Publications by authors named "David J Nelson"

42 Publications

The Effect of Added Ligands on the Reactions of [Ni(COD)(dppf)] with Alkyl Halides: Halide Abstraction May Be Reversible.

Organometallics 2021 Jun 16;40(12):1997-2007. Epub 2021 Jun 16.

WestCHEM Department of Pure and Applied Chemistry, University of Strathclyde, 295 Cathedral Street, Glasgow G1 1XL, Scotland.

The reactions of dppf-nickel(0) with alkyl halides proceed via three-coordinate nickel(0) intermediates of the form [Ni(dppf)(L)]. The effects of the identity of the added ligand (L) on catalyst speciation and the rates of reactions of [Ni(COD)(dppf)] with alkyl halides have been investigated using kinetic experiments and density functional theory calculations. A series of monodentate ligands have been investigated in attempts to identify trends in reactivity. Sterically bulky and electron-donating ligands are found to decrease the reaction rate. It was found that (i) the halide abstraction step is not always irreversible and the subsequent recombination of a nickel(I) complex with an alkyl halide can have a significant effect on the overall rate of the reaction and (ii) some ligands lead to very stable [Ni(dppf)(L)] species. The yields of prototypical (dppf)nickel-catalyzed Kumada cross-coupling reactions of alkyl halides are significantly improved by the addition of free ligands, which provides another important variable to consider when optimizing nickel-catalyzed reactions of alkyl halides.
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http://dx.doi.org/10.1021/acs.organomet.1c00280DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8288641PMC
June 2021

Optimizing Catalyst and Reaction Conditions in Gold(I) Catalysis-Ligand Development.

Chem Rev 2021 Jul 14. Epub 2021 Jul 14.

Department of Chemistry and Center for Sustainable Chemistry, Ghent University, Krijgslaan 281 - S3, 9000 Gent, Belgium.

This review considers phosphine and -heterocyclic carbene complexes of gold(I) that are used as (pre)catalysts for a range of reactions in organic synthesis. These are divided according to the structure of the ligand, with the narrative focusing on studies that offer a quantitative comparison between the ligands and readily available or widely used existing systems.
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http://dx.doi.org/10.1021/acs.chemrev.0c01320DOI Listing
July 2021

Synthesis of Gold(I)-Trifluoromethyl Complexes and their Role in Generating Spectroscopic Evidence for a Gold(I)-Difluorocarbene Species.

Chemistry 2021 Jun 14;27(33):8461-8467. Epub 2021 May 14.

Department of Chemistry and Centre for Sustainable Chemistry, Ghent University, Krijgslaan 281-S3, 9000, Gent, Belgium.

Readily prepared and bench-stable [Au(CF )(NHC)] compounds were synthesized by using new methods, starting from [Au(OH)(NHC)], [Au(Cl)(NHC)] or [Au(L)(NHC)]HF precursors (NHC=N-heterocyclic carbene). The mechanism of formation of these species was investigated. Consequently, a new and straightforward strategy for the mild and selective cleavage of a single carbon/fluorine bond from [Au(CF )(NHC)] complexes was attempted and found to be reversible in the presence of an additional nucleophilic fluoride source. This straightforward technique has led to the unprecedented spectroscopic observation of a gold(I)-NHC difluorocarbene species.
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http://dx.doi.org/10.1002/chem.202100195DOI Listing
June 2021

Unexpected Nickel Complex Speciation Unlocks Alternative Pathways for the Reactions of Alkyl Halides with dppf-Nickel(0).

ACS Catal 2020 Sep 21;10(18):10717-10725. Epub 2020 Aug 21.

WestCHEM Department of Pure and Applied Chemistry, University of Strathclyde, 295 Cathedral Street, Glasgow G1 1XL, Scotland.

