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OPPORTUNITIES IN HOMOGENEOUS AND SINGLE-SITE HETEROGENEOUS CATALYSIS
Tobin Marks, DOE Catalysis Workshop May 2002
I. Current Drivers
II. New Tools and Techniques
III. Single-Site Polymerization. Catalysis Materials
IV. Multi-Site Catalysts and Cocatalysts
V. Carbon-Heteroatom Bond Formation
VI. Homogeneous-Heterogeneous Interface
VII. Biomimetic/Supramolecular, Enantioselective Catalysis
VIII. Opportunities and Needed Resources
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CURRENT DRIVERS FOR RESEARCH IN HOMOGENEOUS (HETEROGENEOUS) CATALYSIS
ENORMOUS ECONOMIC IMPORTANCE!!– Environmental (Green Chemistry, Atom Efficiency, Waste
Remediation, Recycling)– Polymeric Materials (New Polymers and Polymer
Architectures, New Monomers, New Processes)– Pharmaceuticals and Fine Chemicals (Demand for Greater
Chemo-, Regio-, Stereo-, and Enantioselectivity)– Feedstocks (Practical Alternatives to Petroleum and Natural
Gas)– Cost of Energy (More Efficient, Selective Processes)– Completely New Materials (e.g., Carbon Nanotubes)– Cost Squeeze in Chemical Industry– Declining Corporate Investment in Basic Research
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NEW TOOLS FOR HOMOGENEOUS (HETEROGENEOUS) CATALYSIS RESEARCH
SIMPLE TO EXPENSIVE
• New and In Situ Spectroscopies (NMR, EPR, IR/Raman, SPM, EM, X-Ray, EXAFS/XANES)
• Synthetic Techniques (Exotic Ligands, New Elements, Solid State, Sol-Gel, Nanoscale)
• Reaction Techniques (Combinatorial, High-Pressure, Polymerization)
• Computational (DFT, ab initio, MD, combinations)• New Characterization Techniques (Calorimetry,
Polymer, Isotopic, Stop-Flow, Chiral GC/HPLC)
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A NEW GENERATION OF POLYOLEFINS
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Creating Highly Electrophilic d0 “Cations”
On Surfaces
In Solution
Important Questions• What are the Thermodynamic Constraints on Metallocenium Formation?• What is the Structural and Dynamic Nature of the M+ - - - - X- Interaction?• How Does the M+ - - - - X- Interaction Modulate Catalytic Properties?• What is the Ultimate X-?
MR
R
Lewis AcidicSurface M
R
R-
+
MR
-+X
-X = Weakly Coordinating Anion
Lewis Acid(abstractive)
Oxidant
Brønsted Acid(protonolytic)
MR
R
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Single-Site Catalyst Issues, Opportunities
PolymerMolecular WeightTacticityComonomer IncorporationBlock StructureCrosslinkingPolar Functional Groups
MonomerElectronic CharacteristicsSteric CharacteristicsPolar Functional Groups
Cocatalyst/CounteranionCoordinative CharacteristicsStereoelectronic CharacteristicsStereodirecting Characteristics
To What Degree Can Catalyst-Cocatalyst Interactions Tune Reactivity, Productivity, Stereoselectivity, Chain Transfer, Polymer Architecture?
