Download Sigma Bond Metathesis

Sigma Bond Metathesis
Reporter: Changliang Sun
Supervisor: Zhangjie Shi
Outline
¾
Introduction
¾
Mechanism
¾
Examples and Applications
¾
Summary and Outlook
¾
Acknowledgements
2007.10.12
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1
Introduction
The Nobel Prize in Chemistry 2005 :
“for the development of metathesis method in organic synthesis”
Yves Chauvin
Robert H. Grubbs
Richard R. Schrock
A Dance Changing Partners !
2007.10.12
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Introduction
Alkene Metathesis
R
LnM
R
R
Mes N
L nM
L nM
Cl
R'
R'
R'
R'
R'
R'
Cl
Alkyne Metathesis
R
R'
LnM
LnM
R'
R'
R'
R'
H
Ru
PCy3
Ph
R
R
R
L nM
N Mes
MLn
R'
R'
(RO)3W C
t-Bu
R'
Alkane Metathesis
LnM
R'
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R
H
L nM
R'
R
H
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MLn
R
R'
H
?
4
2
Introduction
Natural Gas
Methane
Liquefied Natural Gas
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Introduction
CH4
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higher alkanes
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3
Introduction
Chemical conversions of methane
Syngas
CO , H2
CH4
Steam reforming &
partial oxidation
Transiton metal
activation of C-H bond
CH4 + CmH2m
superacid
OM cat.
[Pt] , [Pd]
O2
CH3OH , HCOOH
Reaction with olefins
for higher alkanes
Coupling with silanes
Cm+1H2(m+1)+2
Alkanes Metathesis
CH4 + CnH2n+2
[TM] cat.
R-H + H-SiR'3
cat.
R-SiR'3 + H2
CmH2m+2 + C(n+1-m)H2(n+1-m)+2
Alkanes' Dehydropolymerization
CmH2m+2 + CnH2n+2
2007.10.12
[TM] cat.
Cm+nH2(m+n)+2 + H2
Jean-Marie Basset, Angew. Chem. Int. Ed. 2004, 43, 5366 –5369
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Introduction
Alkane Metathesis
Significant
C-C , C-H Metathesis
σ Bond Metathesis
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Unreactive
‹
Non-selective
‹
Ineffective
‹
General
‹
Direct
‹
Unique
8
4
Outline
¾
Introduction
¾
Mechanism
¾
Examples and Applications
¾
Summary and Outlook
¾
Acknowledgements
2007.10.12
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Mechanism
General Define
The idea of sigma bond metathesis was developed for the progress of
σbond cleavage and formation that catalyzed by alkyl or hydride
complexes of ‘early’ transition metals with d0 electronic configurations.
Extensive experimental and theoretical studies have led to the concept
of the general four-center transition state.
M
E
M
E
M E'
E'
H
E'
H
E
H
M= Sc , Y , Ln ; Ti , Hf , Zr , W , etc.
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5
Mechanism
d0 Metals
1.
Electropositive, very easy to lose all their valence electrons---highest
permissible oxidation state (d0 configuration complexes).
Oxidative addition and reductive elimination are impossible !
Electron-deficient metal center with one or more vacant orbitals would
provide a low-energy means of approach for H-H, C-H bond to M-R bond.
2.
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Mechanism
Ligand
H
Me
H
H
Me
R
Me
Sc
H
H
Cp
Me
R
Zr
R'
Me
Cp*
1. anionic ligands: necessary for d0 metal center
2. η5 ligands: more stable for the complex
3. bulky ligands: able to prevent dimerization or oligomerization
able to block approach of the π-orbital from substituted olefins.
John E. Bercaw et al., J. Am. Chem. Soc. 1987, 109, 203-219.
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Mechanism
R
R
H
R
(Cp*2)Sc
(Cp*2)Sc
H
(Cp*2)Sc
R'
R'
R'
H
Three steps:
(i)
Approach of the H-H or C-H bond to the vacant orbital of Cp*2ScR’;
(ii) Formation of the transition state described above with H occupying the
central β position in all cases;
(iii) Departure of the new H-H or C-H σbond from the opposite side of the
orbital.
