|
SUMMARIES OF FY 1996
RESEARCH IN THE CHEMICAL
SCIENCES |
Chemical Energy:
Offsite Projects
University of Arizona
Tucson, AZ 85721
Department of Chemistry
A Model Approach to Hydrodenitrogenation Catalysis
Despite the importance of removing nitrogen from petroleum feedstocks to providing more
processable and environmentally sound fuels, the mechanisms of metal-catalyzed,
hydrodenitrogenation (HDN) reactions are not well understood. We are continuing studies of
soluble model compounds that mimic HDN substrate-catalyst interactions and demonstrate
purported HDN reactions. Our primary focus is on the six-membered heterocyclic compounds
such as pyridine and its derivatives. Recent studies allow us to support the following conclusions:
1. The 
2(N,C) binding
mode renders a pyridine ligand susceptible to nucleophilic attack and results in C-N bond
cleavage. 2. The overall reaction between an 2(N,C) pyridine complex and an attacking nucleophile can be
partitioned into two stages: nucleophilic attack at the metal center followed by ligand migration to
the 2 ligand. 3. In our
model system, ligand migration is rate-limiting and the ligand migrates to the substrate as a 
nucleophile. 4. The C-N bond scission
appears to be driven by the formation of a strong metal-nitrogen multiple bond and made possible
by the reduction in pyridine C-N bond order that arises from 2 coordination. 5. Carbon-carbon bond scissions of a
ring-opened pyridine ligand are possible at the same metal site when the pyridine is highly
substituted. 6. Although the first step of quinoline HDN involves hydrogenation to
tetrahydroquinoline, tetrahydroquinoline has not been induced to bind in the 2(N,C) mode. These results offer
new, significant insight into HDN related processes, including the manner by which nitrogen
heterocycles may be further degraded after C-N bond cleavage.
Boston College
Chestnut Hill, MA 02167
Department of Chemistry
High-Temperature Chemistry of Aromatic Hydrocarbons
This work focuses on the fundamental molecular processes involved in the rearrangements and
interconversions of polycyclic aromatic hydrocarbons (PAHs) under conditions of thermal
activation. PAH ring systems figure prominently in the molecular architecture of coal, but prior to
this systematic program of study, little was known about the chemical transformations that PAHs
undergo at high temperatures, such as those employed in the uncatalyzed gasification and
liquefaction of coal. This year several additional examples of fullerene fragment formation from
bay region PAH at high temperatures have been discovered, e.g., the production of
cyclopent[cd]fluoranthene from benz[a]anthracene, dicyclopenta[cd,fg]pyrene from
benz[e]pyrene, inter alia. The possible intermediacy of bay region diradicals in such processes is
supported by the generation of pyracylene from cyclopent[def]phenanthrenone by
decarbonylation-rearrangement. Isotopic labelling experiments with
13C2-picene further support our proposed unified mechanism for
high temperature transformations of this type. The spectacular triple cyclodehydrogenation of
decacyclene to triacenaphthotriphenylene, a 36-carbon bowl-shaped fullerene fragment, has also
been observed at 1200-1300 °C. The long-range objectives of this research are to uncover all
the principal reaction channels available to PAHs at high temperatures and to establish the factors
that determine which channels will be followed in varying circumstances.
California Institute of Technology
Pasadena, CA 91125
Department of Chemistry
Synthetic and Mechanistic Investigations of Olefin Polymerization Catalyzed by Early
Transition Metal Compounds
The objectives of this research program are (1) to discover new types of chemical transformations
between hydrocarbons and transition-metal compounds; (2) to investigate their mechanisms; and
(3) to explore the possibilities of coupling these transformations with others to catalyze chemical
reactions for the preparation of fuels, commodity chemicals, and polymeric materials. A current
focus is the catalytic polymerization of olefins. Ziegler-Natta catalysis is a well-established and
commercially very important process; however, it is clear that new (and superior) polymers with
different microstructures and new homo-block copolymers could be made from the same readily
available monomers if sufficient control over the catalytic process could be achieved.
C2-symmetric yttrocene derivatives with linked cycopentadienyl ligands have
been prepared. The alkyl and hydride derivatives function as well-defined, single component,
isospecific alpha olefin polymerization catalysts well suited to mechanistic investigations. A ligand
capable of affording only one enantiomer of a chiral catalyst has been synthesized. The absolute
facial preferences for olefin insertion into Y-H and Y-C bonds has been established for a chiral,
highly deuterated olefin using NMR methods. Recently a new class of zirconocene catalysts have
been developed that produce highly syndiotactic poly alpha-olefins. A modified version allows the
preparation of polypropylenes with tacticities varying from isotactic to syndiotactic.
University of California, Davis
Davis, CA 95616
Department of Chemical Engineering
Effects of Supports on Metal Complexes and Clusters: Structure and Catalysis
The research is a fundamental investigation of the effects of supports on the structure and
catalytic properties of metal complexes and clusters. The metals are Rh and Ir. The supports are
MgO, 
-Al2O3, and zeolite LTL. The former are
used as high-area powders and as ultrathin layers on metal single crystals. Like the oxides, the
zeolite is basic, incorporating K+ and Ba2+ exchange ions. With
precursors such as [Ir(CO)2(acac)], metal subcarbonyls such as
[Ir(CO)3(OMg)3] are formed (where the braces around MgO
denote groups terminating the MgO). With precursors such as
[HIr4(CO)11]- and
[Ir6(CO)15]2-, supported clusters such as
Ir4 and Ir6 are formed. The supported species are being
characterized structurally with IR, EXAFS, and NMR spectroscopies, TPD, H2
chemisorption, and imaging methods. The samples are being tested as catalysts for ethylene
hydroformylation toluene hydrogenation, and n-butane hydrogenolysis. The goals are to
determine how the support structure and composition affect the structure of the well-defined
supported metal complexes and clusters and their reactivities and catalytic properties. For
example, tetrairidium clusters on MgO were oxidized to give iridium oxide clusters of nearly 4
atoms each, and these were reduced in H2 to give back Ir4. These
latter clusters on MgO catalyze toluene hydrogenation, and the catalytic reaction rate depends
only modestly on the MgO surface hydroxyl content.
University of California, Irvine
Irvine, CA 92697-2025
Department of Chemistry
Synthesis and Chemistry of Yttrium and Lanthanide Metal Complexes
| Investigator(s) |
Evans, W.J.
|
$127,381 |
| Phone | 714-824-5174 |
| E-mail |
wevans@uci.edu |
The purpose of this project is to study the chemistry of complexes of yttrium and the lanthanide
metals, a series of 15 metals readily available in the United States, so that the special properties of
these metals can be utilized in energy-saving optical and magnetic materials and in the catalysis of
conversions of abundant low-value substrates such as CO and CO2 into more
useful chemicals. To achieve this goal, more information is needed on ligands which solubilize the
metals as complexes, which allow full characterization of the chemistry, and which are compatible
with the practical applications. Alkoxide and aryloxide ligands have been found to be effective in
making polymetallic complexes including soluble manipulatible complexes which have interior
structures similar to metal oxides. The nitrogen analogs of aryloxides, arylamido ligands, have
also been found to be valuble ligands for these metals providing a wide range of structural types.
Investigation of "dehydrated" CeCl3 extensively used in organic
synthesis for its unique reactivity in alkylations as CeCl3/RLi has shown that this
ligand system is not as simple as previously assumed. The "dehydrated" material is
actually [CeCl3(H2O)(THF)]n , a fact which
requires reevaluation of reaction mechanisms for this popular reagent.
