Catalytic Deuterium-Exchange Reactions With Organics. XX. A π-Complex Mechanism for the Isomerization and Isotope Exchange of cis- and trans-Stilbenes on Platinum Catalysts

1965 ◽  
Vol 69 (10) ◽  
pp. 3526-3530 ◽  
Author(s):  
J. L. Garnett ◽  
W. A. Sollich-Baumgartner
Keyword(s):  
Isotope Exchange ◽  
Platinum Catalysts ◽  
Deuterium Exchange ◽  
Complex Mechanism ◽  
Exchange Reactions ◽  
Π Complex ◽  
Cis And Trans

Catalytic deuterium exchange reactions with organics. XXVII. The alkylbenzenes on self-activated Group VIII transition metals

1966 ◽  
Vol 19 (12) ◽  
pp. 2299 ◽  
Author(s):  
BD Fisher ◽  
JL Garnett
Keyword(s):  
Transition Metal Oxides ◽  
Exchange Process ◽  
Kinetic Studies ◽  
Platinum Oxide ◽  
Activation Process ◽  
Group Viii ◽  
Exchange Reactions ◽  
Π Complex ◽  
Cis And Trans ◽  
In Cis

Exchange reactions between heavy water and the alkylbenzenes have been investigated on the following self-activated Group VIII transition metal oxides: PtO2,2H2O; PdO; Rh2O3; IrO2,2H2O; RuO2,H2O; ReO2; and Ni2O3. All oxides except Ni2O3 are self-activated by benzene up to 180�. Order of ease of self-activation is Pt > Pd > Rh, Ru, Ir > Re > Ni. Trends in deuteration rates of the alkylbenzenes on self-activated platinum oxide are generally similar to those obtained on hydrogen prereduced platinum. At 130�, some differences in reactivity are observed and these are attributed to reagent displacement effects from the presence of small percentages of dimer (1%) associated with the self-activation process. Compared with hydrogen prereduced catalysts, significant differences in isotope orientation are observed with certain alkylbenzenes on self-activated catalysts. Multiple deuteration effects which are accentuated on self-activated catalysts have been used to confirm isotope orientation and also the participation of a π-complex mechanism for the exchange process. Isomerization and exchange in cis- and trans-stilbenes on self-activated platinum have also been interpreted by the dissociative n-complex substitution mechanism. The advantages of self-activated catalysts in general deuterium and tritium labelling work have been evaluated. Possible correlations between exchange results and electron spin resonance data for charge-transfer adsorption on the above oxides are discussed. Preliminary kinetic studies with self-activation are also reported.

Catalytic deuterium exchange reactions with organics. XII. Further studies in platinum catalyst preparation-the process of self-activation

1965 ◽  
Vol 18 (7) ◽  
pp. 993 ◽  
Author(s):  
JL Garnett ◽  
WA Sollich
Keyword(s):  
Active Sites ◽  
Catalyst Deactivation ◽  
Platinum Catalyst ◽  
Platinum Oxide ◽  
Deuterium Exchange ◽  
Hydrogen Gas ◽  
Distribution Data ◽  
Exchange Reactions ◽  
Π Complex ◽  
Distribution Studies

A new process for the activation of platinum oxide, termed self-activation, is described. This procedure involves the reduction of platinic oxide with an organic compound such as benzene, naphthalene, or n-octane. The potential of the resulting catalyst in deuterium exchange reactions has been evaluated with three characteristic organic compounds, n-octane, naphthalene, and benzene. A comparison has been made in the properties of prereduced catalysts prepared by a self-activation procedure and catalysts activated conventionally with hydrogen gas. For high-temperature exchange reactions ( >90�), the former catalysts are to be preferred since higher final activities of up to 300% may be achieved. The kinetics of self-activation suggest that catalyst deactivation by reagents may be due to modification of active sites. With aromatic compounds, it is proposed that this deactivation occurs through a π-complex interaction. Isotope distribution studies in the labelled benzenes indicate that self-activated, prereduced catalysts, by comparison with hydrogen-activated catalysts, exhibit relatively low M values in relation to their activities. Distribution data are consistent with the explanation that catalyst deactivation by benzene is a process involving the generation of new types of active sites which are more numerous but of lower activity than the original sites. Attempts to stabilize prereduced catalysts by chemical methods were unsuccessful.