Steigerwald, M. L.; Goddard, W. A., III. J. Am. Chem. Soc. 1984, 106, 308.
John E. Bercaw et al., J. Am. Chem. Soc. 1987, 109, 203-219.
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Mechanism
Agostic Interaction
The word “agostic” is derived from the Greek word for “to hold on to
oneself”.(元结作用，抓氢作用) It most commonly refers to a C-H bond on a
ligand that undergoes an interaction with the metal complex. Three-center,
two-electron bridging interaction.
This interaction closely resembles the transition state of an oxidative addition
or reductive elimination reaction. The bonding could also be described as
closely resembling a sigma complex.
Me
H
C
Et
H
B
Mo
N
N
N
N
first example
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P
CO
CO
P
Cl
Cl
Ti
Cl
C
H
Co
H
H
α-agostic interaction
R3P
H
H
H
β-agostic interaction
Cotton, F. A.; LaCour, T.; Stanislowski, A. G. J. Am. Chem. Soc.1974, 96, 754-760.
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Mechanism
H2
C
Cp*
Sc
Cp*
CH2
H
1. The C-H group acts as an electron donor in an interaction with an electron
deficient metal center.
2. One condition for the interaction to be effective is that the hydrogen and the
metal can be brought into contact without straining the system too much.
3. Typical agostic metal-hydrogen distances are 1.9-2.4 Å.
4. The determination of agostic bond strengths is often not possible at all and
only approximate values are proposed. These difficulties lead to uncertain
estimations of those interaction strengths between 1 and 20 kcal.mol-1.
Jorg Grunenberg, et al., Organometallics 2006, 25, 118-121.
Bjorn O. Roos, et al., J. Phys. Chem. A 2007, 111, 6420-6424.
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2007.10.12
Mechanism
Transition State
1.86 A
Cp2Sc
E
H
1.97 A
H
1.53 A
2.11 A
H
H
Cp2Sc
H
0.81 A
H
1.92 A
Cp2Sc
1.85 A
H
H
1.02 A
H
[Cp2ScH] + H2
[Cp2ScH] + H2
Kite-Shaped Transition State
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T. Ziegler, E. Folga, A. Berces, J. Am. Chem. Soc. 1993, 115, 636.
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Mechanism
Selectivity
R
(Cp*2)Sc
H
(Cp*2)Sc
H
R'
R
R'
Thermodynamic control ?
Cp*2Sc-C6H5 + H-CH3
(1)
Cp*2Sc-H + CH3-C6H5
(2)
Cp*2Sc-CH3 + H-C6H5
∆Hθ =∆Hθ (2)-∆Hθ (1)= 4 kcal.mol-1
Consistent with the observed experimental results, but only slightly selective.
Many reactions with other substituents showed a roughly equalΔHθ values.
Steigerwald, M. L.; Goddard, W. A., III. J. Am. Chem. Soc. 1984, 106, 308.
John E. Bercaw et al., J. Am. Chem. Soc. 1987, 109, 203-219.
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Mechanism
Steric effect control ?
A bulky R group, rather than H atom, seems favored atβ position.
Even when R=Me, no C-C coupling product (ethane) was found !
Electronic effect control ?
Difference of electronegativity between C and H.
Much poorer overlap provided by the sp3 C orbital of R in the crucial center β
position results in an overriding, unfavorable electronic effect.
R
(Cp*2)Sc
R'
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H
H
(Cp*2)Sc
R
Unfavored
R'
Steigerwald, M. L.; Goddard, W. A., III. J. Am. Chem. Soc. 1984, 106, 308.