University of California, Riverside
Riverside, CA 92521
Department of Chemistry
Study of the Surface Chemistry of Hydrocarbon Radicals and of Carbonium Ions on Metal
Oxide Surfaces
This project focus on the development of two separate directions related to the characterization of
the surface chemistry of hydrocarbons on metal oxide surfaces. In the first, the oxidation of nickel
surfaces to form thin nickel oxide films spectroscopies is been investigated. In particular, the
effect of argon ion bombardment on the oxidation of nickel films was studied by using X-ray
photoelectron spectroscopy (XPS). In the absence of any ion beams, exposure of nickel surfaces
to an oxygen atmosphere leads to the moderately rapid formation of a thin (3-5 monolayers thick)
nickel oxide overlayer. At room temperature the oxygen uptake stops once this limit is reached,
but at higher temperatures the slow growth of a thicker oxide is seen. The diffusion coefficient for
oxygen through the forming NiO film was determined to be on the order of
2x10-18 cm2/s at 625 K. The simultaneous impingement of argon
ions on the surface during oxygen exposures was found to enhance the oxidation process. Indeed,
ion beam current densities as low as 0.01 µA/cm2 were found to be
sufficient to induce nickel oxidation past the 3-5 ML limit even at room temperature.
The oxidation rate was found to be roughly proportional both to the ion flux and to the square of
the oxygen pressure. The build-up of a NiO film during this Ar+-ion/oxygen
treatment was also found to slow down at higher temperatures, presumably because of the
combined effect of a higher probability for desorption of molecular oxygen from the surface and a
higher atomic oxygen mobility into the bulk. The oxide films prepared at low temperatures appear
to be quite disordered, and display an extra feature in the Ni 2p XPS spectra around 853.2 eV
which could be assigned to partially reduced nickel. Annealing of those films to temperatures
above 400 K leads to the possible ordering of the surface and to the disappearance of the signal
for the Ni+x species in the XPS, and further heating above 600 K leads to the
diffusion of oxygen atoms into the bulk and to the partial reduction of the surface nickel to its
metallic state. Finally, the presence of water in the gas phase during the nickel Ar ions/oxygen
treatment was seen to result in the production of a surface hydroxyl layer, the same as when the
oxidation is carried out in the absence of ion excitation. The second direction of this project has
been to study the conversion of alkyl groups chemisorbed on the oxide surfaces prepared as
described above. On clean nickel surfaces, alkyl species decompose via a combination of
beta-hydride and reductive elimination steps to yield a mixture of alkanes and alkenes.
On the other hand, most of the surface reactivity is inhibited by the presence of surface oxygen,
and only the products of total oxidation reactions, namely, CO, CO2 and
H2O, desorb from fully oxidized surfaces under vacuum. The interesting aspect of
this research is the fact that formation of acetone, a partial oxidation product, was observed for
the reaction of 2-propyl iodide with low oxygen precoverages. The desorption temperature of that
partial oxidation reaction, when compared to the desorption of acetone from Ni(100), suggests
that its formation is reaction limited. The experimental results obtained so far suggest that alkyl
halides adsorb and dissociate on the nickel atoms first, forming the desired alkyl groups. At
slightly higher temperatures, around 200 K, most of those moieties undergo the beta-hydride and
reductive elimination reactions to alkenes and alkanes, respectively, typical of the metallic
function, but a small fraction migrates to the oxygen functionality and to form alkoxy groups,
which then dehydrogenate above 300 K to produce the ketone.
University of California, Santa Barbara
Santa Barbara, CA 93106
Department of Chemical and Nuclear Engineering
Alkane Activation and Reactivity on Iridium, Platinum, and Ruthenium Surfaces
The research objective is to quantify alkane activation on various transition metal surfaces
including Ir(110) and Ir(111). We have employed molecular beam techniques to investigate the
molecular trapping and trapping-mediated dissociative chemisorption of perhydrido- and
perdeutero-ethane and propane, as well as c-C3H6 on Ir(110) at
low beam translational energies, Ei 
5 kcal/mol, and surface temperatures, TS, from 85 to
1200 K. In each of these cases, the cleavage of C-H (C-D) bonds through the trapping-mediated
mechanism is unactivated with respect to a gas-phase energy zero, i.e., the activation energy for
reaction from the physically adsorbed state, Er, is less than the activation energy
for desorption, Ed, from this state. We have also measured the initial adsorption
probability of CH4 and CD4 on Ir(111) under both low pressure
(< 10-3 Torr) and high pressure (1 Torr) conditions. Under low pressure
conditions trapping-mediated chemisorption is the dominant mechanism of methane dissociation
with activation energies of 16.0 and 17.0 kcal/mol for CH4 and
CD4. By diluting the methane in argon at a total pressure of 1 Torr, we have also
examined the direct activation of methane. Under these conditions the translational energy of the
methane is characterized by a Maxwell-Boltzmann distribution at the surface temperature. For
this case the apparent activation energies of methane activation are 17.0 kcal/mol for
CH4 and 17.9 kcal/mol for CD4. For both CH4
and CD4, the rate of reaction is greater for the high pressure experiments than the
low pressure experiments.
University of California, Santa Barbara
Santa Barbara, CA 93106
Department of Chemistry
Studies Relevant to the Catalytic Activation of Carbon Monoxide
This research is concerned with quantitative investigations of fundamental reactions relevant to
the catalytic activation of carbon monoxide and other C1 compounds. New
carbonylation catalysts based on rhodium(III) heterogenized on polyvinyl pyridine polymers have
been developed and these are active in Reppe type hydroformylation and hydrogenation of
alkenes. In addition, exploratory studies have been carried out to use sodium formate as the
reductant in the catalytic reduction of chlorinated organic compounds. Time resolved spectral
techniques have been used to prepare and to investigate the spectra and dynamics of
organometallic intermediates relevant to the activation of hydrocarbon C-H bonds and to
formation of carbon-carbon bonds via CO migratory insertion into metal-alkyl bonds. The latter is
the key reaction in the carbonylations of various organic substrates. The goals are to delineate the
quantitative details of these fundamental processes, to understand chemical principles relevant to
the activity and selectivity of molecular catalysts for activating hydrocarbons and
C1 compounds such as CO, and to define guidelines for designing new,
environmentally friendly and more efficient applications of energy and chemical feedstocks.
Carnegie-Mellon University
Pittsburgh, PA 15213
Department of Chemical Engineering
H2SO4-Modified ZrO2 and
ZrO2/SiO2 Aerogels as Solid Superacids
Manipulation of sulfate content, silica content, and activation temperature provided the means for
controlling the strength of surface Brønsted acid sites in the zirconia-silica-sulfate system. This
approach allowed the development of an acid strength hierarchy, based on the adsorption of
pyridine and isomerization of 1-butene and n-butane, as a rational basis for acid catalyst design.
Introduction of silica into zirconia-sulfate co-gels also provided insight into the activation
behavior of this important class of materials. Silica retarded sintering upon heat treatment, thereby
delaying crystallization of zirconia to higher temperatures. Activation of sulfate to a form capable
of catalyzing the isomerization of n-butane was also delayed to higher heat treatment
temperatures, confirming the role of crystallization in initiating the activation sequence.
Colorado State University
Fort Collins, CO 80523
Department of Chemistry
Polyoxoanion-Stabilized Transition Metal Nanoclusters: Soluble Analogs of Heterogeneous
Catalysts
The first examples of a new type of metal-particle catalyst, polyoxoanion and
Bu4N+-stabilized transition-metal nanoclusters, were discovered recently under
our DOE grant support. Presently, the following knowledge is being gathered, information
necessary to construct a paradigm covering their catalytic applications: an understanding of what
gives rise to their stabilization and isolability, an understanding of how this stabilization can be
enhanced to generate higher temperature-stable nanocluster catalysts, and an understanding of the
nanocluster's catalytic reactions and their underlying mechanisms. Ultimately, our goal is a full
understanding of the strengths and weaknesses of this exciting new subclass of soluble
metal-particle catalysts.
