Complex Organometallic Catalysts Research Articles

The Ziegler catalysts

Fifty-four years after the Nobel Prize was awarded to Karl Ziegler and Giulio Natta for the polymerization of olefins by complex organometallic catalysts, the field continues to elicit enormous interest, both from the academia and the industry. Furthermore, this chemistry and technology occupy a high ground in the annals of 20th-century science. The elegance and simplicity of Ziegler’s chemistry continue to astound researchers even today, and the enormous impact this chemistry has had on the quality of our life is truly incredible. Polyethylene, produced using Ziegler’s chemistry has touched every aspect of common man’s life, so much so that, today it is impossible to imagine life on this planet without polyethylene. Equally fascinating is the story of how Ziegler stumbled on this most impactful discovery. Ziegler’s discipline and rigor in systematically following every lead in the laboratory, however trivial it seemed, and his penchant for understanding the basics of science culminated in 1954, with a simple reaction for converting ethylene to polyethylene, the quintessential carbon-carbon (C-C) bond forming reaction. His life and work hold many lessons for all scientists who dream of making their scientific quests useful and relevant to society. It is also relevant to the contemporary debate on basic versus applied research.

Theory and Modeling of Asymmetric Catalytic Reactions.

Modern density functional theory and powerful contemporary computers have made it possible to explore complex reactions of value in organic synthesis. We describe recent explorations of mechanisms and origins of stereoselectivities with density functional theory calculations. The specific functionals and basis sets that are routinely used in computational studies of stereoselectivities of organic and organometallic reactions in our group are described, followed by our recent studies that uncovered the origins of stereocontrol in reactions catalyzed by (1) vicinal diamines, including cinchona alkaloid-derived primary amines, (2) vicinal amidophosphines, and (3) organo-transition-metal complexes. Two common cyclic models account for the stereoselectivity of aldol reactions of metal enolates (Zimmerman-Traxler) or those catalyzed by the organocatalyst proline (Houk-List). Three other models were derived from computational studies described in this Account. Cinchona alkaloid-derived primary amines and other vicinal diamines are venerable asymmetric organocatalysts. For α-fluorinations and a variety of aldol reactions, vicinal diamines form enamines at one terminal amine and activate electrophilically with NH(+) or NF(+) at the other. We found that the stereocontrolling transition states are cyclic and that their conformational preferences are responsible for the observed stereoselectivity. In fluorinations, the chair seven-membered cyclic transition states is highly favored, just as the Zimmerman-Traxler chair six-membered aldol transition state controls stereoselectivity. In aldol reactions with vicinal diamine catalysts, the crown transition states are favored, both in the prototype and in an experimental example, shown in the graphic. We found that low-energy conformations of cyclic transition states occur and control stereoselectivities in these reactions. Another class of bifunctional organocatalysts, the vicinal amidophosphines, catalyzes the (3 + 2) annulation reaction of allenes with activated olefins. Stereocontrol here is due to an intermolecular hydrogen bond that activates the electrophilic partner in this reaction. We have also studied complex organometallic catalysts. Krische's ruthenium-catalyzed asymmetric hydrohydroxyalkylation of butadiene involves two chiral ligands at Ru, a chiral diphosphine and a chiral phosphate. The size of this combination strains the limits of modern computations with over 160 atoms, multiple significant steps, and a variety of ligand coordinations and conformations possible. We found that carbon-carbon bond formation occurs via a chair Zimmerman-Traxler-type transition structure and that a formyl CH···O hydrogen bond from aldehyde CH to phosphate oxygen, as well as steric interactions of the two chiral ligands, control the stereoselectivity.

Selective dimerization, oligomerization, homopolymerization and copolymerization of olefins with complex organometallic catalysts

Review embarrasses the problems of low molecular weight olefins (ethylene and propylene) selective oligomerization to butene-1, hexene-1, octene-1, 4-methylpentene-1; selective polymerization of olefins to obtain polymers with a given molecular mass, molecular mass distribution, branching (for the polyethylene), chain structure [atactic, iso-, syndio-, gemiisotactic, stereoblock type and containing terminal vinyl and vinylidene bonds (for polypropylene)]; “live” homo-and copolymerization of olefins, and alternating copolymerization of olefins in the presence of complex organometallic catalysts.

