Solvent study of the kinetics of molybdenum radical self-termination

John Linehan, Clement R. Yonker, R. Shane Addleman, S. Thomas Autrey, J. Timothy Bays, Thomas E. Bitterwolf, John L. Daschbach

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Abstract

The kinetics of (n-butylCp)Mo(CO)3 (n-butylCp is n-butyl-η5-cyclopentadienyl) radical self-termination to form a nonequilibrium mixture of trans- and gauche-[(n-butylCp)Mo(CO)3]2 and the kinetics of the gauche-to-trans isomerization have been determined in the liquid solvents n-heptane, tetrahydrofuran, xenon (350 bar), and CO2 (350 bar) at 283 K by step-scan FTIR spectroscopy. The overall rate constant for the disappearance, 2kR, of the (n-butylCp)Mo(CO)3 radical increases with decreasing solvent viscosity as expected, except in CO2, which is anomalously slower. The slower overall termination rate in liquid CO2 is consistent with the formation of a transient molybdenum radical-CO2 complex. The observed overall rate constants for (n-butylCp)Mo(CO)3 self-termination, 2kR, are (7.9 ± 0.5) × 109 M-1 s-1 in xenon; (3.2 ± 0.5) × 109 M-1 s-1 in heptane; (2.2 ± 0.8) × 109 M-1 s-1 in THF; and (1.7 ± 0.5) × 109 M-1 s-1 in CO2. The first determinations of the radical self-termination-to-gauche rate constants, kG, are presented. The values of kG are much slower than the corresponding recombination to trans, kT, reflecting a steric contribution to the rate. The rate of isomerization (rotation about the molydenum-molybdenum bond) from gauche to trans is unaffected by the solvent and is 3 times faster than the reported isomerization rate for the nonsubstituted [CpMo(CO)3]2 molecule.

Original languageEnglish
Pages (from-to)401-407
Number of pages7
JournalOrganometallics
Volume20
Issue number3
DOIs
Publication statusPublished - Feb 5 2001

ASJC Scopus subject areas

  • Inorganic Chemistry
  • Organic Chemistry

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    Linehan, J., Yonker, C. R., Addleman, R. S., Autrey, S. T., Bays, J. T., Bitterwolf, T. E., & Daschbach, J. L. (2001). Solvent study of the kinetics of molybdenum radical self-termination. Organometallics, 20(3), 401-407. https://doi.org/10.1021/om000724j