The mechanism of the reactions between dppf-Ni complexes and alkyl halides has been investigated using kinetic and mechanistic experiments and DFT calculations. The active species is [Ni(κ-dppf)(κ-dppf)], which undergoes a halide abstraction reaction with alkyl halides and rapidly captures the alkyl radical that is formed. The rates of the reactions of [Ni(COD)(dppf)] with alkyl halides and the yields of prototypical nickel-catalyzed Kumada cross-coupling reactions of alkyl halides are shown to be significantly improved by the addition of free dppf ligand.
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http://dx.doi.org/10.1021/acscatal.0c02514DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7507766PMC
September 2020

Straightforward access to chalcogenoureas derived from N-heterocyclic carbenes and their coordination chemistry.

Dalton Trans 2020 Sep 21;49(34):12068-12081. Epub 2020 Aug 21.

Department of Chemistry, Ghent University, Krijgslaan 281, Building S3, 9000 Ghent, Belgium.

Chalcogen-based urea compounds supported by a wide range of N-heterocyclic carbenes are synthesised and fully characterised. Coordination of selenoureas is further explored with Group 11 transition metals to form new copper, gold and silver complexes. Single crystal X-ray analyses unambiguously establish the solid-state coordination of these complexes and show that the geometry of a complex is highly influenced by a combination of electronic properties - mainly π-accepting ability - and steric hindrance of the ligands, as well as the nature of the metal, affording a variety of coordination behaviours. In this report, we investigate these phenomena using several experimental methods.
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http://dx.doi.org/10.1039/d0dt02558eDOI Listing
September 2020

Aldehydes and ketones influence reactivity and selectivity in nickel-catalysed Suzuki-Miyaura reactions.

Chem Sci 2020 Jan 6;11(7):1905-1911. Epub 2020 Jan 6.

WestCHEM Department of Pure and Applied Chemistry, University of Strathclyde 295 Cathedral Street Glasgow G1 1XL Scotland UK

The energetically-favorable coordination of aldehydes and ketones - but not esters or amides - to Ni during Suzuki-Miyaura reactions can lead either to exquisite selectivity and enhanced reactivity, or to inhibition of the reaction. Aryl halides where the C-X bond is connected to the same π-system as an aldehyde or ketone undergo unexpectedly rapid oxidative addition to [Ni(COD)(dppf)] (), and are selectively cross-coupled during competition reactions. When aldehydes and ketones are present in the form of exogenous additives, the cross-coupling reaction is inhibited to an extent that depends on the strength of the coordination of the pendant carbonyl group to Ni. This work advances our understanding of how common functional groups interact with Ni catalysts and how these interactions affect workhorse catalytic reactions in academia and industry.
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http://dx.doi.org/10.1039/c9sc05444hDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8148322PMC
January 2020

Metabolomic Profiling of the Immune Stimulatory Effect of Eicosenoids on PMA-Differentiated THP-1 Cells.

Vaccines (Basel) 2019 Oct 9;7(4). Epub 2019 Oct 9.

Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, 161 Cathedral Street, Glasgow G4 0RE, UK.

Honey bee venom has been established to have significant effect in immunotherapy. In the present study, (Z)-11-eicosenol-a major constituent of bee venom, along with its derivations methyl cis-11-eicosenoate and cis-11-eicosenoic acid, were synthesised to investigate their immune stimulatory effect and possible use as vaccine adjuvants. Stimuli that prime and activate the immune system have exerted profound effects on immune cells, particularly macrophages; however, the effectiveness of bee venom constituents as immune stimulants has not yet been established. Here, the abilities of these compounds to act as pro-inflammatory stimuli were assessed, either alone or in combination with lipopolysaccharide (LPS), by examining the secretion of tumour necrosis factor-α (TNF-α) and the cytokines interleukin-1β (IL-1β), IL-6 and IL-10 by THP-1 macrophages. The compounds clearly increased the levels of IL-1β and decreased IL-10, whereas a decrease in IL-6 levels suggested a complex mechanism of action. A more in-depth profile of macrophage behaviour was therefore obtained by comprehensive untargeted metabolic profiling of the cells using liquid chromatography mass spectrometry (LC-MS) to confirm the ability of the eicosanoids to trigger the immune system. The level of 358 polar and 315 non-polar metabolites were changed significantly ( < 0.05) by all treatments. The LPS-stimulated production of most of the inflammatory metabolite biomarkers in glycolysis, the tricarboxylic acid (TCA) cycle, the pentose phosphate pathway, purine, pyrimidine and fatty acids metabolism were significantly enhanced by all three compounds, and particularly by methyl cis-11-eicosenoate and cis-11-eicosenoic acid. These findings support the proposed actions of (Z)-11-eicosenol, methyl cis-11-eicosenoate and cis-11-eicosenoic acid as immune system stimulators.
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http://dx.doi.org/10.3390/vaccines7040142DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6963534PMC
October 2019

