Kinetic studies of the photoinduced formation of transition metal-dinitrogen complexes using time-resolved infrared and UV-vis spectroscopy

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Previous kinetic studies of photoinitiated transition metal-dinitrogen bond forming reactions are reviewed, with an emphasis on room temperature reactivity, and in particular, the techniques of time-resolved infrared (TRIR) spectroscopy and UV-vis flash photolysis. Our recent results on the reactivity of the formally 16-electron, but agostically stabilized, complex, mer,trans-W(CO)3(PCy3)2 (W) (Cy = cyclohexyl) toward N2 in toluene and n-hexane solution are then discussed. Laser flash photolysis of a toluene solution of W-N2 in the presence of excess N2 resulted in the photoejection of N2. The back reaction of W with N2 was followed by monitoring the decay of the transient absorption of W at 600 nm. The second-order rate constant for the reaction of N2 with W in toluene to generate W-N2 was found to be (3.0 ± 0.2) × 105 M-1 s-1. The rate of the reverse reaction was found to be 100 ± 10 s-1, allowing an estimation of the equilibrium constant, KN2 = (3.0 ± 0.5) × 103 M- 1. Time-resolved step-scan FTIR (s2-FTIR) spectroscopy was also used to spectroscopically characterize the W intermediate and monitor its back-reaction with N2 in n-hexane solution. The rate of formation of W-N2 measured by s2-FTIR agreed well with that measured by flash photolysis. Finally, density functional theory (DFT) calculations have been performed on the model complexes, mer,trans-W(CO)3(PH3)2(L) (L = none and N2) in order to understand the observed IR and UV-vis spectra of W and W-N2 and to determine the nature of the frontier molecular orbitals of W and W-N2, allowing their lowest energy excited states to be assigned.

Original languageEnglish
Pages (from-to)1681-1695
Number of pages15
JournalCoordination Chemistry Reviews
Issue number13-14
Publication statusPublished - Jul 1 2006



  • Binding rates
  • Dinitrogen complex
  • Flash photolysis
  • Nitrogen fixation
  • Time-resolved Infrared

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry
  • Materials Chemistry

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