Imperial College London

Dr Rob Davies

Faculty of Natural SciencesDepartment of Chemistry

Reader in Inorganic Chemistry
 
 
 
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Contact

 

+44 (0)20 7594 5754r.davies

 
 
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Location

 

601JMolecular Sciences Research HubWhite City Campus

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Summary

 

Publications

Publication Type
Year
to

83 results found

Lo Q, Sale D, Braddock D, Davies Ret al., 2019, New insights into the reaction capabilities of ionic organic bases in cu-catalysed amination, European Journal of Organic Chemistry, Vol: 2019, Pages: 1944-1951, ISSN: 1099-0690

The application of ionic organic bases in the copper‐catalyzed amination reaction (Ullmann reaction) has been studied at room temperature, with sub‐mol‐% catalyst loadings, and with more challenging amines at elevated temperatures. The cation present in the base has been shown to have little effect on the reaction at standard catalyst and ancillary ligand loadings, whereas the choice of anion is crucial for good reactivity. A substrate scope carried out at room temperature with the best performing bases, TBAM and TBPM, showed both bases to be highly effective under these mild reaction conditions. Moreover, under sub‐mol % catalyst loadings and room temperature conditions, TBPM gave good to excellent yields for a number of different amines and functionalized aryl iodides (14 examples). However, reactions involving more challenging amines gave little or no yield. By using more forceful conditions (120 °C) moderate to excellent yields of cross‐coupled products containing more challenging amines was achievable using TBPM and to a lesser extent with TBAM. As part of this work a study on the stability of the organic bases at 120 °C was undertaken. TBAM is shown to decompose to give nBu3N and mono‐butylmalonate at higher temperatures, and this can be correlated to a decrease in performance in the coupling reaction. The phosphonium cations in TBPM did not undergo analogous reactivity but were shown instead to experience some degree of deprotonation at the α‐CH2 to generate phosphonium ylides. This however did not lead to a significantly degradation in the activity of the TBPM in the cross‐coupling reaction.

JOURNAL ARTICLE

Pugh D, Ashworth E, Robertson K, Delmas L, White A, Horton P, Tizzard G, Coles S, Lickiss P, Davies Ret al., 2019, Metal-organic frameworks constructed from group 1 metals (Li, Na) and silicon-centered linkers, Crystal Growth and Design, Vol: 19, Pages: 487-497, ISSN: 1528-7483

A series of “light metal” metal–organic frameworks containing secondary building units (SBUs) based on Li+ and Na+ cations have been prepared using the silicon-centered linkers MexSi(p-C6H4CO2H)4-x (x = 2, 1, 0). The unipositive charge, small size, and oxophilic nature of the metal cations give rise to some unusual and unique SBUs, including a three-dimensional nodal structure built from sodium and oxygen ions when using the triacid linker (x = 1). The same linker with Li+ cations generated a chiral, helical SBU, formed from achiral starting materials. One-dimensional rod SBUs are observed for the diacid (x = 2) and tetra-acid (x = 0) linkers with both Li+ and Na+ cations, where the larger size of Na+ compared to Li+ leads to subtle differences in the constitution of the metal nodes.

JOURNAL ARTICLE

Davies RP, Delmas L, Horton P, White A, Coles S, Lickiss Pet al., 2019, Studies on the structural diversity of MOFs containing octahedral siloxane-backboned connectors, Polyhedron, Vol: 157, Pages: 25-32, ISSN: 0277-5387

Four metal–organic frameworks containing hexatopic connectors have been prepared and structurally characterised: [Cd3(L)(DMA)2(H2O)2] (IMP-28), [Ce2(L)(DMF)2(H2O)2] (IMP-29), [Y2(L)(DMF)2(H2O)2] (IMP-30), and [Zn2(L-H2)(4,4′-bipy)2] (IMP-31). All the MOFs have been constructed using the hybrid inorganic–organic siloxane linker hexakis(4-carboxyphenyl)disiloxane (L-H6). In each case, discrete metal-based nodes are cross-linked by the octahedrally disposed connector to afford 3D polymeric structures. The underlying nets in these MOFs have been evaluated through deconstruction of their crystal structures and subsequent topological analysis. Examples of MOFs built from hexatopic linkers, and especially those with octahedral predispositions such as in L, remain scarce and the topologies ascribed to some of these MOFs are unique.