Colorado State University
Fort Collins, CO 80523
Department of Chemistry
Diosmacycloalkanes as Models for the Formation of Hydrocarbons from Surface
Methylenes
Protonation of mono- and dinuclear dialkyl and olefin osmium complexes gives cationic alkyl,
alkylidene, and olefin complexes. In the case of
Os(CO)4(C2H4), both the kinetic and
thermodynamic sites of protonation are Os, but C2H4 inserts into
the Os-H bond in the presence of as weak a coordinating ligand as Et2O. We
have examined the reactivities of these cationic Os complexes toward olefins, alkynes, and CO,
and have found insertion reactions but no utility as polymerization catalysts. In collaboration with
Elliott Burnell of the U. of British Columbia, we have rethought our analysis of the structure of
the parent diosmacyclobutane from nematic phase NMR data. We have prepared
diosmacyclobutanes from strained olefins such as norbornene and cyclobutene. We will now
assess (1) the effect of ring strain on the relative binding affinities and (2) the potential for strained
diosmacyclobutanes to cleave C-C and Os-Os bonds to form tethered alkylidene complexes:
(CO)4Os=CHR-RHC=Os(CO)4.
University of Colorado
Boulder, CO 80309
Department of Chemistry and Biochemistry
Syntheses and Reactions of Pyrrole and Indole Complexes
The objectives of the project are (1) to synthesize new transition metal pyrrole and indole
complexes and (2) to investigate how the metal ion coordination affects the reactivity of the
heterocycle. An understanding of how coordinated heterocycles might be activated toward
reduction, ring opening, or nucleophilic addition reactions may provide a basis for understanding
basic mechanisms of the hydrodenitrogenation catalysts. A series of new 5 pyrrolyl complexes of
ruthenium(II) have been synthesized, and the heterocyclic ligand was found to be activated
toward nucleophilic substitution reactions at the alpha carbon atom. Reactions with alkyl and aryl
lithium reagents and with amide nuleophiles led to the preparation of new derivatives with
substituted pyrrolyl ligands. 2,5-Disubstituted pyrroylyl ligands have also been prepared in some
cases. The new pyrrole ligands can be readily displaced from the ruthenium ion by protonation
reactions, and the free ligands have been isolated. The results demonstrate that these reactions
have potential useful applications for the preparation of new substituted pyrrole rings. In a related
project 5-tetramethylpyrrole, 6-indole, 6-indolyl, and 6-indoline complexes of pentamethylcyclopentadienyl Ir(III) have
been synthesized. Reactions of these complexes with nucleophiles and reducing agents have been
studied. For example, [(5-HNC4Me4)Ir(C5Me5)](OTf)2, 1, undergoes a quasi-reversible
two-electron reduction at - 1.34 V vs Fc. Reaction of 1 with a hydride donor resulted in
a reduced Ir(I) product in which nucleophilic hydride addition to the Cp* ligand had occurred. In
contrast reactions of the indole and indoline complexes with nucleophiles resulted in attack on the
carbocyclic ring of the heterocycle. Further studies of these systems are in progress.
Columbia University
New York, NY 10027
Department of Chemistry
Model Studies in Hydrocarbon Oxidation
The research performed during the last grant period has continued with an investigation of the
chemistry of molecular terminal chalcogenido complexes. By studying the chemistry of a series of
complexes with M=O, M=S, M=Se, and M=Te bonds, it is hoped that this research will provide
results that are relevant to systems concerned with both hydrocarbon oxidation and
hydrodesulfurization processes. For example, we have synthesized the first series of oxo, sulfido,
selenido, and tellurido derivatives of hafnium Cp
2Hf(E)(NC5H5)
(E=O, S, Se, Te), and the first mononuclear telluroformaldehyde complex of tantalum
Cp*2Ta(2-TeCH2)H. Studies on these complexes have
revealed interesting differences in the chemistry of the systems as a function of the chalcogen. For
example, coupling and cleavage reactions play an active role in a variety of important
transformations. However, in spite of the potential importance of reactions involving the
interconversion of [M](E)2 and [M](2-E2) moieties, relatively few well-characterized
examples of such transformations have been described. Significantly, we have reported the first
examples of such transformations for tellurium, thereby suggesting that such reactions are more
facile for tellurium than its lighter congeners. We have also compared the ability of molybdenum
and tungsten centers to activate C-H bonds and have demonstrated that the
hexakis(trimethylphosphine)molybdenum complex only forms aryloxy-hydride complexes in its
reactions with phenols, whereas the corresponding tungsten complex undergoes intramolecular
C-H bond activation. Nevertheless, although C-H bond activation by the molybdenum center is
thermodynamically unfavored, magnetization transfer studies demonstrate that it is kinetically
capable of such reactions.
University of Connecticut
Storrs, CT 06269
Department of Chemistry
Synthetic Todorokite: Preparation, Characterization, and Applications
The goals of this project are to prepare new octahedral molecular sieve (OMS) and octahedral
layer (OL) materials by several methods including sol-gel, reflux, autoclave methods; to prepare
and characterize isomorphously substituted OMS and OL materials; to develop new
characterization methods for OMS and OL systems such as diffuse reflectance UV-visible
spectroscopy; and to optimize catalytic properties of OMS and OL for dehydrogenation of
alkanes to terminal olefins and oxidation of alkanes to terminal alcohols. Materials with transition
metals substituted into framework or tunnel sites of OMS and OL have been prepared.
Characterization of such systems will be done with a variety of methods in order to study
structural, compositional, surface, electronic, electrical, morphological, thermal, magnetic,
electron transfer, redox, and catalytic properties. Characterization of changes in the OMS and OL
catalysts during reaction are being studied. Some reactions of interest are oxidative
dehydrogenation of cyclohexane, decomposition of hydrogen peroxide, and styrene formation.
University of Delaware
Newark, DE 19716
Center for Catalytic Science and Technology
Synthetic Reactions of Oxametallacycles and Related Intermediates on Transition Metal
Surfaces
The goal of this research is to identify the requirements for and competition between activation of
C-H, C-C, and C-O bonds in the synthesis and decomposition of oxygenates on transition metal
surfaces. Current research is focused on surface oxametallacycle chemistry. These intermediates
are implicated in a variety of reactions in homogeneous catalysis, heterogeneous catalysis and
surface science, including epoxide synthesis and carbonylation and decarbonylation processes.
However, spectroscopic evidence for oxametallacycles is generally lacking and the patterns of
reactivity of these intermediates are not well established. We are employing both experimental
techniques (Temperature Programmed Desorption, High Resolution Electron Energy Loss
Spectroscopy, and X-ray Photoelectron Spectroscopy) and theoretical methods (Density
Functional Theory) in these studies. A primary goal is to demonstrate the synthesis of surface
oxametallacycles, and thus to determine the factors which control their formation and the
selectivity of their reactions, and to identify new reactions with ramifications for catalysis. Our
research has produced the first evidence for the participation of oxametallacycles in higher alcohol
chemistry on certain transition metal surfaces, and most recently it has produced the first evidence
both for stable oxametallacycle formation and for novel cyclization chemistry of these
intermediates. This work holds the potential of establishing new principles for surface organic
syntheses, of discovering new chemistry, and thus of providing guidance for the development of
new catalysts and processes for oxygenate synthesis.
University of Delaware
Newark, DE 19716
Department of Chemistry and Biochemistry
Oxidation Catalysis with Tris(pyrazolyl)borate Metal Complexes
This project involves the development of catalysts for the oxidation of organic substrates using
dioxygen as the source of the oxygen. In particular, the approach involves coordination and
symmetric cleavage of the O2 molecule into two reactive metal-oxo moieties by
hindered tris(pyrazolyl)borate complexes of late transition metals. The feasibility of this scheme
has been previously demonstrated using a set of cobalt complexes. In the initial phase of the
research the mechanism of the cobalt mediated stoichiometric reaction will be elucidated in detail,
and some reactions of the cobalt system [Tpt-Bu,MeCo,
Tpt-Bu,Me = hydridotris(3-t-butyl-5-methylpyrazolyl)borate] related to oxidation
catalysis will be investigated. Building on this, the metal complexes will be modified to facilitate
catalytic turnover. To this end the ligands must be "hardened" against oxidative
degradation. This will be done by appropriate substitution of the ligand and/or the metal. In the
long term, catalytic oxidations of various substrates as well as the design of ligands for regio- and
stereo-selective oxidations will be investigated.