Catalyst Ancillary LigationElectronic CharacteristicsSteric CharacteristicsStereodirecting Characteristics
MR R
R
X-
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Organo-Lewis Acid Abstraction ChemistryL2M(CH3)2 + B(C6F5)3 L2M
CH3
H3CB(C6F5)3
Metallocene “Constrained Geometry”
•M+. . . H3CB(C6F5)3- Interaction Largely Electrostatic
•Extremely Active Polymerization Catalysts
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H formation H reorganization
24 24
H
(kc
al/m
ol)
Reaction Coordinate
M = ZrR = CH3
CH3B(C6F5)3-
+ B(C6F5)3
Alkyl Group Effects on Ion Pair Formation and Structural Reorganization Energetics
Calorimetry and Dynamic NMR Data
Bulkier R = Alkyl Groups
Hformation More Negative (More Exothermic); H‡reorganizationSmaller
Polar Solvents
H‡reorganization Smaller; Bulkier R Less Sensitive
Cyclopentadienyl Alkyl Substitution
Hformation More Negative (More Exothermic)
‡
27
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4.72
1.32
2.05 6.49
1.362.372.05
2.16
Transition State
6.62
1.41
2.14
Kinetic Product
5.48
2.93
1.55
1.532.09
-5
5
1.52.02.53.03.5
8
E (
kcal
/mol
)
Reaction Coordinate in Benzene [Ethylene]—[CH3Ti] Distance
(Å)
AB INITIO COMPUTED REACTION COORDINATE FOR OLEFIN INSERTION
2.37 Å
2.80 Å
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B
B
FF
FF F
F
FF
X
X
F F
F
FF
B
FFF
FF
FF
F
FB
FF F
F
FFFB
3
3
3
F
FF
F
FF
F
F
B
F F
F
FF
FF
FF
B(C6F5)2
B(C6F5)2B(C6F5)2
B(C6F5)2
F F
F
FF
B
2
Ar
MODIFICATION OF PERFLUOROARYLBORANE MOLECULAR AND ELECTRONIC STRUCTURE
PNB
DBA
PBB
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F
F
F
F
F
F
F
F
B
2
-
M (OC6F5)n
M = B, Al n=4 M = Ta, Nb n=6B
FF
FF
R
4
-
R = F, Si Si,
F
F
F
F
F
F
F
F
Al
3
-
F
F
H -
-
- -
PBA
R
B(C6F5)2(C6F5)2B
Weakly Coordinating Perfluoroaryl Anions
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L2M(CH3)2 + Ph3C+PBA- + Ph3CCH3
MODULATING CATION-ANION INTERACTION WITH PBA-
• Cation-Anion Interaction Very Sensitive to L2M (19F NMR, Crystal Structure)
• Olefin Polymerization Activity Very Sensitive to L2M
rac-Me2Si(Ind)2Zr(CH3)+PBA- CGCZr(CH3)+PBA-
L2-
MCH3
FAl
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Are There Anion Effects on Me2C(Cp)(Flu)ZrMe2-Mediated Propylene Polymerization ?
Syndiospecific Enchainment Mechanism :
M MM
MM
r r r r
+ + +
++
P P P
PP
X-
X-
X-
X-
X-
M CH3
CH3
Cocatalyst M CH3+
X-
Does chain swinging require ion pair reorganization ? An ideal system to evaluate ion pairing effects !
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Polypropylene 13C NMR Spectra Me2C(Cp)(Flu)ZrMe2 + Cocatalysts
rmmr rrmm
rrmr
rrrr
rrrm(r)
rrrm(m)
PBA 91B(C6F5)4
- (Borate) 84
PBB 84
B(C6F5)3 (Borane) 69 rrrr %
M
[m][mm] [m] [mm]
14.5 14.0 ppm15.015.515.0
Results Concentration Independent Over 32- Fold Range
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O
N
Py
Py
Cu
N
Py
Py
Cu
OOH
HOAsp
O
NiN
N
O
O
NH2 NH2
O
NiN
NO
NLys
HH
H
OAsp
O
NiN
N
O
O
NH2 NH2
O
NiN
NO
NLys
H
HCO2
NH3
+
B
A
B
A
HA = acidic side chain
B = basic side chain
N
HN
FeIII
O
O
O
O
MII
NHN
NNH
H2N
O
OH
O
P O
O
OR
O
NHHNNH
NH
HO
His325
Asp135Asp164
His323
His286
Asn201
His296His202
Tyr167
RhOC
P
P
H
P
PRhOC
C
O
R
N
Me Me
Zna
O
O
RAr
HZnb
R
R
R Ar
H OH
up to 99% ee*
COOPERATIVE MULTIMETALLIC EFFECTS IN CATALYSIS
Enzymatic (Carbonyl Transfer and Phosphoryl)
Synthetic
Noyori Karlin
RuRu Ru
RuRu Ru
PtPt Pt
H
H
C C
PhPh
RuRu Ru
RuRu Ru
PtPt Pt
H
C C PhPhH H
H
C CPh Ph
PhC CPh
H2C C
Ph
H
Ph
H
ONCr
NO
tBu
tBu
tBuN3
ON Cr
NO
tButBu
tBu
N3
O
NMe2
H
Jacobsen Adams
Stanley
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CGCM
x
CGCMx
CHCH2reinsertion
CH2-CH2-
CH2-CH2-
CHH2C
LONG CHAIN BRANCH FORMATION IN ETHYLENE POLYMERIZATION
Branch Formation
How to make reinsertion more probable ?
