N 2 hydrogenation promoted by a side-on bound hafnocene dinitrogen complex

Wesley H. Bernskoetter, Andrea V. Olmos, Emil Lobkovsky, Paul J. Chirik

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Abstract

Reduction of the hafnocene diiodide (η 5-C 5Me 4H) 2HfI 2 with excess sodium amalgam under 1 atm of dinitrogen yielded the hafnocene dinitrogen complex [(η 5- C 5Me 4H) 2Hf] 22, η 22-N 2). X-ray diffraction has established a strongly activated, side-on bound, bridging N 2 ligand with an N-N bond length of 1.423(11) Å. Exposure of the dinitrogen compound to 1 atm of dihydrogen at 23°C resulted in rapid hydrogenation of the N 2 ligand, affording the hydrido hafnocene diazenido complex [(η 5-C 5Me 4H) 2-HfH] 2222-N 2H 2). Confirmation of N 2 hydrogenation has been provided by NMR and IR spectroscopic studies and X-ray diffraction. Pseudo-first-order observed rate constants for H 2 addition have been measured by monitoring the disappearance of a principally LMCT band centered at 886 nm [(η 5-C 5Me 4H) 2Hf] 2-(μ 222-N 2) as a function of time. The hafnocene complex hydrogenates dinitrogen approximately 4 times faster than the corresponding zirconocene compound. Divergent chemistry from zirconium is observed upon thermolysis of [(η 5-C 5Me 4H) 2HfH] 2222-N 2H 2), which results in cyclopentadienyl methyl group cyclometalation rather than N-N bond scission.

Original languageEnglish (US)
Pages (from-to)1021-1027
Number of pages7
JournalOrganometallics
Volume25
Issue number4
DOIs
StatePublished - Feb 13 2006
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

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