Highlights from the 54th EUCHEM Bürgenstock Conference on Stereochemistry, Brunnen, Switzerland, May 2019.

Chem Commun (Camb) 2019 09 9;55(68):10043-10046. Epub 2019 Aug 9.

Laboratoire d'Innovation Moléculaire et Applications, ECPM, UMR 7042, Université de Strasbourg/Université de Haute-Alsace, 25 rue Becquerel, Cedex 67087, Strasbourg, France.

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http://dx.doi.org/10.1039/c9cc90354bDOI Listing
September 2019

The Electrophilic Fluorination of Enol Esters Using SelectFluor: A Polar Two-Electron Process.

Chemistry 2019 Apr 15;25(21):5574-5585. Epub 2019 Mar 15.

WestCHEM Department of Pure and Applied Chemistry, University of Strathclyde, 295 Cathedral Street, Glasgow, G1 1XL, UK.

The reaction of enol esters with SelectFluor is facile and leads to the corresponding α-fluoroketones under mild conditions and, as a result, this route is commonly employed for the synthesis of medicinally important compounds such as fluorinated steroids. However, despite the use of this methodology in synthesis, the mechanism of this reaction and the influence of structure on reactivity are unclear. A rigorous mechanistic study of the fluorination of these substrates is presented, informed primarily by detailed and robust kinetic experiments. The results of this study implicate a polar two-electron process via an oxygen-stabilised carbenium species, rather than a single-electron process involving radical intermediates. The structure-reactivity relationships revealed here will assist synthetic chemists in deploying this type of methodology in the syntheses of α-fluoroketones.
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http://dx.doi.org/10.1002/chem.201900029DOI Listing
April 2019

Steric effects determine the mechanisms of reactions between bis(N-heterocyclic carbene)-nickel(0) complexes and aryl halides.

Chem Commun (Camb) 2018 Sep;54(75):10646-10649

WestCHEM Department of Pure and Applied Chemistry, University of Strathclyde, 295 Cathedral Street, Glasgow, G1 1XL, UK.

Computational investigations of the reactions of [Ni(NHC)2] complexes with aryl halides show that the outcomes are governed by the steric impact of the ligand (NHC = N-heterocyclic carbene). Small ligands permit facile oxidative addition, leading to NiII complexes, while larger NHC ligands prevent coordination of the aryl halide and favour the halide abstraction to form NiI.
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http://dx.doi.org/10.1039/c8cc06379fDOI Listing
September 2018

Coinage metal complexes of selenoureas derived from N-heterocyclic carbenes.

Dalton Trans 2018 Aug 6;47(31):10671-10684. Epub 2018 Jun 6.

WestCHEM Department of Pure & Applied Chemistry, University of Strathclyde, 295 Cathedral Street, Glasgow, G1 1XL, UK.

We describe the synthesis and characterisation of a series of new copper and silver complexes with selenourea ligands derived from common and readily-prepared N-heterocyclic carbenes (NHCs). The copper complexes behave somewhat predictably, typically leading to [CuCl(L)] complexes (with two exceptions). The silver complexes display a diverse range of structural motifs, including [AgCl(μ-L)], [AgCl(L)], [Ag(L)], [Ag(L)], and [(Ag(L))(μ-L)] species. All new complexes are characterised by multinuclear NMR spectroscopy, and several examples are characterised by X-ray crystallography. This study demonstrates the diversity of coordination behaviour that these selenourea ligands can engage in.
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http://dx.doi.org/10.1039/c8dt01506fDOI Listing
August 2018

Interrogating Pd(II) Anion Metathesis Using a Bifunctional Chemical Probe: A Transmetalation Switch.

