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Structural and Mechanistic Aspects of Copper Catalyzed Atom Transfer Radical
Addition Reactions in the Presence of Reducing Agents
William T. Eckenhoff and Tomislav PintauerDepartment of Chemistry and Biochemistry
Duquesne UniversityPittsburgh, PA 15282
1Thesis Defense
Kharasch Addition Reaction
• Free Radical Mechanism• Initiated by light or radical
initiators (e.g. AIBN)PRINCIPLE PROBLEMS:
- Unavoidable radical-radical termination reactions (kt≈1.0×109 M-1s-1)
- Repeating radical addition to alkene to generate oligomers/polymers
- Low chain transfer constant (ktr/kp)
SOLUTIONS:- Search for better halogen
transfer agents (transition metal complexes)
2
Initiation:
Propagation:
Termination:
+ Br3C Brki + CBr3
+kadd Br3C
R
kp
RR Br3C
R
Rn
Br3CR +
ktrBr3C
R
Br
+
radical-radical coupling
+kt
Br3C CBr3
+kt
Br3CR + Br3C
R
kt
etc.
Br3C
monoadduct
R
CBr3R
AIBNΔ
CN+ N2
CN CN
Br
CBr3
Br3C Br CBr3
CBr3 CBr3
CN CN CN
CN
Kharasch, M. S.; Jensen, E. V.; Urry, W. H. Science 1945, 102, 128.
Transition Metal Catalyzed (TMC) ATRA
3
• Transition metal complexes of Fe, Ru, Co, Ni and Cu are particularly effective halogen transfer agents.
• Variety of alkenes and alkyl halides can be utilized.
TO ACHIEVE HIGH YIELDS:- Radical concentration must be
low (ka,1 and ka,2<<kd,1 and kd,2)- Further activation of the
monoadduct should be avoided (ka,1>>ka,2 and ka,2≈0)
- The formation of oligomers/polymers should be suppressed (kd,2[CuIILmX]>>kp[alkene])
Minisci, F. Acc. Chem. Rec. 1975, 8, 165.Clark, A. J. Chem. Soc. Rev. 2002, 31, 1.Severin, K. Curr. Org. Chem. 2006, 10, 217.
kp
RR'
R'n
L=complexing ligandX=halide or pseudo halide
CuIILmX2
CuILmX
R
R X
R'R
kadd
R'
R'
XR
R kt
R R
ka,1
kd,1
ka,2
kd,2
R'
R kt
R'R
R
etc.
K1=ka,1kd,1
K2=ka,2kd,2
kd,1 kd,2
ka,1 ka,2
TMC ATRA in Organic Synthesis• Can be conducted intermolecularly and intramolecularly.• Atom transfer radical cyclization (ATRC) is a particularly
attractive tool because it enables synthesis of functionalized ring systems.
4
CCl3
OO
CH3CN, 110 oC
CuCl (30 mol%)O
ClClCl
O
95% yield16 h
CCl3
NO
CH3CN, RT
CuCl/bpy (5 mol%)15 min
SO3CH3SO3CH3
N
ClClCl
O
91% yield
O O
OEtCl Cl
DCE, 80 oC
CuCl/bpy (25 mol%)18 h
O O
OEtCl
Cl61% yield
H
Clark, A. J. Chem. Soc. Rev. 2002, 31, 1.Yang, D.; Yan, Y. -L.; Zheng, B. -F.; Gao, Q.; Zhu, N.-Y. Org. Lett. 2006, 8, 5757.
γ-lactones and γ-lactams
Cascade TMC ATRA
TMC ATRA is not Widely Used in Organic Synthesis
5SciFinder Scholar Search as of February 1, 2010
Current Drawbacks of TMC ATRA
• TMC ATRA despite being discovered nearly 20 years before tin mediated radical addition to olefins and iodine atom transfer radical addition is still not fully utilized as technique in organic synthesis.
• The principal reason is that TMC ATRA typically requires between 5 and 30 mol% of catalyst relative to alkene.
