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The Formation of Third Generation Poly(pyrazolyl)borate Ligands from Alkyne Coupling Reactions of Fe[(p-IC₆H₄)B(3-Rpz)₃]₂ (R = H, Me; pz = Pyrazolyl): Pathways Toward Controlling an Iron(II) Electronic Spin-State Crossover
Journal of the American Chemical Society
  • Daniel L. Reger
  • James R. Gardinier
  • William R. Gemmill
  • Mark D. Smith
  • Ahmed M. Shahin
  • Gary J. Long, Missouri University of Science and Technology
  • Leïla Rebbouh
  • Fernande Grandjean, Missouri University of Science and Technology
Abstract

Sonogashira coupling reactions of terminal alkynes with Fe[(p-IC6H4)B(3-Mepz)3]2 (pz = pyrazolyl ring) yield Fe[(p-PhC2C6H4)B(3-Mepz)3]2 (2), Fe[(p-Me3SiC2C6H4)B(3-Rpz)3]2 (R = H, 3a, R = Me, 3b), and Fe[(p-HC2C6H4)B(3-Mepz)3] 2 (R = H, 4a, R = Me, 4b), a series of new complexes containing "third generation" poly(pyrazolyl)borate ligands. Complex 2 undergoes a fairly gradual iron(II) electronic spin-state crossover with a 30 K hysteresis, whereas complex 3b is an unusual example of a complex with equivalent iron(II) sites in the high-spin form that shows an abrupt 50% spin crossover. For complex 4b, 50% of the iron(II) sites undergo a gradual spin-state transition between 185 and 350 K with an activation energy of 1590 ± 30 cm-1 and a T1/2 = 280 K and, for the remaining iron(II) sites, an abrupt cooperative spin-state crossover between 106 and 114 K. The crystal structures of 4b obtained for each of the three distinct electronic spin states reveal two crystallographically different iron(II) sites, and analysis of the molecular/supramolecular structures indicates that the difference in the degree of pyrazolyl ring tilting in the ligands between the two sites, rather than the strength of the intermolecular forces, play a prominent role in determining the temperature of the spin-state crossover.

Department(s)
Chemistry
Sponsor(s)
Fonds National de la Recherche Scientifique
National Science Foundation of Belgium
Ministere de la Region Wallonne
National Science Foundation (U.S.)
Petroleum Research Fund
Keywords and Phrases
  • Activation Energy,
  • Complexation,
  • Crystal Structure,
  • Crystallography,
  • Hydrocarbons,
  • Hysteresis,
  • Reaction Kinetics,
  • Supramolecular Chemistry,
  • Alkynes,
  • Electronic Spin State Crossover,
  • Ligands,
  • Sonogashira Coupling Reactions,
  • Molecular Structure,
  • Alkyne,
  • Iron Derivative,
  • Ligand,
  • Methionine Derivative,
  • Poly(Pyrazolyl)borate Ligand,
  • Polymer,
  • Pyrazole Derivative,
  • Unclassified Drug,
  • Acceleration,
  • Chemical Reaction,
  • Chemical Structure,
  • Complex Formation,
  • Crystal Structure,
  • Crystallography,
  • Electrochemical Analysis,
  • Hysteresis,
  • Polymerization,
  • Reaction Analysis,
  • Sonogashira Reaction,
  • Supramolecular Chemistry,
  • Temperature Dependence
Document Type
Article - Journal
Document Version
Citation
File Type
text
Language(s)
English
Rights
© 2005 American Chemical Society (ACS), All rights reserved.
Publication Date
2-1-2005
Publication Date
01 Feb 2005
Disciplines
Citation Information
Daniel L. Reger, James R. Gardinier, William R. Gemmill, Mark D. Smith, et al.. "The Formation of Third Generation Poly(pyrazolyl)borate Ligands from Alkyne Coupling Reactions of Fe[(p-IC₆H₄)B(3-Rpz)₃]₂ (R = H, Me; pz = Pyrazolyl): Pathways Toward Controlling an Iron(II) Electronic Spin-State Crossover" Journal of the American Chemical Society Vol. 127 Iss. 7 (2005) p. 2303 - 2316 ISSN: 0002-7863
Available at: http://works.bepress.com/gary-long/364/