University of Florida
Gainesville, FL 32611
Department of Chemistry
Bimetallic Complexes as Methanol Oxidation Catalysts
The project involves preparation of bimetallic Pt/Ru and Pt/Mo complexes as catalysts for the
electrooxidation of methanol. The currently accepted mechanisms for methanol oxidation at Pt/Ru
anodes involve C-H activation at Pt and "active oxygen transfer" from Ru. Since
these reactions are known individually for mononuclear complexes, the catalysts are designed to
mimic the anode behavior. Design features of the complexes include bridging ligands such as
1,10-phenanthrolinedione or bidentate phosphines to prevent dissociation of the metal centers,
low-valent starting materials that allow a series of oxidation states for each metal to be generated
during oxidation studies, and incorporation of ligands that are relevant to the methanol oxidation
process. Both chemical and electrochemical oxidation of the complexes are being examined and
reaction of the oxidized species with methanol is being investigated. The complexes whose
solution electrochemistry is most promising for methanol oxidation will be deposited on
electrodes for studies of electrocatalysis under the aqueous conditions found in direct methanol
fuel cells.
Harvard University
Cambridge, MA 02138
Department of Chemistry
Model Microcrystalline Mixed-Metal Oxides for Partial Oxidation and Desulfurization
The broad objective of this proposal is to investigate how the constituents of bimetallic materials
function in important catalytic processes. We are currently investigating the activity of mixed Co-S
and Co-O phases supported on Mo(110) for hydrocarbon oxidation, deoxygenation and
desulfurization. A general method for synthesizing small (~100 angstroms) metal clusters on
Mo(110) has been devised, allowing us to compare the chemistry of small particles to that of uniform
films. The reactivity of the small Co clusters is substantially different than a uniform monolayer.
For example, methanol does not react on the Co clusters whereas it decomposes to CO and
dihydrogen on the uniform monolayer at ~375 K. Currently, the reactions of methyl radicals with
adsorbed oxygen and hydroxyl are being investigated on the uniform phases and Co clusters with
the goal of synthesizing methanol. Scanning tunneling microscopy and theoretical studies are
planned to develop an understanding of the contributions of geometric and electronic structure
effects in determining the reactivity differences. These studies have broad significance in that they
serve as a test of aspects of the cluster-surface analogy and may provide a means of manipulating
product distributions in catalytic processes via variation in particle sizes.
University of Illinois at Urbana-Champaign
Urbana, IL 61801
School of Chemical Sciences
Electron Transfer Activation of Coordinated Thiophene
The presence of organic sulfur compounds in fossil fuels poses very serious environmental and
engineering challenges. The most effective method for addressing these problems is through the
hydrodesulfurization (HDS) process whereby the sulfur is removed by hydrogenolysis of C-S
bonds in the fossil fuel matrix. The project objectives are threefold: (1) elucidate mechanisms for
metal-catalyzed HDS, (2) develop new methods for desulfurization of fossil fuels, and (3) develop
new uses for organosulfur components of fossil fuels. Most of these studies employ thiophenes as
representative substrates. Experiments focus on HDS pathways that involve electron transfer to a
metal-thiophene ensemble followed by protonation, i.e., heterolytic hydrogen activation. The
stereochemistry and energetics for individual steps are examined for model systems based on
ruthenium complexes. New desulfurization methods and new uses for the organosulfur
components in fossil fuels are developed through the addition of nucleophiles to metal thiophene
ensembles.
Indiana University
Bloomington, IN 47405
Department of Chemistry
Chemical Principles Relevant to Materials Precursor Design and Synthesis
The project objective is to determine, by a series of case studies, which chemical routes are
particularly facile for the conversion of mixed-metal alkoxides to solid-state oxide materials. The
transformation from molecule to infinite lattice solid will be effected by thermolysis, hydrolysis,
and plasma treatment. The groups L to be considered include simple hydrocarbon-derived
alkoxides, heavily fluorinated alkoxides, and vicinal diolates. These are chosen to incorporate
progressively more complex chemical features, each of whose typical reaction patterns are
well-established. Chemically-facile routes are expected in certain cases because elimination of
known neutral organic molecules can be envisioned. Such "weak" bonds will cause
the precursor-to-product process to occur under very mild conditions. This research involves
establishing whether such expectation will be realized under CVD processing conditions.
Incorporation of mobile protons will also be considered as a "trigger" for precursor
processing at especially low temperatures. In every case, mechanistically diagnostic experiments
will be executed in order to allow generalization of these results to make more rational the design
of effective molecular precursors to technologically-valuable solid materials.
Indiana University
Bloomington, IN 47405
Department of Chemistry
Alkoxide Ligands in Organometallic Chemistry and Catalysis
Alkoxide and related aryloxide and siloxide ligands are hard 
-donor ligands and complement the now traditional soft -acceptor ligands such as tertiary phosphines, carbonyls and -hydrocarbyl ligands. We are using the former with
hard metals such as early transition elements, lanthanides and group 2 and 3 main group elements
as ancillary ligands for the development of a new field of organometallic chemistry. Current areas
of research include (i) the development of selective hydrogenation catalysts for conjugated dienes
employing W2(OR)6 compounds; (ii) the use of bidentate and tridentate diols and triols to impose
specific coordination geometries at the metal atoms; (iii) studies of opening of sulfur, nitrogen and
oxygen containing aromatic rings as models for steps in HDS, HDN and HDO catalysis and (iv)
the development of single site metal alkoxide catalysts for the ring-opening of epoxides and
strained cyclic esters.
Indiana University
Bloomington, IN 47405
Department of Chemistry
A Model Approach to Vanadium Involvement in Crude Oil Refining
The project is directed toward characterizing the initial fate of crude oil vanadyl impurities under
the reducing and sulfur-rich conditions of industrial hydrodemetallation (HDM) and
hydrodesulfurization (HDS) processes. The impurities are ultimately converted to insoluble
vanadium sulfides (primarily V2S3 and
V3S4), which lower the activity of, and eventually poison, the
Mo heterogeneous catalyst. Recent work has concentrated on detailed characterization of various
V/S clusters that represent models for intermediate stages of V sulfide polymer growth. A number
of di- and trinuclear species have ben prepared and studied by a range of techniques, including
x-ray crystallography, VT magnetic susceptibility measurements, VT 1H NMR
studies, and EHT MO calculations. Selected complexes under study include
[V3Cl6(SCH2CH2S)3]3-,
[V2(SCH2CH2S)4]z- (z=1 or 2) and [VxOy(pyt)z]
(pyt=pyridine-2-thiolate), which represent models of small V species adsorbed on the surface of
the growing V2S3/V3S4 phases.
The V/pyt complexes have been investigated by EI mass spectrometry, the observed MS
fragmentation patterns (C-S and C-N bond cleavage) being employed as a model system for the
fragmentation pathways of organovanadium impurities during the high temperature conditions of
crude oil refining. The work has most recently been extended to include a variety of
V/O/carboxylate clusters; the latter organic functionality is common in crude oils. A number of
tetranuclear and pentanuclear species have been prepared and characterized by crystallographic
and physical methods, including magnetochemistry. Aggregation methodology has been
developed for the stepwise conversion of mononuclear vanadyl species to penta-, ennea-, and
pentadecanuclear products, and all these species have undergone detailed characterization. The
reaction of such species with H2S is also being investigated as a model system
for V sulfide polymer formation under refining conditions.
