computational characterization of the form of ag(phen
TRANSCRIPT
Computational Characterization of the Form of Ag(phen) Catalyst for Amination and Aziridination
Reactions
Paige BirschbachDr. Joe ScanlonRipon College
Disilver Catalysts He group at U. of Chicago• Disilver catalyst = Ag2(tButPy)2
Aziridination
Amination
NN
N
tBu
tBu
tBu
NN
N
tBu
tBu
tBu
Ag
Ag
2+
N
NAg(I)
N
NAg(I)
Ph
Ph
Ph
Ph
A New Catalyst
Aziridination and intramolecular amination
Intermolecular amination of cycloalkanes Impressive since both intermolecular and unactivated C-H bond
Why Two Silvers?
Two possible explanations: Both silver (I) ions donate an electron
o Avoids having a radical in the reaction
Two silver (II) ions stabilize the nitrene intermediate
Ag(phen)2 Nitrene Intermediate
Amination or Aziridination? (Agphen)2 can catalyze amination and aziridination What if reactant was an olefin and had an available C-H
bond?
Schomaker at UW-Madison experimentally investigated the effect of varying the amount of phenanthroline ligand
Amination or Aziridination?
Entry Ag:Phen Azirdination:Amination
1 0.2:0.1 5:12 0.2:0.2 5.8:13 0.2:0.25 6.2:14 0.2:0.3 5.8:15 0.2:0.4 1:46 0.2:0.6 1:38
C5H11
H H
O
MeMe
NH2
O H
C5H11
N O
Me
MeH
O
+O
HN O
C5H11
H
H
Me Me
Ag:Phen
H
PhI(OAc)2
• •
Aziridination Amination
Why does this happen?Schomaker proposed: Potential equilibrium between Ag(phen) and Ag(phen)2
Ag:Phen ratios 1:1 produces monomer Ag(phen) 1:3 produces Ag(phen)2
Spectroscopic analysis suggests two new forms of the catalyst
(Amination)
Proposed MechanismsPhI N O
O
H
Et
NO
OH
EtO N
O
Et
N
NAg
N NAg
NNN
NAgN
O
O
Et
PhI
N NAg NN
N
OEtO
H H
steric congestionfavors insertion
Phen
PhI
less stericcongestion favors
aziridination
• Highlighted is reactant and the two forms of the catalyst: Ag(phen) (left) and
Ag(phen)2 (right).
Proposed MechanismsPhI N O
O
H
Et
NO
OH
EtO N
O
Et
N
NAg
N NAg
NNN
NAgN
O
O
Et
PhI
N NAg NN
N
OEtO
H H
steric congestionfavors insertion
Phen
PhI
less stericcongestion favors
aziridination
• Ag(phen) pathway• tail of the reactant has room to swing around due to less steric hindrance• easily attacks the alkene forming the aziridination product
Proposed MechanismsPhI N O
O
H
Et
NO
OH
EtO N
O
Et
N
NAg
N NAg
NNN
NAgN
O
O
Et
PhI
N NAg NN
N
OEtO
H H
steric congestionfavors insertion
Phen
PhI
less stericcongestion favors
aziridination
• Ag(phen)2 pathway• tail is no longer able to swing over due to steric congestion from two
phenanthroline ligands• attacks the C-H bond forming the amination product
Methods MU3C Cluster and WebMO Gaussian09 Program Method
M06L density functional
Basis Setso Nonmetals(with the exception of Iodine): 6-31G(d)o Silver: SDD basis set and effective core potential (ECP)o Iodine: MIDIXo Density Fitting
Solvationo Single point energy using SMD model with dichloromethaneo 6-311+G(2d,p)
Amination Mechanism
Ag(phen)n Amination
0.0 0.3
ReactantAg(Phen)
I1
Ag(Phen)2I1
11.8
2.1TS
AminationProduct
-54.7
TS
14.8
Ag(phen) I1
Ag(phen)2 I1
Aziridination Mechanism
Ag(phen)n Aziridination
N,C=C coord. I1
Rel
.G(k
cal/m
ol)
• Black = ag(phen) aziridination• Found alkene coordinated intermediate
• Red = ag(phen)2 aziridination• N,O coordinated intermediate
Ag(phen)2 Aziridination
Ag(phen)2 I2
Rel
.G(k
cal/m
ol)
Form of Catalyst Rel. G solvation (kcal/mol)
Ag(phen)2-16.0
Ag(phen)0.0
(Agphen)29.3
Formation of Ag(phen)2 is favorable
Conclusions• Both Ag(phen) and Ag(phen)2 had small barriers for amination
(1.8-3 kcal/mol)
• Nitrene intermediate is more stabilized with Ag(phen), 0.3
kcal/mol, compared to Ag(phen)2, 11.8 kcal/mol
• Aziridination requires a N,C=C coordination (8.5 kcal/mol), not
found for Ag(phen)2
• Amination is preferred over aziridination for both forms of
catalyst
• Formation of Ag(phen)2 is favorable (-16.0 kcal/mol)
Future Research Can alkene coordination lower barrier for PhI=N bond
breaking to form nitrene?
Coordination of PhI and effect on reaction
Ag(phen) favored for amination?
Is aziridination possible for Ag(phen)2?
Acknowledgements Dr. Joe Scanlon Dr. Colleen Byron Ripon College Chemistry
Department Eugene Schneider Micheal Enright, Rachel
Vanden Berg, PrasoonSaurabh, & KelceyAnderson
MU3C Oyster Scholar Fund
References He, C.; Zigzang, L; Eur. J. Org. Chem. 2006, 4313.
He, C.; Rahaman R.; Capretto, D. A.; Zigang L. Angew. Chem.
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Schomaker, J. M.; Rigoli, J. W.; Weatherly, C. D.; Alderson, J.
M.; Vo, B. T. J. Am. Chem. Soc. 2013, 135, 17238.
Comba, P.; Lang C.; Laorden, C. L.; Muruganantham, A.;
Rajaraman, G.; Wadepohl, H.; Zajaczkowski, M. Chem. Eur. J.
2008, 14, 5313.