CGCMx
-H transfer CHH2CCH2CH2
Macromonomer
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CATALYST NUCLEARITY MATRIX
Increasing catalyst nuclearity
Increasing cocatalyst n
uclearity
CH2 CH2
N
SiMe2
NMe2Si ZrMe MeZr
B(C6F5)3
Me
CH2CH3
Me
MeZr
B4
Me
CH2CH3
Me
MeZr
B4
Me
CH2CH3
Me
MeZr
Me Zr
CH3CH2
CH2 CH2
N
SiMe2
N
Me2Si
MeZr
ZrMe
B4
B4
Me
Me (C6F5)3B
F
F
F
F
N
Si
F
F F
F
F
N
Si
F
F F
F
F
N
Si
F
F F
F
F
F
F F
F
F
Si
N
Zr1 B1 Zr2 2B1
2Zr1 B2 Zr2 B2
B(C6F5)3(C6F5)3B
F
F
F
F
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CH2
CH2M
P'M
P
Et
M
P'
M
CH
CH2
P
CHCH2M
P'M
P
CH2 CH2H
CH2 CH2
Et
M
P'
M CH2
CH
P
Reinsertion
CHCH2
M
P'MP
CH2CH3
CH2CH3
M
M
CHCH2
Chain Transfer
P'
P
Reinsertion
ETHYL AND LONG CHAIN BRANCH BRANCH FORMATION FACILITATED BY BINUCLEAR MACROMONOMER BINDING
Long Chain Branch Formation
Ethyl Branch Formation
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1. Nonpolar + Polar Monomer Copolymerization
2. Control of Polymer Architecture
Telechelic
Controlled Branching
Block Structures
X X
A A B B B A A
hard + soft
Controlled ComonomerIncorporation
Controlled Tacticity
Stars, Dendrimers
long chain branching
X X X
= acrylate, vinyl acetate, vinyl chloride, acrylonitrile
Grand Challenges in Catalytic Single-Site Polymerization
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Palladium-Catalyzed Hydroamination of 1,3-Dienes
+2 mol% Pd(PPh3)4
10 mol% CF3CO2H
toluene, 25 ºC, 24h4 equiv.
ArHN
Entry Amine Yield(%)
NH2 991
NH2 852
NH2963 EtO2C
(48 h)