JOURNAL ARTICLE

Delmas L, White A, Pugh D, Horton P, Coles S, Lickiss P, Davies RPet al., 2018, Trisiloxane-centred metal-organic frameworks and hydrogen bonded assemblies, CrystEngComm, Vol: 20, Pages: 4541-4545, ISSN: 1466-8033

A hexacarboxylic acid with a trisiloxane backbone (L-H6) has been prepared and applied in MOF construction. L-H6 itself crystallizes as an unusual 2D hydrogen-bonded network. Reaction of L-H6 with Mn(II) gave IMP-20 and with Zn(II) gave IMP-21: both are 3D MOFs incorporating Si–O–Si–O–Si linkages.

JOURNAL ARTICLE

Grigoropoulos A, McKay AI, Katsoulidis AP, Davies RP, Haynes A, Brammer L, Xiao J, Weller AS, Rosseinsky MJet al., 2018, Encapsulation of Crabtree's catalyst in sulfonated MIL-101(Cr): enhancement of stability and selectivity between competing reaction pathways by the MOF chemical microenvironment, Angewandte Chemie International Edition, Vol: 57, Pages: 4532-4537, ISSN: 1521-3757

Crabtree's catalyst was encapsulated inside the pores of the sulfonated MIL-101(Cr) metal-organic framework (MOF) by cation exchange. This hybrid catalyst is active for the heterogeneous hydrogenation of non-functionalized alkenes either in solution or in the gas phase. Moreover, encapsulation inside a well-defined hydrophilic microenvironment enhances catalyst stability and selectivity to hydrogenation over isomerization for substrates bearing ligating functionalities. Accordingly, the encapsulated catalyst significantly outperforms its homogeneous counterpart in the hydrogenation of olefinic alcohols in terms of overall conversion and selectivity, with the chemical microenvironment of the MOF host favouring one out of two competing reaction pathways.

JOURNAL ARTICLE

Lo QA, Sale D, Braddock DC, Davies RPet al., 2017, Mechanistic and Performance Studies on the Ligand Promoted Ullmann Amination Reaction, ACS Catalysis, Vol: 8, Pages: 101-109, ISSN: 2155-5435

Over the last two decades many different auxiliary ligand systems have been utilized in the copper-catalyzed Ullmann amination reaction. However, there has been little consensus on the relative merits of the varied ligands and the exact role they might play in the catalytic process. Accordingly, in this work some of the most commonly employed auxiliary ligands have been evaluated for C–N coupling using reaction progress kinetic analysis (RPKA) methodology. The results reveal not only the relative kinetic competencies of the different auxiliary ligands but also their markedly different influences on catalyst degradation rates. For the model Ullmann reaction between piperidine and iodobenzene using the soluble organic base bis(tetra-n-butylphosphonium) malonate (TBPM) at room temperature, N-methylglycine was shown to give the best performance in terms of high catalytic rate of reaction and comparatively low catalyst deactivation rates. Further experimental and rate data indicate a common catalytic cycle for all auxiliary ligands studied, although additional off-cycle processes are observed for some of the ligands (notably phenanthroline). The ability of the auxiliary ligand, base (malonate dianion), and substrate (amine) to all act competitively as ligands for the copper center is also demonstrated. On the basis of these results an improved protocol for room-temperature copper-catalyzed C–N couplings is presented with 27 different examples reported.

JOURNAL ARTICLE

Davies RP, Delmas L, Horton PN, White AJP, Coles SJ, Lickiss PDet al., 2017, Siloxane-based linkers in the construction of hydrogen bonded assemblies and porous 3D MOFs, Chemical Communications, Vol: 53, Pages: 12524-12527, ISSN: 1359-7345

A siloxane-based hexacarboxylic acid (L1-H6) has been prepared and applied in MOF construction. L1-H6 itself crystallizes as an unusual interpenetrated 3D hydrogen-bonded framework. Reaction of L1-H6 with Zn(II) gave IMP-18 – a 3D MOF incorporating Si–O–Si functionality. Cleavage of L1-H6 gives a silanol-based triacid which is shown to give a coordination polymer (IMP-19) with Zn(II).