• Problems in product separation and catalyst recycling.• Process is environmentally unfriendly and expensive.
6
Methodologies developed to overcome these drawbacks: Design of solid supported catalysts Use of biphasic systems (fluorous solvents) Development of highly active complexes based on ligand
design Catalyst regeneration in the presence of reducing
agents✓Clark, A. J. Chem. Soc. Rev. 2002, 31, 1.
Catalyst Regeneration in the Presence of Reducing Agents
Eckenhoff, W. T.; Pintauer, T. Cat. Rev. - Sci. Eng. 2010, 51, 1-59.Ricardo, C.; Pintauer, T. Chem. Comm. 2009, 21, 3029-3031.Pintauer, T.; Matyjaszewski, K. Chem. Soc. Rev. 2008, 37, 1087.Eckenhoff, W. T.; Garrity, S. T.; Pintauer, T. Eur. J. Inorg. Chem. 2008, 563.Eckenhoff, W. T.; Pintauer, T. Inorg. Chem. 2007, 46, 5844.Quebatte, L.; Thommes, K.; Severin, K. J. Am. Chem. Soc. 2006, 128, 7440.Matyjaszewski, K.; Jakubowski, W.; Min, K.; Tang, W.; Huang, J.; Braunecker, W. A.; Tsarevsky, N. V. Proc. Natl. Acad. Sci. U.S.A. 2006, 103, 15309.
AIBN
N2
CN
X
CN Δ
+ R X + Rka,1
kd,1
R R
kt
MtnLm Mtn+1LmX • Originally developed for atom transfer radical polymerization (ATRP).
• Successfully applied to ATRA catalyzed by copper(II) and ruthenium(III) complexes.
• The rate of alkene consumption in ATRA depends on the ratio of concentrations of activator (CuI) and deactivator (CuII-X):
• Deactivator accumulates during the process as a result of radical termination reactions.
• Reducing agents can be used to regenerate activator.
7
€
−d[M]dt
= kadd[M][R•] =kaddKATRA[M][RX][CuI]
[CuII − X]
TMC-ATRA in the Presence of Reducing Agents
8
ATRA Catalyzed by CuI(TPMA)Cl Complex in the Presence of Reducing Agent AIBN
• Can be conducted using either copper(I) or copper(II) complex.• TONs for 1-octene (4350-6700) and 1-hexene (4900-7200) highest so far for copper
mediated ATRA.• Previous TONs ranged between 0.1 and 10!
9Eckenhoff, W. T.; Pintauer, T. Inorg. Chem. 2007, 46, 5844.
Entry Alkene RCl [Alkene]0/[CuI]0 Yield (%) TON
1 2 3 4 5 6 7 8 9 10 11 1 2
1-hexene 1-octene styrene methyl acrylate 1-hexene 1-octene styrene methyl acrylate
CCl4
CCl4
CCl4
CCl4 CHCl3
CHCl3
CHCl3
CHCl3
10000:1 5000:1 10000:1 5000:1 1000:1 500:1 250:1 1000:1 1000:1 500:1 1000:1 1000:1
72 98 67 87 42 54 85 60 56 49 58 6 3
7200 4900 6700 4350 420 270 212 600 560 245 580 630
TPMA
• Highest TONs for copper mediated ATRA
• Highly efficient ATRA in the presence of 5-100 ppm of copper
10
ATRA Catalyzed by [CuII(TPMA)Br][Br] Complex in the Presence of Reducing Agent AIBN
Entry Alkene RBr [Alkene]0:[CuII]0 Yield (%) TON1 methyl acrylate CBr4 / 32 /2 200,000:1 81(76) 1.6×105
3 100,000:1 94 9.4×104
4 styrene CBr4 / 72 /5 200,000:1 95(86) 1.9×105
6 100,000:1 99 9.9×104
7 methyl acrylate CHBr3 1,000:1 57 5.7×102
8 500:1 66 3.3×102
9 styrene CHBr3 10,000:1 70 7.0×103
10 5,000:1 77 3.9×103
11 1,000:1 92 9.2×102
12 1-hexene CHBr3 10,000:1 61(59) 6.1×103
13 1-octene CHBr3 10,000:1 69(54) 6.9×103
14 1-decene CHBr3 10,000:1 63(64) 6.3×103
Eckenhoff, W. T.; Garrity, S. T.; Pintauer, T. Eur. J. Inorg. Chem. 2008, 563.