J Am Chem Soc 2018 01 22;140(1):126-130. Epub 2017 Dec 22.

Department of Pure and Applied Chemistry, University of Strathclyde , 295 Cathedral Street, Glasgow G1 1XL, U.K.

Ligand metathesis of Pd(II) complexes is mechanistically essential for cross-coupling. We present a study of halide→OH anion metathesis of (Ar)Pd complexes using vinylBPin as a bifunctional chemical probe with Pd(II)-dependent cross-coupling pathways. We identify the variables that profoundly impact this event and allow control to be leveraged. This then allows control of cross-coupling pathways via promotion or inhibition of organoboron transmetalation, leading to either Suzuki-Miyaura or Mizoroki-Heck products. We show how this transmetalation switch can be used to synthetic gain in a cascade cross-coupling/Diels-Alder reaction, delivering borylated or non-borylated carbocycles, including steroid-like scaffolds.
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http://dx.doi.org/10.1021/jacs.7b11180DOI Listing
January 2018

Halide Abstraction Competes with Oxidative Addition in the Reactions of Aryl Halides with [Ni(PMe Ph ) ].

Chemistry 2017 Nov 20;23(66):16728-16733. Epub 2017 Nov 20.

Institute of Chemical Research of Catalonia, The Barcelona Institute of Science and Technology, Avgda. Països Catalans 16, 43007, Tarragona, Spain.

Density functional theory (DFT) calculations have been used to study the oxidative addition of aryl halides to complexes of the type [Ni(PMe Ph ) ], revealing the crucial role of an open-shell singlet transition state for halide abstraction. The formation of Ni versus Ni has been rationalised through the study of three different pathways: (i) halide abstraction by [Ni(PMe Ph ) ], via an open-shell singlet transition state; (ii) S 2-type oxidative addition to [Ni(PMe Ph ) ], followed by phosphine dissociation; and (iii) oxidative addition to [Ni(PMe Ph ) ]. For the overall reaction between [Ni(PMe ) ], PhCl, and PhI, a microkinetic model was used to show that our results are consistent with the experimentally observed ratios of Ni and Ni when the PEt complex is used. Importantly, [Ni(PMe Ph ) ] complexes often have little, if any, role in oxidative addition reactions because they are relatively high in energy. The behaviour of [Ni(PR ) ] complexes in catalysis is therefore likely to differ considerably from those based on diphosphine ligands in which two coordinate Ni complexes are the key species undergoing oxidative addition.
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http://dx.doi.org/10.1002/chem.201702331DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5725734PMC
November 2017

The preference for dual-gold(i) catalysis in the hydro(alkoxylation vs. phenoxylation) of alkynes.

Org Biomol Chem 2017 Aug;15(30):6416-6425

Institut de Química Computacional i Catàlisi, Departament de Química, University de Girona, Campus de Montilivi sn, 17003 Girona, Catalonia, Spain.

Dinuclear gold complexes and their use in catalysis have received significant recent attention, but there are few critical comparisons of mono- versus dual gold-catalysed pathways. Herein we study the hydroalkoxylation and hydrophenoxylation of alkynes using density functional theory calculations, and compare two possible mechanisms that have been proposed previously on the basis of theoretical and experimental studies, which unravel different preferences because of both the nature of the alkyne and alcohol and the non-innocent role of the counter-anion of a dual gold based catalyst. Entropy is found to have a significant effect, rendering the nucleophilic attack of the monoaurated intermediate [Au(L)(η-alkyne)] difficult both kinetically and thermodynamically; this mechanism cannot easily form only the trans-alkene product that is observed experimentally. Instead, a reaction via a dual gold catalysed mechanism presents much lower barriers. In addition, for the sake of direct comparison with recent results by Belanzoni and Zuccaccia, oversimplification of the N-heterocyclic carbene (NHC) ligand in the calculations might decrease the enthalpy barrier and lead to results that are not directly applicable to experiments. Moreover, the alkylic or arylic nature of the alkyne and/or alcohol is also tested.
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http://dx.doi.org/10.1039/c7ob01457kDOI Listing
August 2017

Correction: Quantifying and understanding the steric properties of N-heterocyclic carbenes.

