Chloride Cocatalyst Research Articles

Mechanism-Inspired Synthesis of Poly(alkyl malonates) via Alternating Copolymerization of Epoxides and Meldrum's Acid Derivatives.

Direct incorporation of malonate units into polymer backbones is a synthetic challenge. Herein, we report the alternating and controlled anionic copolymerization of epoxides and Meldrum's acid (MA) derivatives to access poly(alkyl malonates) using (N,N'-bis(salicylidene)phenylenediamine)AlCl and a tris(dialkylamino)cyclopropenium chloride cocatalyst. This unique copolymerization yields a malonate-containing repeat unit while releasing a small molecule upon MA-derivative ring-opening. Mechanistic and computational studies reveal that the nature of the small molecule released influences overall polymerization kinetics, side reaction behavior, and molecular weight control. Controlled copolymerization of MA derivatives with a range of epoxides ultimately yields a library of new poly(alkyl malonates) with diverse and tunable thermal properties.

The Co-catalyst Effects of Mn(II), Zn(II), and Cr(III) Chlorides on Acidic Ionic Liquid Catalyzed Synthesis of Value-added Products from Cellulose in Aqueous Ethanol

Background: Catalytic depolymerization and processing of cellulose can be used to produce value-added renewable feedstock chemicals. Objective: This study aimed to develop an acidic ionic liquid-metal ion chloride catalyst system-based single-reactor method for processing cellulose into value-added products. Methods: The effect of metal chlorides as co-catalysts on 1-(1-propylsulfonic)-3-methylimidazolium chloride acidic ionic liquid catalyzed degradation of cellulose in 40% (v/v) aq. ethanol was studied by measuring levulinic acid, ethyl levulinate, and 5-hydroxymethylfurfural yields. Results: In experiments with Mn(II) and Zn(II) chloride co-catalysts at 160 and 170°C for 12 h, the initial yields of ethyl levulinate and 5-hydroxymethylfurfural improved from ~ 7% to ~ 12-15% due to co-catalytic effects. The highest enhancements in ethyl levulinate yields were observed with CrCl3, where the yield increased from 6 to 27% with the addition of a 10 mol% co-catalyst. Conclusion: All three transition metal chlorides studied caused improvements in yields of secondary products, ethyl levulinate and 5-hydroxymethylfurfural, in acidic ionic liquid catalyzed degradation of cellulose in aqueous ethanol. The most significant enhancements in ethyl levulinate yields were observed with CrCl3 as a co-catalyst.

Iron Complexes for Cyclic Carbonate and Polycarbonate Formation: Selectivity Control from Ligand Design and Metal-Center Geometry.

A family of 17 iron(III) aminobis(phenolate) complexes possessing different phenolate substituents, coordination geometries, and donor arrangements were used as catalysts for the reaction of carbon dioxide (CO2) with epoxides. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry of the iron complexes with a bis(triphenylphosphine)iminium chloride cocatalyst in negative mode revealed the formation of six-coordinate iron "ate" species. Under low catalyst loadings (0.025 mol % Fe and 0.1 mol % chloride cocatalyst), all complexes showed good-to-excellent activity for converting propylene oxide to propylene carbonate under 20 bar of CO2. The most active complex possessed electron-withdrawing dichlorophenolate groups and for a 2 h reaction time gave a turnover frequency of 1240 h-1. Epichlorohydrin, styrene oxide, phenyl glycidyl ether, and allyl glycidyl ether could also be transformed to their respective cyclic carbonates with good-to-excellent conversions. Selectivity for polycarbonate formation was observed using cyclohexene oxide, where the best activity was displayed by trigonal-bipyramidal iron(III) complexes having electron-rich phenolate groups and sterically unencumbering tertiary amino donors. Those containing bulky tertiary amino ligands or those with square-pyramidal geometries around iron showed no activity for polycarbonate formation. While the overall conversions declined with decreasing CO2 pressure, CO2 incorporation remained high, giving a completely alternating copolymer. The difference in the optimum catalyst reactivity for cyclic carbonate versus polycarbonate formation is particularly noteworthy; that is, electron-withdrawing-group-containing phenolates give the most active catalysts for propylene carbonate formation, whereas catalysts with electron-donating-group-containing phenolates are the most active for polycyclohexene carbonate formation. This study demonstrates that the highly modifiable aminophenolate ligands can be tailored to yield iron complexes for both CO2/epoxide coupling and ring-opening copolymerization activity.

