50 results found
Gesslbauer S, Hutchinson G, White A, et al., 2021, Chirality-Induced catalyst aggregation: insights into catalyst speciation and activity using chiral aluminum catalysts in cyclic ester ring-opening polymerization, ACS Catalysis, Vol: 11, Pages: 4084-4093, ISSN: 2155-5435
A series of chiral-at-metal aluminum complexes have been synthesized using chiral catam ligands. Reactivity studies demonstrate the importance of alkoxide bulkiness and complex chirality in inducing catalyst aggregation. This has been exploited in cyclic ester ring-opening polymerization (ROP). For ε-Cl ROP, enantiopure catalysts were found to outperform a racemic mixture of catalysts, as the racemic mixture resulted in lower activity heterodimeric catalytic species and reduced polymerization rates. In the case of L-LA, one catalyst enantiomer was found to be the most active of the series and outperformed both the other enantiomer and the corresponding achiral catalyst. Very high activities were observed and up to 9,200 equivalents of L-LA were polymerized in 4.5 min at 150 °C with TOF > 100,000 h–1 under industrially relevant conditions. Analysis of the catalyst orders for these reactions provided a meaningful catalyst speciation-activity relationship enabling improved understanding of both catalyst speciation and the activity of each catalytic species involved in cyclic ester ROP using chiral aluminum catalysts.
Romain C, Bellemin-Laponnaz S, Dagorne S, 2020, Recent progress on NHC-stabilized early transition metal (group 3-7) complexes: Synthesis and applications, COORDINATION CHEMISTRY REVIEWS, Vol: 422, ISSN: 0010-8545
Romain C, 2020, Going from rooster to roast beef, the experience of a chemist on the other side of the Channel, Actualite Chimique, ISSN: 0151-9093
Romain C, 2020, Going from rooster to roast beef, the experience of a chemist on the other side of the Channel, Actualite Chimique, ISSN: 0151-9093
Tay DWP, Nobbs JD, Romain C, et al., 2020, gem-dialkyl effect in diphosphine Ligands: synthesis, coordination behavior, and application in Pd-catalyzed hydroformylation, ACS Catalysis, Vol: 10, Pages: 663-671, ISSN: 2155-5435
A series of palladium complexes with C3-bridged bidentate bis(diphenylphosphino)propane ligands with substituents of varying steric bulk at the central carbon have been synthesized. The size of the gem-dialkyl substituents affects the C–C–C bond angles within the ligands and consequently the P–M–P ligand bite angles. A combination of solid-state X-ray diffraction (XRD) and density functional theory (DFT) studies has shown that an increase in substituent size results in a distortion of the 6-membered metal–ligand chair conformation toward a boat conformation, to avoid bond angle strain. The influence of the gem-dialkyl effect on the catalytic performance of the complexes in palladium-catalyzed hydroformylation of 1-octene has been investigated. While hydroformylation activity to nonanal decreases with increasing size of the gem-dialkyl substituents, a change in chemoselectivity toward nonanol via reductive hydroformylation is observed.
Gesslbauer S, Savela R, Chen Y, et al., 2019, Exploiting noncovalent interactions for room-temperature heteroselective rac-lactide polymerization using aluminum catalysts, ACS Catalysis, Vol: 9, Pages: 7912-7920, ISSN: 2155-5435
Whereas harnessing noncovalent interactions (NCIs) has largely been applied to late-transition-metal complexes and to the corresponding catalytic reactions, there are very few examples showing the importance of NCIs in early-transition-metal and main-group-metal catalysis. Here, we report on the effects of hydrogen bond donors in the catalytic pocket to explain the high activity and stereoselectivity of a series of aluminum catam complexes in rac-lactide ring-opening polymerization (ROP). Four original aluminum catam catalysts have been synthesized and fully characterized. Structure–activity relationships and isotope effects show the importance of the NH moieties of the ligand in rac-lactide ROP. Computational studies highlight beneficial hydrogen bonds between the ligand and the monomer. Overall, structural characterization of the catalysts and mechanistic, kinetic, and computational studies support the benefits of noncovalent interactions in the catalytic pocket.