Chem Commun (Camb) 2017 03;53(23):3385

Department of Inorganic and Physical Chemistry, Ghent University, Krijgslaan 281 - S3, 9000 Gent, Belgium.

Correction for 'Quantifying and understanding the steric properties of N-heterocyclic carbenes' by Adrián Gómez-Suárez et al., Chem. Commun., 2017, 53, 2650-2660.
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http://dx.doi.org/10.1039/c7cc90091kDOI Listing
March 2017

Quantifying and understanding the steric properties of N-heterocyclic carbenes.

Chem Commun (Camb) 2017 Feb;53(18):2650-2660

Department of Inorganic and Physical Chemistry, Ghent University, Krijgslaan 281 - S3, 9000 Gent, Belgium.

This Feature Article presents and discusses the use of different methods to quantify and explore the steric impact of N-heterocyclic carbene (NHC) ligands. These include (a) the percent buried volume (%V), which provides a convenient single number to measure steric impact and (b) steric maps, which provide a graphical representation of the steric profile of a ligand using colour-coded contour maps. A critical discussion of the scope and limitations of these tools is presented, along with some examples of their use in organometallic chemistry and catalysis. This Article should provide all users of NHCs, from organic, organometallic, and inorganic chemistry backgrounds, with an appreciation of how these tools can be used to quantify and compare their steric properties.
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http://dx.doi.org/10.1039/c7cc00255fDOI Listing
February 2017

Synthesis and characterisation of an N-heterocyclic carbene with spatially-defined steric impact.

Dalton Trans 2016 Aug 23;45(29):11772-80. Epub 2016 Jun 23.

WestCHEM Department of Pure and Applied Chemistry, University of Strathclyde, Thomas Graham Building, 295 Cathedral Street, Glasgow, G1 1XL, UK.

The synthesis and co-ordination chemistry of a new 'bulky yet flexible' N-heterocyclic carbene ("IPaul") is reported. This carbene has spatially-defined steric impact; steric maps show that two quadrants are very bulky while the other two are quite open. The electronic properties of this carbene are very similar to those of other 1,3-diarylimidazol-2-ylidenes. Copper, silver, iridium, and nickel complexes of the new ligand have been prepared. In solution, the ligand adopts two different conformations, while X-ray crystallographic analyses of the transition metal complexes suggest that the syn-conformer is preferred in the solid state due to intermolecular interactions. The copper(i) chloride complex of this new ligand has been shown to be highly-active in the hydrosilylation of carbonyl compounds, when compared to the analogous IPr, IMes, IPr* and IPr*(OMe) complexes.
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http://dx.doi.org/10.1039/c6dt02100jDOI Listing
August 2016

Mechanism of the Transmetalation of Organosilanes to Gold.

ChemistryOpen 2016 02 10;5(1):60-4. Epub 2015 Sep 10.

KAUST Catalysis Center Physical Sciences and Engineering Division King Abdullah University of Science and Technology Thuwal 23955-6900 Saudi Arabia.

Density functional theory (DFT) calculations were carried out to study the reaction mechanism of the first transmetalation of organosilanes to gold as a cheap fluoride-free process. The versatile gold(I) complex [Au(OH)(IPr)] permits very straightforward access to a series of aryl-, vinyl-, and alkylgold silanolates by reaction with the appropriate silane reagent. These silanolate compounds are key intermediates in a fluoride-free process that results in the net transmetalation of organosilanes to gold, rather than the classic activation of silanes as silicates using external fluoride sources. However, here we propose that the gold silanolate is not the active species (as proposed during experimental studies) but is, in fact, a resting state during the transmetalation process, as a concerted step is preferred.
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http://dx.doi.org/10.1002/open.201500172DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4906480PMC
February 2016

Half-sandwich nickel(II) complexes bearing 1,3-di(cycloalkyl)imidazol-2-ylidene ligands.