University of Iowa
Iowa City, IA 52242
Department of Chemistry
Synthesis and Chemistry of Cationic d0 Metal Alkyl Complexes
The objective of this research is to design and synthesize new types of electrophilic organometallic
complexes for use in fundamental studies of olefin polymerization and C-H activation chemistry,
and for exploitation in catalysis. Earlier studies of Cpp2Zr(R)(L)+
complexes identified the key features required for high insertion reactivity in early metal systems:
an electrophilic metal center, a do metal electron configuration, and one or more
vacant (or virtual) coordination sites cis to the M-R ligand. Current work is directed to the
development of new classes of cationic early metal alkyls, which incorporate these features in
non-Cp2M ligand environments. A series of Zr and Hf alkyl complexes
(N4-macrocyle)M(R)2 (R = CH3,
CH2Ph, CH2SiMe3) containing dianionic
tetra-aza macrocycles (N4-macrocycle = Me8-taa,
Me4-taen) in place of Cp ligands has been prepared. The pockets of these
macrocycles are too small to accommodate the large group 4 metal ions, so the metal sits out of
the N4-plane and cis structures are imposed. Base-stabilized cations
[cis-(N4-macrocycle)M(R)(L)][BPh4] (L = THF, RCN,
PMe2Ph), and base-free cationic systems
[(N4-macrocycle)M(R)][B(C6F5)4], have been prepared by protonolysis routes. The base-free systems are moderately active
ethylene polymerization catalysts. One example,
(Me8-taa)Hf(CH3)+, also undergoes clean single insertion of
vinyltrimethylsilane, and clean double insertion of dimethylacetylene. Ortho C-H activation of
2-methylpyridine and vinyl C-H activation of 2-vinylpyridine have also been observed with these
cationic systems. Cationic alkyls based on tetradentate Schiff base ligands, e.g.,
(F6-acen)Zr(R)+, have been prepared more recently. These systems are active
olefin polymerization catalysts in the presence of AIR3 cocatalysts. Chiral
analogues catalyze the stereoselective polymerization of propylene to isotactic polypropylene.
Current efforts are focused on more highly electron-withdrawing chelating ligands, which should
maximize the electrophilicity of the metal center in these systems and thus increase reactivity.
Additionally, studies of other ligand systems, including bidentate O,N donors and chiral chelating
bis-amide ligands are being pursued.
Kansas State University
Manhattan, KS 66506
Department of Chemistry
Homogeneous Models of Ammoxidation Catalysis
| Investigator(s) |
Maatta, E.
|
$121,587 |
| Phone | 913-532-6687 |
| E-mail |
eam@ksu.ksu.edu |
We continue to exploit the discoveries of simple and efficient routes to a wide variety of
organoimido-substituted derivatives of the hexamolybdate cluster,
[Mo6O19]2-. Since the hexamolybdate displays
an MoO6 coordination environment conspicuously similar to that within the
ammoxidation catalyst component MoO3, attention has focused on the
preparation of benzyl- and allylimido-hexamolybdates, which would represent the closest
approximation yet available of purported ammoxidation surface species. Reaction of the
hexamolybdate with the benzylimido delivery reagent
Ph3P=NCH2Ph in acetonitrile in fact yields benzonitrile in 37%
yield, presumably through the intermediacy of the benzylimido hexamolybdate
[Mo6O18(NCH2Ph)]2-, thus
providing the first example of a functional ammoxidation mimic. This reaction also produces a
substantial amount (34%) of PhCH=NCH2Ph; this product derives from reaction
of benzyl amine, which itself arises as a result of unwanted hydrolysis of the benzylimido ligand.
The intermediates in this ammoxidation mimicry are being sought and attempts are underway to
transfer this chemistry into solvents which can be dried more efficiently.
Lehigh University
Bethlehem, PA 18015
Department of Chemical Engineering
Molecular Structures and Reactivity of Mixed Metal Oxide Monolayer Catalysts
| Investigator(s) |
Wachs, I.E.
|
$183,000 |
| Phone | 610-758-4274 |
| E-mail |
iew0@Lehigh.EDU |
Metal oxide monolayer catalysts, supported metal oxide catalysts possessing the active metal
oxide components as a surface phase, find extensive applications in the energy industries of
petroleum refining, pollution control from power generation plants, and automotive pollution
control. To help bridge the knowledge gap between model and industrial metal oxide monolayer
catalysts, a fundamental research program will address the relationships between the molecular
structures and surface acidity and the molecular structures and surface redox chemistry of mixed
metal oxide monolayer catalysts. For the fundamental surface acidity portion of the research
program the alumina-supported tungsten oxide system will be the focus of the investigation, and
for the fundamental surface redox chemistry portion of the research program the
alumina-supported vanadium oxide system will be the focus. The influence of secondary metal
oxides upon the molecular structures and reactivity of these systems will be investigated. The
molecular structures will be primarily determined with in situ Raman spectroscopy, but
complementary structural spectroscopies (solid state nuclear magnetic resonance (NMR) and
extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure
(XANES)) will also be applied. The surface chemistry will be probed by surface acidity and
surface redox measurements. This fundamental information should allow better understanding of
the synergistic interactions that occur in mixed surface metal oxides.
Lehigh University
Bethlehem, PA 18015
Department of Chemistry
Mechanisms and Controlling Characteristics of the Catalytic Oxidation of Methane
| Investigator(s) |
Klier, K.; Simmons, G.W.; Herman, R.G.
|
$122,000 |
| Phone | 610-758-3577 |
| E-mail |
kk04@Lehigh.EDU |
The general objectives addressed in this research are: the mode of methane activation on metals,
the structure-sensitivity of the C-H bond activation, the nature of surface species originating from
methane, oxygen, and dopants, the relationship between surface structure and dynamics of
elementary catalytic steps, and the controlling characteristics of partial oxidation of methane.
Palladium is the metal of choice because of its ability to activate methane at relatively low
temperatures and a weak Pd-O surface bond. Methane was found to dissociatively chemisorb on Pd surfaces
at <400K with an observed structure sensitivity of Pd(679) > Pd(311) > Pd(111).
New fundamental methodology involving angle-resolved X-ray photoelectron spectroscopy
(ARXPS), surface core level shifts, and X-ray photoelectron diffraction (XPD) at high energy
resolution and valence band (VB) spectroscopy has also been developed. It was shown from XPD
behavior of O/Pd surface core level shifts that O induced Pd surface states to exponentially decay
to 5 subsurface layers. The resultant model of angular dependence in the photoelectron intensity
attenuation has been extended to other overlayer systems (i.e. CO, S, Cl, and NO on Pd[100]), as
well as to studies of the initial state atomic orbital character of trigonal prismatic layered
MoS2. Upon doping the MoS2(0002) surface with Cs, no
Cs-induced surface relaxation was observed, but a new photoemission peak 1.6 eV above the VB
edge of MoS2 was observed corresponding to an electron donor-acceptor surface
complex (J. Phys. Chem. 1996, 100, 10739;
http://acsinfo.acs.org/plweb/journals/jpchax/100/i25/abs/jp9605865.html). Hartree-Fock and
density functional theory calculations are being performed on model Pd surfaces to better
understand the Pd-adsorbate bonding interactions. Computational efforts to elucidate the
electronic structure of MoS2 and Cs/MoS2 are also in progress.
Louisiana State University
Baton Rouge, LA 70803
Department of Chemistry
Polynuclear Aromatic Hydrocarbons with Curved Surfaces: Models and Precursors for
Fullerenes
The remarkable discovery that buckminsterfullerene or "buckyball,"
C60, is a stable molecule has led to a flood of research focused on this new family
of three-dimensional carbon cages known as fullerenes. These unique structures can be produced
by laser vaporization of graphite or coal. Metal derivatives show promise as superconductors.
This program deals with the synthesis, structural analysis, and chemistry of polynuclear
hydrocarbons with carbon frameworks represented on the buckminsterfullerene surface
("buckyball" fragments referred to as "buckybowls"). These curved-surface hydrocarbons are
expected to serve as models for the fullerenes in some of their chemical and physical properties.
