 17) were synthesized and characterized by multinuclear NMR spectroscopy, electrospray ionization mass spectrometry, and in some cases X-ray diffraction analysis. The influence of the 15 bidentate ligands L2 on the13Ccarbene signals of the iPr2-bimy reporter ligand in the chelate complexes was studied, on the basis of which a facile methodology for the donor strength determination of bidentate ligands was developed.

http://pubs.acs.org/doi/abs/10.1021/ic501325j?journalCode=inocaj&quickLinkVolume=53&quickLinkPage=10964&selectedTab=citation&volume=53

Conversion of CO2 from Air into Methanol Using a Polyamine and a Homogeneous Ruthenium Catalyst

http://pubs.acs.org/doi/abs/10.1021/jacs.5b12354
 
Conversion of CO2 from Air into Methanol Using a Polyamine and a Homogeneous Ruthenium Catalyst
Jotheeswari Kothandaraman, Alain Goeppert, Miklos Czaun, G. K. Surya Prakash, and George A Olah
J. Am. Chem. Soc., Just Accepted Manuscript
DOI: 10.1021/jacs.5b12354
Publication Date (Web): December 29, 2015
Copyright © 2015 American Chemical Society

Abstract: A highly efficient homogeneous catalyst system for the continuous production of CH3OH from CO2 using PEHA and Ru-Macho-BH (1) at 125-165 °C in an ethereal solvent has been developed (initial TOF = 70 h-1 at 145 °C). Ease of separation of CH3OH is demonstrated by simple distillation from the reaction mixture. The robustness of the catalytic system was shown by recycling the catalyst over 5 runs without significant loss of activity (TON>2000 h-1). Various sources of CO2 can be used for this reaction including the air, despite its low CO2 concentration (400 ppm). For the first time, we have demonstrated that CO2 captured from air can be directly converted to CH3OH in 79% yield using the homogeneous catalytic system.