Synthesis of Dialkyl-substituted Terminal Olefin

Dialkyl-substituted terminal olefins were synthesized from the coupling reaction of a-olefins which were catalyzed by zirconocene dichloride/methylalumoxane （MAO） catalyst system under mild condition. High yield was gained and no other oligmer was detected. It was found that the ratio of AI/Zr is responsible for the selectivity of product.     

Polymerization Mechanism of α-Linear Olefin

The density functional theory on the level of B3LYP/6-31G was empolyed to study the chain growth mechanism in polymerization process of α-linear olefin in TiCl₃/AlEt₂Cl catalytic system to synthesize drag reduction agent. Full parameter optimization without symmetryrestrictions for reactants, products, the possible transition states, and intermediates wascalculated. Vibration frequency was analyzed for all of stagnation points on the potential energy surface at the same theoretical level. The internal reaction coordinate was calculated from the transition states to reactants and products respectively. The results showed as flloes:(i) Coordination compounds were formed on the optimum configuration of TiCl₃/AlEt₂Cl.(ii) The transition states were formed. The energy di?erence between transition states and the coordination compounds was 40.687 kJ/mol. (iii) Double bond opened and Ti-C(4) bond fractured, and the polymerization was completed. The calculation results also showedthat the chain growth mechanism did not essentially change with the increase of carbon atom number of α-linear olefin. From the relationship between polymerization activation energy and carbon atom number of the α-linear olefin, it can be seen that the α-linear olefin monomers with 6-10 carbon atoms had low activation energy and wide range. It was optimum to synthesize drag reduction agent by polymerization.     

Early Transition Metal Catalysis for Olefin–Polar Monomer Copolymerization

Introducing polar functional groups into widely used polyolefins can enhance polymer surface, rheological, mixing, and other properties, potentially upgrading polyolefins for advanced, value-added applications. The metal catalyst-mediated copolymerization of non-polar olefins with polar comonomers represents the seemingly most straightforward, atom- and energy-efficient approach for synthesizing polar functionalized polyolefins. However, electrophilic early transition metal (groups 3 and 4)-catalyzed processes which have achieved remarkable success in conventional olefin polymerizations, encounter severe limitations here, largely associated with the Lewis basicity of the polar co-monomers. In recent years, however, new catalytic systems have been developed and successful strategies have emerged. In this Minireview, we summarize the recent progress in early transition metal polymerization catalyst development, categorized by the catalytic metal complex and polar comonomer identity. Furthermore, we discuss advances in the mechanistic understanding of these polymerizations, focusing on critical challenges and strategies that mitigate them.     

A Preferred Intramolecular ‘Ene’ Reaction Between Ketene and Olefin

Aplysin (1), a marine sesquiterpene was isolated from ‘aplysia kurodai’ and its structure was ellucidated by Hirata-et-al¹. They also reported the synthesis of racemic aplysin². Their synthetic route involved cyclopentanone (2) as a well-characterized intermediate. We visualized the synthesis of cyclobutanone (3) and its subsequent conversion to (2) as an attractive alternative. But during our attempts to synthesize the said cyclobutanone, we have come across a very facile intramolecular ‘ene’ reaction between ketene and olefin. We report our unexpected observations in this communication.     

A Convenient Route to α-Alkoxy Ester from Olefin Vla Organoborane-Catalyzed Hydroalumintaion

Organoborane-catatyzed hydroalumination of olefin with dichloroaluminum hydride and subsequent functionalization of the resulting organoaluminum with methyl α-chloro-α-methoxyacetate give rise to the corresponding α-methoxy ester in good yield.     