Mechanism of fixation of CO2 with an epoxide catalyzed by ZnBr2 and a choline chloride co-catalyst: a DFT study

The cycloaddition mechanism of the reaction of propylene oxide with CO2 catalyzed by ZnBr2/choline chloride is elucidated using a DFT method.

Copolymerisation of Propylene Oxide and Carbon Dioxide by Dinuclear Cobalt Porphyrins

AbstractTwo dinuclear cobalt porphyrins comprising different structural tethering motifs at the porphyrin periphery were synthesised, along with a representative mononuclear cobalt porphyrin, and their catalytic activities tested towards carbon dioxide–propylene oxide copolymerisation in the presence of bis(triphenylphosphoranyl)ammonium chloride cocatalyst. The catalytic activities of the mononuclear and the bis‐para‐tethered dinuclear cobalt porphyrin with selective formation of poly(propylene carbonate) are largely comparable, showing no benefit of dinuclearity in contrast to the case of cobalt salen complexes and suggesting that polymer growth proceeds exclusively from one metal centre. The alternative bis‐ortho‐tethered porphyrin demonstrated considerably reduced activity, with dominant formation of cyclic propylene carbonate, as a result of hindered substrate approach at the metal centre. Time‐resolved UV/Vis spectroscopic studies suggested a general intolerance of the cobalt(III) porphyrin catalysts towards the copolymerisation conditions in the absence of carbon dioxide pressure, leading to catalytically inactive cobalt(II) species. In the presence of carbon dioxide, the bis‐ortho‐tethered catalyst showed the fastest deactivation, which is related to an unfavourable steric arrangement of the linker fragment, as was also confirmed by NMR spectroscopic measurements.

Palladium complexes of bulky ortho-trifluoromethylphenyl-substituted phosphines: Unusually regioselective catalysts for the hydroxycarbonylation and alkoxycarbonylation of alkenes

The reactions of the very bulky phosphine ligands containing both tert-butyl and ortho-trifluoromethylphenyl substituents with [PdCl 2(PhCN) 2] have been studied, in order to assess the impact of steric and electronic effects on a ligand's coordination ability. The palladium complexes of tert-butyl( ortho-trifluoromethylphenyl)methyl phosphine and tert-butyl( ortho-trifluoromethylphenyl)( n-butyl)phosphine were characterised by X-ray crystallography and shown to be good precatalysts for the hydroxy- and alkoxycarbonylation of alkenes relative to Pd complexes of tricyclohexylphosphine and triphenylphosphine. A notable feature of Pd complexes of tert-butyl( ortho-trifluoromethylphenyl)methyl phosphine is significantly enhanced regioselectivity relative to previous state-of-the-art catalysts in the hydroxycarbonylation of styrene, even if lithium chloride co-catalysts are not used. These catalysts derived from large cone angle ligands consistently give higher regioselectivity in the alkoxycarbonylation of styrene using ethanol, n-propanol, and i-propanol as nucleophiles. These Pd complexes are also active in the Suzuki coupling of activated aryl chlorides, and in both carbonylation and Suzuki reactions, tert-butyl( ortho-trifluoromethylphenyl)methyl phosphine gives more productive catalysts than its bulkier analogues.