The simplest example of such a hydrocarbon is corannulene,
C20H10, which represents the polar cap of buckminsterfullerene.
However, corannulene undergoes rapid bowl-to-bowl inversion that may lessen its utility as a
fullerene model. Consequently, a goal of this program was to produce a "locked"
bowl-shaped hydrocarbon; this was accomplished by the addition of a second five-membered ring
to corannulene to afford cyclopentacorannulene. More recently, this program produced the first
semibuckminsterfullerenes (C30H12) representing half of the
C60 surface. In theory, the C30H12 with 3-fold
symmetry might be dimerized to produce buckminsterfullerene itself, and this exciting reaction is
being explored. The synthesis of additional fullerene related hydrocarbons is a current goal of the
program.
University of Louisville
Louisville, KY 40292
Department of Chemistry
Metallocarboxylate Chemistry
Compounds having a carbon dioxide ligand bound to a metal center are models for surface-bound
CO2 in catalytic processes. Our work is centered on the synthesis and
characterization of such compounds, especially those with carbon dioxide bridged between two
metal centers. In the present period, new compounds of the symmetric
µ2-3 type have been structurally characterized; these, together with
others of the same type, allow correlation of the IR 
asym band of the ligated CO2 to be made with the
coordination geometry of the metal center which binds the carboxyl oxygens. The sym band varies only slightly
with changes in the metallocarboxylate. New synthetic routes have been established for
compounds having the carboxyl oxygens bound to zirconium by using transmetalation reactions of
related tin complexes. A further new direction involves the synthesis and chemistry of ruthenium
complexes with chelating nitrogen ligands (bipyridyl, terpyridyl, etc.) that also bear
C1 ligands; such compounds are little-known but are implicated as intermediates
in reductions of CO2 catalyzed by ruthenium complexes. Thus, the reaction of
Ru(bpy)2(CO)(CHO)+ PF6- with
water in the presence of oxygen leads to the corresponding µ2-2 CO2-bridged
complex; furthermore, the reaction can be photoassisted.
University of Maryland at College Park
College Park, MD 20742
Department of Chemistry and Biochemistry
Odd-Electron Organometallic Chemistry of Relevance to Hydrocarbon Functionalization
Investigations of transition metal hydride complexes that are potential precursors to highly
unsaturated odd-electron organometallics has continued. The structure of
Cp*MoH3(dppe) has revealed an unexpected and unprecedented
pseudo-trigonal prismatic geometry, while a product of protonation,
[Cp*MoH(MeCN)2(dppe)]2+ shows the expected
pseudo-octahedral structure. These studies, as well as a structural study on
CpMoH3(PMe2Ph)2 and parallel theoretical
investigations, have allowed a better understanding of the mechanism of hydride fluxionality in
these trihydride complexes of Mo(IV). The electrochemical oxidation of
Cp*MoH3(dppe) affords the EPR active 17-electron
[Cp*MoH3(dppe)]+, which decomposes over
several hours at room temperature. The decomposition involves reductive elimination of
H2 and trapping by a donor solvent to afford a stable
[Cp*MoH(S)(dppe)]+ radical, which has been isolated and is
currently being characterized. The radical can be reversible deprotonated by a number of bases.
The deprotonated radical, presumably
[Cp*Mo(S)2(dppe)]+, has also been isolated. The
decomposition of [Cp*MoH3(dppe)]+ using
nondonor solvents, which presents the potential of generating highly reactive 15-electron
[Cp*MoH(dppe)]+ or Cp*Mo(dppe) species, will
be a subject of future investigation. The generation of such intermediates in the presence of
substrates whose C-H and C-C bonds can be selectively activated will be a particular focus of
our research. Further knowledge has been gained on the role of external bases
for the mechanism and stoichiometry of oxidation/deprotonation of transition metal hydrides. The
ubiquitous external base for bulk electrochemical oxidations of hydride complexes is water.
Investigation of oxidations of CpMoH(L)(CO)2 (L =
PMe3 or PPh3) and
CpMoH(PMe3)3 in the presence or absence of water has
revealed: (i) the action of the base as a "proton shuttle", featuring proton capture
from the 17-electron hydride cation and later delivery to the 18-electron hydride precursor,
followed by irreversible elimination of H2; (ii) formation, isolation, and
crystallographic characterization of a Mo(III) hydroxo complex,
[CpMo(OH)(PMe3)3]+ and a Mo(IV) oxo
complex, [CpMo(O)(PMe3)2]+.
Massachusetts Institute of Technology
Cambridge, MA 02139
Department of Chemistry
High-Pressure Heterogeneous Catalysis in a Low-Pressure, Ultrahigh Vacuum
Environment
| Investigator(s) |
Ceyer, S.T.
|
$109,000 |
| Phone | 617-253-4537 |
| E-mail |
StCeyer@mit.edu |
The major thrust of this project is to carry out high-pressure, heterogeneous catalytic reactions in
a low-pressure, ultrahigh vacuum environment. These studies have now become possible because
of the culmination of several investigations in the laboratory over the last five years resulting in
the development of new physical processes and techniques: collision-induced absorption;
collision-induced recombinative desorption; bulk vibrational spectroscopy; and the synthesis of
adsorbed, reactive intermediates by translational and collision-induced activation. These new
processes allow the simulation of a high-pressure environment while maintaining the
single-collision conditions in which microscopic reaction steps and intermediates can be elucidated
and detected by molecular beam scattering coupled with high-resolution electron energy loss
spectroscopy. Results to date show that bulk H is the reactive species in the high pressure
reaction involving the hydrogenation of C2H4.
Massachusetts Institute of Technology
Cambridge, MA 02139
Department of Chemistry
Controlled Synthesis of Polyenes by Catalytic Methods
| Investigator(s) |
Schrock, R.R.
|
$130,000 |
| Phone | 617-253-1596 |
| E-mail |
RRS@MIT.EDU |
A way has been found to synthesize totally new polyenes in a controlled living fashion from
dipropargyl derivatives employing well-characterized alkylidene complexes of the type
M(CHCMe2R)(NAr)(OR')2 (M = Mo or W, R = Me or Ph, Ar =
2, 6 diisopropylphenyl, R' = OCMe3,
OCMe2(CF3), OCMe(CF3)2, or
various phenoxides) as catalysts. Dipropargyl derivatives of the type HC
CCH2XCH2CCH (X = NR, O,
C(CO2R)2, SiMe2, and so forth) are
cyclopolymerized to give soluble polyenes that contain either six-membered rings (head-to-tail
cyclopolymerization) or five-membered rings (tail-to-tail cyclopolymerization). The reaction can
be controlled by varying the solvent and the type of catalyst so that "dangling"chains
resulting from simple insertion of one of the propargyl groups are absent. Addition of one of the
acetylene bonds to an alkylidene to yield a new disubstituted alkylidene normally would essentially
terminate polymerization, since the disubstituted alkylidene would not react readily with more
terminal acetylene. This problem is avoided by the speed of the intramolecular cyclization reaction
to give a five-membered ring and a new monosubstituted alkylidene. This new polymerization
reaction will lead to a large number of new materials since the conditions of polymerization are
relatively mild (versus Ziegler-Natta conditions) and many functionalities therefore tolerated. In
addition to investigating the scope and details of this new controlled cyclopolymerization reaction,
the properties (nonlinear, conductivity, electrochemical, and so forth) of these new materials as a
function of chain length will be studied, a fundamental question that remains largely unresolved in
the area of unsaturated polymers (polyanilines, polythiophenes, polyparaphenylene, and so forth).
It seems possible that, owing to the control excercised in their preparation, a wide variety of new materials will become available that may rival the
more established unsaturated polymers in applications, as well as in fundamental research.