JOURNAL ARTICLE

Mohamed NA, Davies RP, Lickiss PD, Ahmetaj-Shala B, Reed DM, Gashaw HH, Saleem H, Freeman GR, George PM, Wort SJ, Morales-Cano D, Barreira B, Tetley TD, Chester AH, Yacoub MH, Kirkby NS, Moreno L, Mitchell JAet al., 2017, Chemical and biological assessment of metal organic frameworks (MOFs) in pulmonary cells and in an acute in vivo model: relevance to pulmonary arterial hypertension therapy, Pulmonary Circulation, Vol: 7, Pages: 1-11, ISSN: 2045-8940

Pulmonary arterial hypertension (PAH) is a progressive and debilitating condition. Despite promoting vasodilation, current drugs have a therapeutic window within which they are limited by systemic side effects. Nanomedicine uses nanoparticles to improve drug delivery and/or reduce side effects. We hypothesize that this approach could be used to deliver PAH drugs avoiding the systemic circulation. Here we report the use of iron metal organic framework (MOF) MIL-89 and PEGylated MIL-89 (MIL-89 PEG) as suitable carriers for PAH drugs. We assessed their effects on viability and inflammatory responses in a wide range of lung cells including endothelial cells grown from blood of donors with/without PAH. Both MOFs conformed to the predicted structures with MIL-89 PEG being more stable at room temperature. At concentrations up to 10 or 30 µg/mL, toxicity was only seen in pulmonary artery smooth muscle cells where both MOFs reduced cell viability and CXCL8 release. In endothelial cells from both control donors and PAH patients, both preparations inhibited the release of CXCL8 and endothelin-1 and in macrophages inhibited inducible nitric oxide synthase activity. Finally, MIL-89 was well-tolerated and accumulated in the rat lungs when given in vivo. Thus, the prototypes MIL-89 and MIL-89 PEG with core capacity suitable to accommodate PAH drugs are relatively non-toxic and may have the added advantage of being anti-inflammatory and reducing the release of endothelin-1. These data are consistent with the idea that these materials may not only be useful as drug carriers in PAH but also offer some therapeutic benefit in their own right.

JOURNAL ARTICLE

Jin X, Davies RP, 2017, Copper-catalysed aromatic-Finkelstein reactions with amine-based ligand systems, Catalysis Science & Technology, Vol: 7, Pages: 2110-2117, ISSN: 2044-4753

A new efficient and low-cost ligand, diethylenetriamine, has been utilised to promote the iodination of 16 different bromo-substrates via the copper catalysed Finkelstein halogen exchange reaction under mild conditions. In contrast to earlier methods, the use of inert atmosphere conditions was not required to obtain high yields and purity. Studies on the speciation of the catalyst in solution indicate rapid disproportionation of copper(I) in the presence of diethylenetriamine to give copper(0) and a bis-ligated copper(II) complex which is characterised by X-ray diffraction. This copper(II) complex was also shown to be catalytically active in the halogen exchange reaction. In contrast, no significant disproportionation was observed using dimethylethylenediamine as the ligand, and the solid-state structures of a copper(I) dimeric complex and a 2D polymeric network of copper(I) iodide tetramers are reported. The catalytic activity of diethylenetriamine and dimethylethylenediamine with both copper(I) and copper(II) salts are compared, and possible mechanistic implications discussed.

JOURNAL ARTICLE

Aragoni MC, Arca M, Coles SJ, Crespo Alonso M, Coles née Huth SL, Davies RP, Hursthouse MB, Isaia F, Lai R, Lippolis Vet al., 2016, Coordination polymers and polygons using di-pyridyl-thiadiazole spacers and substituted phosphorodithioato Ni II complexes: potential and limitations for inorganic crystal engineering, CrystEngComm, Vol: 18, Pages: 5620-5629, ISSN: 1466-8033