Copper Catalyzed ATRA of Highly Active Alkenes
11
• Alkenes with high propagation rate constants in free radical polymerization require large catalyst loadings.
• Competing radical polymerization initiated by AIBN at elevated temperatures.
• Solution is to utilize redox reducing agents (ascorbic acid, glucose, magnesium, etc.) or low temperature free radical initiators such as V-70
Pintauer, T.; Eckenhoff, W.T.; Balili, M. N. C.; Biernesser, A. B.; Noonan, S. J.; Ricardo, C.; Taylor, M. J. W. Chem. Eur. J. 2009, 15, 38.Beuermann, S.; Buback, M. Prog. Poly. Sci. 2002, 27, 191-254
Alkenekp (M-1 s-1)
60oC 25oC
2.8x104 1.3x104
3.1x104 1.5x104
7.9x103 3.4x103
Highly Efficient Ambient Temperature ATRA in the Presence of V-70 as a Reducing Agent
12Pintauer, T.; Eckenhoff, W.T.; Balili, M. N. C.; Biernesser, A. B.; Noonan, S. J.; Ricardo, C.; Taylor, M. J. W. Chem. Eur. J. 2009, 15, 38.
• For simple α-olefins, efficient ATRA was achieved using as little as 0.002 mol% of [CuII(TPMA)X][X] complexes (20 ppm!!!).
• Reactions were also very efficient for methyl acrylate, methyl methacrylate and vinyl acetate.
Structural Features of CuI(TPMA)Cl and [CuII(TPMA)Cl][Cl] Complexes
• Copper(I) and copper(II) complexes are structurally similar.13
CuI(TPMA)Cl [CuII(TPMA)Cl][Cl]
Eckenhoff, W. T.; Pintauer, T. Inorg. Chem. 2007, 46, 5844.
14
Structural Features of CuI(TPMA)Br and [CuII(TPMA)Br][Br] Complexes
• Copper(I) and copper(II) complexes are structurally similar.
CuI(TPMA)Br [CuII(TPMA)Br][Br]
Eckenhoff, W. T.; Garrity, S. T.; Pintauer, T. Eur. J. Inorg. Chem. 2008, 563.
15
Questions about ATRA Mechanism
MtnLm Mtn+1Lm + eKET
X + eKEA
X
R-X R + X
X + Mtn+1Lm Mtn+1LmX
KBH
KHP
MtnLm + RX Mtn+1LmX + RKATRA
Electron Transfer
Electron Affinity
Bond Homolysis
Halidophilicity
For a given alkyl halide KATRA will depend on
KET and KHP
KATRA=KEAKBHKHPKET
KATRAKEAKBH
= KETKHP
• The role of halide anion coordination to [CuI(TPMA)]+ remains unclear.
• Nature of ATRA (ISET or OSET)?
• Equilibrium constant for ATRA can be expressed in terms of:
Lin, C.Y.; Coote, M.L.; Gennaro, A.; Matyjaszewski, K. J. Am. Chem. Soc. 2008, 130(38), 12762-12774
16
Correlating Redox Potential with Catalyst Activity
E1/2 / mV v.s. SCE0 -50 -100 -150 -200 -250 -300 -350 -400 -450 -500
N N
RR
N N R
N
N
N
NN
N
R
R RN
NNN
N
N
NN
N
N N
N
More Reducing CuIBr ComplexesHigher Activity in ATRA
Qiu, J.; Matyjaszewski, K.; Thouin, L.; Amatore, C. Macromol. Chem. Phys. 2000, 201, 1625-1631.
