Dibutyl Magnesium Research Articles

A Constrained Geometry Fluorenyl Amido Magnesium Catalyst for Amine‐Borane Dehydrocoupling

AbstractA fluorenyl amido constrained geometry magnesium complex is described, which was obtained by deprotonation of the corresponding neutral ligand system with dibutyl magnesium. Its structure was determined by SC‐XRD and it was shown to be a potent catalyst for amine‐borane dehydrogenation/dehydrocoupling.

A Comprehensive Study on the Parameters Affecting Magnesium Plating/Stripping Kinetics in Rechargeable Mg Batteries

AbstractMg metal anode‐based battery is a more sustainable, lower cost, and higher energy density alternative to Li‐ion. However, this battery chemistry also faces several challenges associated with the high charge density of Mg2+, including achieving high reversibility and low voltage hysteresis for Mg metal plating/stripping. While significant improvements are achieved in last decades, they involve rather complex electrolyte formulations and/or Mg salts difficult to produce, and the use of unpractical substrates such as platinum. Here, significant improvement in terms of Mg plating kinetics is achieved in electrolytes containing commercial magnesium bis(trifluoromethanesulfonyl)imide salt (Mg(TFSI)2) by using titanium substrate with similar crystal structure and lattice parameter as Mg leading to lower nucleation overpotential. Low salt concentration electrolyte and addition of dibutyl magnesium (Mg(butyl)2) also enable the formation of thinner interphase, richer in solvent based decomposition products, further improving Mg plating kinetics. This work highlights the complex role of Mg(butyl)2, often considered as a simple drying agent, and how it impacts ion solvation favoring the mobility of electroactive cationic species, paving the way toward better electrolyte design with improved cation transference number.

Novel Effective Catalyst Systems Based on Titanium(IV) Alkoxide Complexes for Copolymerization of Ethylene and Hexene-1

The catalytic activity of bis(isopropoxo)titanium(4+) complexes containing 1,2-diolate ligands activated with aluminum alkyl chlorides and dibutyl magnesium in the copolymerization of ethylene and hexene-1 has been studied. The effect of the precatalyst structure and the organoaluminum activator composition on the catalytic activity, the incorporation of hexene-1, and the copolymer microstructure has been studied. The synthesized copolymers have been characterized by DSC, GPC, and 13C NMR. The complexes containing perfluorophenyl substituents exhibit the highest activity in this set and provide the highest degree of incorporation of the comonomer. The replacement of Et2AlCl with Et3Al2Cl2 leads to a significant decrease in both productivity and the degree of incorporation of hexene-1 into the copolymer. The mechanical properties of the resulting copolymers have been studied.

In Situ Formation of Metal Hydrides Inside Carbon Aerogel Frameworks for Hydrogen Storage Applications

Nano-confined chemical reactions bear great promise for a wide range of important applications in the near-to-medium term, e.g., within the emerging area of chemical storage of renewable energy. To explore this important trend, in the present work, resorcinol-/formaldehyde-based carbon aerogels were prepared by sol-gel polymerisation of resorcinol, with furfural catalysed by a sodium-carbonate solution using ambient-pressure drying. These aerogels were further carbonised in nitrogen to obtain their corresponding carbon aerogels. Through this study, the synthesis parameters were selected in a way to obtain minimum shrinkage during the drying step. The microstructure of the product was observed using Scanning Electron Microscopy (SEM) and Field Emission Scanning Electron Microscopy (FESEM) imaging techniques. The optimised carbon aerogels were found to have pore sizes of ~21 nm with a specific accessible surface area equal to 854.0 m2/g. Physical activation of the carbon aerogel with CO2 generates activated carbon aerogels with a surface area of 1756 m2/g and a total porosity volume up to 3.23 cm3/g. The product was then used as a scaffold for magnesium/cobalt-hydride formation. At first, cobalt nanoparticles were formed inside the scaffold, by reducing the confined cobalt oxide, then MgH2 was synthesised as the second required component in the scaffold, by infiltrating the solution of dibutyl magnesium (MgBu2) precursor, followed by a hydrogenation reaction. Further hydrogenation at higher temperature leads to the formation of Mg2CoH5. In situ synchrotron X-ray diffraction was employed to study the mechanism of hydride formation during the heating process.

