computational characterization of the form of ag(phen

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.

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Comba, P.; Lang C.; Laorden, C. L.; Muruganantham, A.;

Rajaraman, G.; Wadepohl, H.; Zajaczkowski, M. Chem. Eur. J.

2008, 14, 5313.