Beilstein J Org Chem 2015 12;11:2171-8. Epub 2015 Nov 12.

WestCHEM Department of Pure and Applied Chemistry, University of Strathclyde, Thomas Graham Building, 295 Cathedral Street, Glasgow G1 1XL, UK.

Two new nickel catalysts have been prepared using a convenient procedure where nickelocene, the NHC·HBF4 salts, and [Et4N]Cl were heated in THF using microwave irradiation. The resulting [NiCl(Cp)(NHC)] complexes are air- and moisture stable in the solid state, and represent two new members of this valuable and practical class of nickel catalysts. The new species were fully characterised using methods including NMR spectroscopy and X-ray crystallography. When tested in model Suzuki-Miyaura cross-coupling reactions, these complexes were found to be active for the cross-coupling of aryl bromides and aryl chlorides.
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http://dx.doi.org/10.3762/bjoc.11.235DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4660989PMC
December 2015

On the Mechanism of the Digold(I)-Hydroxide-Catalysed Hydrophenoxylation of Alkynes.

Chemistry 2016 Jan 11;22(3):1125-32. Epub 2015 Dec 11.

Institut de Química Computacional i Catàlisi and Departament de Química, Universitat de Girona, Campus Montilivi, 17071, Girona, Catalonia, Spain.

Herein, we present a detailed investigation of the mechanistic aspects of the dual gold-catalysed hydrophenoxylation of alkynes by both experimental and computational methods. The dissociation of [{Au(NHC)}2 (μ-OH)][BF4 ] is essential to enter the catalytic cycle, and this step is favoured by the presence of bulky, non-coordinating counter ions. Moreover, in silico studies confirmed that phenol does not only act as a reactant, but also as a co-catalyst, lowering the energy barriers of several transition states. A gem-diaurated species might form during the reaction, but this lies deep within a potential energy well, and is likely to be an "off-cycle" rather than an "in-cycle" intermediate.
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http://dx.doi.org/10.1002/chem.201503097DOI Listing
January 2016

Discovery of a Potent and Orally Bioavailable Dual Antagonist of CC Chemokine Receptors 2 and 5.

ACS Med Chem Lett 2015 Apr 4;6(4):439-44. Epub 2015 Mar 4.

Departments of Discovery Chemistry, Lead Discovery & Optimization, Preclinical Candidate Optimization, Molecular Discovery Technologies, and Disease Sciences & Biology, Research and Development, Bristol-Myers Squibb Company , Princeton, New Jersey 08543, United States.

We describe the hybridization of our previously reported acyclic and cyclic CC chemokine receptor 2 (CCR2) antagonists to lead to a new series of dual antagonists of CCR2 and CCR5. Installation of a γ-lactam as the spacer group and a quinazoline as a benzamide mimetic improved oral bioavailability markedly. These efforts led to the identification of 13d, a potent and orally bioavailable dual antagonist suitable for use in both murine and monkey models of inflammation.
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http://dx.doi.org/10.1021/ml500505qDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4394346PMC
April 2015

What can NMR spectroscopy of selenoureas and phosphinidenes teach us about the π-accepting abilities of -heterocyclic carbenes?

Chem Sci 2015 Mar 16;6(3):1895-1904. Epub 2015 Feb 16.

