Transcript Document

Synthesis of Iron Phosphine Complexes for
Small Gas Molecule Binding
James Patton, Dr. David R. Tyler and Dr. Joel W. Gohdes
Department of Chemistry| Pacific University | 2043 College Way | Forest Grove, OR 97116 | [email protected]
Summary of NMR Shifts of TeSt Complexes
Abstract:
Reaction Pathways
Small gas molecule binding complexes have important
applications ranging from understanding ammonia
formation in the nitrogen cycle to separating N2
impurities from natural gas. A series of trans-octahedral
iron(II) complexes were synthesized containing a bis
bidentate phosphine derivatized with 4-vinylbenzyl
groups, called the TeSt ligand. Beginning with the FeL2Cl2
complex, a series of reactions were mapped out to afford
a wide range of trans-axial ligand substitution patterns.
The compounds were characterized spectroscopically and
two were characterized via x-ray crystallography.
The goal being to synthesize FeL2HCl, there are many
pathways that can be taken. The figure below represents
the various attempts that were made.
Compound
31P
Hydride 1H
DVBPE
-13.5
-
FeL2Cl2
69.5
-
FeL2HCl
87.6
-29.8(q)
FeL2H(H2)+
86.7
-10(br), -14(q)
FeL2H(N2)+
77.6
-17.3
FeL2H(MeCN)+
83.5
-23.0
Background
Approximately 15% of United States natural gas reserves
are contaminated with elemental nitrogen. As the natural
gas is burned, the triple bonds of the nitrogen absorb
some of the energy, lowering the natural gas’s energy
density. Traditional methods of removal include cryogenic
distillation and membrane separation. However, due to
the similar melting points, size, and H2O solubilities, N2
and CH4 separations can be costly and ineffective.
Radius (Å)
N2
2.49
CH4
2.58
Boiling Point (K)
77
112
H2O Solubility (x 10-5)
1.3
2.8
FeL2Cl2 Crystal Structure
Synthesis via MeCN+ Complex
FeL2Cl2
NaBPh4, NaBH4 / MeOH, MeCN
31P
31P{1H}
A solution to this problem is to use water soluble small
gas molecule binding iron phosphine (FePhos)
complexes. The natural gas can be purified using a
pressure swing absorption.
FeL2HMeCN+
1H
Low pressure
FeL2HCl Crystal Structure
10
8
6
3
3 (M
absorbent)
gas/M
2N
Solubility
4
2
Bu4NCl / Acetone
FeL2HMeCN+
CH4 solubility
FeL2HCl
N2 solubility
0
0
50
100
150
200
250
31P{1H}
300
N2 Partial Pressure (psia)
High pressure
Tyler, D. R.; et. al., Inorg. Chem. 2002, 41, 5453-65.
These FePhos compounds, however, decompose when
exposed to water or oxygen gas. Thus, all chemistry was
performed either in a nitrogen atmosphere glove box or
in sealed, pressurized containers.
FeL2HCl Crystal Structure
TeSt Ligand Synthesis and Characterization
Conclusion
Synthesis Via H2 and Proton Sponge
, 36+ hrs
31P{1H}
We were able to synthesize the hydride/chloride iron
phosphine complex, but were not yet able to do so with
high enough yield or purity to copolymerize the complex
with EGDMA and MMA. Future goals for the project
include measuring the H2 and N2 binding properties of
the already polymerized dichloride complex and the yet
to be polymerized hydride/chloride complex,
characterize the polymers, and to further characterize
other complexes in the reaction scheme such as
FeL2HN2+ and FeL2Cl+
31P
31P{1H}
References:
•
1H
Tyler, D. R.; et. al., Inorg. Chem. 2002, 5453-65.
1H
Acknowledgements:
•Murdock Charitable Trust PRISM Grant
•National Science Foundation
•University of Oregon Chemistry Department
•Lev Zakharov
•Tyler Group