Flack T, Romain C, White A, et al., 2019, Design, synthesis and conformational analysis of oligobenzanilides as multi-facial alpha-helix mimetics, Organic Letters, Vol: 21, Pages: 4433-4438, ISSN: 1523-7052
The design, synthesis, and conformationalanalysis of an oligobenzanilide helix mimetic scaffold capableof simultaneous mimicry of two faces of an α-helix is reported.The synthetic methodology provides access to diversemonomer building blocks amenable to solid-phase assemblyin just four synthetic steps. The conformational flexibility ofmodel dimers was investigated using a combination of solidand solution state methodologies supplemented with DFTcalculations. The lack of noncovalent constraints allows forsignificant conformational plasticity in the scaffold, thuspermitting it to successfully mimic residues i, i+2, i+4, i+6, i+7, and i+9 of a canonical α-helix.
Vriamont CEJJ, Chen T, Romain C, et al., 2019, From lignin to chemicals: Hydrogenation of lignin models and mechanistic insights into hydrodeoxygenation via low-temperature C-O bond cleavage, ACS Catalysis, Vol: 9, Pages: 2345-2354, ISSN: 2155-5435
The catalytic hydrogenation of a series of lignin model compounds, including anisole, guaiacol, 1,2-dimethoxybenzene, 4-propyl-2-methoxyphenol, and syringol, has been investigated in detail, using a Ru/C catalyst in acetic acid as the solvent. Both hydrogenation of the aromatic unit and C–O bond cleavage are observed, resulting in a mixture of cyclohexanes and cyclohexanols, together with cyclohexyl acetates due to esterification with the solvent. The effect on product composition of the reaction parameters temperature (80–140 °C), pressure (10–40 bar), and reaction time (0.5–4 h) has been evaluated in detail. The lignin model compound 4-propyl-2-methoxyphenol was converted to 4-propylcyclohexanol in 4 h at 140 °C and 30 bar of H2 pressure with 84% conversion and 63% selectivity. Mechanistic studies on the reactivity of reaction intermediates have shown that C–O bond cleavage under these relatively mild conditions does not involve a C–O bond hydrogenolysis reaction but is due to elimination and hydrolysis reactions (or acetolysis in acetic acid solvent) of highly reactive cyclohexadiene- and cyclohexene-based enols, enol ethers, and allyl ethers.
Barba A, Dominguez S, Gomez C, et al., 2019, Workflows allowing creation of journal article Supporting Information and FAIR-enabled publication of Spectroscopic data, ACS Omega, Vol: 4, Pages: 3280-3286, ISSN: 2470-1343
There is an increasing focus on the part of academic institutions, funding agencies, and publishers, if not researchers themselves, on preservation and sharing of research data. Motivations for sharing include research integrity, replicability, and reuse. One of the barriers to publishing data is the extra work involved in preparing data for publication once a journal article and its supporting information have been completed. In this work, a method is described to generate both human and machine-readable supporting information directly from the primary instrumental data files and to generate the metadata to ensure it is published in accordance with findable, accessible, interoperable, and reusable (FAIR) guidelines. Using this approach, both the human readable supporting information and the primary (raw) data can be submitted simultaneously with little extra effort. Although traditionally the data package would be sent to a journal publisher for publication alongside the article, the data package could also be published independently in an institutional FAIR data repository. Workflows are described that store the data packages and generate metadata appropriate for such a repository. The methods both to generate and to publish the data packages have been implemented for NMR data, but the concept is extensible to other types of spectroscopic data as well.
Gesslbauer S, Cheek H, White A, et al., 2018, Highly active aluminium catalysts for room temperature ring-opening polymerisation of rac-lactide, Dalton Transactions, Vol: 31, ISSN: 1477-9226
A new series of aluminium complexes bearing ‘catam’ ligands has been synthesised and fully characterised. They were found to exhibit high activity at room temperature for rac-lactide ring-opening polymerisation, a rather rare feature for aluminium-based catalysts.
Romain C, Garden JA, Trott G, et al., 2017, Di-Zinc-Aryl Complexes: CO2 Insertions and Applications in Polymerisation Catalysis, CHEMISTRY-A EUROPEAN JOURNAL, Vol: 23, Pages: 7367-7376, ISSN: 0947-6539
Thevenon A, Romain C, Bennington M, et al., 2017, Dizinc lactide polymerization catalysts: Hyperactivity by control of ligand conformation and metallic cooperativity, 253rd National Meeting of the American-Chemical-Society (ACS) on Advanced Materials, Technologies, Systems, and Processes, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Thevenon A, Romain C, Bennington M, et al., 2017, Switchable di-zinc macrocycle catalysts: From highly active lactide polymerization to block copolymers, 253rd National Meeting of the American-Chemical-Society (ACS) on Advanced Materials, Technologies, Systems, and Processes, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
zhu Y, romain C, Williams CK, 2016, Sustainable polymers from renewable resources, Nature, Vol: 540, Pages: 354-362, ISSN: 0028-0836
Renewable resources are used increasingly in the production of polymers. In particular, monomers such as carbon dioxide, terpenes, vegetable oils and carbohydrates can be used as feedstocks for the manufacture of a variety of sustainable materials and products, including elastomers, plastics, hydrogels, flexible electronics, resins, engineering polymers and composites. Efficient catalysis is required to produce monomers, to facilitate selective polymerizations and to enable recycling or upcycling of waste materials. There are opportunities to use such sustainable polymers in both high-value areas and in basic applications such as packaging. Life-cycle assessment can be used to quantify the environmental benefits of sustainable polymers.