KAUST Catalyst Center , Physical Sciences and Engineering Division , King Abdullah University of Science and Technology , Thuwal , 23955-6900 , Saudi Arabia . Email:

The electronic nature of the interaction of NHCs with metal centres is of interest when exploring their properties, how these properties influence those of metal complexes, and how these properties might depend on ligand structure. Selenourea and phosphinidene complexes have been proposed to allow the measurement of the π-accepting ability of NHCs, independent of their σ-donating ability, the collection of Se or P NMR spectra, respectively. Herein, the synthesis and characterisation of selenoureas derived from a range of imidazol-2-ylidenes, 4,5-dihydroimidazol-2-ylidenes and triazol-2-ylidenes are documented. Computational studies are used to explore the link between the shielding of the selenium centre and the electronic properties of the NHCs. Results show that is correlated to the energy gap between a filled lone pair orbital on Se and the empty π* orbital corresponding to the Se-NHC bond. Bond energy decomposition analysis indicated no correlation between the orbital σ-contribution to bonding and the chemical shielding, while a good correlation was found between the π-contribution to bonding and the chemical shielding, confirming that this technique is indeed able to quantify the ability of NHCs to accept π-electron density. Calculations conducted on phosphinidene adducts yielded similar results. With the link between and and π-back bonding ability clearly established, these compounds represent useful ways in which to fully understand and quantify this aspect of the electronic properties of NHCs.
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http://dx.doi.org/10.1039/c4sc03264kDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5812343PMC
March 2015

Iridium(I) hydroxides in catalysis: rearrangement of allylic alcohols to ketones.

Org Biomol Chem 2014 Sep;12(34):6672-6

EaStCHEM School of Chemistry, University of St Andrews, North Haugh, Fife, KY16 9ST, UK.

The iridium(I) hydroxide complex [Ir(OH)(COD)(I(i)Pr)] has been shown to be a competent catalyst for the rearrangement of allylic alcohols to ketones. Reactions proceed in short reaction times (1-1.5 h) with microwave heating, in the absence of additives.
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http://dx.doi.org/10.1039/c4ob01428fDOI Listing
September 2014

Key processes in ruthenium-catalysed olefin metathesis.

Chem Commun (Camb) 2014 Sep;50(72):10355-75

EaStCHEM School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife, KY16 9ST, UK.

While the fundamental series of [2+2]cycloadditions and retro[2+2]cycloadditions that make up the pathways of ruthenium-catalysed metathesis reactions is well-established, the exploration of mechanistic aspects of alkene metathesis continues. In this Feature Article, modern mechanistic studies of the alkene metathesis reaction, catalysed by well-defined ruthenium complexes, are discussed. Broadly, these concern the processes of pre-catalyst initiation, propagation and decomposition, which all have a considerable impact on the overall efficiency of metathesis reactions.
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http://dx.doi.org/10.1039/c4cc02515fDOI Listing
September 2014

Insights into the decomposition of olefin metathesis precatalysts.

Angew Chem Int Ed Engl 2014 Aug 2;53(34):8995-9. Epub 2014 Jun 2.

EaStCHEM School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife, KY16 9ST (UK).

The decomposition of a series of benzylidene, methylidene, and 3-phenylindenylidene complexes has been probed in alcohol solution in the presence of base. Tricyclohexylphosphane-containing precatalysts are shown to yield [RuCl(H)(H2)(PCy3)2] in isopropyl alcohol solutions, while 3-phenylindenylidene complexes lead to η(5)-(3-phenyl)indenyl products. The potential-energy surfaces for the formation of the latter species have been probed using density functional theory studies.
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http://dx.doi.org/10.1002/anie.201403770DOI Listing
August 2014

Does the rate of competing isomerisation during alkene metathesis depend on pre-catalyst initiation rate?

Dalton Trans 2014 Mar;43(12):4674-9

WestCHEM/Department of Pure & Applied Chemistry, University of Strathclyde, 295 Cathedral Street, Glasgow, G1 1XL, UK.

Experimental studies of the ring-closing metathesis reaction of 1,8-nonadiene and the ROMP reaction of cycloheptene show that the rate of isomerisation is not correlated to the initiation rate of the pre-catalyst, and that the absence of phosphine leads to a greatly increased rate of isomerisation. A range of pre-catalysts and solvents were probed and it is proposed that the isomerisation is mediated by a ruthenium hydride complex; our results are consistent with the rate-determining formation of such a species, which might be trapped in situ by tricyclohexylphosphane.
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http://dx.doi.org/10.1039/c4dt00007bDOI Listing
March 2014

From ruthenium olefin metathesis catalyst to (η5-3-phenylindenyl)hydrido complex via alcoholysis.

