99 research outputs found
Matched ligands for small, stable colloidal nanoparticles of copper, cuprous oxide and cuprous sulfide
This work applies organometallic routes to copper(0/I) nanoparticles and describes how to match ligand chemistries with different material compositions. The syntheses involve reacting an organo-copper precursor, mesitylcopper(I) [CuMes]z (z=4, 5), at low temperatures and in organic solvents, with hydrogen, air or hydrogen sulfide to deliver Cu, Cu2 O or Cu2 S nanoparticles. Use of sub-stoichiometric quantities of protonated ligand (pro-ligand; 0.1-0.2â
equivalents vs. [CuMes]z ) allows saturation of surface coordination sites but avoids excess pro-ligand contaminating the nanoparticle solutions. The pro-ligands are nonanoic acid (HO2 CR1 ), 2-[2-(2-methoxyethoxy)ethoxy]acetic acid (HO2 CR2 ) or di(thio)nonanoic acid, (HS2 CR1 ), and are matched to the metallic, oxide or sulfide nanoparticles. Ligand exchange reactions reveal that copper(0) nanoparticles may be coordinated by carboxylate or di(thio)carboxylate ligands, but Cu2 O is preferentially coordinated by carboxylate ligands and Cu2 S by di(thio)carboxylate ligands. This work highlights the opportunities for organometallic routes to well-defined nanoparticles and the need for appropriate ligand selection
Matched Ligands for Small, Stable Colloidal Nanoparticles of Copper, Cuprous Oxide and Cuprous Sulfide
This work applies organometallic routes to copper(0/I) nanoparticles and describes how to match ligand chemistries with different material compositions. The syntheses involve reacting an organo-copper precursor, mesitylcopper(I) [CuMes]z (z=4, 5), at low temperatures and in organic solvents, with hydrogen, air or hydrogen sulfide to deliver Cu, Cu2O or Cu2S nanoparticles. Use of sub-stoichiometric quantities of protonated ligand (pro-ligand; 0.1â0.2 equivalents vs. [CuMes]z) allows saturation of surface coordination sites but avoids excess pro-ligand contaminating the nanoparticle solutions. The pro-ligands are nonanoic acid (HO2CR1), 2-[2-(2-methoxyethoxy)ethoxy]acetic acid (HO2CR2) or di(thio)nonanoic acid, (HS2CR1), and are matched to the metallic, oxide or sulfide nanoparticles. Ligand exchange reactions reveal that copper(0) nanoparticles may be coordinated by carboxylate or di(thio)carboxylate ligands, but Cu2O is preferentially coordinated by carboxylate ligands and Cu2S by di(thio)carboxylate ligands. This work highlights the opportunities for organometallic routes to well-defined nanoparticles and the need for appropriate ligand selection
Catalytic Synergy Using Al(III) and Group 1 Metals to Accelerate Epoxide and Anhydride Ring-Opening Copolymerizations
The controlled synthesis of polyesters via epoxide/anhydride ring-opening copolymerization is a versatile and generally applicable method to make many sustainable polymers, but catalyst activities are limited and the required catalyst loadings are typically high. Here, novel heterodinuclear complexes, featuring Al(III)/M(I) (M = Na, K, Rb, Cs), show exceptional activities for phthalic anhydride and cyclohexene oxide copolymerization (catalyst = Al(III)/K(I), turnover frequency = 1072 hâ1, 0.25 mol % catalyst loading vs anhydride, 100 °C). The Al(III)/K(I) catalyst is also tolerant to low loadings, maintaining a good performance at 0.025 mol % catalyst vs anhydride loading and 0.005 mol % vs epoxide. It rapidly polymerizes other epoxide/anhydride combinations yielding various semi-aromatic, rigid, and/or functionalizable polyesters and also shows activity in carbon dioxide/epoxide copolymerizations. The results of structureâactivity, X-ray crystallography, polymerization kinetics, and density functional theory investigations support a mechanism with chain growth alternation between the metals. The rate-limiting step is proposed to involve epoxide coordination at Al(III) with K(I) carboxylate attack. Future exploitation of abundant and inexpensive Group 1 metals to deliver synergic polymerization catalysts is recommended
Reversible dihydrogen activation and catalytic H/D exchange with group 10 heterometallic complexes