Ring opening polymerization and copolymerization of L‐lactide and ɛ‐caprolactone by bis‐ligated magnesium complexes

ABSTRACTSeven magnesium complexes (1–7) were synthesized by reaction of new (L 3‐H–L 5‐H) and previously reported ketoimine pro‐ligands with dibutyl magnesium and were isolated in 59–70% yields. Complexes 1–7 were characterized fully and consisted of bis‐ligated homoleptic ketoiminates coordinated in distorted octahedral geometry around the magnesium centers. The complexes were investigated for their ability to initiate the ring opening polymerization (ROP) of l‐lactide (L‐LA) to poly‐lactic acid (PLA) and ɛ‐caprolactone (ɛCL) to poly‐caprolactone in the presence of 4‐fluorophenol co‐catalyst. For L‐LA polymerization, complexes containing ligand electron‐donating groups (1–5) achieved >90% conversion in 2 h at 100 °C, while the presence of CF3 groups in 6 and 7 slowed or resulted in no PLA detected. With ɛCL, ROP initiated with 1–7 resulted in lower percentage conversion with similar electronic effects. Moderate molecular weight PLA polymeric material (14.3–21.3 kDa) with low polydispersity index values (1.23–1.56) was obtained, and ROP appeared to be living in nature. Copolymerization of L‐LA and ɛCL yielded block copolymers only from the sequential polymerization of ɛCL followed by L‐LA and not the reverse sequence of monomers or the simultaneous presence of both monomers. Polymers and copolymers were characterized with NMR, gel permeation chromatography, and differential scanning calorimetry. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 48–59

Synthesis of a linear low‐density polyethylene/MgO@Mg(OH)2 nanocomposite using modified in situ polymerization

AbstractComposites of linear low‐density polyethylene were obtained in toluene slurry by in situ copolymerization of ethylene and 1‐octene in the presence of untreated magnesium oxide–hydroxide nanoparticles (MgO@Mg(OH)2) of ±50 nm and such treated with dibutylmagnesium (DBM) as support for a bis(n‐butylcyclopentadienyl)zirconium dichloride–methylaluminoxane (MAO) catalyst system. Treatment of the nanoparticles with DBM (0.5–6 mmol g−1 MgO@Mg(OH)2) allows one to decrease the amount of MAO by 1.2 mmol Al g−1 MgO@Mg(OH)2, while reaching the same average catalyst activity and a finer distribution of the particles. Energy‐dispersive X‐ray mapping shows that the MAO is mainly associated with the filler. The crystallinity of the matrix polymer decreases with filler content. © 2018 Society of Chemical Industry

Hydrogen Storage Stability of Nanoconfined MgH2 upon Cycling

It is of utmost importance to optimise and stabilise hydrogen storage capacity during multiple cycles of hydrogen release and uptake to realise a hydrogen-based energy system. Here, the direct solvent-based synthesis of magnesium hydride, MgH2, from dibutyl magnesium, MgBu2, in four different carbon aerogels with different porosities, i.e., pore sizes, 15 < Davg < 26 nm, surface area 800 < SBET < 2100 m2/g, and total pore volume, 1.3 < Vtot < 2.5 cm3/g, is investigated. Three independent infiltrations of MgBu2, each with three individual hydrogenations, are conducted for each scaffold. The volumetric and gravimetric loading of MgH2 is in the range 17 to 20 vol % and 24 to 40 wt %, which is only slightly larger as compared to the first infiltration assigned to the large difference in molar volume of MgH2 and MgBu2. Despite the rigorous infiltration and sample preparation techniques, particular issues are highlighted relating to the presence of unwanted gaseous by-products, Mg/MgH2 containment within the scaffold, and the purity of the carbon aerogel scaffold. The results presented provide a research path for future researchers to improve the nanoconfinement process for hydrogen storage applications.

