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] 2(μ 2, η 2:η 2-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] 2(μ 2,η 2:η 2-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 2,η 2:η 2-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] 2(μ 2,η 2:η 2-N 2H 2), which results in cyclopentadienyl methyl group cyclometalation rather than N-N bond scission.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry