Mark Beckman - Flight DynamicsMB-1 Lunar Flight Dynamics Mark Beckman July 12, 2012.
William A. Goddard, III, [email protected] 316 Beckman Institute, x3093
description
Transcript of William A. Goddard, III, [email protected] 316 Beckman Institute, x3093
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 Ch120a-Goddard-
L01
1
Nature of the Chemical Bond with applications to catalysis, materials
science, nanotechnology, surface science, bioinorganic chemistry, and energy
William A. Goddard, III, [email protected] Beckman Institute, x3093
Charles and Mary Ferkel Professor of Chemistry, Materials Science, and Applied Physics,
California Institute of Technology
Teaching Assistants: Caitlin Scott <[email protected]>Hai Xiao [email protected]; Fan Liu <[email protected]>
Lecture 13 February 1, 2011Pd and Pt, MH+ bonding, metathesis
Course number: Ch120aHours: 2-3pm Monday, Wednesday, Friday
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 2
Last time
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 3
Compare chemistry of column 10
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 4
Ground state of group 10 column
Pt: (5d)9(6s)1 3D ground statePt: (5d)10(6s)0 1S excited state at 11.0 kcal/molPt: (5d)8(6s)2 3F excited state at 14.7 kcal/mol
Pd: (5d)10(6s)0 1S ground statePd: (5d)9(6s)1 3D excited state at 21.9 kcal/molPd: (5d)8(6s)2 3F excited state at 77.9 kcal/mol
Ni: (5d)8(6s)2 3F ground stateNi: (5d)9(6s)1 3D excited state at 0.7 kcal/molNi: (5d)10(6s)0 1S excited state at 40.0 kcal/mol
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 5
Salient differences between Ni, Pd, Pt
Ni Pd Pt
4s more stable than 3d 5s much less stable than 4d 6s, 5d similar stability3d much smaller than 4s(No 3d Pauli orthogonality)Huge e-e repulsion for d10
4d similar size to 5s (orthog to 3d,4s
Differential shielding favors n=4 over n=5,
stabilize 4d over 5s d10
2nd row (Pd): 4d much more stable than 5s Pd d10 ground state
3rd row (Pt): 5d and 6s comparable stability Pt d9s1 ground state
Relativistic effects of 1s huge decreased KE contraction stabilize and contract all ns destabilize and expand nd
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 6
Mysteries from experiments on oxidative addition and reductive elimination of CH and CC bonds on Pd and Pt
Why is CC coupling so much harder than CH coupling?
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 7
Step 1: examine GVB orbitals for (PH3)2Pt(CH3)
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 8
Analysis of GVB wavefunction
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 9
Alternative models for Pt centers
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 10
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 11
energetics
Not agree with experiment
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 12
Possible explanation: kinetics
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 13
Consider reductive elimination of HH, CH and CC from Pd
Conclusion: HH no barrier
CH modest barrierCC large barrier
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 14
Consider oxidative addition of HH, CH, and CC to Pt
Conclusion: HH no barrier
CH modest barrierCC large barrier
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 15
Summary of barriers
But why?
This explains why CC coupling not occur for Pt while CH and HHcoupling is fast
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 16
How estimate the size of barriers (without calculations)
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 17
Examine HH coupling at transition state
Can simultaneously get good overlap of H with Pd sd hybrid and with the other H
Thus get resonance stabilization of TS low barrier
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 18
Examine CC coupling at transition state
Can orient the CH3 to obtain good overlap with Pd sd hybrid OR can orient the CH3 to obtain get good overlap with the other CH3
But CANNOT DO BOTH SIMULTANEOUSLY, thus do NOT get resonance stabilization of TS high barier
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 19
Examine CH coupling at transition state
H can overlap both CH3 and Pd
sd hybrid simultaneously but CH3 cannot
thus get ~ ½ resonance
stabilization of TS
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 20
Now we understand Pt chemistry
But what about Pd?