Studying the effects of SiO2 specifications and properties of (SiO2/MgCl2/TEOS/TiCl4/AlEt3) catalyst system on kinetic behavior and hydrogen responsibility of ethylene slurry polymerization

AbstractA series of silica gels with different physico‐chemical properties such as average pore size diameter, pore volume, attrition quality index, and bulk density were prepared, characterized, and subjected to treatment in special thermal program. Catalyst precursors were prepared by reaction of these silica gels with dibutyl magnesium (MgBu2) at 50°C and then addition of tetraethoxy ortho silicate and subsequent impregnation with titanium tetrachloride (TiCl4). Polymerization of ethylene by these catalysts at comparable conditions and also at different PH2/PC2 ratio was carried out; the results showed that support properties have significant influence on polymerization behaviors such as activity profile, productivity, and hydrogen responsibility. To quantitative analysis of the results, a new kinetic relation for rate‐time profiles was derived, and these kinetic parameters were used to study and calculate of the effects of support specification. It was observed that trends of activity profiles were mainly affected by support properties and as well as PH2/PC2 ratio. Interestingly enough, catalysts with different pore volume diameter show different behavior with variation of PH2/PC2 ratio. Increasing in pore size diameter from 60 to 200 Å give raises catalyst activity by two times. Finally, mentioned variables were attributed to different particle growth and mechanism of fragmentation during polymerization. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Synthesis and characterization of bis[4-N-(cyclohexylimino)-2-pentanonato]magnesium(II)

A novel β-ketoimine, 4-N-(cyclohexylimino)-2-pentanone, was synthesized and reacted with dibutyl magnesium to afford the desired magnesium bis(β-ketoiminate). The complex, bis[4-N-(cyclohexylimino)-2-pentanonato]magnesium(II), has been structurally characterized by single-crystal X-ray diffraction methods. Crystallographic analysis shows the four-coordinate complex to be homoleptic and monomeric in the solid state. The geometry around the Mg(II) atom is a distorted tetrahedron. The bulky cyclohexyl groups provide enough steric bulk about magnesium to inhibit intermolecular interactions. The crystal structure of the complex is triclinic, space group , with a = 8.301(3), b = 11.301(4), c = 12.023(4) Å, α = 75.840(6), β = 88.867(6), γ = 84.611(6)°, Z = 2. The two normal Mg–O and Mg–N bond lengths are, respectively, 1.9162(11), 1.9265(11) and 2.0699(13), 2.0822(12) Å.

Solvent influences on the molecular aggregation of magnesium aryloxides: synthesis, crystal structure, and solution characterization of Mg(OAr) 2(L) 3 (OAr=DMP, DIP, TCP) and [Mg(DIP) 2] 3

Magnesium aryloxides were prepared in a variety of solvents through the reaction of dibutyl magnesium with sterically varied aryl alcohols: 2,6-dimethylphenol (H-DMP), 2,6-diisopropylphenol (H-DIP), and 2,4,6-trichlorophenol (H-TCP). Upon using a sufficiently strong Lewis-basic solvent, the solvated monomeric species Mg(DMP) 2(py) 3 ( 1, py=pyridine), Mg(DIP) 2(THF) 3, ( 2a, THF=tetrahydrofuran) Mg(TCP) 2(THF) 3 ( 3) were isolated. Each of these complexes possesses a five-coordinate magnesium that adopts a trigonal bipyramidal geometry. In the absence of a Lewis base, the reaction with H-DIP yields a soluble trinuclear complex, [Mg(DIP) 2] 3 ( 2b). The Mg metal centers in 2b adopt a linear arrangement with a four-coordinate central metal while the outer metal centers are reduced to just three-coordinate. Solution spectroscopic methods suggest that while 2b remains intact, the monomeric species ( 1, 2a, and 3) are involved in equilibria which facilitate intermolecular ligand transfer.