17
Cyclic Voltammetry of [CuI(TPMA)][A] Complexes
• Coordination of bromide anion to [CuI(TPMA)]+ results in a formation of much more reducing CuI(TPMA)Br complex.
• Based on CV (KATRA), CuI(TPMA)Br complex should be a MILLION times more active in ATRA.
Complex Supp. Elect. E1/2 /mV ΔEp / mV ipa/ipc
[CuI(TPMA)][BPh4] TBA-BPh4 -397 107 1.17
TBA-Br -699 109 0.94
[CuI(TPMA)][ClO4] TBA-ClO4 -422 94 0.95
TBA-Br -706 97 0.92
[CuI(TPMA)][PF6] TBA-PF6 -421 88 0.94
TBA-Br -711 88 0.91
CuI(TPMA)Br TBA-Br -720 93 1.08
CuI(TPMA)Cl TBA-Cl -742 111 1.16
Potentials are reported vs. Fc/Fc+.
Eckenhoff, W. T.; Pintauer, T. unpublished resultsEckenhoff, W. T.; Garrity, S. T.; Pintauer, T. Eur. J. Inorg. Chem. 2008, 563.
Cyclic Voltammetry of [CuI(TPMA)][A] Complexes
18Eckenhoff, W. T.; Pintauer, T. unpublished results
• TBA-Br was titrated into a solution of [CuI(TPMA)BPh4] and was observed to quantitatively displace BPh4 from copper(I) complex.
• Explains effect of supporting salt on E1/2 on [CuI(TPMA)X] complexes.
• Displays strongly affinity of Br- to Cu(I).
Eckenhoff, W. T.; Pintauer, T. unpublished results 30
Conductivity of Copper Complexes
• Conductance of copper(I) species reflect degree of ionic character.
• Complexes with halide anions were found to have less conductivity than those with non-coordination counter-ions.
• Suggests association in solution19
Complex Conductivity (µS)CuI(TPMA)Cl 2.64(±0.01)CuI(TPMA)Br 3.01(±0.02)
CuI(TPMA)ClO4 5.50(±0.05)CuI(TPMA)BPh4 6.29(±0.02)CuI(TPMA)PF6 6.39(±0.11)
Eckenhoff, W. T.; Pintauer, T. unpublished results
Catalytic Performance of [CuII(TPMA)][A] Complexes in ATRA
• The counter-ion appears to have little or no effect on catalytic performance in ATRA in the presence of AIBN.
• Does the counter-ion effect the rate of alkene consumption?20
Complex R-X Alkene Alkene:Catalyst Conversion Selectivity Yield
[Cu(TPMA)Cl][Cl] CCl4 Hexene 5000:1 100% 100% 100%[Cu(TPMA)Cl][ClO4] 100% 100% 100%
[Cu(TPMA)Cl][PF6] 100% 100% 100%
[Cu(TPMA)Cl][BPh4] 100% 100% 100%
[Cu(TPMA)Cl][Cl] CCl4 Octene 5000:1 99% 100% 99%
[Cu(TPMA)Cl][ClO4] 99% 100% 99%
[Cu(TPMA)Cl][PF6] 99% 100% 99%
[Cu(TPMA)Cl][BPh4] 95% 100% 95%
[Cu(TPMA)Cl][Cl] CCl4 Styrene 1000:1 76% 59% 45%
[Cu(TPMA)Cl][ClO4] 83% 60% 50%
[Cu(TPMA)Cl][PF6] 81% 60% 49%
[Cu(TPMA)Cl][BPh4] 79% 59% 47%
[Cu(TPMA)Cl][Cl] CCl4 Methyl Acylate 1000:1 100% 45% 45%
[Cu(TPMA)Cl][ClO4] 100% 48% 48%
[Cu(TPMA)Cl][PF6] 100% 48% 48%
[Cu(TPMA)Cl][BPh4] 100% 44% 44%Reactions performed at 60oC in CH3CN, [alkene]0:[R-X]0:[AIBN]0=1:1:0.05, [alkene]0=2.10 M. Conv., Prod., and Yields determined by 1H NMR
Eckenhoff, W. T.; Pintauer, T. unpublished results
Catalytic Performance of [CuII(TPMA)X][Y] Complexes in ATRA with AIBN
21
[1-Oct]0:[CCl4]0:[AIBN]0:[CuII]0=5000:5000:250:1 • Rate of consumption of alkene is independent on counter-ion.