Features of copolymerization of ethylene with acetylene on complex organometallic catalysts

Features of copolymerization of ethylene with acetylene on complex organometallic catalysts

Aspects of the copolymerization of ethylene with acetylene on complex organometallic catalysts

The effect of various factors on the kinetics of the consumption of the comonomers during polymerization of ethylene with acetylene on vanadium- and titanium-containing complex catalysts and on the structure of the products formed has been studied. The kinetic method shows that the reactivity of acetylene in the course of copolymerization on complex catalysts exceeds that of ethylene. The copolymerization products of ethylene with acetylene are coloured, contain conjugated and vinyl double bonds, attach ozone, bromine, iodine and maleic anhydride, display paramagnetism and contain a considerable quantity of the crystalline phase. All this indicates that they are block copolymers of ethylene with acetylene. It is shown that the block copolymers in the course of combined polymerization of the two monomers can form only with the condition k 12→0 and k 21→0.

Properties of block-copolymers of ethylene with acetylene, prepared on complex organometallic catalysts

The copolymerization products of ethylene with acetylene or phenylacetylene are coloured, nonconductive, can get strongly charged, melt in the range 80–140°C, in the nascent state or in films contain a considerable fraction of the crystalline phase, are completely soluble in tetralin at 130°C, and exhibit low values of the melt flow index. Thermomechanical data and the results of the studies of these copolymers by DSC and thermogravimetry indicate that they undergo crosslinking without initiators or accelerators. The acetylene blocks initiate crosslinking, act as the crosslinking agent and also appear as part of the generated structuralized material. The crosslinked copolymers of ethylene with acetylene differ very little from LDPE concerning their molecular or supermolecular structure, and stress-strain characteristics.

Characterization of 1-butene polymerization in the presence of graphite-supported complex organometallic catalysts

Characterization of 1-butene polymerization in the presence of graphite-supported complex organometallic catalysts

Radical stages in reactions between components of complex organometallic catalysts

1. It has been established by means of mass spectrometry and chromatography that in the reactions of (C5H5)2TiCl2, (C5H5)2TiC2H5Cl, TiCl4, and VOC13 with (C2H5)nAlCl3−n and (CH3)2A1C1 in an octadeuterotoluene medium, the solvent takes part in reactions between the components of the complex catalysts. 2. The decomposition of the alkyl derivatives of titanium and vanadium in complex catalysts limits homolysis of the bond between the transition metal and the carbon.

Transformations of 3-methyl- 1-butene on complex organometallic catalysts

1. The transformation of 3-methyl-1-butene was studied and it was shown that on complex organometallic catalysts the maximum yield of poly(3-methyl-1-butene), which is equal to 3–8 g/g of Ti, and the stereoregularity of the polymer, are respectively practically independent of the nature of the catalytic system and the nature of the aluminum alkyl. 2. The catalytic activity of the various complex organometallic catalysts, determined from the values of the initial polymerization rates of 3-methyl-1-butene, correspond to the order: Al(i-C4H9)3+TiCl4 > A1(C2H5)3+TiCl4 ≈ Al(i-C4H9)3+ TiCl3 > Al(C2H5)2Cl+TiCl4. 3. The low specific yield of poly (3-methyl-1-butene) is apparently caused by the adsorption of the polymer on the catalytically active centers and the resultant diffusion inhibition of the polymerization, and also by the adsorption of 2-methyl-2-butene and 2-methy 1-1-butene, which are formed as the result of the competing isomerization reaction, on the catalytically active centers.

Some characteristics of alkylation of toluene with propylene in presence of Ziegler catalyst

1. The alkylation of toluene in the presence of the complex organometallic catalyst: TiCl4 + Al (i-C4H9)2Cl+CH3OH is the consequence of the cationic telomerization of propylene. 2. A method was proposed for determining the mean degree of alkylation and the structure of the reaction products was studied.