Reaction of a hexagonal planar palladium complex featuring a [PdMg3H3] core with H2 is reversible and leads to the formation of a new [PdMg2H4] tetrahydride species alongside an equivalent of a magnesium hydride co-product [MgH]. While the reversibility of this process prevented isolation of [PdMg2H4], analogous [PtMg2H4] and [PtZn2H4] complexes could be isolated and characterised through independent syntheses. Computational analysis (DFT, AIM, NCIPlot) of the bonding in a series of heterometallic tetrahydride compounds (NiâPt; Mg and Zn) suggests that these complexes are best described as square planar with marginal metal-metal interactions; the strength of which increases slightly as group 10 is descended and increases from Mg to Zn. DFT calculations support a mechanism for H2 activation involving a ligand-assisted oxidative addition to Pd. These findings were exploited to develop a catalytic protocol for H/D exchange into magnesium hydride and zinc hydride bonds
Insights into the mechanism of carbon dioxide and propylene oxide ring-opening copolymerization using a Co(III)/K(I) heterodinuclear catalyst
A combined computational and experimental investigation into the catalytic cycle of carbon dioxide and propylene oxide ring-opening copolymerization is presented using a Co(III)K(I) heterodinuclear complex (Deacy, A. C. Co(III)/Alkali-Metal(I) Heterodinuclear Catalysts for the Ring-Opening Copolymerization of CO2 and Propylene Oxide. J. Am. Chem. Soc. 2020, 142(45), 19150â19160). The complex is a rare example of a dinuclear catalyst, which is active for the copolymerization of CO2 and propylene oxide, a large-scale commercial product. Understanding the mechanisms for both product and byproduct formation is essential for rational catalyst improvements, but there are very few other mechanistic studies using these monomers. The investigation suggests that cobalt serves both to activate propylene oxide and to stabilize the catalytic intermediates, while potassium provides a transient carbonate nucleophile that ring-opens the activated propylene oxide. Density functional theory (DFT) calculations indicate that reverse roles for the metals have inaccessibly high energy barriers and are unlikely to occur under experimental conditions. The rate-determining step is calculated as the ring opening of the propylene oxide (ÎGcalcâ = +22.2 kcal molâ1); consistent with experimental measurements (ÎGexpâ = +22.1 kcal molâ1, 50 °C). The calculated barrier to the selectivity limiting step, i.e., backbiting from the alkoxide intermediate to form propylene carbonate (ÎGcalcâ = +21.4 kcal molâ1), is competitive with the barrier to epoxide ring opening (ÎGcalcâ = +22.2 kcal molâ1) implicating an equilibrium between alkoxide and carbonate intermediates. This idea is tested experimentally and is controlled by carbon dioxide pressure or temperature to moderate selectivity. The catalytic mechanism, supported by theoretical and experimental investigations, should help to guide future catalyst design and optimization
Phosphine-alkene ligand-mediated alkyl-alkyl and alkyl-halide elimination processes from palladium(II)
N-Diphenylphosphino-7-aza-benzobicyclo[2.2.1]hept-2-ene (2) behaves as a chelating phosphineâalkene ligand for Pd0 and PdII, promoting direct alkylâalkyl and indirect alkylâhalide reductive elimination reactions due to the stabilisation of the resulting bis(phosphineâalkene)Pd0 complex
Probing Unexpected Reactivity in Radiometal Chemistry: Indium-111-Mediated Hydrolysis of Hybrid Cyclen-Hydroxypyridinone Ligands
Chelators based on hydroxypyridinones have utility in
incorporating
radioactive metal ions into diagnostic and therapeutic agents used
in nuclear medicine. Over the course of our hydroxypyridinone studies,
we have prepared two novel chelators, consisting of a cyclen (1,4,7,10-tetraazacyclododecane)
ring bearing two pendant hydroxypyridinone groups, appended via methylene
acetamide motifs at either the 1,4-positions (L1) or 1,7-positions (L2) of the cyclen ring. In radiolabeling reactions of L1 or L2 with the Îł-emitting radioisotope, [111In]In3+, we have observed radiometal-mediated hydrolysis of a single
amide group of either L1 or L2. The reaction of either [111In]In3+ or [natIn]In3+ with either L1 or L2, in aqueous alkaline solutions at 80 °C, initially results
in formation of [In(L1)]+ or [In(L2)]+, respectively. Over time, each of these species undergoes In3+-mediated hydrolysis of a single amide group to yield species
in which In3+ remains coordinated to the resultant chelator,
which consists of a cyclen ring bearing a single hydroxypyridinone
group and a single carboxylate group. The reactivity toward hydrolysis
is higher for the L1 complex
compared to that for the L2 complex.