ArNH2
Löber, O; Kawatsura, M.; Hartwig, J. F. J. Am. Chem. Soc. 2001, 123, 4366-4367
LnPd-HPhHN
LnPd
NH2Ph
LnPd
NH2Ph
ArNH2 +
5 mol%[Pd(-allyl)Cl]2
11 mol% Ligand
1.2 M THF, 25 ºC4 equiv.
ArHN
Entry Amine Time (h)
NH2 1201
NH2 1202
NH21203 EtO2C
Yield (%) ee (%)
HNNHOO
P PPh2 Ph2
87 89 (S)
78 86 (S)
83 95 (S)
Ligand =
PhHN
LnPdLnPd
NH2Ph
NH2Ph
LnPd
PhHN
Mechanism in the presence of acid
Mechanism in the absence of acid
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·NH2
Ar
NTi
N NMe2
NMe2
SO2Ar
SO2Ar
C C6 H6
N CH3Ar
5 mol%
79 - 95%75
Zr
N
Ar
THFPhCH C CHPh
C
-THF
C C CH
Ph
H
Ph
(S)
(R)
C C CH
Ph
H
Ph
(S,S)
1 equiv
+
Racemic1.8 equiv
25
+
98 % ee
90 % ee
ZrN
Ph
Ph
Ar
H
H1 equiv
Al2O3
0.8 equiv
Use of Imido Complexes in Catalytic Hydroamination and Enantioselective Reactions of Allenes
Ackermann, L.; Bergman, R.G. “A Highly Reactive and Selective Precatalyst for Intramolecular Hydroamination Reactions” Org. Let. 2002; 4, 1475. Sweeney, Z. K.; Salsman, J. L.; Andersen, R. A.; Bergman, R. G. “Synthesis of Chiral, Enantiopure Zirconocene Imido Complexes: Highly Selective Kinetic Resolution and Stereoinversion of Allenes, and Evidence for a Non-Concerted [2+2] Cycloaddition/Retrocyclization Reaction Mechanism,” Angew. Chem. Int. Ed. Engl. 2000, 39, 2339.
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Catalytic Pathways for d0,fn-Metal Mediated C-Heteroatom Bond Formation
Insertion / Protonolysis Hydride Insertion / Transposition
M XR2 M H
M XR2 M H
HXR2
RnXH
HXR2 RnXH
X = H, Hydrogenation B, Hydroboration Si, Hydrosilation
X = N, Hydroamination P, Hydrophosphination
New Routes to Heteroatom-Substituted Molecules and Polymers
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THERMODYNAMICALLY BASED STRATEGIES FOR CATALYTIC HETEROATOM ADDITION
LnX
ii i
Ln
Ln
ii i
Ln X
XHX
XH
XR
R
R
X
HX
H
EXAMPLE: Olefinic Substrates (X = Heteroatom Group)
Intramolecular Intermolecular
EXPECTATIONS• S, S‡ Favor Intramolecular Process• Hii < Hi
• kii > ki
• Hi (X): CH3 H < Pr2, NR2 < SR, OR
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Diastereoselectivity in Aminodiene Cyclization
Good to excellent 2,5-Good to excellent 2,5-trans trans (80% de), and 2,6-(80% de), and 2,6-cis cis (99% de) diastereoselectivities(99% de) diastereoselectivities
NH
()-PinidineH
LnN
H
HConcise synthesis of (Concise synthesis of (±)-pinidine ±)-pinidine
with excellent stereocontrols with excellent stereocontrols
(2,6-(2,6-cis cis and and transtrans-alkene)-alkene)
NH
NH
NH
H2N
H2N
2,5-cis
Entry Subtsrate Products Product Ratiob Nt, h-1 (oC)c
cis : trans
1.
2.
Pre-Catalyst
1.0 (25)Cp'2LaCH(TMS)2
78 (25)CGCSmN(TMS)2
3.7 (25)Cp'2LaCH(TMS)2
4.0 (60)CGCSmN(TMS)2
aDetermined by 1H-NMR, bDetermined by GC-MS ratio of the corresponding hydrogenated Boc derivatives, cTurnover frequencies measured
in C6D6 with 6 mol% precatalyst, dcis: trans = 178:1; Alkene isomer ratio (E: Z: allyl)= 94: 1: 5
Conversiona
> 95
> 95
> 95
(%)
NH
42 : 58
10 : 90
99.4 : 0.6d
78 : 22
2,5-trans
2,6-cis 2,6-trans
> 95
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Is Hydrophosphination Analogous?
