John J. Rooney

Mechanism for the stereospecific polymerization of olefins by Ziegler–Natta catalysts

A mechanism for the stereospecific polymerization of olefins by Ziegler–Natta catalysts is developed which differs significantly from previous mechanisms in the proposal that it proceeds via a 1,2-hydrogen shift from the α-carbon of the polymer chain and formation of metallocycle and carbene intermediates.

The catalytic exchange with deuterium of polymethylcyclopentanes on metal films. Evidence for π-bonded intermediates

Abstract A new mechanistic theory has been developed to explain several reactions of hydrocarbons on metal catalysts. Interconversion can take place on the surface not only between σ-bonded monoadsorbed and diadsorbed intermediates but also between π-bonded species provided that the reactant hydrocarbons contain three or more adjacent nonquaternary carbon atoms. Evidence for this theory has been obtained by the catalytic exchange with deuterium of several polymethylcyclopentanes on films of rhodium, palladium, platinum, and nickel, using a mass-spectrometric analytical technique. Studies on cis-trans isomerization, followed by gas-liquid chromatography, have provided further support for the theory. Palladium gave the most striking evidence for π-bonded intermediates. Rhodium was the most active metal for the exchange reactions and at low temperatures the role of σ-bonded intermediates was much greater than that of the π-bonded which only participated in the reactions at higher temperatures comparable to those needed to bring about exchange on palladium. The behavior of nickel and platinum was intermediate between that of rhodium and palladium. Evidence is presented to show that on rhodium and nickel αα-diadsorbed intermediates permit the exchange process to propagate from the hydrogens on one side of cyclopentane rings to those on the other side. Platinum can cause exchange by αγ-diadsorbed intermediates at the same temperatures as required to form π-bonded species. Explanations are given for some apparently anomalous features of the distributions of deutero-compounds formed on rhodium. The application of the theory to several aspects of the reactions of hydrocarbons on metal catalysts is discussed.

The exchange with deuterium of two cycloalkanes on palladium films: π-Bonded intermediates in heterogeneous catalysis

Abstract The catalytic exchange of 1,1,3,3-tetramethylcyclohexane and 1,1-dimethylcyclo-butane with deuterium on palladium films has been studied by means of a mass spectrometer. The results for 1,1,3,3-tetramethylcyclohexane provide further evidence for the theory that π-bonded intermediates are important in various reactions of hydrocarbons on transition metal catalysts. Some improvements in the details of the mechanistic aspects of this theory, presented in a recent report, are also suggested. Reasons are given for the anomalous behavior of 1,1-dimethylcyclobutane, which has little tendency to exchange by a multiple process in contrast to the other cycloalkanes previously investigated.

Evidence to challenge the universality of the Horiuti-Polanyi mechanism for hydrogenation in heterogeneous catalysis: origin and trend of the preference of a non-Horiuti-Polanyi mechanism.

The Horiuti-Polanyi mechanism has been considered to be universal for explaining the mechanisms of hydrogenation reactions in heterogeneous catalysis for several decades. In this work, we examine this mechanism for the hydrogenation of acrolein, the simplest α,β-unsaturated aldehyde, in gold-based systems as well as some other metals using extensive first-principles calculations. It is found that a non-Horiuti-Polanyi mechanism is favored in some cases. Furthermore, the physical origin and trend of this mechanism are revealed and discussed regarding the geometrical and electronic effects, which will have a significant influence on current understandings on heterogeneous catalytic hydrogenation reactions and the future catalyst design for these reactions.

Dramatic solvent effects on ring-opening metathesis polymerization of cycloalkenes

Abstract A series of metathesis polymers and copolymers have been formed and their structures were analysed by 13 C NMR spectroscopy. Noble metal and non-noble metal salt catalysts are distinguished by their behaviour in various solvents. Thus, in phenolic solvents, the former class produce alternating copolymers from cyclopentene and norbornene, while the latter are unaffected and produce random copolymers. In contrast, ether solvents have the effect of markedly increasing the cis content of polymers from the latter catalysts while the former are unaffected. The tacticity of various polymers are correlated through their hydrogenated derivatives and found to depend on the type of monomer as well as the catalysts.