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Outline
¾
Introduction
¾
Mechanism
¾
Examples and Applications
¾
Summary and Outlook
¾
Acknowledgements
2007.10.12
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Examples and Applications
1. IIIB Metals: Sc Y La-Lu Ac-Lr
2. IVB Metals: Ti Zr Hf
3. VB Metals: V Nb Ta
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10
Examples and Applications
1. IIIB Metals: Sc Y La-Lu Ac-Lr
M(η5-Cp*)2CH3 +
13
cyclohexane
CH4
o
M(η5-Cp*)213CH3 + CH4
70 C
M = Lu , Y
H3
C
+ CH4
Lu
Lu
CH3
- CH4
H
C
H3
Patricia L. Watson, J. Am. Chem. Soc. 1983, 105, 6491-6493
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Examples and Applications
1. IIIB Metals: Sc Y La-Lu Ac-Lr
-CH4
Cp*2MCH3
M
M
H
13
13
CH4
Cp*2M13CH3
CH3
Aaron D. Sadow and T. Don Tilley , J. Am. Chem. Soc. 2003, 125, 9462-9475
Carol M. Fendrick and Tobin J. Marks , J. Am. Chem. Soc. 1984, 108, 425-437
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11
Examples and Applications
1. IIIB Metals: Sc Y La-Lu Ac-Lr
CH2C(CH3)3
Th
CH2C(CH3)3
H2
C
closed container
Th
cyclohexane , 50oC
(H3C)3C
H2 C
C(CH3)2
+ H-CH2C(CH3)3
C
H2
H
2*CpTh
CH2
H 2C
C(CH3)2
Carol M. Fendrick and Tobin J. Marks , J. Am. Chem. Soc. 1984, 106, 2214-2216
2007.10.12
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Examples and Applications
1. IIIB Metals: Sc Y La-Lu Ac-Lr
H2
C
Th
cyclohexane , 30oC
C(CH3)2 +
Cp*
Cp*
C(CH3)2 +
CH3
H
H
Th
H
CH3
H
Th
H
H2
C
Th
80±10% yield by NMR
C
H2
H
CH3
H
cyclohexane , 30oC
C
H2
Th
Unstable
β-C elimination !
2007.10.12
Carol M. Fendrick and Tobin J. Marks , J. Am. Chem. Soc. 1984, 108, 425-437
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12
Examples and Applications
1. IIIB Metals: Sc Y La-Lu Ac-Lr
δ-
δ+
R'
H
LnSc-R' + R-H
LnSc-R + R'-H
LnSc
R
δ+
δ-
R, R' = H, alkyl, alkenyl, aryl, alkynyl
An appropriate model for the transition states of such σ bond metathesis
reactions must accommodate the observed order of reactivity of R-H bonds
with Cp*2Sc-R' bonds :
R = R' = H >> R = H, R' = alkyl >> R-H = sp C-H, R' = alkyl > R-H = sp2
C-H, R' = alkyl > R-H = sp3 C-H, R' = alkyl .
John E. Bercaw et al., J. Am. Chem. Soc. 1987, 109, 203-219.
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2007.10.12
Examples and Applications
1. IIIB Metals: Sc Y La-Lu Ac-Lr
Cp*2ScCH3 + CH2=CMe2
80oC
σ-bond metathesis
Cp*2ScCH3
CH2=CHMe
25oC
olefin insertion
Cp*2ScCH2CHMe2
H
Cp2*Sc
C
CMe2
+ CH4
CH2=CHMe
H
Cp2*Sc
80oC, -CH3CHMe2
C
CHMe
σ-bond metathesis
Bulky Cp* ligands block approach of the π-orbitals from substituted olefins !
How about other less sterically encumbered ligands?
2007.10.12
John E. Bercaw et al., J. Am. Chem. Soc. 1987, 109, 203-219.
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13
Examples and Applications
1. IIIB Metals: Sc Y La-Lu Ac-Lr
R
R
OpSc-H =
[OpSc-H]
Sc
Me2Si
H
R
R'
(n+2)
R'
[(Cp*SiNR)(PMe3)ScH] X
R'
(Cp*SiNR)Sc
o
25 C ; -PMe3
R'
n
H2
-[(Cp*SiNR)ScH]
R'
[(Cp*SiNR)(PMe3)ScH] = Me2Si
N
R'
R'
R'
n
R'
H
Ziegler-Natta Catalysts
Me3C
2007.10.12
R'
n
PMe3
Sc
slow β-H elim.
-[(Cp*SiNR)ScH]
John E. Bercaw, Pure & Appl. Chem., 1990, 62, 1151-1154.