Coordinatively unsaturated P-substituted dithiophosphonato, dithiophosphato, and dithiophosphito complexes {[Ni((MeO)2PS2)2] (1), [Ni((EtO)2PS2)2] (2), [Ni(MeOdtp)2] (3), and [Ni((Ph)2PS2)2] (4)} were reacted with the bis-functional ligands 3,5-di-(4-pyridyl)-1,2,4-thiadiazole (L1) and 3,5-di-(3-pyridyl)-1,2,4-thiadiazole (L2) to give the coordination polymers (1–4·L1)∞, (3·L2)∞, and (4·L2·2C7H8)∞ and the discrete dimers (1–2·L2)2, all characterised by single crystal X-ray diffraction. A comparison of the structures shows that L1 can be exploited for the predictable assembly of undulating chains independent of the nature of the NiII complex, while L2 allows for the existence of different supramolecular constructs ensuing from different ligand conformations deriving from the rotation of the pyridyl rings.

JOURNAL ARTICLE

Sung S, Sale D, Braddock DC, Armstrong A, Brenan C, Davies RPet al., 2016, Mechanistic studies on the copper-catalyzed N-arylation of alkylamines promoted by organic soluble ionic bases, ACS Catalysis, Vol: 6, Pages: 3965-3974, ISSN: 2155-5435

Experimental studies on the mechanism of copper-catalyzed amination of aryl halides have been undertaken for the coupling of piperidine with iodobenzene using a Cu(I) catalyst and the organic base tetrabutylphosphonium malonate (TBPM). The use of TBPM led to high reactivity and high conversion rates in the coupling reaction, as well as obviating any mass transfer effects. The often commonly employed O,O-chelating ligand 2-acetylcyclohexanone was surprisingly found to have a negligible effect on the reaction rate, and on the basis of NMR, calorimetric, and kinetic modeling studies, the malonate dianion in TBPM is instead postulated to act as an ancillary ligand in this system. Kinetic profiling using reaction progress kinetic analysis (RPKA) methods show the reaction rate to have a dependence on all of the reaction components in the concentration range studied, with first-order kinetics with respect to [amine], [aryl halide], and [Cu]total. Unexpectedly, negative first-order kinetics in [TBPM] was observed. This negative rate dependence in [TBPM] can be explained by the formation of an off-cycle copper(I) dimalonate species, which is also argued to undergo disproportionation and is thus responsible for catalyst deactivation. The key role of the amine in minimizing catalyst deactivation is also highlighted by the kinetic studies. An examination of the aryl halide activation mechanism using radical probes was undertaken, which is consistent with an oxidative addition pathway. On the basis of these findings, a more detailed mechanistic cycle for the C–N coupling is proposed, including catalyst deactivation pathways.

JOURNAL ARTICLE

Mohamed NA, Ahmetaj-Shala B, Duluc L, Mackenzie LS, Kirkby NS, Reed DM, Lickiss PD, Davies RP, Freeman GR, Wojciak-Stothard B, Chester AH, El-Sherbiny IM, Mitchell JA, Yacoub MHet al., 2016, A New NO-Releasing Nanoformulation for the Treatment of Pulmonary Arterial Hypertension., Journal of Cardiovascular Translational Research, Vol: 9, Pages: 162-164, ISSN: 1937-5395

Pulmonary arterial hypertension (PAH) is a chronic and progressive disease which continues to carry an unacceptably high mortality and morbidity. The nitric oxide (NO) pathway has been implicated in the pathophysiology and progression of the disease. Its extremely short half-life and systemic effects have hampered the clinical use of NO in PAH. In an attempt to circumvent these major limitations, we have developed a new NO-nanomedicine formulation. The formulation was based on hydrogel-like polymeric composite NO-releasing nanoparticles (NO-RP). The kinetics of NO release from the NO-RP showed a peak at about 120 min followed by a sustained release for over 8 h. The NO-RP did not affect the viability or inflammation responses of endothelial cells. The NO-RP produced concentration-dependent relaxations of pulmonary arteries in mice with PAH induced by hypoxia. In conclusion, NO-RP drugs could considerably enhance the therapeutic potential of NO therapy for PAH.