Nitrene-Mediated Enantioselective Intramolecular Olefin Oxyamination to Access Chiral γ-Aminomethyl-γ-Lactones

Attaching a nitrene precursor to an intramolecular nucleophile allows for a catalytic asymmetric intramolecular oxyamination of alkenes in which the nucleophile adds in an endocyclic position and the amine in an exocyclic fashion. Using chiral-at-ruthenium catalysts, chiral γ-aminomethyl-γ-lactones containing a quaternary carbon in γ-position are provided in high yields (up to 99 %) and with excellent enantioselectivities (up to 99 % ee). DFT calculations support the possibility of both a singlet (concerted oxyamination of the alkene) and triplet pathway (stepwise oxyamination) for the formation of the predominant stereoisomer. γ-Aminomethyl-γ-lactones are versatile chiral building blocks and can be converted to other heterocycles such as δ-lactams, 2-oxazolidinones, and tetrahydrofurans.     

Studies on Diastereoselective Intramolecular meta-Cycloaddition ofArene to Olefin (Part I)

AprinciPalchallengeof0rganicsynthesisistheinventionofreactionsandstrategiesthatallowf0rthefacileconversionofsimPlec0mP0undsillt0comPlexmaterials,medi-cines,ormoleculesoftheoreticalinterest.WiththecaPacityt0produceuPto3newringsand6newstere0geniccentersinonestep,thearene-alkeneph0tocycloadditionreactionprovidesaremarkablyeffectivemeansofaddressingthischallenge.'-'Wehavereported"'thatintramolecularhydrogenbondeffectcouldsignificantlyincreasethedi-astereoselectivityinsuchcycloaddition.Asanextens…     

Benzosuberyl Substituents as a “Sandwich-like” Function in Olefin Polymerization Catalysis

For the rational design of metal catalyst in olefin polymerization catalysis, various strategies were applied to suppress the chain transfer by bulking up the axial positions of the metal center, among which the "sandwich" type turned out to be an efficient category in achieving high molecular weight polyolefin. In the α-diimine system, the "sandwich" type catalysts were built using the typical 8-aryl-naphthyl framework. In this contribution, by introducing the rotationally restrained benzosuberyl substituent into the ortho-position of N-aryl rings, a new class of "sandwich-like" α-diimine nickel catalysts was constructed and fully identified. The rotationally restrained benzosuberyl substituents played a "sandwich-like" function by capping the nickel center from two axial sites. Compared to the nickel catalyst Ni1 bearing freely rotated benzhydryl substituent, Ni2 featuring benzosuberyl substituent enabled the increase(8 times) of polymer molecular weights from 8 kDa to 65 kDa in the polymerization of ethylene. By further increasing the steric bulk of another ortho-site of the N-aryl ring, the polymer molecular weight even reached an ultrahigh level of 833 kDa(M_w=1857 kDa) using the optimized Ni3. Notably, these nickel catalysts could also mediate the copolymerization of ethylene with methyl 10-undecenoate, with Ni3 giving the highest copolymer molecular weight(88 kDa) and the highest incorporation of comonmer(2.0 mol%), along with high activity of up to 10~5 g·mol~(-1)·h~(-1).     

Studies on Diastereoselective Intramolecular meta-Cycloaddition of Arene to Olefin (Part Ⅱ)

Wththecapacityt0pr0duceuPt03newringsand6newstereogeniccentersinonestep,thearene-athenephotocycloadditionreactionprovidesaremarkablyeffectivemeansinthesynthesistowardspolyquinanesalldfenestranes.2-'Asfarastheregioselectivityisconcemed,itisbelievedthatsubstitUentsatthear0maticringandthenon-bondedinteractionsbetWeensuchsubstitUentsandthesidechaincontrolthemode0fthecycloadditi0n.Wehaverep0rted"'thatintramolecularhydrogenbondeffectcouldsignificantlyincreasethediastereoselectivityinsuchcycloadditio…     

Effects of Anions and Cations on π-Complexation Between Olefin and Metal Halide

Introduction Separation,recoveryofolefinorremovalof tracequantitiesofolefinfromitsmixturesbyusing π-complexatonisamostpromisingsolution,com- paredwithenergy-intensivedistillationorotheral- ternatives.π-Complexationisasubgroupofchemi- calcomplexationwhereamixtureisbroughtinto contactwithasecondphasecontainingacomplex- ingagent[1].Forexample,theadsorbentscontain- ingAg+orCu+canselectivelyadsorbolefinfroman ethylene/ethaneorpropylene/propanemixture. Becausetheπ-complexationbondsarestronger th…     