Dagorne S, Romain C, 2016, PolymerizationCatalysis by Metal Phenolates, Pages: 1-44
Thevenon A, Romain C, Bennington MS, et al., 2016, Innentitelbild: Dizinc Lactide Polymerization Catalysts: Hyperactivity by Control of Ligand Conformation and Metallic Cooperativity (Angew. Chem. 30/2016), Angewandte Chemie, Vol: 128, Pages: 8600-8600, ISSN: 0044-8249
Thevenon A, Romain C, Bennington MS, et al., 2016, Inside Cover: Dizinc Lactide Polymerization Catalysts: Hyperactivity by Control of Ligand Conformation and Metallic Cooperativity (Angew. Chem. Int. Ed. 30/2016), Angewandte Chemie - International Edition, Vol: 55, Pages: 8460-8460, ISSN: 1433-7851
Thevenon A, Romain C, Bennington M, et al., 2016, Di-zinc Lactide Polymerization Catalysts: Hyper-Activity by Control of Ligand Conformation and Metallic Cooperativity, Angewandte Chemie - International Edition, Vol: 55, Pages: 8680-8685, ISSN: 1433-7851
Understanding how to moderate and improve catalytic activity is critical to improving degradable polymer production. Here, di- and mono-zinc catalysts, coordinated by bis(imino)diphenylamido ligands, show remarkable activities and allow determination of the factors controlling performance. In most cases, the di-zinc catalysts significantly out-perform the mono-zinc analogues. Further, for the best di-zinc catalyst, the ligand conformation controls activity: the catalyst with ‘folded’ ligand conformations show TOF values up to 60,000 h-1 (0.1 mol% loading, 298 K, [LA] = 1 M), whilst that with a ‘planar’ conformation is much slower, under similar conditions (TOF = 30 h-1). Di-zinc catalysts also perform very well under immortal conditions, showing improved control, and are able to tolerate loadings as low as 0.002 mol% whilst conserving high activity (TOF = 12,500 h-1).
Romain C, Zhu Y, Dingwall P, et al., 2016, Chemoselective polymerizations from mixtures of epoxide, lactone, anhydride, and carbon dioxide, Journal of the American Chemical Society, Vol: 138, Pages: 4120-4131, ISSN: 1520-5126
Controlling polymer composition starting from mixtures of monomers is an important, but rarely achieved, target. Here a single switchable catalyst for both ring-opening polymeri-zation (ROP) of lactones and ring-opening copolymerization (ROCOP) of epoxides, anhydrides and CO2 is investigated, using both experimental and theoretical methods. Different combinations of four model monomers: -caprolactone, cyclohexene oxide, phthalic anhydride and carbon dioxide are investigated using a single dizinc catalyst. The catalyst switches between the distinct polymerization cycles and shows high monomer selectivity resulting in block sequence control and predictable compositions (esters and car-bonates) in the polymer chain. The understanding gained of the orthogonal reactivity of monomers, specifically con-trolled by the nature of the metal-chain end group, opens the way to engineer polymer block sequences.
Giarola S, Romain C, Williams C, et al., 2016, Techno-economic assessment of the production of phthalic anhydride from corn stover, Chemical Engineering Research & Design, Vol: 107, Pages: 181-194, ISSN: 1744-3563
Phthalic anhydride is used worldwide for an extremely broad range of applications spanning from the plastics industry to the synthesis of resins, agricultural fungicides and amines. This work proposes a conceptual design of a process for the production of phthalic anhydride from an agricultural residue (i.e. corn stover), energy integration alternatives as well as water consumption and life cycle greenhouse emissions assessment. The techno-economic and financial appraisal of the flowsheet proposed is performed. Results show how the valorization of all the carbohydrate-rich fractions present in the biomass as well as energy savings and integration is crucial to obtain an economically viable process and that it is in principle possible to produce renewable phthalic anhydride in a cost-competitive fashion with a lower impact on climate change compared to the traditional synthetic route.