Aromatic Hydrogen Isotope Exchange Reactions Catalyzed by Iridium Complexes in Aqueous Solution

1995 ◽  
Vol 48 (1) ◽  
pp. 79 ◽  
Author(s):  
CA Lukey ◽  
MA Long ◽  
JL Garnett
Keyword(s):  
Hydrogen Isotope ◽  
Isotope Exchange ◽  
Active Catalyst ◽  
Good Evidence ◽  
Ion Concentration ◽  
Iridium Complexes ◽  
Exchange Reactions ◽  
Hydrogen Ion Concentration ◽  
Hydrogen Isotope Exchange ◽  
Π Complex

Sodium hexachloroiridate (III) and sodium hexachloroiridate (IV) have been used as homogeneous catalysts for hydrogen isotope exchange between benzenoid compounds and water. The ideal solvent consisted of 50 mole % acetic acid/water, and the optimum temperature was found to be 160°C. Under these conditions the rate of incorporation of deuterium into benzene was significant (typically 15% D in 6 h), and reduction to iridium metal was minimized. The active catalytic species was identified as a solvated iridium(III) species, which is also postulated to be the active catalyst in solutions containing hexachloroiridate (IV). The kinetics of exchange in benzene catalysed by sodium hexachloroiridate (III) were elucidated, and found to be more complex than for the corresponding sodium tetrachloroplatinate (II) catalysed exchange, in that a two-term rate dependence was found for catalyst concentration and the reaction was inversely dependent on hydrogen ion concentration. The reaction was found to be independent of chloride ion concentration, this confirming that the active catalyst is a solvated species. Isotopic labelling in all compounds was confined to the aromatic ring, and most substituted benzenes exhibited deactivation of the ortho positions, indicating that a dissociative π-complex exchange mechanism was operating. This was confirmed by exchange into naphthalene, where it was found that labelling was predominantly in the β position. Facile exchange into nitrobenzene provided good evidence of homogeneous catalysis, and not catalysis by precipitated metal.

Deuterium Exchange Reactions with Substituted Aromatics. III. Heterocyclics and Polycyclic Hydrocarbons

1962 ◽  
Vol 15 (1) ◽  
pp. 56 ◽  
Author(s):  
JL Garnett ◽  
WA Sollich
Keyword(s):  
Adsorption Mechanism ◽  
Lone Pair ◽  
Deuterium Exchange ◽  
Catalyst Poisoning ◽  
Polycyclic Aromatics ◽  
Exchange Reactions ◽  
Aromatic Molecules ◽  
Π Complex ◽  
Additional Interaction ◽  
A Charge

Platinum-catalysed deuterium exchange reactions between heavy-water and polycyclic aromatics and heterocyclics have been investigated. The results confirm a charge-transfer-no-bond adsorption mechanism for catalytic chemisorption. Degree of catalyst poisoning increases with decreasing ionization potential for aromatic molecules of similar complexity, e.g., anthracene and phenanthrene. As the number of nodal planes in the bonding orbitals of the more complex polycyclic aromatics increases, a decrease is observed in catalyst poisoning. Exchange of pyridine is slower than benzene and this is attributed to an additional interaction of the pyridine molecule with the catalyst through its lone-pair of electrons. The reactivity of n-octane supports extension of the authors' π-complex chemisorption theory to molecules possessing only σ-electrons. Anisole, cyclohexane, nitrobenzene, cyclohexene, and phenyl cyanide exchange in an anomalous manner.

Catalytic deuterium exchange reactions with organics. LXXI. Homogeneous platinum catalysed deuteration of the long-chain alkylbenzenes. Relationship toalkane exchange

1974 ◽  
Vol 27 (5) ◽  
pp. 1033 ◽  
Author(s):  
JL Garnett ◽  
RS Kenyon
Keyword(s):  
Deuterium Exchange ◽  
Side Chain ◽  
Exchange Reactions ◽  
Degree Of Branching ◽  
Isotope Incorporation ◽  
Π Complex ◽  
Long Chain

The long-chain alkylbenzenes out to nonylbenzene have been exchanged with D2O in the presence of homogeneous platinum, deuteration occurring in both ring and side chain. ortho-Deactivation in the ring is observed, consistent with a mechanism involving a π-dissociative process. Total isotope incorporation in a particular compound decreases with increase in length and degree of branching of the side chain. In the side chain α and terminal positions deuterata predominantly, degree of isotope incorporation in these positions decreasing gradually down the series to nonylbenzene. For butylbenzene and higher homologues, deuteration of methylene positions is low. Orientation of isotope in the side chain of l',l?-dimethylpropylbenzene is unique and is used as a basis for a novel terminal abstraction π-complex (TAPC) mechanism proposed to explain terminal exchange in the alkylbenzenes. Concepts involving 'inner' and 'outer' π-complexes are shown to be of value in discussing mechanisms of exchange in other positions of these compounds. The data may be related to mechanisms for simple alkane exchange using this same catalyst.

scholarly journals Are rate and selectivity correlated in iridium-catalysed hydrogen isotope exchange reactions?

2021 ◽  
Author(s):  
Daria S. Timofeeva ◽  
David M Lindsay ◽  
W. J. Kerr ◽  
David James Nelson
Keyword(s):  
Functional Groups ◽  
Hydrogen Isotope ◽  
Isotope Exchange ◽  
Reaction Rate ◽  
Exchange Reactions ◽  
Reaction Selectivity ◽  
Hydrogen Isotope Exchange ◽  
The Relationship

Herein we examine the relationship between reaction rate and reaction selectivity in iridium-catalysed hydrogen isotope exchange (HIE) reactions directed by Lewis basic functional groups. We have recently develped a directing...

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