Cyclomagnesation of dienes catalyzed by a chiral ansa-zirconocene

The biphenyl-bridged, chiral zirconocene complex rac-2,2′-biphenyl-bis(3,4-dimethylcyclopentadienyl)zirconium dichloride catalyzes the reaction of 1,6- and 1,7-dienes with excess dibutyl magnesium to bis(butyl-magnesio-methyl)-substituted cycloalkane derivatives. Analogous reactions occur with butyl magnesium chloride and with heteroatom-containing dienes. The preference of 1,6-dienes for trans-fused cyclization products and that of 1,7-dienes for cis-fusion at ambient and for trans-fusion at elevated temperatures is similar to that observed before for unsubstituted zirconocene complexes. The R-enantiomer of the biphenyl-bridged zirconocene complex gives trans-fused cyclization products with an optical purity of only 15 ± 1% ee. The stereochemistry of these cyclomagnesation reactions is explained in terms of the relative rates of mutually competing cyclization and transmetalation steps.

5614456 Catalyst for bimodal molecular weight distribution ethylene polymers and copolymers

The interaction of silica, previously calcined at 600 °C, with dibutylmagnesium (DBM), 1-butanol and titanium tetrachloride and a solution of methylalumoxane (MAO) and (BuCp)2ZrCl2 provides a catalyst that, in the absence of a trialkylaluminum (AlR3) cocatalyst, produces polyethylene with a bimodal MWD.

Synthesis and structure of trinuclear methoxy-bridged titanium(III) -magnesium complexes: [(C 5H 5− nMe n) 2Ti( μ-OMe) 2] 2Mg (n = 4 and 5)

The hydride complexes [(C 5Me 5) 2Ti(μ-H) 2] 2Mg ( 1) and [(C 5HMe 4) 2Ti(μ-H) 2] 2Mg ( 2) smoothly react with four equivalents of methanol to give the methoxy complexes [(C 5Me 5) 2Ti(μ-OMe) 2] 2Mg ( 3) and [(C 5HMe 4) 2Ti(μ-OMe) 2] 2Mg ( 4). The X-ray crystal analysis of 4 revealed a nearly linear arrangement of the metal atoms in an unsymmetrical molecule. The EPR spectra of the frozen toluene glass of 3 and 4 showed the triplet state spectra with very similar zero field splitting of rhombic symmetry. The distance between the unpaired electrons in 4 was estimated from the value of D = 0.00958 cm −1 to be 6.43 Å, in good agreement with the crystallographic Ti IIITi III distance of 6.329(1) Å. Complex 4 reacts with excess dibutyl magnesium to give a mixture of 2 and [(C 5HMe 4) 2Ti(μ-H]) 2Mg(μ-OMe)] 2 ( 6). A mixture of 4 and methylalumoxane (1 : 100) did not induce the polymerization of ethylene.

Sequential formation of trans and cis butadiene homopolymers with one catalyst system

When butadiene is polymerized in dichloroethane using dibutyl magnesium plus neodymium versatate as catalyst, high- trans polymer is formed during the first few hours of polymerization, followed by slow polymerization of the remaining butadiene to high- cis polymer after 7–8 h. This change probably occurs as a result of slow reaction between catalyst and solvent.

Ziegler–Natta catalysts on silica for ethylene polymerization

AbstractThe amount of dibutylmagnesium (DBM) or triethylaluminum (TEAL) that reacted with silica at 55–60°C depended on the silica calcining temperature. Lower silica calcining temperatures resulted in more Mg or Al fixed to the silica surface, indicating greater amounts of DBM or TEAL reacting with the silica. The amount of the metal alkyls butyl(octyl) magnesium ethoxide, ethylaluminum dichloride, tri‐n‐hexylaluminum, and diethyl(ethyldimethylsilanolato) aluminum that reacted with 600°C calcined silica was also determined. The metal alkyl can react with the silica at two sites, a surface hydroxyl group and a siloxane group. The silica surface hydroxyl groups can be chemically converted to trimethylsilyl groups so that only the siloxane groups are available for attack. After the metal alkyl was reacted with silica, the resulting intermediate was treated with titanium tetrachloride to yield an ethylene polymerization catalyst in the presence of TEAL. When no metal alkyl was employed, titanium tetrachloride reacted only with the silica surface hydroxyl groups to yield a weakly active ethylene polymerization catalyst.