Polymerization of Propene and 1,3‐Butadiene with Vanadyl(V) Monoamidinate Precatalysts and MAO or Dialkylaluminum Chloride Cocatalysts

AbstractSummary: Two new vanadyl(V) amidinates have been synthesized and characterized by single crystal X‐ray diffraction and 1H NMR. The complexes are dimeric with Cl bridges and monodentate coordination of the amidinate ligand to pseudooctahedral vanadium. In the presence of organometallic compounds of aluminum, these vanadyl complexes promote polymerization of propene and 1,3‐butadiene.image

Zirconium complexes as catalysts for the oligomerisation of ethylene: the role of chelate ligands and the Lewis acid cocatalyst in the generation of the active species

Highly effective catalysts for the conversion of ethylene into linear α-olefins may be generated in situ from zirconium tetrachloride, a β-aminoketone or β-aminothioketone ligand and an alkylaluminium chloride Lewis acid cocatalyst. Catalysts may also be generated from ZrCl 4·2HL adducts (where HL=monodentate, oxygen-bound β-aminoketones), and from bis-ligand complexes of the type ZrCl 2L 2 (where L=monovalent, bidentate β-aminoketones or β-aminothioketones) on treatment with an alkylaluminium chloride cocatalyst. Product distribution and catalyst activity can be adjusted by ligand substituent variation and/or by the method of catalyst formation. Catalyst systems generated from preformed complexes, ZrCl 2L 2, were in general significantly more active than those formed in situ or from the bis-ligand adducts, ZrCl 4·2HL. Activities of up to 60,000 turnovers/h were obtained with selected complexes. However, in situ mixtures and bis-ligand adducts generally gave a much narrower oligomer distribution, with up to 95% of the oligomers occurring in the C 4–C 10 range for a number of the systems tested. In situ NMR (nuclear magnetic resonance) tests indicate that complex ligand/cocatalyst interactions are present and that these new oligomerisation systems are active even under very mild conditions, 30°C and 1 atm ethylene.

ChemInform Abstract: Highly Chemoselective Palladium‐Catalyzed Conjugate Reduction of αβ‐Unsaturated Carbonyl Compounds with Silicon Hydrides and Zinc Chloride Cocatalyst.

AbstractThe three‐component system (A) is capable of efficient conjugate reduction of unsaturated carbonyl compounds such as (I), (III), (V), (VII), (IX), or (XI) to the respective products shown in the scheme.

Highly chemoselective palladium-catalyzed conjugate reduction of .alpha.,.beta.-unsaturated carbonyl compounds with silicon hydrides and zinc chloride cocatalyst

A three-component system comprised of a soluble palladium catalyst, hydridosilane, and zinc chloride is capable of efficient conjugate reduction of a,&unsaturated ketones and aldehydes. The optimal set of conditions includes diphenylsilane as the most effective hydride donor, any soluble palladium complex in either the 0 or I1 oxidation state, when it is stabilized by phosphine ligands, and ZnCll as the best Lewis acid cocatalyst. The reaction is very general with respect to a broad range of unsaturated ketones and aldehydes, and it is highly selective for these Michael acceptors, as reduction of a,@-unsaturated carboxylic acid derivatives is very sluggish under these conditions. When dideuteriodiphenylsilane is used to reduce unsaturated ketones, deuterium is stereoselectively introduced at the less-hindered face of the substrate and regioselectively at the 8-position. Conversely, when reductions are carried out in the presence of traces of D20, deuterium incorporation occurs at the a-position. On the basis of deuterium-incorporation experiments and 'H NMR studies, a catalytic cycle is postulated in which the first step involves reversible coordination of the palladium complex to the electron-deficient olefin and oxidative addition of silicon hydride to form a hydridopalladium olefin complex. Migratory insertion of hydride into the coordinated olefin produces an intermediate palladium enolate which, via reductive elimination, collapses back to the Pd(0) complex and a silyl enol ether, which is then hydrolyzed to the saturated ketone. In addition to catalyzing that hydrolysis, ZnC12 facilitates the hydrosilation process. Despite the bewildering variety of reducing agents available for synthetic chemistry, new and ever more selective reductants are in constant demand. Most popular of selective reducing agents are the various metal hydrides, mainly those of boron and alu- minum,' an abundance of which have been designed over the past 4 decades and new derivatives of which are continuously being developed.* However, the hydridic nature of most of these group 13 and other metal hydrides can limit their usefulness, particularly when high chemoselectivity is required.