Romain C, Thevenon A, Saini P, et al., 2016, Dinuclear Metal Complex-Mediated Formation of CO2-Based Polycarbonates, Carbon Dioxide and Organometallics, Editors: Lu, Publisher: Springer International Publishing, Pages: 101-141, ISBN: 978-3-319-22077-2
Williams CK, Romain C, White AJP, et al., 2015, Macrocyclic dizinc(II) alkyl and alkoxide complexes: Reversible CO2 uptake and polymerization catalysis testing, Inorganic Chemistry, Vol: 54, Pages: 11842-11851, ISSN: 1520-510X
The synthesis of three new dizinc(II) complexes bearing a macrocyclic [2 + 2] Schiff base ligand is reported. The bis(anilido)tetraimine macrocycle reacts with diethylzinc to form a bis(ethyl)dizinc(II) complex, [LEtZn₂Et₂] (1). The reaction of complex 1 with isopropyl alcohol is reported, forming a bis(isopropyl alkoxide)dizinc complex, [LEtZn₂(iPrO)₂] (2). Furthermore, complex 1, with 2 equiv of alcohol, is applied as an initiator for racemic lactide ring-opening polymerization. It shows moderately high activity, resulting in a pseudo-first-order rate coefficient of 9.8 × 10⁻³ min⁻¹, with [LA] = 1 M and [initiator] = 5 mM at 25 °C and in a tetrahydrofuran solvent. Polymerization occurs with good control, as evidenced by the linear fit to a plot of molecular weight versus conversion, the narrow dispersities, and the limited transesterification. The same initiating system is inactive for the ring-opening copolymerization of carbon dioxide (CO₂) and cyclohexene oxide at 80 °C and 1 bar of CO₂ pressure. However, stoichiometric reactions between complex 2 and CO₂, at 1 bar pressure, result in the reversible formation of new dizinc carbonate species, [LEtZn₂(iPrO)(iPrOCO₂)] (3a) and [LEtZn₂(iPrOCO₂)₂] (3b), and the reaction was studied using density functional theory calculations. All of the new complexes, 1–3b, are fully characterized, including NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction.
Romain C, Specklin D, Miqueu K, et al., 2015, Unusual Benzyl Migration Reactivity in NHC-Bearing Group 4 Metal Chelates: Synthesis, Characterization, and Mechanistic Investigations, ORGANOMETALLICS, Vol: 34, Pages: 4854-4863, ISSN: 0276-7333
Zhu Y, Romain C, Williams CK, 2015, Selective polymerization catalysis: controlling the metal chain end group to prepare block copolyesters, Journal of the American Chemical Society, Vol: 137, Pages: 12179-12182, ISSN: 1520-5126
Selective catalysis is used to prepare block copolyesters by combining ring-opening polymerization of lactones and ring-opening copolymerization of epoxides/anhydrides. By using a dizinc complex with mixtures of up to three different monomers and controlling the chemistry of the Zn–O(polymer chain) it is possible to select for a particular polymerization route and thereby control the composition of block copolyesters.
Williams CK, Paul S, Romain C, et al., 2015, Sequence selective polymerization catalysis: A new route to ABA block copoly(ester-b-carbonate-b-ester), Macromolecules, Vol: 48, Pages: 6047-6056, ISSN: 0024-9297
The preparation of ABA type block copoly(ester-b-carbonate-b-ester) from a mixture of ε-caprolactone, cyclohexene oxide, and carbon dioxide monomers and using a single catalyst is presented. By using a dinuclear zinc catalyst, both the ring-opening polymerization of ε-caprolactone and the ring-opening copolymerization of cyclohexene oxide and carbon dioxide are achieved. The catalyst shows high selectivity, activity, and control in the ring-opening copolymerization, yielding poly(cyclohexene carbonate) polyols, i.e., α,ω-dihydroxyl end-capped polycarbonates. It also functions efficiently under immortal conditions, and in particular, the addition of various equivalents of water enables the selective preparation of polyols and control over the polymers’ molecular weights and dispersities. The catalyst is also active for the ring-opening polymerization of ε-caprolactone but only in the presence of epoxide, generating α,ω-dihydroxyl-terminated polycaprolactones. It is also possible to combine the two polymerization pathways and, by controlling the chemistry of the growing polymer chain-metal end group, to direct a particular polymerization pathway. Thus, in the presence of all three monomers, the selective ring-opening copolymerization occurs to yield poly(cyclohexene carbonate). Upon removal of the carbon dioxide, the polymerization cycle switches to ring-opening polymerization and a triblock copoly(caprolactone-b-cyclohexene carbonate-b-caprolactone) is produced. The ABA type block copolymer is fully characterized, including using various spectroscopic techniques, size exclusion chromatography, and differential scanning calorimetry. The copolymers can be solvent cast to give transparent films. The copolymers show controllable glass transition temperatures from −54 to 34 °C, which are dependent on the block compositions.