JOURNAL ARTICLE

Saleem H, Rafique U, Davies RP, 2016, Investigations on post-synthetically modified UiO-66-NH2 for the adsorptive removal of heavy metal ions from aqueous solution, MICROPOROUS AND MESOPOROUS MATERIALS, Vol: 221, Pages: 238-244, ISSN: 1387-1811

JOURNAL ARTICLE

Campbell J, Burgal JDS, Szekely G, Davies RP, Braddock DC, Livingston Aet al., 2016, Hybrid polymer/MOF membranes for Organic Solvent Nanofiltration (OSN): chemical modification and the quest for perfection, Journal of Membrane Science, Vol: 503, Pages: 166-176, ISSN: 1873-3123

One of the main challenges in the field of Organic Solvent Nanofiltration (OSN) is to improve the selectivity of membranes, allowing the separation of closely related solutes. This objective might be achieved by constructing membranes with uniform porous structures. Hybrid Polymer/Metal Organic Framework (MOF) membranes were prepared by in-situ growth (ISG) of HKUST-1 within the pores of polyimide membranes. To improve the performances of ISG membranes, chemical modification was performed. Aryl carboxylic acid moieties were introduced to polyimide P84 ultrafiltration membranes allowing coordination of the HKUST-1 directly on to the polymer. Chemically modified ISG membranes outperformed non-modified ISG membranes in both solute retentions and permeance. Retentions of polystyrene solute in acetone were used to calculate theoretical pore size distributions for each of the membranes tested. It was found that the chemically modified ISG membrane had he narrowest calculated pore size distribution.

JOURNAL ARTICLE

Grigoropoulos A, Whitehead GFS, Perret N, Katsoulidis AP, Chadwick FM, Davies RP, Haynes A, Brammer L, Weller AS, Xiao J, Rosseinsky MJet al., 2015, Encapsulation of an organometallic cationic catalyst by direct exchange into an anionic MOF, Chemical Science, Vol: 7, Pages: 2037-2050, ISSN: 2041-6539

Metal–Organic Frameworks (MOFs) are porous crystalline materials that have emerged as promising hosts for the heterogenization of homogeneous organometallic catalysts, forming hybrid materials which combine the benefits of both classes of catalysts. Herein, we report the encapsulation of the organometallic cationic Lewis acidic catalyst [CpFe(CO)2(L)]+ ([Fp–L]+, Cp = η5-C5H5, L = weakly bound solvent) inside the pores of the anionic [Et4N]3[In3(BTC)4] MOF (H3BTC = benzenetricarboxylic acid) via a direct one-step cation exchange process. To conclusively validate this methodology, initially [Cp2Co]+ was used as an inert spatial probe to (i) test the stability of the selected host; (ii) monitor the stoichiometry of the cation exchange process and (iii) assess pore dimensions, spatial location of the cationic species and guest-accessible space by single crystal X-ray crystallography. Subsequently, the quasi-isosteric [Fp–L]+ was encapsulated inside the pores via partial cation exchange to form [(Fp–L)0.6(Et4N)2.4][In3(BTC)4]. The latter was rigorously characterized and benchmarked as a heterogeneous catalyst in a simple Diels–Alder reaction, thus verifying the integrity and reactivity of the encapsulated molecular catalyst. These results provide a platform for the development of heterogeneous catalysts with chemically and spatially well-defined catalytic sites by direct exchange of cationic catalysts into anionic MOFs.

JOURNAL ARTICLE

Sung S, Braddock DC, Armstrong A, Brennan C, Sale D, White AJP, Davies RPet al., 2015, Synthesis, Characterisation and Reactivity of Copper(I) Amide Complexes and Studies on Their Role in the Modified Ullmann Amination Reaction, CHEMISTRY-A EUROPEAN JOURNAL, Vol: 21, Pages: 7179-7192, ISSN: 0947-6539

JOURNAL ARTICLE

Campbell J, Davies RP, Braddock DC, Livingston AGet al., 2015, Improving the permeance of hybrid polymer/metal-organic framework (MOF) membranes for organic solvent nanofiltration (OSN) - development of MOF thin films via interfacial synthesis, JOURNAL OF MATERIALS CHEMISTRY A, Vol: 3, Pages: 9668-9674, ISSN: 2050-7488