Density functional theory calculations corroborate these experimental
findings and importantly indicate that the activation energy required
for the hydrolysis of L1 is significantly
lower than that required for L2. This is the first reported example of a chelator undergoing radiometal-mediated
hydrolysis to form a radiometalated complex. It is possible that metal-mediated
amide bond cleavage is a source of instability in other radiotracers,
particularly those in which radiometal complexation occurs in aqueous,
basic solutions at high temperatures. This study highlights the importance
of appropriate characterization of radiolabeled products
Correlating metal redox potentials to Co(III)K(I) catalyst performances in carbon dioxide and propene oxide ring opening copolymerization
Carbon dioxide copolymerization is a front-runner CO2 utilization strategy but its viability depends on improving the catalysis. So far, catalyst structure-performance correlations have not been straightforward, limiting the ability to predict how to improve both catalytic activity and selectivity. Here, a simple measure of a catalyst ground-state parameter, metal reduction potential, directly correlates with both polymerization activity and selectivity. It is applied to compare performances of 6 new heterodinuclear Co(III)K(I) catalysts for propene oxide (PO)/CO2 ring opening copolymerization (ROCOP) producing poly(propene carbonate) (PPC). The best catalyst shows an excellent turnover frequency of 389â
hâ1 and high PPC selectivity of >99â% (50â°C, 20â
bar, 0.025â
mol% catalyst). As demonstration of its utility, neither DFT calculations nor ligand Hammett parameter analyses are viable predictors. It is proposed that the cobalt redox potential informs upon the active site electron density with a more electron rich cobalt centre showing better performances. The method may be widely applicable and is recommended to guide future catalyst discovery for other (co)polymerizations and carbon dioxide utilizations
Influence of fuel properties on fundamental spray characteristics and soot emissions using different tailor-made fuels from biomass
This work evaluates the potential of some new biomass-derived fuels as candidates for compression ignition
operation. Thus, fundamental spray characteristics related to fuel vaporization and fuel/air mixing
process for 2-Methyltetrahydrofuran, Di-n-butyl ether and 1-octanol has been studied and compared
with conventional EN590 Diesel fuel. For this purpose, OHâ chemiluminescence and shadowgraphy measurements
in a high pressure chamber as well as 1D simulations with a spray model have been carried
out at different operating conditions representative of the NEDC driving cycle. Finally, measured soot
emissions in the single-cylinder engine were presented and discussed.
Results from the high pressure chamber presented very good agreement in terms of liquid length and
vapor penetration with simulation results. Thus, some analytical expressions related to macroscopic
spray characteristics have been proposed and validated experimentally for all four fuels. Finally, the
single-cylinder engine results confirmed the relevant role of soot formation on final emissions for
1-octanol and 2-MTHF. In addition, DNBE showed greater soot oxidation potential than diesel and other
TMFB candidates.This work was performed as part of the Cluster of Excellence "Tailor-Made Fuels from Biomass", which is funded by the Excellence Initiative by the German federal and state governments. Simulation works have been partially funded by Spanish government under the grant "Jose Castillejo" (CAS12/000097).GarcĂa MartĂnez, A.; Monsalve Serrano, J.; Heuser, B.; Jakob, M.; Kremer, F.; Pischinger, S. (2016). Influence of fuel properties on fundamental spray characteristics and soot emissions using different tailor-made fuels from biomass. Energy Conversion and Management. 108:243-254. https://doi.org/10.1016/j.enconman.2015.11.010S24325410
High iso aldehyde selectivity in the hydroformylation of short-chain alkenes
The authors thank the Eastman Chemical Company for funding (LI, and later JAF) and permission to publish. The EPSRC (EP/M003868/1) is also acknowledged for funding (JAF).The hydroformylation of propene to give predominantly isoâbutanal has been achieved; classâleading selectivity is possible even at higher temperatures that deliver fast conversion. Racemic rhodium complexes of bidentate phospholane phosphites derived from troposâbiphenols and unusual solvent systems are the key to the selectivity observed.PostprintPeer reviewe
- âŚ