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Title: Electronic and steric influences of pendant amine groups on the protonation of molybdenum bis (dinitrogen) complexes

Abstract

The synthesis of a series of P EtP NRR' (P EtP NRR' = Et₂PCH₂CH₂P(CH₂NRR')₂, R = H, R' = Ph or 2,4-difluorophenyl; R = R' = Ph or iPr) diphosphine ligands containing mono- and disubstituted pendant amine groups, and the preparation of their corresponding molybdenum bis(dinitrogen) complexes trans-Mo(N₂)₂(PMePh₂)₂(P EtP NRR') is described. In situ IR and multinuclear NMR spectroscopic studies monitoring the stepwise addition of (HOTf) to trans-Mo(N₂)₂(PMePh₂)₂(P EtP NRR') complexes in THF at -40 °C show that the electronic and steric properties of the R and R' groups of the pendant amines influence whether the complexes are protonated at Mo, a pendant amine, a coordinated N2 ligand, or a combination of these sites. For example, complexes containing mono-aryl substituted pendant amines are protonated at Mo and pendant amine to generate mono- and dicationic Mo–H species. Protonation of the complex containing less basic diphenyl-substituted pendant amines exclusively generates a monocationic hydrazido (Mo(NNH₂)) product, indicating preferential protonation of an N₂ ligand. Addition of HOTf to the complex featuring more basic diisopropyl amines primarily produces a monocationic product protonated at a pendant amine site, as well as a trace amount of dicationic Mo(NNH₂) product that contain protonated pendant amines. In addition, trans-Mo(N₂)₂(PMePh₂)₂(depe)more » (depe = Et₂PCH₂CH₂PEt₂) without a pendant amine was synthesized and treated with HOTf, generating a monocationic Mo(NNH₂) product. Protonolysis experiments conducted on select complexes in the series afforded trace amounts of NH₄⁺. Computational analysis of the series of trans-Mo(N₂)₂(PMePh₂)₂(P EtP NRR') complexes provides further insight into the proton affinity values of the metal center, N₂ ligand, and pendant amine sites to rationalize the differing reactivity profiles. This research was supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. Computational resources provided by the National Energy Research Scientific Computing Center (NERSC) at Lawrence Berkeley National Laboratory. Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.« less

Authors:
 [1];  [2];  [1]
  1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
  2. Washington State Univ., Pullman, WA (United States)
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1208742
Report Number(s):
PNNL-SA-107233
Journal ID: ISSN 0020-1669; KC0307010
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Inorganic Chemistry
Additional Journal Information:
Journal Volume: 54; Journal Issue: 9; Journal ID: ISSN 0020-1669
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
molybdenum; dinitrogen; ammonia; phosphines

Citation Formats

Labios, Liezel A., Heiden, Zachariah M., and Mock, Michael T. Electronic and steric influences of pendant amine groups on the protonation of molybdenum bis (dinitrogen) complexes. United States: N. p., 2015. Web. doi:10.1021/acs.inorgchem.5b00209.
Labios, Liezel A., Heiden, Zachariah M., & Mock, Michael T. Electronic and steric influences of pendant amine groups on the protonation of molybdenum bis (dinitrogen) complexes. United States. doi:10.1021/acs.inorgchem.5b00209.
Labios, Liezel A., Heiden, Zachariah M., and Mock, Michael T. Mon . "Electronic and steric influences of pendant amine groups on the protonation of molybdenum bis (dinitrogen) complexes". United States. doi:10.1021/acs.inorgchem.5b00209.
@article{osti_1208742,
title = {Electronic and steric influences of pendant amine groups on the protonation of molybdenum bis (dinitrogen) complexes},
author = {Labios, Liezel A. and Heiden, Zachariah M. and Mock, Michael T.},
abstractNote = {The synthesis of a series of PEtPNRR' (PEtPNRR' = Et₂PCH₂CH₂P(CH₂NRR')₂, R = H, R' = Ph or 2,4-difluorophenyl; R = R' = Ph or iPr) diphosphine ligands containing mono- and disubstituted pendant amine groups, and the preparation of their corresponding molybdenum bis(dinitrogen) complexes trans-Mo(N₂)₂(PMePh₂)₂(PEtPNRR') is described. In situ IR and multinuclear NMR spectroscopic studies monitoring the stepwise addition of (HOTf) to trans-Mo(N₂)₂(PMePh₂)₂(PEtPNRR') complexes in THF at -40 °C show that the electronic and steric properties of the R and R' groups of the pendant amines influence whether the complexes are protonated at Mo, a pendant amine, a coordinated N2 ligand, or a combination of these sites. For example, complexes containing mono-aryl substituted pendant amines are protonated at Mo and pendant amine to generate mono- and dicationic Mo–H species. Protonation of the complex containing less basic diphenyl-substituted pendant amines exclusively generates a monocationic hydrazido (Mo(NNH₂)) product, indicating preferential protonation of an N₂ ligand. Addition of HOTf to the complex featuring more basic diisopropyl amines primarily produces a monocationic product protonated at a pendant amine site, as well as a trace amount of dicationic Mo(NNH₂) product that contain protonated pendant amines. In addition, trans-Mo(N₂)₂(PMePh₂)₂(depe) (depe = Et₂PCH₂CH₂PEt₂) without a pendant amine was synthesized and treated with HOTf, generating a monocationic Mo(NNH₂) product. Protonolysis experiments conducted on select complexes in the series afforded trace amounts of NH₄⁺. Computational analysis of the series of trans-Mo(N₂)₂(PMePh₂)₂(PEtPNRR') complexes provides further insight into the proton affinity values of the metal center, N₂ ligand, and pendant amine sites to rationalize the differing reactivity profiles. This research was supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. Computational resources provided by the National Energy Research Scientific Computing Center (NERSC) at Lawrence Berkeley National Laboratory. Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.},
doi = {10.1021/acs.inorgchem.5b00209},
journal = {Inorganic Chemistry},
issn = {0020-1669},
number = 9,
volume = 54,
place = {United States},
year = {2015},
month = {5}
}