Fluxional Behavior of cis-Fe(DMeOPrPE)2(H)2 (DMeOPrPE = 1,2-[bis(dimethoxypropyl)phosphino]ethane); Implications for the Pressure Swing Purification of Natural Gas

Susan R. Cooper; Bryan P. Nell; David R. Tyler

doi:10.1007/s10904-017-0572-2

Fluxional Behavior of cis-Fe(DMeOPrPE)₂(H)₂ (DMeOPrPE = 1,2-[bis(dimethoxypropyl)phosphino]ethane); Implications for the Pressure Swing Purification of Natural Gas

Susan R. Cooper, Bryan P. Nell, David R. Tyler

Research output: Contribution to journal › Article › peer-review

Abstract

Materials such as trans-Fe(DMeOPrPE)₂(X)(H₂O)⁺ (DMeOPrPE = 1,2-[bis(dimethoxypropyl)phosphino]ethane; X = Cl or H) show considerable promise as sorbents for the removal of N₂ from natural gas in a pressure swing process. One problem, however, is that in long-term tests these sorbents slowly degrade over a period of many weeks. This study probed the degradation mechanism for the purpose of finding ways to stabilize the sorbents. To investigate the likelihood of degradation initiated by Fe–P bond dissociation, the fluxional behavior of the related cis-Fe(DMeOPrPE)₂(H)₂ complex was investigated by variable temperature ¹P{¹H} NMR spectroscopy. Analysis of the spectra gave the following activation parameters for the fluxional process: ΔH^‡ = 11.6 kcal/mol and ΔS^‡ = −9.2 cal/mol K. These results suggest that Fe–P bond dissociation (20–45 kcal/mol) is not occurring in the fluxional process and by implication that Fe–P bond dissociation is not initiating the decomposition of the trans-Fe(DMeOPrPE)₂(X)(H₂O)⁺ sorbents. Consequently, macrocycle ligands may not be the best approach for stabilizing the sorbents, as we have previously proposed. A “tetrahedral jump” mechanism is proposed for the fluxional process in cis-Fe(DMeOPrPE)₂(H)₂.

Original language	English (US)
Pages (from-to)	57-62
Number of pages	6
Journal	Journal of Inorganic and Organometallic Polymers and Materials
Volume	27
DOIs	https://doi.org/10.1007/s10904-017-0572-2
State	Published - Nov 1 2017

Bibliographical note

Funding Information:
Acknowledgements Acknowledgment is made to the NSF (CHE-1503550) for support of this research. Acknowledgment is also made to the donors of the American Chemical Society Petroleum Research Fund (ACS PRF 53962-ND3).

Funding Information:
Acknowledgment is made to the NSF (CHE-1503550) for support of this research. Acknowledgment is also made to the donors of the American Chemical Society Petroleum Research Fund (ACS PRF 53962-ND3).

Publisher Copyright:
© 2017, Springer Science+Business Media New York.

Keywords

Dinitrogen complexes
Fluxional molecules
NMR spectroscopy
Pressure-swing absorption

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Fluxional Behavior of cis-Fe(DMeOPrPE)₂(H)₂ (DMeOPrPE = 1,2-[bis(dimethoxypropyl)phosphino]ethane); Implications for the Pressure Swing Purification of Natural Gas. / Cooper, Susan R.; Nell, Bryan P.; Tyler, David R.
In: Journal of Inorganic and Organometallic Polymers and Materials, Vol. 27, 01.11.2017, p. 57-62.

Research output: Contribution to journal › Article › peer-review

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abstract = "Materials such as trans-Fe(DMeOPrPE)2(X)(H2O)+ (DMeOPrPE = 1,2-[bis(dimethoxypropyl)phosphino]ethane; X = Cl or H) show considerable promise as sorbents for the removal of N2 from natural gas in a pressure swing process. One problem, however, is that in long-term tests these sorbents slowly degrade over a period of many weeks. This study probed the degradation mechanism for the purpose of finding ways to stabilize the sorbents. To investigate the likelihood of degradation initiated by Fe–P bond dissociation, the fluxional behavior of the related cis-Fe(DMeOPrPE)2(H)2 complex was investigated by variable temperature 1P{1H} NMR spectroscopy. Analysis of the spectra gave the following activation parameters for the fluxional process: ΔH‡ = 11.6 kcal/mol and ΔS‡ = −9.2 cal/mol K. These results suggest that Fe–P bond dissociation (20–45 kcal/mol) is not occurring in the fluxional process and by implication that Fe–P bond dissociation is not initiating the decomposition of the trans-Fe(DMeOPrPE)2(X)(H2O)+ sorbents. Consequently, macrocycle ligands may not be the best approach for stabilizing the sorbents, as we have previously proposed. A “tetrahedral jump” mechanism is proposed for the fluxional process in cis-Fe(DMeOPrPE)2(H)2.",

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AB - Materials such as trans-Fe(DMeOPrPE)2(X)(H2O)+ (DMeOPrPE = 1,2-[bis(dimethoxypropyl)phosphino]ethane; X = Cl or H) show considerable promise as sorbents for the removal of N2 from natural gas in a pressure swing process. One problem, however, is that in long-term tests these sorbents slowly degrade over a period of many weeks. This study probed the degradation mechanism for the purpose of finding ways to stabilize the sorbents. To investigate the likelihood of degradation initiated by Fe–P bond dissociation, the fluxional behavior of the related cis-Fe(DMeOPrPE)2(H)2 complex was investigated by variable temperature 1P{1H} NMR spectroscopy. Analysis of the spectra gave the following activation parameters for the fluxional process: ΔH‡ = 11.6 kcal/mol and ΔS‡ = −9.2 cal/mol K. These results suggest that Fe–P bond dissociation (20–45 kcal/mol) is not occurring in the fluxional process and by implication that Fe–P bond dissociation is not initiating the decomposition of the trans-Fe(DMeOPrPE)2(X)(H2O)+ sorbents. Consequently, macrocycle ligands may not be the best approach for stabilizing the sorbents, as we have previously proposed. A “tetrahedral jump” mechanism is proposed for the fluxional process in cis-Fe(DMeOPrPE)2(H)2.

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