Computational Studies of Carboxylate-Assisted C-H Activation and Functionalization at Group 8-10 Transition Metal Centers

Computational studies on carboxylate-assisted C-H activation and functionalization at group 8-10 transition metal centers are reviewed. This Review is organized by metal and will cover work published from late 2009 until mid-2016. A brief overview of computational work prior to 2010 is also provided, and this outlines the understanding of carboxylate-assisted C-H activation in terms of the "ambiphilic metal-ligand assistance" (AMLA) and "concerted metalation deprotonation" (CMD) concepts. Computational studies are then surveyed in terms of the nature of the C-H bond being activated (C(sp(2))-H or C(sp(3))-H), the nature of the process involved (intramolecular with a directing group or intermolecular), and the context (stoichiometric C-H activation or within a variety of catalytic processes). This Review aims to emphasize the connection between computation and experiment and to highlight the contribution of computational chemistry to our understanding of catalytic C-H functionalization based on carboxylate-assisted C-H activation. Some opportunities where the interplay between computation and experiment may contribute further to the areas of catalytic C-H functionalization and applied computational chemistry are identified

Computational Studies of Carboxylate-Assisted C-H Activation and Functionalization at Group 8-10 Transition Metal Centers

Computational studies on carboxylate-assisted C-H activation and functionalization at group 8-10 transition metal centers are reviewed. This Review is organized by metal and will cover work published from late 2009 until mid-2016. A brief overview of computational work prior to 2010 is also provided, and this outlines the understanding of carboxylate-assisted C-H activation in terms of the "ambiphilic metal-ligand assistance" (AMLA) and "concerted metalation deprotonation" (CMD) concepts. Computational studies are then surveyed in terms of the nature of the C-H bond being activated (C(sp(2))-H or C(sp(3))-H), the nature of the process involved (intramolecular with a directing group or intermolecular), and the context (stoichiometric C-H activation or within a variety of catalytic processes). This Review aims to emphasize the connection between computation and experiment and to highlight the contribution of computational chemistry to our understanding of catalytic C-H functionalization based on carboxylate-assisted C-H activation. Some opportunities where the interplay between computation and experiment may contribute further to the areas of catalytic C-H functionalization and applied computational chemistry are identified

(Arene)ruthenium Complexes with Bis(oxazolines): Synthesis and Applications as Asymmetric Catalysts for Diels−Alder Reactions

Reaction of the dimers [RuCl2(arene)]2 (arene = benzene, p-cymene, mesitylene) with bis(oxazolines) (N-N = bis(2-oxazoline) (box), 2,2-bis(2-oxazolinyl)propane (bop), 1,2-bis(2-oxazolinyl)benzene (benbox)) in the presence of NaSbF6 gives the complexes [RuCl(N-N)(arene)][SbF6] (1−8), which have been fully characterized. Treatment of these cations with AgSbF6 generates dications which in some cases are enantioselective catalysts for Diels−Alder reaction of methacrolein and cyclopentadiene. Two complexes, [RuCl(iPr-benbox)(p-cymene)][SbF6] (5) and [Ru(OH2)(iPr-bop)(mes)][SbF6]2 (10; mes = mesitylene), have been characterized by X-ray crystallography

Preparation of single enantiomers of chiral at metal bis-cyclometallated iridium complexes

Reaction of [Ir(C^N)[subscript 2]Cl][subscript 2] with chiral bidentate N^OH ligands provides complexes [Ir(C^N)[subscript 2](N^O)] as a 1 : 1 mixture of diastereomers which can be separated by crystallisation. A pure diastereomer can be converted to [Ir(C^N)[subscript 2](bipy)][CF[subscript 3]CO[subscript 2]] with complete retention of stereochemistry at the metal

Computational Study of the Mechanism of Cyclometalation by Palladium Acetate

Various mechanisms for the cyclometalation of dimethylbenzylamine by palladium acetate have been studied by DFT calculations. Contrary to previous suggestions, the rate-limiting step is the electrophilic attack of the palladium on an ortho arene C−H bond to form an agostic complex rather than a Wheland intermediate. The cyclometalated product is then formed by intramolecular deprotonation by acetate via a six-membered transition state; this step has almost no activation barrier