On features of ionic coordination polymerization of vinyl cyclohexane

The work is devoted to the ionic coordination polymerization of vinyl cyclohexane. During the polymerization of vinyl cyclohexane, side reactions (viz. isomerization into unreactive isomers with internal double bond and transformation of monomer into ethylcyclohexane) occur on complex organometallic catalysts. A procedure has been developed for studying the kinetics of vinyl cyclohexane transformation by analytical gas-liquid chromatography. The effects of various catalytic systems and their individual components on the rates of these reactions have been investigated. From the experimental data, a reaction mechanism has been suggested. It is supposed that ethylcyclohexane is formed by catalytic hydrogenation of monomer with hydrogen evolved during formation of organometallic complex, as well as by the decomposition of the products of the interaction of vinyl cyclohexane with organo-aluminium compounds or titanium derivatives. Most of the isomers with internal double bond (exo- and endocyclic) are formed by a mechanism involving π-bonded intermediates between a monomer and a transition metal and the subsequent σ-alkyl or π-allylic intra- or intermolecular hydrogen transfer.

Hydrogenation of olefins in the presence of complex organometallic catalysts

Hydrogenation of olefins in the presence of complex organometallic catalysts

Infrared spectra and structure of polyisobutenes produced on a complex organometallic catalyst

Isobutene polymerizes with parts of anomalous structure when an Al(C2H5)3+TiCl4, catalyst with a high Al∶Ti ratio is used. It is found that isobutene can polymerize by head-to-head and head-to-tail mechanisms when a TiCl4 or Ziegler catalyst is used.

Hydrogenation of substituted olefins with certain complex organo-metallic catalysts

Hydrogenation of substituted olefins with certain complex organo-metallic catalysts

Soluble complex organometallic catalysts for polymerization: The activity and structure of complexes derived from di-isobutyl-aluminium hydride and bis-cyclopentadienyl-titanium dichloride

Complexes arising when dicyclopentadienyl-titanium dichloride reacts with di-isobutyl-aluminium hydride were identified by e.s.r. spectra. The interaction of the various complexes with styrene was studied.

Polymerization of hex-1-ene and hept-1-ene with an Al( iso-C 4H 9) 3 + TiCl 4 catalytic system

1. 1. A study has been made of the polymerization of hex-1-ene and hept-1-ene with a complex organometallic catalyst based on triisobutylaluminium and titanium tetrachloride and the basic features of the reaction elucidated. 2. 2. Polyhexene and polyheptene, while amorphous at conventional temperatures, partially crystalline on cooling to the temprature of liquid nitrogen. 3. 3. Polyhexene and polyheptene have been fractioned within a wide shown that all polymer fractions are amorphus substances within a wide range of molecular weight. Crystalline formations plasticized by an amorphous component could not be detected. A hydrothesis has been put forward to explain the formation of only amorphous polymers from hex-1-ene and hept-1-ene.

Structure of the soluble complex organometallic catalyst for the polymerization of acetylene

1. The system AlEt3 and VC10H14O5 is homogeneous in benzene medium. 2. The valence state of the vanadium in the catalytic complex was established. 3. A hypothesis was given for the structure of the catalytic complex.

Structure of product of the polymerization of silvan in presence of a complex organometallic catalyst

1. Possible structures were examined for the product of the polymerization of silvan in presence of a complex organometallic catalyst. 2. In the polymerization of silvan one of the double bonds becomes saturated, probably the one between carbon atoms not carrying substituents.

Copolymerization of Butadiene and Isoprene through Use of Complex Organometallic Catalysts

Abstract Processes were investigated for the copolymerization of butadiene and isoprene, with the catalyst systems: aluminum triisobutyl/TiCl4 and aluminum diisobutyl chloride/cobalt chloride, complexed with ethyl alcohol. From study of the properties of the resulting polymers, and of butadiene/ isoprene homopolymer mixtures, it was established that in the presence of the cited catalysts, genuine copolymers were in fact obtained from the mixtures of isoprene and butadiene. Constants were determined for the copolymerization of butadiene and isoprene, in presence of the indicated catalysts, by tracer techniques.

Synthesis and formation kinetics of low molecular α-olefins on complex organometallic catalysts—I. Polymerization of propylene in the presence of the catalytic system TiCl 4 and Al( iso-C 4H 9) 2Cl : O. N. Pirogov, Yu. V. Kissin and N. M. Chirkov, Vysokomol. soyed. 5: No. 5, 633–638, 1963.

Synthesis and formation kinetics of low molecular α-olefins on complex organometallic catalysts—I. Polymerization of propylene in the presence of the catalytic system TiCl 4 and Al( iso-C 4H 9) 2Cl : O. N. Pirogov, Yu. V. Kissin and N. M. Chirkov, Vysokomol. soyed. 5: No. 5, 633–638, 1963.