• Rate should depend only on AIBN concentration.
• However, product distribution (particularly for highly active alkenes) MUST depend on catalyst nature (ka and kd)
€
kp[alkene]kd[CuII]
Controls the product yield
RX + CuILXka
kdR + CuIILX2
Eckenhoff, W. T.; Pintauer, T. unpublished results
Reactions performed at 60oC in CH3CN, [alkene]0:[CCl4]0:[AIBN]0 =1:1:0.05, [alkene]0=2.10 M. Conv. determined by 1H NMR
Catalytic Performance of [CuI(TPMA)Y] Complexes in ATRA without AIBN
• Using 50:1 alkene to copper ratio, without AIBN present, complexes with non-coordinating counter-ions were more active
22Eckenhoff, W. T.; Pintauer, T. unpublished results
Reactions performed at 60oC in CH3CN, [alkene]0:[CCl4]0 =1:1, [alkene]0=2.10 M. Conv. determined by 1H NMR
[MA]0:[CCl4]0:[Cu]0=50:50:1
Complex KATRA (10-7)
[CuI(TPMA)Cl] 2.21(±0.07)
[CuI(TPMA)ClO4] 4.65 (±0.03)
[CuI(TPMA)BPh4] 4.48 (±0.07)
Structural Features of CuI(TPMA)Br in Solution
• Low T 1H NMR consistent with X-ray structure.
23
1H NMR400 MHz, (CD3)2CO
Proton Δδ / ppmH1 0.60H2 0.12H3 0.05H4 -0.32H5 0.10
• Broadening of the spectra is induced by fluxional processes:
• Dimer formation unlikely (inequivalent methylene protons).
1. TPMA dissociation 2. Br- dissociation
Eckenhoff, W. T.; Garrity, S. T.; Pintauer, T. Eur. J. Inorg. Chem. 2008, 563.
Solution Equilibria for CuI(TPMA)X Complexes
24
Possible Reasons for TPMA Fluxionality1. Halide dissociation2. TPMA arm dissociation
298 K
Eckenhoff, W. T.; Pintauer, T. Unpublished results
• Addition of TBA-Br results TPMA signals shifting towards free ligand.
• Binding of TPMA is probably in equilibrium driven to the uncomplexed form.
Structural Features of [CuI(TPMA)(CH3CN)][BPh4]
25
Similar to CuI(TPMA)XCu1-N1=2.430(6) ÅCu1-N2=2.069(6) ÅCu1-N3=2.077(6) ÅCu1-N4=2.122(6) ÅCu1-N5=1.990(6) Å
Axial elongationof Cu-N bond
Eckenhoff, W. T.; Pintauer, T. Inorg. Chem. 2010, 49(22), 10617-10626
• First example of a dimer where one arm of TPMA ligand coordinates to the second metal center
26
Structural Features of [CuI(TPMA)]2[ClO4]2
Distorted TetrahedralCu1-N1=2.2590(13) ÅCu1-N2=1.9909(12) ÅCu1-N3=2.2213(16) ÅCu1-N4=1.9593(13) Å
1H NMR (400 MHz, (CD3)2CO)
Eckenhoff, W. T.; Pintauer, T. Inorg. Chem. 2010, 49(22), 10617-10626 Eckenhoff, W. T.; Pintauer, T. Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.) 2008, 49(2), 282.