Paul S, Romain C, Williams C, 2015, Combining ring opening polymerisation and ring opening copolymerisation to synthesise block copolymers, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Zhu Y, Williams CK, 2015, Chemoselective Polymerization: From Multi-Component Feedstocks to Sequence Controlled Block Copolyesters, 250th National Meeting of the American-Chemical-Society (ACS), ISSN: 0065-7727
Zhu Y, Romain C, Poirier V, et al., 2015, Influences of a Dizinc Catalyst and Bifunctional Chain Transfer Agents on the Polymer Architecture in the Ring-Opening Polymerization of epsilon-Caprolactone, Macromolecules, Vol: 48, Pages: 2407-2416, ISSN: 0024-9297
The polymerization of ε-caprolactone is reported using various bifunctional chain transfer agents and a dizinc catalyst. Conventionally, it is assumed that using a bifunctional chain transfer agent (CTA), polymerization will be initiated from both functional groups; however, in this study this assumption is not always substantiated. The different architectures and microstructures of poly(ε-caprolactone) samples (PCL) are compared using a series of bifunctional and monofunctional alcohols as the chain transfer agents, including trans-1,2-cyclohexanediol (CHD), ethylene glycol (EG), 1,2-propanediol (PD), poly(ethylene glycol) (PEG), 2-methyl-1,3-propanediol (MPD), 1-hexanol, 2-hexanol, and 2-methyl-2-pentanol. A mixture of two architectures is observed when diols containing secondary hydroxyls are used, such as cyclohexanediol or propanediol; there are chains that are both chain-extended and chain-terminated by the diol. These findings indicate that not all secondary hydroxyl groups initiate polymerization. In contrast, chain transfer agents containing only primary hydroxyl groups in environments without steric hindrance afford polymer chains of a single chain extended architecture, whereby polymer chains are initiated from both hydroxyl groups on the diol. Kinetic analyses of the polymerizations indicate that the propagation rate constant (kp) is significantly higher than the initiation rate constant (ki): kp/ki > 5. A kinetic study conducted using a series of monofunctional chain transfer agents shows that the initiation rate, ki, is dependent on the nature of the hydroxyl group, with the rates decreasing in the order ki(primary) > ki(secondary) > ki(tertiary). It is proposed that two polymer architectures are present as a consequence of slow rates of initiation from the secondary hydroxyl groups, on the diol, compared to propagation which occurs from a primary hydroxyl group. In addition to the reactivity differences of the alcohols, steric
Paul S, Zhu Y, Romain C, et al., 2015, Ring-opening copolymerization (ROCOP): synthesis and properties of polyesters and polycarbonates, Chemical Communications, Vol: 51, Pages: 6459-6479, ISSN: 1364-548X
Controlled routes to prepare polyesters and polycarbonates are of interest due to the widespread application of these materials and the opportunities provided to prepare new copolymers. Furthermore, ring-opening copolymerization may enable new poly(ester–carbonate) materials to be prepared which are inaccessible using alternative polymerizations. This review highlights recent advances in the ring-opening copolymerization catalysis, using epoxides coupled with anhydrides or CO2, to produce polyesters and polycarbonates. In particular, the structures and performances of various homogeneous catalysts are presented for the epoxide–anhydride copolymerization. The properties of the resultant polyesters and polycarbonates are presented and future opportunities highlighted for developments of both the materials and catalysts.
Giarola S, Romain C, Williams CK, et al., 2015, Production of phthalic anhydride from biorenewables: process design, 12TH INTERNATIONAL SYMPOSIUM ON PROCESS SYSTEMS ENGINEERING AND 25TH EUROPEAN SYMPOSIUM ON COMPUTER AIDED PROCESS ENGINEERING, PT C, Vol: 37, Pages: 2561-2566, ISSN: 1570-7946
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