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Examples and Applications
1. IIIB Metals: Sc Y La-Lu Ac-Lr
Initial investigation in σbond metathesis
Stoichiometric amount of complex,
rather than catalystic reaction !
III B group metal
complex catalysts:
Providing the general models of investigation
on theoretical calculation.
Unknown Lanthanide series and Actinium series……
2007.10.12
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14
Examples and Applications
2. IVB Metals: Ti Zr Hf
Catalytic dehydrogenative polymerization of silanes
by Ti and Zr metallocene derivatives
R
Cp2MR2
n RSiH3
Si
H
H
(n-1) H2
H +
n
Significance:
A number of applications for polysilanes: photoresists, photoconductors,
semiconductors, nonlinear optical meterials.
As an investigation ahead for methane (alkanes) dehydropolymerization,
which probably shares the same mechanism.
2007.10.12
Hee-Gweon Woo and T. Don Tilley, J. Am. Chem. Soc. 1989, 111, 3757-3158
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Examples and Applications
2. IVB Metals: Ti Zr Hf
Cl
Cp*CpZr
Si(SiMe3)3
+ PhSiH3
Failed to isolate !
Cl
Cp*CpHf
Si(SiMe3)3
2007.10.12
Cl
hν
+ HSi(SiMe3)3
Cp*CpZr
benzene-d6
SiH2Ph
(-SiHPh-)n
+ [CpCp*ZrHCl]
heat or hν
+ PhSiH3
Cl
+ HSi(SiMe3)3
Cp*CpHf
benzene-d6
M
Si
Si
H
SiH2Ph
Hee-Gweon Woo and T. Don Tilley, J. Am. Chem. Soc. 1989, 111, 3757-3158
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15
Examples and Applications
n RSiH3
H
Si
H
Hydrolysis
M
R
Cp2MR2
2. IVB Metals: Ti Zr Hf
H +
(n-1) H2
n
Si
Si
H
+
H
M
H
M
H +
H
Si
Si
M
H' +
H
Si
H
M
Si' +
H
Si
Si
M
Si +
H
Si
H
Hydrogen exchange
M
H
+
H'
H'
Si
M
H
Silane exchange
M
Si
+
Si'
H
Si'
M
Si
Si-Si bond cleavage/formation
M
H
+
Si
Si
Si
M
H
2007.10.12
Hee-Gweon Woo and T. Don Tilley, J. Am. Chem. Soc. 1992, 114, 7047-1055
Hee-Gweon Woo and T. Don Tilley, J. Am. Chem. Soc. 1989, 111, 8043-8044
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Examples and Applications
2. IVB Metals: Ti Zr Hf
Hydrolysis
Cl
H2
Cp*CpM
H
H
Cp*CpClM
Si
(SiMe3)3
Si(SiMe3)3
- HSi(SiMe3)3
Cl
Cp*CpM
H
M = Zr, Hf
H2 should be excess absolutely !
Reverse
Cl
Cp*CpHf
H
PhSiH3
H
H
Cp*CpClHf
H
Si
H
Ph
- H2
Cl
Cp*CpHf
SiH2Ph
Silanes should be excess absolutely !
2007.10.12
Hee-Gweon Woo and T. Don Tilley, J. Am. Chem. Soc. 1992, 114, 7047-1055
Hee-Gweon Woo and T. Don Tilley, J. Am. Chem. Soc. 1989, 111, 8043-8044
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Examples and Applications
2. IVB Metals: Ti Zr Hf
Silane exchange
H
RR'SiH2
Cl
R'
- HSi(SiMe3)3
H
Cp*CpClHf
Cp*CpHf
A
R
Si
Cl
Cp*CpHf
Si
(SiMe3)3
Si(SiMe3)3
SiHRR'
Occur when the starting complex possesses a bulky, easily displaced silyl group !
A : A good starting material !!!