Why are Pt and Pd so dramatically different
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 21
new
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 22
Pt goes from s1d9 to d10 upon reductive eliminationthus product stability is DECREASED by 12 kcal/mol
Using numbers from QM
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 23
Ground state configurations for column 10
Ni Pd Pt
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 24
Pd goes from s1d9 to d10 upon reductive eliminationthus product stability is INCREASED by 20 kcal/mol
Using numbers from QM
Pd and Pt would be ~ same
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 25
Thus reductive elimination from Pd is stabilized by an extra 32 kcal/mol than for Pt due to the ATOMIC nature of the states
The dramatic stabilization of the product by 35 kcal/mol reduces the barrier from ~ 41 (Pt) to ~ 10 (Pd)
This converts a forbidden reaction to allowed
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 26
Summary energetics
Conclusion the atomic character of the metal can
control the chemistry
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 27
Examine bonding to all three rows of transition metals
Use MH+ as model because a positive metal is more representative of organometallic and inorganic complexes
M0 usually has two electrons in ns orbitals or else one
M+ generally has one electron in ns orbitals or else zero
M2+ never has electrons in ns orbitals
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 28
Ground states of neutral atoms
Sc (4s)2(3d)Ti (4s)2(3d)2V (4s)2(3d)3Cr (4s)1(3d)5Mn (4s)2(3d)5Fe (4s)2(3d)6Co (4s)2(3d)7Ni (4s)2(3d)8Cu (4s)1(3d)10
Sc++ (3d)1Ti ++ (3d)2V ++ (3d)3 Cr ++ (3d)4Mn ++ (3d)5Fe ++ (3d)6 Co ++ (3d)7 Ni ++ (3d)8 Cu++ (3d)10
Sc+ (4s)1(3d)1Ti+ (4s)1(3d)2V+ (4s)0(3d)3Cr+ (4s)0(3d)5Mn+ (4s)1(3d)5Fe+ (4s)1(3d)6Co+ (4s)0(3d)7Ni+ (4s)0(3d)8Cu+ (4s)0(3d)10
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 29
Bond energies MH+
Cr
Mo
Re
Ag
Cu
Au
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 30
Exchange energies:
Get 6*5/2=15 exchange terms5Ksd + 10 KddResponsible for Hund’s rule
Ksd KddMn+ 4.8 19.8 Tc+ 8.3 15.3Re+ 11.9 14.1
kcal/mol
Form bond to H, must lose half the exchange stabilization for the orbital bonded to the H
A[(d1a)(d2a)(d3a)(d4a)(d5a)(sa)]
Mn+: s1d5
For high spin (S=3)
A{(d1a)(d2a)(d3a)(d4a)(sdba)[(sdb)H+H(sdb)]( -ab ba)}sdb is a half the time and b half the time
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 31
Ground state of M+ metalsMostly s1dn-1Exceptions:1st row: V, Cr-Cu2nd row: Nb-Mo, Ru-Ag3rd row: La, Pt, Au
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 32
Size of atomic orbitals, M+
Valence s similar for all three rows,5s biggest
Big decrease from La(an 57) to Hf(an 72
Valence d very small for 3d
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 33
Charge transfer in MH+ bondselectropositive
electronegative
1st row all electropositive
2nd row: Ru,Rh,Pd
electronegative3rd row:
Pt, Au, Hg electronegative
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 34
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 35
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 36
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 37
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 38
1st row
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 39
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 40Schilling
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 41
Steigerwald
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 42
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 43
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 44
2nd row
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 45
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 46
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 47
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 48
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 49
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 50
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 51
3rd row
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 52
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 53
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 54
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 55
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 56
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 57
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 58
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 59
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 60
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 61
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 62
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 63
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 64
Physics behind Woodward-Hoffman Rules
For a reaction to be allowed, the number of bonds must be conserved. Consider H2 + D2
2 bonds TS ? bonds 2 bonds
Bonding2 elect
nonbonding1 elect
antibonding0 elect
Have 3 electrons, 3 MO’s
Have 1 bond. Next consider 4th atom, can we get 2 bonds?
To be allowed must have 2 bonds at TSHow assess number of bonds at the TS. What do the dots mean? Consider first the fragment
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 65
Can we have 2s + 2s reactions for transition metals?
2s + 2s forbidden for organics
X
Cl2Ti Cl2Ti Cl2Ti? ?
2s + 2s forbidden for organometallics?
Cl2Ti Cl2Ti Cl2TiMe
Me
Me
Me
Me
Me
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 66
Physics behind Woodward-Hoffman Rules
Bonding2 elect
nonbonding1 elect
antibonding0 elect
Have 1 bond. Question, when add 4th atom, can we get 2 bonds?
Can it bond to the nonbonding orbital?
Answer: NO. The two orbitals are orthogonal in the TS, thus the reaction is forbidden
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 67
Now consider a TM case: Cl2TiH+ + D2
Orbitals of reactants
GVB orbitals of TiH bond for Cl2TiH+
GVB orbitals of D2
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 68
Is Cl2TiH+ + D2 Cl2TiD+ + HD allowed?
Bonding2 elect
nonbonding1 elect
antibonding0 elect
when add Ti 4th atom, can we get 2 bonds?
