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


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.


Pressure-swing absorption Dinitrogen complexes Fluxional molecules NMR spectroscopy 



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).


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Copyright information

© Springer Science+Business Media New York 2017

Authors and Affiliations

  • Susan R. Cooper
    • 1
  • Bryan P. Nell
    • 1
  • David R. Tyler
    • 1
  1. 1.Department of Chemistry and Biochemistry1253 University of OregonEugeneUSA

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