A catalyst has now been prepared that
cyclopolymerizes dipropargyl diethylmalonate to only six-membered rings, and another that
polymerizes o- trimethylsilyphenylacetylene in a living manner to give low polydispersity polyenes
that contain between 10 and 100 double bonds. Nonlinear optical measurements on both types of
polymers are being carried out in order to correlate 
and with chain
length and structure.
University of Massachusetts at Amherst
Amherst, MA 01003
Department of Chemical Engineering
Zeolite Characterization and Dynamics: The Effect on Molecular Transport and Catalyst
Selectivity
| Investigator(s) |
Conner, W.C.; Laurence, R.L.; Ragle, J.L.
|
$92,000 |
| Phone | 413-545-0316 |
| E-mail |
wconner@ecs.umass.edu |
Zeolitic materials are most often crystalline alumina-silicates with microporosity (less than
20Å) created by interconnected ring-like structures. These channels give sorbing molecules
access to the intraparticle surface where chemisorption and reactions occur. Since the channels
within the lattice are similar in size to sorbing molecules, the term "configurational
diffusion" has been used to describe intraparticle transport. The limited size of the
products for the reactions of hydrocarbons, selective sorption, and selectivity in isomerization and
trans-alkylation reactions have been ascribed to this "shape selectivity." This research
focuses on three related aspects of zeolites: the mutual interactions between adsorbing molecules
and the zeolite lattice, the nature of the pore structure of the zeolite characterized during
adsorption, and the influence of extreme steric constraints on cracking and isomerization reactions
for cycloalkanes. Earliest perceptions of the pore structure within a zeolite have depended on the
visualization of the Si(Al)-oxygen crystalline bond network. This representation and analysis
depends upon an image of a fixed pore configuration based primarily upon X-ray diffraction
(XRD) studies of the solid structure. Recent studies employing solids nuclear magnetic resonance
(NMR) and in situ XRD have documented that the shape of the adsorbing pores can change on
adsorption. More recently, detailed spectroscopic studies of adsorption and of adsorbing
molecules have begun to provide a picture of the pore structure and the sorbing species during
sorption. In situ infrared spectrometry (specifically far-FTIR) and thermal or gravimetric analyses
(DTA and TGA) can also be employed to understand the dynamic configurational changes in the
sorbing species and the energetics of these interactions. Several of these techniques have been
developed, and each will be used in concert to understand the effects of the interactions between
adsorbing molecules, their transport, and their reactivity. Specifically, 29Si,
129Xe, and 15N NMR will be employed in conjunction with high
resolution adsorption, HRADS, with DTA-TGA, and with FTIR for the initial studies of the
adsorption of C6 and C7 cycloalkanes within ten- and twelve-member ring zeolites. In addition,
the rate of adsorption/diffusion will be quantified by solids-gas chromatography (SGC). The
cracking and isomerization reaction of these cycloalkanes will be studied to understand the
symbiotic relationship between dynamic pore/adsorbate interactions and the resultant reactions of
these cycloalkanes.
University of Memphis
Memphis, TN 38152
Department of Chemistry
Towards Computer Aided Catalyst Design: Three Effective Core Potential Studies of C-H
Activation
We have focused on methane activation. Study of this reaction also provides the impetus for improved
modeling of inorganic systems. Research has focused primarily on methane activation by transition
metal (TM) imidos (L n M=NZ), and mercury complexes. Since hydrocarbons other
than methane are present in natural gas, a conversion catalyst must operate in a
multisubstrate environment. To complement experiments by Wolczanski, we studied CH
activation of hydrocarbons larger than methane by Zr-imidos. This work provides new insight into
substrate effects in CH activation allowing us to address questions relevant to selectivity. A
major question of interest in catalysis involves modifying a complex to make it more active.
Previous work has focused on the role of metal and ancillary ligands in methane activation. Our
most recent research indicates it is difficult to tailor imido reactivity through electronic
modification of imido substituents (Z), because most substituents studied are found to exert
their influence primarily through inductive effects localized on the sigma framework. This
suggests several profitable areas to be pursued. Hg(II) and complexes of related electrophilic, late
TMs have attracted much experimental interest. A main impediment to their development is lack
of an intimate understanding of the CH activation mechanism. Our objective is to study how
prototypical hard and soft anionic ligands control the kinetics and thermodynamics of methane
activation by Hg(II) complexes. The great sensitivity shown by these systems to ligand
modification suggests that these ligands can be modified to effect lower CH activation barriers. This
research suggests several logical extensions to greater activity including replacing mercury with
related metals and going to cationic complexes.
University of Michigan
Ann Arbor, MI 48109
Department of Chemistry
The Role of Hydrogen in C-N, C-C, and C-S bond activation on Ni and Pt surfaces
C-N, C-C, and C-S bond activation reactions play an important role in catalytic processes used in
both the fuels and chemical industries. We are examining the role of hydrogen in bond activation
reactions on Ni and Pt surfaces in order to establish a basic understanding of the primary factors
which control bond activation. The primary methods include spectroscopic characterization of
adsorbed intermediates using a combination of surface spectroscopies and transient kinetic studies
of stoichiometric surface reactions. Over the year we have focused our research primarily on
developing a fundamental information regarding two reaction systems on nickel. Phenylthiolate is
the dominant intermediate independent of hydrogen availability during C-S bond activation in
phenylthiol. Hydrogen appears to be directly involved in C-S bond activation on Ni. For C-S bond
activation, tilted orientations of the adsorbed phenylthiolate intermediates appear to be most
favorable for hydrogenolysis. Adsorption in perpendicular or nearly perpendicular orientations
limits bond activation as well as interactions with the attached phenyl group. Coadsorbed
hydrogen does not activate C-C bonds in small hydrocarbons. However, we have found that
energetic forms of hydrogen activate strained C-C bonds in cyclic hydrocarbons at low
temperature. After initial atomic hydrogen addition from the gas phase to form an adsorbed alkyl
group, coadsorbed hydrogen adds to form the alkane. Efforts to activate C-C bonds in unstrained
ring systems like cyclohexane, cyclohexene, and toluene were unsuccessful suggesting that even
these reactions are kinetically controlled on the surface. These studies establish a method of
probing hydrogen induced C-C bond activation and also provide a new approach for preparing
adsorbed alkyl species on Ni. In summary, over the past year we have developed substantial new
understanding of the role of hydrogen in C-S and C-C bond activation reactions on Ni.
University of Minnesota
Minneapolis, MN 55455
Department of Chemical Engineering and Materials Science
Homogeneous--Heterogeneous Combustion: Chemical and Thermal Coupling
The roles of homogeneous and heterogeneous reactions in catalytic oxidation processes are being
studied experimentally and theoretically by measuring rates and concentration and temperature
profiles near reacting surfaces and by calculating these profiles for known kinetics. Laser-induced
fluorescence methods are being developed to measure the concentrations of free-radical
intermediates near reacting surfaces for several combustion reactions on polycrystalline platinum
and rhodium as functions of surface temperatures and reactant composition, pressure, and
temperature. Concentrations of stable and radical intermediates with and without homogeneous
reaction will be measured directly. Concentration and temperature profiles are also being
calculated for various reaction processes and flow conditions. Of particular interest is the
occurrence of multiple steady states and oscillations for various models of
homogeneous-heterogeneous processes. Reaction rate expressions for individual surface and
homogeneous reactions are used to simulate the experimentally observed behavior. Particular
interest centers on the selectivity of partial oxidation reaction such as production of CO and
hydrogen from methane oxidation, olefins by oxidative dehydrogenation of alkanes, and
oxygenates by oxygen addition to alkanes. The objective of this research is to understand the
contributions of each type of reaction in practical situations in catalytic reactors and combustors
in order to determine their implications in reactor selectivity for chemical synthesis and for
pollution abatement.