Chem Commun (Camb) 2014 Feb 16;50(17):2205-7. Epub 2014 Jan 16.

EaStCHEM School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife KY16 9ST, UK.

The synthesis and characterisation of [Ru(H)(η(5)-3-phenylindenyl)((i)Bu-Phoban)2] 4 is reported ((i)Bu-Phoban = 9-isobutyl-9-phosphabicyclo-[3.3.1]-nonane). 4 is obtained via alcoholysis of metathesis pre-catalyst M11, in a process that was previously thought to be limited to analogous complex [RuCl2(PPh3)2(3-phenylindenylidene)] (M10).
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http://dx.doi.org/10.1039/c3cc49481kDOI Listing
February 2014

Synthesis, characterization and luminescence studies of gold(I)-NHC amide complexes.

Beilstein J Org Chem 2013 28;9:2216-23. Epub 2013 Oct 28.

EaStCHEM School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife, KY16 9ST, UK.

A flexible, efficient and straightforward methodology for the synthesis of N-heterocyclic carbene gold(I)-amide complexes is reported. Reaction of the versatile building block [Au(OH)(IPr)] (1) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) with a series of commercially available (hetero)aromatic amines leads to the synthesis of several [Au(NRR')(IPr)] complexes in good yields and with water as the sole byproduct. Interestingly, these complexes present luminescence properties. UV-vis and fluorescence measurements have allowed the identification of their excitation and emission wavelengths (λmax). These studies revealed that by selecting the appropriate amine ligand the emission can be easily tuned to achieve a variety of colors, from violet to green.
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http://dx.doi.org/10.3762/bjoc.9.260DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3817481PMC
November 2013

Synthesis and reactivity of new bis(N-heterocyclic carbene) iridium(I) complexes.

Inorg Chem 2013 Nov 22;52(21):12674-81. Epub 2013 Oct 22.

EaStCHEM, School of Chemistry, University of St Andrews , North Haugh, St Andrews, Fife KY16 9ST, United Kingdom.

New complexes of the type trans-[IrCl(η(2)-COE)(NHC)2] (COE = cis-cyclooctene; NHC = N-heterocyclic carbene) have been prepared in one step from the reaction of ca. 4 equiv of NHC or [AgCl(NHC)] with [IrCl(η(2)-COE)2]2 in benzene. These new complexes have been characterized by techniques including NMR and IR spectroscopy, X-ray crystallography, and elemental analysis. Exposing trans-[IrCl(COE)(I(i)Pr(Me))2] to CO yielded trans-[IrCl(CO)(I(i)Pr(Me))2], which is the only bis(NHC) analogue of Vaska's complex trans-[IrCl(CO)(PPh3)2] known to date. The synthesis of trans-[Ir(CO)(I(i)Pr(Me))2(R)] (R = MeO, PhCC, OSiPh3, O2CPh) complexes has been achieved via deprotonation reactions involving the new hydroxide species trans-[Ir(OH)(CO)(I(i)Pr(Me))2].
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http://dx.doi.org/10.1021/ic4018773DOI Listing
November 2013

CO2 fixation employing an iridium(I)-hydroxide complex.

Chem Commun (Camb) 2014 Jan 16;50(3):286-8. Epub 2013 Oct 16.

EaStCHEM, School of Chemistry, University of St Andrews North Haugh, St Andrews, Fife, KY16 9ST, UK.

The reactivity of a number of Ir(I) complexes towards CO2 is explored using [Ir(NHC)(OH)] as a key synthon. CO2 insertion into Ir-O and Ir-N bonds proved facile, yielding a number of Ir(I)-carbonates and -carbamates. Most importantly, reaction between CO2 and Ir(I)-OH led to isolation of the novel [{Ir(I)}2-(μ-κ(1):κ(2)-CO3)] complex.
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http://dx.doi.org/10.1039/c3cc46922kDOI Listing
January 2014
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