Structural Features of [CuI(TPMA)(CH3CN)][BPh4]
27
90% Monomeric10% Dimeric
[CuI(TPMA)]2[ClO4]2
[CuI(TPMA)BPh4]
180 K
[CuI(TPMA)][BPh4]
Trigonal PyramidalCu1-N1=2.211(3) Å
Cu1-Cu2=2.832(5) Å
1H NMR (400 MHz, (CD3)2CO)
Eckenhoff, W. T.; Pintauer, T. Inorg. Chem. 2010, 49(22), 10617-10626
Structural Features of [(CuI(TPMA))-µBr][BPh4]
• Originated from attempted synthesis of [CuI(TPMA)BPh4] by salt metathesis with [CuI(TPMA)Br]
• Shows another motif of copper(I) stabilization not previously considered
• Also indicates strong preference for halide binding
28
Bimetallic Distorted TetrahedralCu1-N1=2.429(2) ÅCu1-N2=2.067(2) ÅCu1-N3=2.131(2) ÅCu1-N4=2.065(2) Å
Cu1-Br1=2.5228(4) ÅEckenhoff, W. T.; Pintauer, T. Inorg. Chem. 2010, 49(22), 10617-10626
1H NMR of CuI(TPMA)Br with Excess TPMA
29
1H NMR (400 MHz)(CD3)2CO
CuI(TPMA)Br + TPMA* CuI(TPMA)*Br + TPMAK
-3
-2
-1
0
1
2
3
4
0.0035 0.004 0.0045 0.005 0.0055
ln(k/T)
1/T(K)
Eckenhoff, W. T.; Pintauer, T. Unpublished results
ΔH‡=2.96 KJΔS‡=-60 J K-1
ΔG‡=43.25 KJ (10.3 kcal)
TPMA Arm Dissociation from Copper(I) Center
• Large coordinating ligands can displace single arm of TPMA.• Also demonstrated previously with 1,4-diisocyanobenzene.
30
Molecular Structure of [CuI(TPMA)2(4,4’-dipyridyl)][BPh4]2
Cu-Nax 2.325 ÅCu-Neq 2.085, 2.052 ÅCu-Ndis 2.523 ÅCu-Ndp 1.998 Å
Eckenhoff, W. T.; Pintauer, T. Inorg. Chem. 2010, 49(22), 10617-10626Hsu, S.C.; Chien, S.S.; Chen, H.H.; Chiang, M.Y. J. Chin. Chem. Soc. 2007, 54(3), 685-692
ATRA Inhibition with PPh3
• PPh3 bonds strongly to copper, displacing a pyridyl arm
• Tetrahedral geometry• Oxidatively stable in air• Pyridine signals shifted upfield from
PPh3 donation/weaker Py coordination• 31P NMR shows downfield shift
31
Molecular Structure of [CuI(TPMA)2PPh3][BPh4]2
Cu-Nax 2.214 ÅCu-Neq 2.073, 2.114ÅCu-Ndis 3.327 ÅCu-P 2.1853 Å
Eckenhoff, W. T.; Pintauer, T. Inorg. Chem. 2010, 49(22), 10617-10626
Tyeklar, Z.; Jacobson, R. R.; Wei, N.; Murthy, N. N.; Zubieta, J.; Karlin, K. D.J. Am. Chem. Soc. 1993, 115, 2677-2689.
-N-CH2-BPh4
BPh4
BPh4
Py -CH
Py -CH+ PPh3
PPh3
Py -CH
ATRA Inhibition with PPh3
• Addition of more than stoichiometric quantities of PPh3 inhibited ATRA, but small amounts had little effect
• Rate decreased by a factor of 10, almost completely stopped with 20 eq. of PPh3 with the [Cu(TPMA)Cl][Cl] catalyst
• Similar effect found with P-(OBu)4
32Eckenhoff, W. T.; Pintauer, T. unpublished results
Reactions performed at 60oC in CH3CN, [alkene]0:[R-X]0:[AIBN]0=1:1:0.05, [alkene]0=2.21 M. Yields determined by 1H NMR
Alkene R-X Alk./Cat. 0 Eq. PPh3 20 Eq. PPh3 40 Eq. PPh3
1-Hexene CCl4 5000:1 100% 95% 78%1-Octene CCl4 5000:1 100% 76% 22%
Styrene CCl4 1000:1 26% 0%Methyl Acrylate CCl4 1000:1 44% 28%
ATRA in the presence of PPh3
• ATRA catalyzed by [Cu(TPMA)PPh3][BPh4] proceeds similarly to [Cu(TPMA)Cl][Cl].