University of Missouri at Columbia
Columbia, MO 65211
Department of Chemistry
Late Transition Metal Oxo and Imido Complexes
This project involves the exploration of the chemistry of late-transition metal oxygen and nitrogen
bonds and is of relevance to catalytic processes in chemical manufacturing and pollution control.
Recent highlights include the chemical and structural characterization of the only model for the
binding of dinitrogen inside the nitrogenase Mo/Fe cluster, the synthesis and characterization of a
dioxo centered M/Au (M = Rh, Ir) clusters with square pyramidal coordination geometry about
oxygen stabilized by Au-Au and Au-M bonds, and the synthesis and characterization of
unexpectedly stable dppm and dppm-H imido complexes. The nitrogenase model complex is our
previously synthesized gold complex
[(LAu)3N2(AuL)3]2+ (L =
PPh3). Our recently completed structural characterization of this complex reveals
that it contains a dinitrogen unit inside a cluster of six Au atoms. Each nitrogen atom is bonded to
three metal atoms as has been proposed by Rees and others for the bonding of dinitrogen inside
the Mo/Fe cluster of nitrogenase. Reduction of
[(LAu)3N2(AuL)3]2+ in the
presence of a proton source produces ammonia indicating that
[(LAu)3N2(AuL)3]2+
structurally and chemically models nitrogenase. The dioxo clusters
[(COD)2M2(O)2(AuL)4]2+ (M = Rh, Ir; L = PPh3) were prepared by the reaction of
[(LAu)3(O)]+ and [(COD)MCl]2 and contain oxygen atoms in an
usual square pyramidal coordination geometry. These clusters are related to a class of complexes
containing all-gold metal atoms which are stabilized by "aurophilic" Au-Au bonds.
Our dioxo clusters contain not only stabilizing Au-Au bonds but also stabilizing Au-M bonds
indicating the likely existence of a new class of complexes related to the all-gold complexes.
Finally, we have succeeded in expanding our previously reported dimeric Pt oxo complexes
[L4Pt2(O)2] (L = a phosphine) to the analogous
imido complexes. However, while the oxo complexes were prepared for a large variety of
phosphine ligands the only effective phosphine for the imido complexes is dppm and dppm-H.
This unique ability of the dppm and dppm-H ligand to stabilize the imido complexes is not
understood at this time.
University of North Carolina at Chapel Hill
Chapel Hill, NC 27599
Department of Chemistry
Mechanistic Studies of Transition Metal-Catalyzed Alternating Copolymerizations of Carbon
Monoxide with Olefins
| Investigator(s) |
Brookhart, M.
|
$105,000 |
| Phone | 919-962-0362 |
| E-mail |
caulder@unc.edu |
Polyketones are a significant new class of polymers prepared from alternating copolymerization of
CO and olefins. The basic objective of the program is to elucidate the fundamental mechanisms of
these copolymerization reactions catalyzed by Pd(II) and Ni(II) species. Well-defined Pd(II)
catalysts of the type (N-N)PdCH3(solv)+
BAr'4- (N-N = bipyridine, phenanthroline; Ar' =
3,5-(CF3)2-C6H3-) have been
prepared. A highly detailed mechanism of copolymerization of ethylene and CO has recently been
reported (J. Am. Chem. Soc. 1996, 118, 4746-4764). All potential intermediates in the catalytic
cycle have been independently generated including the alkyl ethylene complexes (N-N)Pd(C[sub
2}H4)R+, alkyl carbonyl complexes
(N-N)Pd(CO)R+, acyl carbonyl complexes (N-N)Pd(CO)COR+,
acyl ethylene complexes (N-N)Pd(C2H4)COR+
and chelate complexes (N-N)PdCH2CH2COR+
and (N-N)PdC(O)CH2CH2COR+. Migratory
insertion rates for all carbonyl and olefin complexes have been measured as well as relative
binding affinities of ethylene and CO to key species. This kinetic and thermodynamic data has
been combined to provide a detailed picture of the mechanism of copolymerization and which
intermediates are of significance in the catalytic cycle. The data obtained accurately predicts the
observed turnover frequency and the observed kinetic dependence (first-order in ethylene, inverse
order in CO). Work has continued on the development of chiral bis-oxazoline-based Pd(II)
catalysts for synthesis of isotactic, optically active polyketones based on styrenic monomers.
Unique ligand exchange processes have been developed which provide a new method of synthesis
of stereoblock polyketones and a deeper understanding of chain-end versus enantiomorphic site
control of polymer microstructure. A fundamental study of substituent effects on migratory
insertion rates in a series of substituted styrene complexes
(phenantroline)Pd(CH3)(CH2 =
CHC6H4X)+ (X = H, CF3, Cl,
CH3, OCH3) has been completed (J. Am. Chem. Soc. 1996,
118, 2436-2448). These studies clearly show that ground state energies are more sensitive to
substituent variation than transition state energies and electron-donating substituents stabilize the
ground state and thus retard the overall rate of migratory insertion. Work is in progress on the
complete mechanistic analysis of copolymerizations catalyzed by bidentate phosphine-based
systems and the development of new bidentate ligands for use with both Pd(II) and Ni(II)
systems.
University of North Carolina at Chapel Hill
Chapel Hill, NC 27599
Department of Chemistry
Reductive Coupling of Carbon Monoxide to C2 Products
| Investigator(s) |
Templeton, J.L.
|
$98,350 |
| Phone | 919-966-4575 |
| E-mail |
joetemp@unc.edu |
A variety of synthetic routes to tungsten nitrene complexes have been developed. Nitrene transfer
from cationic tungsten nitrene monomers to trimethylphosphine has been achieved, and a copper
catalyst for nitrene transfer from PhINTs to olefins has been prepared. These results are
encouraging for developing systems that will transfer the neutral nitrene NR fragment to
electron-rich olefins to form aziridines. Another result in M-N-C chemistry is the selective
regiochemistry for electrophile addition to W=N-CR2 units. With an ancillary
alkyne ligand in the coordination sphere, a coordinated imine ligand forms
(M-NH=CR2+). The regioselectivity of proton addition is
reversed when the nitrogen lone pair is involved in a simple 2-center-2-electron bond as
protonation then occurs at carbon to form a nitrene ligand
(M=N-CHR2+). The Tp'(CO)2W fragment avidly
seeks three electrons, and the stability of six-coordinate monomers incorporating a three-electron
donor into the sixth site has allowed us to isolate analogous N, NH+, and CH
complexes. In addition to the CH carbyne complex, alkyl carbyne derivatives
Tp'(CO)2WCCH2CH2R and their vinyl and allyl
isomers have been prepared. By combining complementary carbyne reagents,
Tp'(CO)2MoCCl and deprotonated
Tp'(CO)2WCCH3, dimers containing the CCH2C
linkage can be synthesized. These dimers are susceptible to deprotonation and oxidation to form
simple CCC bridged dinuclear products.
Northwestern University
Evanston, IL 60208
Department of Chemical Engineering
Solid-State, Surface, and Catalytic Studies of Oxides
| Investigator(s) |
Kung, H.H.
|
$138,000 |
| Phone | 847-491-7492 |
| E-mail |
hkung@nwu.edu |
Multicomponent oxides are catalysts for a number of technologically important reactions,
including the selective conversion of low-priced saturated hydrocarbons by oxidation (selective
oxidation) to unsaturated hydrocarbons, aromatics, alcohols, aldehydes, or acids that are of much
higher value, and for the removal of nitorgen oxides, which is an atmospheric pollutant from
exhausts of lean-burn, gasoline engines (lean NOx conversion). The emphasis of
this project is to identify the properties of oxidic catalysts that determine their catalytic properties
in these reactions. In selective oxidation, it was found that modification of a silica-supported
vanadium oxide catalysts with phosphorus resulted in significant increases in the selectivity for the
formation of maleic anhydride. Spectroscopic characterization of the samples suggested that the
high selectivity could be correlated with the formation of a phosphorus-vanadium oxide
compou