Gas-phase conformational preference of the methyl group from equilibration of 1-, 3-, and 4-methyldiamantane on a chlorinated platinum–alumina catalyst

On a chlorinated platinum–alumina catalyst/hydrogen chloride co-catalyst, the isomeric methyldi-amantanes establish equilibrium, the temperature dependence of which yields a value of 2·14 kcal mol–1 for the gas-phase conformational ethalpy of the methyl group.

Stereoregular Polymerization of Butadiene with Alkylaluminum Chlorides and Cobalt Octoate

Abstract The requirement of water or oxygen to activate the diethylaluminum chloride co-catalyst used with a cobalt compound to produce 98 per cent cis-1,4 poly-butadiene was reported previously. Activation is considered to form two alkylaluminum compounds differing in Lewis acidity. Several reactions presumed to lead to the formation of the higher acid were carried out with a minor proportion of the diethylaluminum chloride by partial dealkylation with organic hydroperoxide, halogen, tertiary alcohol, organic halide or aluminum. Water is neither necessary nor desirable in the ethylaluminum sesquichloride-cobalt octoate catalyst system. Polar solvents do not appreciably alter the cis-1,4 catalysis with diethylaluminum chloride/water/cobalt octoate, but do decrease the rate or extent of polymerization with increasing dielectric constant of the solvent. A mechanism of cobalt catalysis of butadiene polymerization is proposed.

Ziegler polymerization of olefins. V. Site removal and site activation by electron donors

AbstractElectron donors having different structures have been incorporated into the Ziegler catalyst, ZnEt2 + γ‐Alx Tiy Clz‐160, in order to understand the site removal and the site activation processes. Donors which were studied in the present work include: azulenes, unsaturated compounds, aromatics, substituted pyridines and quinolines, cyclopentadienyl compounds of V, Cr, Ni, and Co, (C6H6)2Cr, and PF3. Their effect on the polymerization of propylene was determined. It was found that the site removal and the site activation processes could be brought about by many different donors. Variations were noted among the donor types. This finding shows that a variety of isolated sites with different abilities to coordinate and orient the α‐olefin are found on the crystal surface of the titanium chloride cocatalyst.

Oxyaluminum compound catalysts for the polymerizations of cyclic ethers and vinyl monomers

AbstractPreparation of a species which was assumed to resemble partly the AlEt3—H2O system was tried by the reaction between oxyaluminum chloride and AlEt3. The product of this reaction as well as oxyaluminum halides were examined in the catalytic activity for the polymerization of three‐, four‐ and five‐membered cyclic ethers and of vinyl monomers such as styrene, α‐methylstyrene, and i‐butyl vinyl ether. In the reaction of AlOCl with AlEt3, most chlorine atoms were replaced by ethyl groups and a soluble product was formed which we called oxyaluminum ethyl, AlOEt. These oxyaluminum compounds, AlOCl, AlOBr, AlOI, and AlOEt, induced the polymerizations of vinyl monomers with or without t‐butyl chloride cocatalyst and a mechanism of cationic polymerization was proposed. The polymerizations of i‐butyl vinyl ether carried out in toluene with AlOCl, AlOBr or AlOEt catalysts gave crystalline isotactic polymers. The polymerizations of 3,3‐bis(chloromethyl)oxacyclobutane and tetrahydrofuran were also induced by oxyaluminum compound—alkylene oxide systems. By oxyaluminum catalysts and by the binary systems of oxyaluminum compound and metal alkyl, alkylene oxides such as propylene oxide and epichlorohydrin were polymerized to give a product containing fairly amount of acetone‐insoluble crystalline part.