Effects of Anions and Cations on π-Complexation Between Olefin and Metal Halide

An ab initio molecular orbital study was performed to determine the effects of anions and cations on the π-complexation of C2H4 on MX(M=Ag, Cu; X=F, Cl). The calculated results show the following order of adsorption strength: F-＞Cl- for anions; Cu ＞Ag for cations. The results can be explained by the detailed analysis of atomic charge, orbital energy and orbital population by using the natural bond orbital(NBO) theory: (1) anions with stronger electronegativity can attract more electrons from the s orbital of M, while at the same time it does not obviously weaken the d orbital occupation of M, thus the nearly vacant s orbital and the sufficiently filled d orbitals of M help with forming σ-donation and d-π* backdonation with the π orbital and the π* orbital of olefin, respectively; (2) a smaller energy gap of symmetry-adapted orbitals between olefin and a cation can favor the electron transfer, that is why Cu forms stronger adsorption with olefin than Ag does.     

Estimation of Olefin Dimerisation Products by GC/GC–MS and IR Techniques

A GC and IR based protocol was developed for monitoring the isobutene dimerisation process wherein the complete characterisation of the products was carried out by GC coupled with mass spectrometry. In the dimerisation process, LPG from FCC process comprising a mixture of saturated and unsaturated C4 hydrocarbons is subjected to a dimerisation process using a catalyst to produce C8 hydrocarbons. The reaction is carried out keeping in view the demand for high-octane blending components in gasoline. The isooctene generated in the process (mainly from the dimerisation of isobutene) is converted into isooctane having the RON and MON value 100. The monitoring process requires the use of two different column chemistries, viz., a 100 m CPSIL PONA CB non-polar column for C8 and its isomers and an Alumina PLOT column for C4 hydrocarbons. A 100 m non-polar column does not separate the C4 mixture since the column is meant for gasoline range products containing C5 and above hydrocarbons. Therefore, a need was felt for an improvised method which can handle both the analyses simultaneously. A cryogenic oven program starting from 0 °C was developed for separating the isomers of C4 hydrocarbons and C8 hydrocarbons on a single column during the single run by Detailed Hydrocarbon Analyzer. The data obtained using the cryo programme was validated with data obtained using Alumina PLOT column on C4 mixture since the Alumina PLOT column is the widely accepted column chemistry for separating the C4 hydrocarbons. An IR method for the estimation of the total olefin content was developed using 2,2,4-trimethyl pentene-1 as the reference standard. The total olefins generated during the process were identified by GC–MS, quantified by DHA-FID and validated by infrared spectroscopy. A good correlation was found between GC and IR spectral results (correlation coefficient R ²  = 0.99).     

Transition Metal-Free Alkyne-Aldehyde Reductive C−C Coupling trough Cascade Borylation/Olefin Isomerization

A direct approach to γ-keto esters through cascade alkyne-aldehyde reductive C−C coupling of propargyl esters and aromatic aldehydes under transition-metal-free (TM-free) fashion was developed. Compared with multistep processes, this procedure provides a fast path using commercially available materials and could be handled conveniently to produce various γ-keto esters in moderate yields.     

Increasing Olefin Metathesis Activity of Silica-Supported Molybdenum Imido Adamantylidene Complexes through E Ligand σ-Donation

Molybdenum imido adamantylidene complexes with different substituents on the imido ligand (dipp=2,6-diisopropylphenyl, Ar_F5=C₆F₅, and ^tBu) having distinct electron donating abilities were investigated for the metathesis of internal and terminal olefins, for both molecular and silica-supported species using standardized protocols. Here we show that surface immobilization of these compounds results in dramatically increased activity compared to their molecular counterparts. Additionally, we show that electron withdrawing imido groups increase the activity of the compound towards terminal olefins while they simultaneously decrease the ability to metathesize internal olefins. Furthermore, these systems also show high stability when used as initiators in olefin metathesis, although the species that display higher initial activity deactivate faster than those that show more a more moderate reaction rate at first. Our catalytic studies, augmented by DFT calculations, show that all investigated compounds have a remarkably small energy difference between the trigonal bipyramidal (TBP) and square planar (SP) configurations of the metallacyclobutane intermediates, which has previously been linked to high activity.     