Microstructure and mechanism of formation of the ring-opened polymers of SYN- and AATI-7-methylbicyclo-[2.2.1]hept-2-ene initiated with metathesis catalysts

Abstract A 51:49 mixture of syn- and anti-7-methylbicyclo[2.2.1]hept-2-ene was subjected to a number of Ru-, Os-, Ir-, W- and Re-based catalysts, and the structures of the polymers and their hydrogenated analogues determined by 13C NMR spectroscopy. Except in one case, the polymer consisted exclusively of ring-opened units of the anti isomer; the syn isomer could be recovered in good yield. This confirms that the exo face of norbornenes is normally highly reactive whereas the endo face is relatively inert towards metathesis. The exception was the highly reactive (mesitylene)W(CO)3/ EtAlCl2/epoxide catalyst, where a small proportion of syn units was found in the soluble part of the polymer. The same catalyst also polymerises the syn isomer in the presence of a small amount of anti isomer and effects its copolymerisation with norbornene. It will also polymerise bicycio [2.2.2]-oct-2-ene by ring-opening, but not 1,7,7-trimethylbicyclo[2.2.1]hept-2-ene. The ring dyad tacticity with respect to both cis and trans junctions could be determined directly from the spectra of the ring-opened polymers of the anti isomer, and the overall tacticity from the spectra of the corresponding hydrogenated polymers. The fractions of m and r dyads for trans and cis junctions respectively are generally in the range 0.5–1.0, but are not always equal, with noble metal catalysts having a tendency (which is especially marked in the case of initiation by the Ru-TFA complex) for trans junctions to be atactic and cis junctions syndic tactic. The cis/trans double bond distribution is often blocky. These results confirm that, in general, two types of metal-carbene complex are important propagating species; one in which the last formed unit (cis) is still coordinated, thereby sterically biasing the next monomer insertion in favour of another cis unit, while in the second the last formed unit (trans) has detached from the metal ion before the metal carbene reacts with monomer, which it then does with a strong bias towards the formation of a trans junction. Various possible chiral and achiral forms of these two species together with appropriate relaxation processes are briefly discussed.

Ring-opening polymerization of endo and exo-dicyclopentadiene and their 7,8-dihydro derivatives

A range of metathesis catalysts have been used to prepare polymers from the title monomers. The fraction of cis double bonds, σc, in the polymers was determined by 13C NMR spectroscopy. The spectra of polymers containing mainly cis or trans double bonds in the main chain, as well as polymers derived from these by hydrogenation, were analysed in detail in terms of orientational and tacticity effects. With endo-dicyclopentadiene, the catalyst RuC3·3H2O produced a high-cis polymer. This anomalous result is believed to be due to a steric effect at the catalyst site caused by endo-dicyclopentadiene also acting as a permanent ligand because of its unique potential, among these monomers, to chelate in a bidentate fashion.

The polymerization of propylene on silica-alumina

Abstract The reaction of propylene on a silica-alumina catalyst was studied in a static system at 58 °, 100 °, 150 °, and 200 °C, respectively. A complex distribution of products, which were analyzed in detail in the range C 3 to C 6 by gas-liquid chromatography, was obtained at all temperatures and it was clear that polymerization was accompanied by cracking, isomerization, hydrogen transfer, and coke formation. The sequence of these reactions was partially elucidated by reacting propylene at varying contact times at 100 °C and by investigating the influence on the product distribution of the prior adsorption of tetralin on fresh catalyst. Attempts were made to define the nature and function of the active sites responsible for these reactions by using catalyst which had either been exchanged with sodium ions or had been treated with quinoline, perylene or ammonia. Two types of sites which are not readily interconverted were demonstrated, those with Bronsted acidity capable of undergoing base exchange and active in the polymerization of propylene, and those with Lewis acidity inactive for polymerization but promoting aromatization and coke-forming reactions together with saturation of olefins by hydrogen transfer.

Eyring transition-state theory and kinetics in catalysis

Abstract It is shown that for catalysis in general the kinetics of reactions can be discussed in terms of an extended Eyring rate equation which takes account of equilibria between free reactants and catalyst-reactant complexes as well as the equilibrium between complexed reactants and transition state. This extended equation, k exp = kT h·K ads ·K ≠ , where Kads incorporates all the complexation or Langmuir adsorption coefficients necessary is the basis of a novel understanding of the well-known compensation effect.

Remarkable alternating effect in metathesis copolymerization of norbornene and cyclopentene using modified Grubbs ruthenium initiators

Abstract High trans and mainly cis directing Grubbs Ru initiators, I–III, and IV, respectively have been investigated as catalysts for metathesis copolymerization of norbornene and cyclopentene. When the Lewis acid, MoCl5 or WCl6, is added to these Lewis bases initiators, I–III, a cage effect develops such that the polymers become alternating caused by the severe or almost total denial of access of norbornene to the propagating metallacarbenes. Addition of ethers destroys the cages and removes the effect. In marked contrast the N-heterocyclic ligand Grubbs initiator, IV, does not show the effect, as addition of MoCl5 only seems to retard the overall reaction, but does not change the copolymer composition.