2007.10.12
Hee-Gweon Woo and T. Don Tilley, J. Am. Chem. Soc. 1992, 114, 7047-1055
Hee-Gweon Woo and T. Don Tilley, J. Am. Chem. Soc. 1989, 111, 8043-8044
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Examples and Applications
2. IVB Metals: Ti Zr Hf
Si-Si bond cleavage/formation
Cl
PhSiH3
Cp*CpHf
A
SiPhH2
H
SiPhH2
Cp*CpClHf
H
Si
H
Ph
Cl
+
Cp*CpHf
B
PhH2SiSiPhH2
H
A or B
(SiHPh)n
PhSiH3
SiPhH3 should be excess absolutely !
B is a crucial complex in this process !
2007.10.12
Hee-Gweon Woo and T. Don Tilley, J. Am. Chem. Soc. 1992, 114, 7047-1055
Hee-Gweon Woo and T. Don Tilley, J. Am. Chem. Soc. 1989, 111, 8043-8044
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Examples and Applications
2. IVB Metals: Ti Zr Hf
Dehydropolymerization Catalytic Mechanism
H(SiHR)m(SiHR)nH
MH
H(SiHR)nH
R
H
M
H
R
Si(SiRH)n-1H
Si(SiRH)n-1H
H
M
Si(SiRH)m-1H
H
R
Si-Si bond formation
H(SiHR)mH
2007.10.12
H
H
dehydrogenation
M(SiHR)nH
H2
Hee-Gweon Woo and T. Don Tilley, J. Am. Chem. Soc. 1992, 114, 7047-1055
Hee-Gweon Woo and T. Don Tilley, J. Am. Chem. Soc. 1989, 111, 8043-8044
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Examples and Applications
2. IVB Metals: Ti Zr Hf
Notes:
1.
This polymerization involves step growth of polymer rather than chain growth.
So the relatively low molecular weights are produced, and high monomer
concentration and high vacuum to remove hydrogen can increased MW.
2.
It is well-known that Si has an lower electronegativity to H and can form stable
compounds with expanded 3d coordination spheres.
So the Si atom can occupy the β position in transition state. But C atom seems
very difficult !
Electronegativity:
2007.10.12
Si: 1.9
H: 2.2
C: 2.5
Hee-Gweon Woo and T. Don Tilley, J. Am. Chem. Soc. 1992, 114, 7047-1055
Hee-Gweon Woo and T. Don Tilley, J. Am. Chem. Soc. 1989, 111, 8043-8044
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18
Examples and Applications
3. VB Metals: V Nb Ta
The silica-supported transition metal hydrides:
Si-O Si
Si-O
Ta
H
2
CnH2n+2
Cn+iH2(n+i)+2
+ Cn-iH2(n-i)+2
with i = 1, 2, ......n-1 , but where i = 1 is generally favored.
Successful metathesis of alkanes !
2007.10.12
V. Vidal, A. Theolier, J. Thivolle-Cazat, J.-M. Basset, Science 1997, 276, 99
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Examples and Applications
3. VB Metals: V Nb Ta
2007.10.12
V. Vidal, A. Theolier, J. Thivolle-Cazat, J.-M. Basset, Science 1997, 276, 99
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19
Examples and Applications
3. VB Metals: V Nb Ta
[Ta]S
H
CH3 CH3
H2
[Ta]S CH2CH3
CH4
CH3 CH2
H
CH3 CH3
CH3
[Ta]S CH3
CH3
[Ta]S CHCH3
[Ta]S CH3
CH3 CH3
CH3 CH2CH3
V. Vidal, A. Theolier, J. Thivolle-Cazat, J.-M. Basset, Science 1997, 276, 99
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2007.10.12
Examples and Applications
3. VB Metals: V Nb Ta
cat.
2 C 2H 6
CH4
150oC
+ C3 H8
ΔGθ = - 8.2 kJ·mol-1 .(at 150°C driven by the formation of methane)
Reverse direction :
H2
C3H8
+
CH4
C3H8
CH4
1
/2 C2H6
+ C 3H 8
+
+
cat.