Answer: YES. The two orbitals can have high overlap at the TS orthogonal in the TS, thus the reaction is allowed
Now the bonding orbital on Ti is d-like. Thus at TS have
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 69
GVB orbitals at the TS for Cl2TiH+ + D2 Cl2TiD+ + HD
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 70
GVB orbitals for the Cl2TiD+ + HD productNote get phase change for both orbitals
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 71
Follow the D2 bond as it
evolves into the HD bond
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 72
Follow the TiH bond as it
evolves into the TiD bond
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 73
Barriers small, thus allowed
Increased d character in bond smaller barrier
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 74
Are all MH reactions with D2 allowed? No
Example: ClMn-H + D2
Here the Mn-Cl bond is very polar
Mn(4s-4pz) lobe orbital with Cl:3pz
This leaves the Mn: (3d)5(4s+4pz), S=3 state to bond to the HBut spin pairing to a d orbital would lose
4*Kdd/2+Ksd/2= (40+2.5) = 42.5 kcal/mol
whereas bonding to the (4s+4pz) orbital loses
5*Ksd/2 = 12.5 kcal/mol
As a result the H bonds to (4s+4pz), leaving a high spin d5.
Now the exchange reaction is forbidden
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19
Thus ClMn-H bond is sp-likeClMnH
Mn (4s)2(3d)5
The Cl pulls off 1 e from Mn, leaving a d5s1 configurationH bonds to 4s because of exchange stabilization of d5
Mn-H bond character0.07 Mnd+0.71Mnsp+1.20H
This cannot overlap the antisymmetric orbital delocalized over the three H atoms in the TSAs a result at the Transition state the MnH bond has the character of H3
- with both electrons on the H3.
This leads to a high barrier, ~45 kcal/mol
© copyright 2011 William A. Goddard III, all rights reservedCh120a-Goddard-L19 76
Show reaction for ClMnH + D2
Show example reactions
© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 77
Olefin Metathesis
Diego Benitez, Ekaterina Tkatchouk, Sheng Ding
2+2 metal-carbocycle reactions
© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 78
Mechanism: actual catalyst is a metal-alkylidene
R1 R1 R2 R2+
R1 R22
M
R2
R1 R3
M
R2
R1 R3
M
R2
R1 R3
Catalytically make and break double bonds!
OLEFIN METATHESIS
© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 79
Ru Olefin Metathesis Basics
© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 80
Common Olefin Metathesis Catalysts
© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 81
Applications of the olefin metathesis reaction
Acc. Chem. Res. 2001, 34, 18-29
http://www.pslc.ws/macrog/pdcpd.htmbulletproof resin
Small scale synthesisto industrial polymers
© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 82
History of Olefin Metathesis Catalysts
Ch120-L20 13/11/02GODDARD 83
Well-defined metathesis catalysts
RuPCy3
Ph
Cl
ClNN MesMes
RuPCy3
Ph
Cl
ClNN MesMes
R R
R=H, Ph, or -CH2-(CH2)2-CH2-
R R
R=H, Cl
NMo
PhCH3
CH3(F3C)2MeCO(F3C)2MeCO
iPr iPrRuPCy3
PCy3
Ph
Cl
Cl
1 2 3 4Schrock 1991alkoxy imido molybdenum complexa
Bazan, G. C.; Oskam, J. H.; Cho, H. N.; Park, L. Y.; Schrock, R. R. J. Am. Chem. Soc. 1991, 113, 6899-6907
Grubbs 1991 ruthenium
benzylidene complexb
Grubbs 19991,3-dimesityl-imidazole-2-ylidenes
P(Cy)3 mixed ligand system”c
Scholl, M.; Trnka, T. M.; Morgan, J. P.; Grubbs, R. H. Tetrahedron Lett. 1999, 40, 2247-2250.
Wagener, K. B.; Boncella, J. M.; Nel, J. G. Macromolecules 1991, 24, 2649-2657
© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 84
Examples of Common Second Generation Grubbs-typeMetathesis Catalysts and Mechanism Overview
Ru
NNMes MesCl
Cl PhPCy3
Ru
NNMes MesCl
Cl PhPy
Ru
NNMes MesCl
ClO
i-Pr
slow initiating catalyst ultra-fast-initiating catalystfast-initiating catalyst
RuCl
IMesCl
RLPh
IMes
Ru
LCl
ClInitiation
Ru
Cl
IMesCl
Cl
IMesClR
R2
RuR3
RuCl
IMesCl
R1
PropagationR2R3
R3
R2
R1
+
Examples 2nd Generation Grubbs Metathesis Catalysts
General mechanism of Metathesis
© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 85
Schrock and Grubbs catalysts make olefin metathesis practical
Schrock catalyst –very active, but destroysmany functional groups
Grubbs catalyst –very stable, high functionalgroup tolerance, but not asreactive as Schrock
Catalysts contain many years of evolutionary improvements