An activated side-on-bound ansa-zirconocene dinitrogen complex, [Me 2Si(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 N 2 ligand to yield one diastereomer of the hydrido zirconocene diazenido complex. Kinetic measurements have yielded the barrier for H 2 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 N=N 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-C5Me 4)(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.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry
- Inorganic Chemistry