Prev. Article Next Article Table of Contents

Article

Diazene Dehydrogenation Follows H₂ Addition to Coordinated Dinitrogen in an ansa-Zirconocene Complex

Supporting Info

Tamara E. Hanna, Ivan Keresztes, Emil Lobkovsky, and Paul J. Chirik*

Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853

Inorg. Chem., 2007, 46 (5), pp 1675–1683

DOI: 10.1021/ic0620539

Publication Date (Web): February 1, 2007

To whom correspondence should be addressed. E-mail: pc92@cornell.edu.

Abstract

An activated side-on-bound ansa-zirconocene dinitrogen complex, [Me₂Si(η⁵-C₅Me₄)(η⁵-C₅H₃-3-^tBu)Zr]₂(μ₂,η²,η²-N₂), has been prepared by sodium amalgam reduction of the corresponding dichloride precursor under an atmosphere of N₂. Both solution spectroscopic and X-ray diffraction data establish diastereoselective formation of the syn homochiral dizirconium dimer. Addition of 1 atm of H₂ resulted in rapid hydrogenation of the N₂ ligand to yield one diastereomer of the hydrido zirconocene diazenido complex. Kinetic measurements have yielded the barrier for H₂ addition and in combination with isotopic labeling studies are consistent with a 1,2-addition pathway. In the absence of H₂, the hydrido zirconocene diazenido product undergoes swift diazene dehydrogenation to yield an unusual hydrido zirconocene dinitrogen complex. The NN bond length of 1.253(5) Å determined by X-ray crystallography indicates that the side-on-bound N₂ ligand is best described as a two-electron reduced [N₂]²^- fragment. Comparing the barrier for deuterium exchange with [Me₂Si(η⁵-C₅Me₄)(η⁵-C₅H₃-3-^tBu)ZrH]₂(μ₂,η²,η²-N₂H₂) to diazene dehydrogenation is consistent with rapid 1,2-elimination of dihydrogen followed by rate-determining hydride migration to the zirconium. This mechanistic proposal is also corroborated by H₂ inhibition and the observation of a normal, primary kinetic isotope effect for dehydrogenation.

View: Full Text HTML | Hi-Res PDF

Tools

SciFinder Links

History

Published In Issue March 05, 2007
Received October 26, 2006

Recommend & Share

Related Content

Extreme NN Bond Elongation and Facile N-Atom Functionalization Reactions within Two Structurally Versatile New Families of Group 4 Bimetallic “Side-on-Bridged” Dinitrogen Complexes for Zirconium and HafniumJournal of the American Chemical Society
- Extreme NN Bond Elongation and Facile N-Atom Functionalization Reactions within Two Structurally Versatile New Families of Group 4 Bimetallic “Side-on-Bridged” Dinitrogen Complexes for Zirconium and Hafnium
  Masakazu Hirotsu, Philip P. Fontaine, Peter Y. Zavalij, and Lawrence R. Sita
  Journal of the American Chemical Society 2007 129 (42), pp 12690–12692
  Abstract: Chemical reduction of (η⁵-C₅Me₄R)M[N(R‘)C(X)N(R‘)]Cl₂ (M = Zr or Hf, X = NMe₂ or Me, R = H or Me, R‘ = i-Pr, Et) with 3 equiv of potassium graphite (KC₈) in tetrahydrofuran (THF) provides modest isolated yields of the corresponding “side-on-bridged” ...
  Abstract | Full Text HTML | Hi-Res PDF
Kinetics and Mechanism of N₂ Hydrogenation in Bis(cyclopentadienyl) Zirconium Complexes and Dinitrogen Functionalization by 1,2-Addition of a Saturated C−H BondJournal of the American Chemical Society
- Kinetics and Mechanism of N₂ Hydrogenation in Bis(cyclopentadienyl) Zirconium Complexes and Dinitrogen Functionalization by 1,2-Addition of a Saturated C−H Bond
  Wesley H. Bernskoetter, Emil Lobkovsky, and Paul J. Chirik
  Journal of the American Chemical Society 2005 127 (40), pp 14051–14061
  Abstract: The rates of hydrogenation of the N₂ ligand in the side-on bound dinitrogen compounds, [(η⁵-C₅Me₄H)₂Zr]₂(μ₂,η²,η²-N₂) and [(η⁵-C₅Me₅)(η⁵-C₅H₂-1,2-Me₂-4-R)Zr]₂(μ₂,η²,η²-N₂) (R = Me, Ph), to afford the corresponding hydrido zirconocene diazenido complexes ...
  Abstract | Full Text HTML | Hi-Res PDF
N−C Bond Formation Promoted by a Hafnocene Dinitrogen Complex: Comparison of Zirconium and Hafnium Congeners N−C Bond Formation Promoted by a Hafnocene Dinitrogen Complex: Comparison of Zirconium and Hafnium CongenersJournal of the American Chemical Society
- N−C Bond Formation Promoted by a Hafnocene Dinitrogen Complex: Comparison of Zirconium and Hafnium Congeners N−C Bond Formation Promoted by a Hafnocene Dinitrogen Complex: Comparison of Zirconium and Hafnium Congeners
  Wesley H. Bernskoetter, Andrea V. Olmos, Jaime A. Pool, Emil Lobkovsky, and Paul J. Chirik
  Journal of the American Chemical Society 2006 128 (33), pp 10696–10697
  Abstract: Nitrogen−carbon bond formation from coordinated dinitrogen has been observed upon addition of 2 equiv of PhNCO to the hafnocene dinitrogen complex, [(η⁵-C₅Me₄H)₂Hf]₂(μ₂,η²,η²-N₂). The resulting product most likely arises from initial NC cycloaddition of ...
  Abstract | Full Text HTML | Hi-Res PDF

Article

Diazene Dehydrogenation Follows H₂ Addition to Coordinated Dinitrogen in an ansa-Zirconocene Complex