Reactions of Cyclometalated Oxazoline Half-Sandwich Complexes of Iridium and Ruthenium with Alkynes and CO

The ligand 4,4-dimethyl-2-oxazolinylbenzene is easily cyclometalated by [IrCl2Cp*]2 or [RuCl(MeCN)2(p-cymene)]PF6 in the presence of sodium acetate. In the case of iridium the resultant complex dissolves in acetonitrile in the presence of KPF6 to give an acetonitrile-coordinated cationic complex. The analogous complex is formed directly in the ruthenium cyclometalation reaction. These labile cationic complexes undergo insertion reactions with internal and terminal alkynes. Internal alkynes give only monoinsertion products, whereas terminal alkynes give mono- or di-insertion products. The cations will also react with CO, but no insertion occurs in this case

A Tiny Adventure: The introduction of problem based learning in an undergraduate chemistry course

Year 1 of the chemistry degree at the University of Leicester has been significantly changed by the integration of a problem based learning (PBL) component into the introductory inorganic/physical chemistry module, "Chemical Principles". Small groups of 5-6 students were given a series of problems with real world scenarios and were then given the responsibility of planning, researching and constructing solutions to the problem on a group wiki hosted on the Universty’s Virtual Learning Environment (VLE). The introduction of PBL to the course was evaluated both quantitatively and qualitatively. Class test and exam results were analysed and compared with those achieved in previous years (i.e. before the introduction of PBL). It was found that student performance was at least as good as it had been before the introduction of PBL. Retention figures after PBL had risen sharply (not one PBL student dropped out of the course during the first term). Student and staff feedback was also collected for qualitative analysis of the impact of the change. Combining these findings showed that students appeared to show an improvement in, and recognition of the acquisition of, transferable skills and that group work on immediate arrival at university (representing an opportunity to use social skills within an academic exercise) led to high student retention within the PBL cohort

Deep Eutectic Solvents Formed between Choline Chloride and Carboxylic Acids: Versatile Alternatives to Ionic Liquids

Deep Eutectic Solvents (DES) can be formed between a variety of quaternary ammonium salts and carboxylic acids. The physical properties are significantly affected by the structure of the carboxylic acid but the phase behavior of the mixtures can be simply modeled by taking account of the mole fraction of carboxylic acid in the mixture. The physical properties such as viscosity, conductivity, and surface tension of these DES are similar to ambient temperature ionic liquids and insight into the cause of these properties is gained using hole-theory. It is shown that the conductivity and viscosity of these liquids is controlled by ion mobility and the availability of voids of suitable dimensions, and this is consistent with the fluidity of other ionic liquids and molten salts. The DES are also shown to be good solvents for metal oxides, which could have potential application for metal extraction

Triazoles from N-Alkynylheterocycles and Their Coordination to Iridium

N-alkynylheterocycles (benzimidazole and indazole) are converted to triazoles by click chemistry, and the resulting triazoles react with [IrCl₂Cp*]₂. The benzimidazole-triazole coordinates in a monodentate fashion through the benzimidazole, whereas the indazole-triazole is bidentate through coordination of both heterocycles. Reaction of the benzimidazole-triazole with methyliodide gives a benzimidazolium salt that deprotonates on coordination to afford a rare example of a bidentate NHC–triazole

Cu-Catalyzed N<i>-</i>Alkynylation of Imidazoles, Benzimidazoles, Indazoles, and Pyrazoles Using PEG as Solvent Medium

A facile and efficient Cu(I)-catalyzed cross-coupling method is reported for the preparation of N-alkynyl or N-bromoalkenyl heteroarenes from bromoalkynes. Generally superior yields and functional group tolerance were obtained with microwave (MW) irradiation using imidazole, benzimidazole, pyrazole, and indazole substrates and poly(ethylene glycol) 400 (PEG400) as an additive. We speculate that PEG400 acts as both a Cu(I)-stabilizing ligand as well as a phase transfer solvent