2 C 2H 6
C2H6
1
/2 C4H10
methane/propane = 1250:1
Jean-Marie Basset, Angew. Chem. Int. Ed. 2004, 43, 5366 –5369
2007.10.12
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20
Examples and Applications
3. VB Metals: V Nb Ta
[(
Si O )xTa( CHCMe3 )(CH2CMe3)(3-x)]
x=1, or 2
CH3 R'
CH3 R'
Ta
Ta
R
R
H CH2R'
H
CH2R'
R
R
Ta
Ta
CH3 R'
Ta
R
C-C bond activation
H
CH2R'
R
Ta
C-H bond activation(alkane exchange)
Jean Thivolle-Cazat, Jean-Marie Basset, Angew. Chem. Int. Ed. 2001, 40, 2331-2334
2007.10.12
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Examples and Applications
3. VB Metals: V Nb Ta
Ta
C-C bond activation
C-H bond activation
C1
C
Ta
H
Ta
>
C2
C2
Ta
>
C1 larger than C2
C1
reverse
C-H bond activation
H
C
Ta
>>
not abserved
Jean Thivolle-Cazat, Jean-Marie Basset, Angew. Chem. Int. Ed. 2001, 40, 2331-2334
2007.10.12
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21
Examples and Applications
3. VB Metals: V Nb Ta
Notes:
‹
Silica-supported catalysts have special properties and
have already been used in industrial applications.
‹
Selectivity needs more improvement.
‹
Still difficult for formation of higher alkanes.
Jean Thivolle-Cazat, Jean-Marie Basset, Angew. Chem. Int. Ed. 2001, 40, 2331-2334
2007.10.12
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Outline
¾
Introduction
¾
Mechanism
¾
Examples and Applications
¾
Summary and Outlook
¾
Acknowledgements
2007.10.12
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22
Summary and Outlook
Sigma bond metathesis is a kind of mechanism applied in the progress of σbond
cleavage and formation that catalyzed by alkyl or hydride complexes of ‘early’
transition metals with d0 electronic configurations.
Initial investigation
Stoichiometric reaction
Dehydropolymerization
of Silanes
Silica-supported
alkane metathesis
Where is the future of sigma bond metathesis ?
2007.10.12
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Summary and Outlook
H3C (CH2)n CH3
+
H3C (CH2)n+m-x
+
PR2
O
PR2
X
H3C (CH2)n CH3
CH3
O
H3C (CH2)x CH3
Ir(L)
1: R= t-Bu, X=H
L= C2H4, H2
PR2
2MH2
2M
2
R
olefin metathesis
R
2
X
Ir(L)
PR2
2MH2
R
+ H2C
R
CH2
2M
R
R
+
H3C
CH3
2a: R=t-Bu, X=H
2b: R=i-Pr, X=OMe
L= H2 and/or H4
i
i
-Pr
-Pr
N
(H3C)(F3C)CO
A new idea for alkane metathesis !
2007.10.12
Mo
CHC(CH3)2Ph
(H3C)(F3C)CO
3
A. S. Goldman, et al, Science 2006, 312, 257 – 261.
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23
Summary and Outlook
2007.10.12
A. S. Goldman, et al, Science 2006, 312, 257 – 261.
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Summary and Outlook
This system involves a single metal with dual properties in
contrast to the Goldman–Brookhart system !
i-Pr
i-Pr
N
t-Bu
t-Bu
Mo
O
O
Si
O
O
O
O
Si
O
There are also new methods to afford alkane metathesis, and
sigma bond metathesis is just a kind of them !
C. Copret,* J. T.Cazat, and J.M. Basset, Angew. Chem. Int. Ed. 2006, 45, 6201 –6203
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Summary and Outlook
“This represents a great step forward for ‘green chemistry,’
reducing potentially hazardous waste through smarter production.
Metathesis is an example of how important basic science has been
applied for the benefit of man, society and the environment,”
------ the committee’s comment on 2005 Nobel Prize in Chemistry .
Next Nobel Prize in Organic Chemistry ?
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Outline
¾
Introduction
¾
Mechanism
¾
Examples and Applications
¾
Summary and Outlook
¾
Acknowledgements
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Acknowledgements
PKU, CCME, OPSS
‹
Prof. Zhangjie Shi
‹
All members in my group
‹
All professors and students here
‹
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