Hydrogenation and cleavage of dinitrogen to ammonia with a zirconium complex.
Molecular nitrogen is relatively inert owing to the strength of its triple bond, nonpolarity and high ionization potential. As a result, the fixation of atmospheric nitrogen to ammonia under mild conditions has remained a challenge to chemists for more than a century. Although the Haber-Bosch process produces over 100 million tons of ammonia annually for the chemical industry and agriculture, it requires high temperature and pressure, in addition to a catalyst, to induce the combination of hydrogen (H2) and nitrogen (N2). Coordination of molecular nitrogen to transition metal complexes can activate and even rupture the strong N-N bond under mild conditions, with protonation yielding ammonia in stoichiometric and even catalytic yields. But the assembly of N-H bonds directly from H2 and N2 remains challenging: adding H2 to a metal-N2 complex results in the formation of N2 and metal-hydrogen bonds or, in the case of one zirconium complex, in formation of one N-H bond and a bridging hydride. Here we extend our work on zirconium complexes containing cyclopentadienyl ligands and show that adjustment of the ligands allows direct observation of N-H bond formation from N2 and H2. Subsequent warming of the complex cleaves the N-N bond at 45 degrees C, and continued hydrogenation at 85 degrees C results in complete fixation to ammonia.
Pool
Jaime A
JA
Department of Chemistry and Chemical Biology, Baker Laboratory Cornell University, Ithaca, New York 14853, USA.
Lobkovsky
Emil
E
Chirik
Paul J
PJ
D000641:Ammonia / Q000737:chemistry*; D002384:Catalysis; D018360:Crystallography, X-Ray; D006859:Hydrogen / Q000737:chemistry*; D006860:Hydrogen Bonding; D006865:Hydrogenation; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D009584:Nitrogen / Q000737:chemistry*; D011522:Protons; D013696:Temperature; D015040:Zirconium / Q000737:chemistry*
D011522:Protons; D000641:Ammonia; D006859:Hydrogen; D015040:Zirconium; D009584:Nitrogen