• R-X homolytic cleavage might occur through PPh3 dissociation or partial TPMA dissociation
• Large excesses of PPh3 can cause total TPMA displacement, producing a complex that is ATRA inactive
33
Cu-P1: 2.3199(15) Å Cu-P2: 2.3169(15) ÅCu-P3: 2.3086(15) ÅCu-P4: 3.9551(17) Å
Cu-P1: 2.3150(5) ÅCu-P2: 2.3362(5) ÅCu-P3: 2.3147(5) ÅCu-N1: 2.1010(17) Å
[CuI(PPh3)(PPh3)][BPh4] [CuI(PPh3)3CH3CN][ClO4]
Eckenhoff, W. T.; Pintauer, T. unpublished results
Copper complexes with TDAPA Ligand
• Very similar ligand structure to highly active ligands
• Coordinates to copper similarly
34
[CuII(TDAPA)X][Y] Performance in ATRA
• Copper Complexes with the TDAPA ligand showed very little ATRA activity
• Ligand dissociation should be much slower as compared to TPMA
• Slight counter-ion effect observed
35
Alkene Anion Yield1-hexene Cl- 24%1-octene 25%1-hexene BPh4- 60%1-octene 45%1-hexene BF4- 55%1-octene 59%
[Alkene]0:[CCl4]0:[AIBN]0:[CuII]0=250:250:12.5:1
Reactions performed at 60oC in CH3CN, [alkene]0=2.39 M. Yields determined by 1H NMR
Eckenhoff, W. T.; Pintauer, T. unpublished results
Conclusions• Synthesis, characterization and exceptional activity of [CuII
(TPMA)X][X] (X=Br- and Cl-) complexes in ATRA of polyhalogenated compounds to alkenes in the presence of reducing agent AIBN was presented.
• [CuII(TPMA)Br][Br] in conjunction with AIBN effectively catalyzed ATRA of CBr4 and CHBr3 to alkenes with concentrations between 5 and 100 ppm, which is the lowest number achieved in copper mediated ATRA.
• Structural and mechanistic studies indicate that partial TPMA dissociation may be required for ATRA.
• The rate of alkene consumption was found to depend only on the AIBN concentration.
• In the absence of AIBN, copper(I) complexes with non-coordinating counter-ions were found to proceed faster than the corresponding chloride analogues.
36
• Advisor: • Dr. Pintauer
• Duquesne University Committee members: • Dr. Basu• Dr. Fleming
• Outside Reader: • Dr. Matyjaszewski
• My Family: • Dana Eckenhoff• Parents - Drs Roderic and Maryellen Eckenhoff
37
Acknowledgments
Graduate Students
• Dr. Marielle Balili• Carolynne Ricardo• April Hill• Raj Kaur• Merton Pajibo
38
AcknowledgmentsUndergraduate Students
• Sean Noonan• Matthew Taylor• Ashley Biernesser• Tom Ribelli
Acknowledgments
Special Thanks to:
• The Bayer School Instrumentation Staff
• Dan Bodnar
• Dave Hardesty
• Lance Crosby
• Ian Welsh
• Sandy Russell, Amy Stroyne, Heather Costello
Acknowledgments
Funding
• NSF Career Award (CHE-0844131)
• Duquesne University Start-up Grant
• NSF X-ray Facility Grant (CRIF-0234872)
• NSF NMR Grant (CHE-0614785)
40
Thank You!