JOURNAL ARTICLE

Timokhin I, White AJP, Lickiss PD, Pettinari C, Davies RPet al., 2014, Microporous metal-organic frameworks built from rigid tetrahedral tetrakis(4-tetrazolylphenyl)silane connectors, CRYSTENGCOMM, Vol: 16, Pages: 8094-8097, ISSN: 1466-8033

JOURNAL ARTICLE

Bomparola R, Davies RP, Hornaeur S, White AJPet al., 2014, Lithium heterocuprates: the influence of the amido group on organoamidocuprate structures, DALTON TRANSACTIONS, Vol: 43, Pages: 14359-14367, ISSN: 1477-9226

JOURNAL ARTICLE

Campbell J, Szekely G, Davies RP, Braddock DC, Livingston AGet al., 2014, Fabrication of hybrid polymer/metal organic framework membranes: mixed matrix membranes versus in situ growth, JOURNAL OF MATERIALS CHEMISTRY A, Vol: 2, Pages: 9260-9271, ISSN: 2050-7488

JOURNAL ARTICLE

Davies RP, Patel L, 2013, Chalcogen-Phosphorus (and Heavier Congener) Compounds, Handbook of Chalcogen Chemistry, New Perspectives in Sulfur, Selenium and Tellurium. 2nd Edition. Volume 1, Editors: Devillanova, du Mont, Publisher: The Royal Society of Chemistry, ISBN: 9781849736237

BOOK CHAPTER

Timokhin I, Torres JB, White AJP, Lickiss PD, Pettinari C, Davies RPet al., 2013, Organosilicon linkers in metal organic frameworks: the tetrahedral tetrakis(4-tetrazolylphenyl)silane ligand, DALTON TRANSACTIONS, Vol: 42, Pages: 13806-13808, ISSN: 1477-9226

JOURNAL ARTICLE

Bomparola R, Davies RP, Lal S, White AJPet al., 2012, Functionalized Organocuprates: Structures of Lithium and Magnesium Grignard 2-Methoxyphenylcuprates, ORGANOMETALLICS, Vol: 31, Pages: 7877-7883, ISSN: 0276-7333

JOURNAL ARTICLE

Davies RP, Patel L, White AJP, 2012, Preparations of Metal Trichalcogenophosphonates from Organophosphonate Esters, INORGANIC CHEMISTRY, Vol: 51, Pages: 11594-11601, ISSN: 0020-1669

JOURNAL ARTICLE

Davies RP, Lickiss PD, Robertson K, White AJPet al., 2012, An organosilicon hexacarboxylic acid and its use in the construction of a novel metal organic framework isoreticular to MOF-5, CRYSTENGCOMM, Vol: 14, Pages: 758-760, ISSN: 1466-8033

JOURNAL ARTICLE

Davies RP, 2011, The structures of lithium and magnesium organocuprates and related species, COORDINATION CHEMISTRY REVIEWS, Vol: 255, Pages: 1226-1251, ISSN: 0010-8545

JOURNAL ARTICLE

Davies RP, Lickiss PD, Robertson K, 2011, Coordination polymers containing novel silicon-based connectors, 241st National Meeting and Exposition of the American-Chemical-Society (ACS), Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727

CONFERENCE PAPER

Hall JJ, Davies RP, Long NJ, Marsh Set al., 2011, Oxidative stability of biodiesel in the crankcase environment, 241st National Meeting and Exposition of the American-Chemical-Society (ACS), Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727

CONFERENCE PAPER

Davies RP, Patel L, 2011, Trithio- and triseleno-phosphonates: Heavier chalcogen homologs for organophosphonates, 241st National Meeting and Exposition of the American-Chemical-Society (ACS), Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727

CONFERENCE PAPER

Davies RP, Lickiss PD, Robertson K, White AJPet al., 2011, Mg-II, Ca-II, and Co-II Metal-Organic Framework Materials with [Si(p-C6H4CO2)(3)(p-C6H4CO2H)](3-) Struts, AUSTRALIAN JOURNAL OF CHEMISTRY, Vol: 64, Pages: 1237-1244, ISSN: 0004-9425

JOURNAL ARTICLE

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