H ~ -17 kcal/mol (alkenes)H ~ -7 kcal/mol (allenes)H ~ -7 kcal/mol (alkynes)
step ii
step i
H ~ +2 kcal/mol (alkenes)H ~ -30 kcal/mol (allenes)H ~ -33 kcal/mol (alkynes)
AM-1 calculations:(Heat of formation using methyl phosphine and carbon fragment) H = -15 kcal/mol (alkenes) H = -38 kcal/mol (alkynes) H = -37 kcal/mol (allenes)
CH(TMS)2 H2P
HP
Ln
HP
n
+
n
CH2(TMS)2
n
ii i
Ln
Ln
H2P n
HP
n
P
H
trans
P
trans
H
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Metallocene – Metal Oxide Chemisorption
1. Lewis Acid Surfaces (Dehydroxylated Al2O3, MgCl2)
2. Weak Brønsted Acid Surfaces
(SiO2, Partially Dehydroxylated Al2O3)
High Catalytic Activity
Active Sites ~8%
Poorly Electrophilic
Negligible Catalytic Activity
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Catalysis with Organozirconium Hydrocarbyls Supported on Sulfated Zirconia
Most active benzene hydrogenation catalyst known
Polymerization activity varies with coordinative unsaturation: ZrR4 > CpZrR3 > Cp2ZrR2
Solid BrØnsted Super Acid
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Scott’s Cr/SiO2 Ethylene Polymerization Catalyst
S. Scott, J. Aijou J.Am.Chem.Soc. 2000, 122(37), 8968-76.S. Scott, J. Aijou Chem.Eng.Sci. 2001, 56, 4155-68.
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OH OH OH OHOH OH OH
OOFe
OHO
O SiSi
OtBuOtBu
OtButBuO
tBuO
tBuO
OH O O OOH O O
Si SiO O
Fe
OH
OO
OH OH OH OHOH OH OH
SBA-15 silica surface
1.0 OH nm-2- HOSi(OtBu)3
- CH2 CMe2
- H2O
(tBuO)3SiOFe
(tBuO)3SiO
OSi(OtBu)3
O
molecular precursor andspectroscopic model
well-defined, isolated sites
0.23 Fe nm-2
isolated, pseudo-tetrahedral O-Fe(OSiO3) sites
Molecular Precursor Routes to Well-Defined, Active, Single-Site Catalysts
- selective oxidation catalysts for various organic compounds with H2O2:
OH
O
OH O
selectivity TOF, mol (mol Fe)-1 s-1
100%
99%
100%
2.5 x 10-3
6.2 x 10-4
1.2 x 10-2
C. Nozaki, C. G. Lugmair,A. T. Bell, T. D. Tilley,submitted.
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Alkane Metathesis by Basset
ethane metathesis propane metathesis
isobutane metathesis
Vidal, V., et.al. Science, 1997, 276, 99 – 102.
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•Tailored Supports
•Molecular Precursors (chemo-, regio-, stereoselectivity)
Close Proximity Multiple Coupled Transformations
Ziegler SiteOligomerization SiteROMP SiteChain Transfer Site
Cationic SiteAnionic SiteSecond Ziegler SiteHydrogenation Site
Bifunctional Single-Site Supported Catalysts
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CO2 + H2O H2CO3
Nt ~ 107 – 109 sec-1
Structure of Carbonic Anhydrase A Metalloenzyme
Now with Cd:T.W. Lane and F.M.M MorelProc. Nat. Acad. Sci. USA 2000, 97, 4627-4631
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Artificial Enzyme for Olefin Epoxidation
•Encapsulation of catalyst ==> 100-fold increase in lifetime.
