Green Oxidation Catalysts Synthesis of a catalyst for environmentally benign oxidation by N2O

Addie Summitt and Megumi Fujita*Department of Chemistry, University of West Georgia, Carrollton, GA 30118

Introduction

Ni Complexation

Acknowledgments• GEMS Summer Research Program

• National Science Foundation STEP grant #DUE-0336571

• Amna Ali, a senior research student

However, the complex resulted in internal oxidation, and was not catalytic.

N2OMe3PNi

Me3P Me3PNi

OO=PMe3

2

+

(Hillhouse3)

Previously Known N2O-Activating Complexes Involving Ni

Hillhouse published a Ni complex that reacted with N2O and activated the O atom.

Catalyst Design

N

N

NNi

(THF)

(THF)

Br

Br

(THF)

2+

1-

1-

Nickel was selected as a central metal ion because of the previous example by Hillhouse that showed N2O activation by a Ni complex.

The catalyst is made up of a bulky tridentate ligand around a metallic center, in this case a Ni center. It was proposed that activation of nitrous oxide requires two coordination sites next to each other. This ligand allows three available coordination sites, two of which may be used for N2O activation.

Another advantage is the overall -2 ligand charge, which neutralizes the central metal ion. This will create an overall neutral metal complex which is compatible with organic reaction media.

Ligand Synthesis

+ Na2CO3

CH3CN

NH2

NBS/CCl4

r.t.N

OO

Br

Br

N

OOHN 1. LiHMDS -78oC

2.(CH3O)2CO

1/2

N

Br

N

Br

OCH3

O

OCH3

O

N

NH

Br

HN

BrN

NH2NH2*HCl + KOH

MeOH

94 % 81%

0oC

91%

81%

Ligand in CD3CN (burnt orange)

NH

Br

HN

BrN

2NaH

N

Br

N

BrN

NiCl2

/ THF"the catalyst"

Overall reaction took about 3 days.

AS-07-12-07-LIGANDNCD3CN

9 8 7 6 5 4 3 2 1 0Chemical Shift (ppm)

0

8

16

24

32

40

48

56

64

72

80

No

rma

lize

d In

ten

sity

14.9612.9639.3911.0426.7121.8110.38

M01(br. s.)

0.7

6

1.2

6

1.5

0

1.9

42

.15

2.4

7

3.8

2

7.1

7

7.4

3

9.6

1

Pure crystals were obtained from ethyl acetate as 1:1 co-crystals with the solvent, confirmed by elemental analysis.

Ligand + 2NaH in CD3CN (brown)AS-07-13-07-LIGAND+NAH-IN-CD3CN

8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0Chemical Shift (ppm)

0

8

16

24

32

40

48

56

64

72

80

No

rma

lize

d In

ten

sity

22.8918.13104.2917.6935.9630.0313.77

M01(br. s.)

0.8

40

.96

1.1

9

1.5

4

1.9

4

2.4

62

.60

3.7

03

.80

4.5

0

4.8

7

6.7

8

7.1

77

.32

7.4

8

8.4

2

AS-7-16-07-NICOMPLEX2-CD3CN

10 9 8 7 6 5 4 3 2 1Chemical Shift (ppm)

0

8

16

24

32

40

48

56

64

72

80

Nor

mal

ized

Inte

nsity

11.526.5940.991.825.132.584.052.351.751.22

M02(br. s.)

M01(br. s.)

M03(br. s.)

M04(br. s.)

0.76

0.89

1.32

1.47

1.75

1.94

2.48

3.82

4.18

4.887.157.46

7.63

7.69

7.94

9.92

Ni Complexation in CD3CN (dark purple)

1H NMRs

Attempts for Crystallization

Conclusion and Future Work

After a solubility test in toluene, diethyl ether, and hexanes, a crystallization attempt of the Ni Complexation was done with toluene- hexanes two solvent method; toluene being the good solvent and hexanes being the poor solvent.

Nitrous oxide is a very destructive greenhouse gas released by many industrial waste sites; however, in the presence of a well designed metal catalyst, this gas has the potential to be an oxidation reagent. This potential oxidation by N2O could be exploited in many industrial oxidation processes as an environmentally friendly alternative because the only byproduct of the oxidation would be an environmentally benign N2 gas. The use of such a catalyst in industries would contribute to the reduction of N2O into the environment, which in turn would help reduce the destruction of the Earth’s ozone layer.

Our research goal is to develop a transition metal catalyst to activate N2O and mediate in the oxygen atom transfer to an organic substrate.

The synthesis reactions conducted thus far have been very successful. Future work includes having a successful reaction between the tridentate ligand and NiCl2, and then testing the catalyst for catalytic behavior.

MLn

L3 = ancillary ligand

N2O

n+ = initial oxidation state

n+

M O(n+2)+

Ln

"oxo" species

initial state

N2

CH3OH

CH4

M = Metal

Mechanism of N2O Activation

The first step in the N2O activation is to have a ligand with a metal center (our catalyst) take the oxygen atom from the N2O. The catalyst then acts as the oxidizing agent as it transfers the oxygen to a gas like CH4. A good catalyst would be able to repeat this cycle over and over again.

* *(s)

(s) (s) (s)(s)

(s)

(s) : starting ligand

**

****(s)

* : new species (Ni complex?)

(u) : unknown impurity

(u)

No NH peak: deprotonation complete

(u)

NH

The yield of each step has been improved by optimizing the reaction, workup, and purification conditions. This is the first time our lab produced this ligand in a large (2 g) scale, which allows us to explore metal complexation chemistry.

† : tentatively assigned as Na salt of ligand

†††

†

††††

(u)(u)(u)