Olefin Cross‐Metathesis: A Powerful Tool for Constructing Vaccines Composed of Multimeric Antigens

The preparation of biologically pertinent glycosylamino acids from O‐pentenyl glycosides is described. The procedure involves sequential cross‐metathesis reactions followed by hydrogenation. The generality and value of this procedure have been demonstrated by the preparation of peracetylated Gb3, GM2, and fucosyl GM1 glycosylamino acids, which are of potentially large value in the preparation of future anticancer vaccines.     

Liquid Chromatographic Separation of Olefin Oligomers and its Relation to Separation of Polyolefins – an Overview

Summary: Linear and branched alkanes are oligomers of polyethylene. Alkanes with higher molar masses are called waxes. These substances are widely used as fuels, oils, lubricants, etc. and for these reasons many groups have tried to analyse, separate and characterise alkanes by various methods, including liquid chromatography. Alkanes may be separated according to their size in solution by SEC. In addition to chromatographic systems separating in the SEC mode, various sorbent-solvent systems have been published, where alkanes have been separated one from another by adsorption and/or precipitation mechanism. The mobile phase is either a non-polar solvent or a polar solvent or a mixture of a solvent and a non-solvent for alkanes. Even near critical conditions, which have several advantages for applications of HPLC in polymer analysis, have been identified for alkanes. Moreover, selective separations of branched alkanes according to their structure have been published. In the majority of these published studies, solvents with low boiling points have been used as the mobile phases, which do not allow dissolution of crystalline polyolefins at atmospheric pressure. However, taking into account experiences with the separation of alkanes, new HPLC systems for the separation of polyolefins may be developed. This is a major challenge and first results are presented in this contribution.     

DFT Investigation on the Enantioselectivity of Olefin Carboacylation Catalyzed by a Rh(Ⅰ) Complex

The C–C bond activation and recyclization of benzocyclobutenone to poly-fused rings catalyzed by the [Rh(R,S-L)]+ complex producing the R,S-, S,R-, R,R-and S,S-product were investigated systematically at the BP86/6-31 G(d,p) level in gas phase and THF, and the R,S-and S,R-reaction pathways were revisited at the M062 X/6-31 G(d,p) level in THF. The computational results reveal that THF only marginally alters the free-energy barriers, but elevates the relative energies of all species. The BP86 functional testifies that in both gas phase and THF, the activation of strained C–C bonds bears relatively low free-energy barriers, and the rate-determining steps of S,R-and R,R-channels are different from those of R,S-and S,S-channels. The BP86 functional also predicts that the R,S-channel is energetically most favorable in gas phase, but the S,R-product is dominant in THF. The change of NPA charges can mirror the variation of molecular structures to elucidate reaction mechanisms.     

Do Anti‐Bredt Natural Products Exist? Olefin Strain Energy as a Predictor of Isolability

Bredt’s rule holds a special place in the realm of physical organic chemistry, but its application to natural products chemistry—the field in which the rule was originally formulated—is not well defined. Herein, the use of olefin strain (OS) energy as a readily calculated predictor of the stability of natural products containing a bridgehead alkene is introduced. Schleyer first used OS energies to classify parent bridgehead alkenes into “isolable”, “observable”, and “unstable” classes. OS calculations on natural products, using contemporary forcefield methods, unequivocally predict all structurally verified bridgehead alkene natural products to be “isolable”. Thus, when one assigns the structure of a putative bridgehead alkene natural product, an OS in the “observable” or “unstable” ranges is a red flag for error.