• Incorporation of ligands predictably modifies the internal cavity size to induce substrate selectivity
Nguyen, Hupp and coworkers
R1 R1
O
+
R2
[O] R2
Polymers
Food Products
Pharmaceuticals
Paints, Resins
Fibers
NNN NN NZn
NNN NN NZn
N
NN
N
N
N
Zn
N
N N
N
N
N
Zn
Cl(CO)3Re
Re(CO)3Cl
Re(CO)3Cl
Cl(CO)3Re
NNN NN NMn
N
O
O
N
O
O
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Cyclic Carbonates from CO2 + Epoxides
O
R+ CO2
OO
O
R
NCr
Ph
N
Ph
OtBu
tBu
O
tBu
tBuCl
DMAP, 75 oC, 1.5-6 h
R = Me, Ph, CH2Cl, vinyl, CH2Ph, Hex 95-98% yield, 100% selectivity
50 psig
O
Me+ CO2
OO
O
Me
NCo
N
OtBu
tBu
O
tBu
tBuOAc
DMAP50 psig
(R) (R)
(S)
70% ee at -20oC
Nguyen and coworkers
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High Activity Allows Polymerization of More Sterically Hindered Monomers
Me2SiMe2Si Zr
Cl
Cl
S
R,S
R
(isotactic)poly(S-3,4-dimethylpentene-1)
+
s =kSkR
> 12
• Kinetic resolutions of inexpensive monomers for production of chiral polymers and resolved olefin monomers
+ MAO
John Bercaw, et al
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Thermal, Catalytic, Regiospecific Functionalization of Alkanes
Entry Substrate catalyst time (hours) Yield of RBpin (%)
1 n-Octane 5.0 mol% 25 88
2 2-Methylheptane 1.0 mol% 60 61
3 Methylcyclohexane 6.0 mol% 80 49
4 n-Butyl ether 4.0 mol% 80 64
5 Benzene 5.0 mol% 2.5 92
mol %
OB
OB
O
O
(pinBBpin)
+ BO
OHB
O
O+
Cp*Rh( C6Me6)2
150 ºC
150 ºC Cp*Rh( C6Me6)2
(RBpin)
[Rh]H(X)
[Rh]H(X)(Y)(Bpin)
[Rh](X)(Bpin)
[Rh]H(X)(R)(Bpin)
Y-Bpin
HYR-H
R-Bpin
[Rh]=Cp*Rh
X, Y = H or Bpin
Cp*RhL2
excessXBpinR-H
Chen, H.; Schlecht, S.; Semple, T.C.; Hartwig, J. F. Science 2000, 287(5460), 1995-1997
• terminal product only steric preference for a
linear metal-alkyl complex
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Electrochemical Synthesis of Diamines
Yudin and coworkers
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SUMMARY. FUTURE OPPORTUNITIES• MULTINUCLEAR / MULTIFUNCTIONAL CATALYSTS
– Multisite Substrate Activation, Conversion– New Polymer Architectures, Modifications
• NEW SURFACES– New Molecular Catalyst Activation Routes– Single-Site Ensembles
• NEW OR IMPROVED TRANSFORMATIONS– Improved Selectivity (Chemo-, Regio-, Enantio-)– C-Heteroatom Formation (C-O, C-N, C-P, C-S, etc.)
– Abundant Feedstocks (CO2, SiO2, Saturated Hydrocarbons, Biomass, Bioproducts, Waste)
– Atom-Efficient, Heat-Efficient Transformations
• NEW ELEMENTS, LIGANDS, COCATALYSTS– Early Transition Metals, Lanthanides, Actinides– Ligand Engineering– Cocatalyst Engineering
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Catalytic Cycle for Aryl Ether Synthesis
Pd2(dba)3 + L L Pd L
L Pd
PdL Ar
X OR
RO
C-O BondFormation
X
L Pd
Ar
X
-OR
C-X Bond Activation
L = Chelating Phosphine Ligand
Buchwald, et al J . Am. Chem. Soc. 2000, 12, 12097
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L Pd
L PdAr
X
PdX NHRR'
L Ar
L PdAr
NHR
YX
HNRR'
NaO-tBu
HO-tBu
YRNH
Turnover With Carbene Ligand: > 5000
Pd2(dba)m + L L Pd L
Carbene Ligand Used:
N N
Catalytic Cycle for Amination of Aryl Halides
Hartwig et al., Organic Letters, 2000, 2 , 1423.
CATALYTIC CARBON-HETEROATOM BOND FORMATION