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

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

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)

A NEW GENERATION OF POLYOLEFINS

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

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-

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

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

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

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

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

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

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 !

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

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

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

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

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

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

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

·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.

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

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

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

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

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

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

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.

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.

Alkane Metathesis by Basset

ethane metathesis propane metathesis

isobutane metathesis

Vidal, V., et.al. Science, 1997, 276, 99 – 102.

•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

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

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

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

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

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

Electrochemical Synthesis of Diamines

Yudin and coworkers

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

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

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