Organo-nitrogen Compounds from Molecular Nitrogen

INTRODUCTION Industrial nitrogen fixation plays an important role in sustaining approximately 40% of the Earth’s population through generation of synthetic fertilizers. Annually, ca. 500 million tons of anhydrous ammonia, ammonium nitrate, and urea are produced through the Haber-Bosch process, which requires harsh conditions (200 atm, 450-500C) and affords low yields 10-20%. It has been estimated that this accounts for 1% of the world’s annual energy consumption. An efficient, mild method for fixating molecular nitrogen would be of great worth not only due to the immediate energy savings but it would also serve to provide novel reactivity possibly capable of generating organo-nitrogen compounds from molecular nitrogen. The first, stable dinitrogen coordination complex, [Ru(NH3)5(N2)], was isolated in 1965 by Allen and Senoff, and this initial observation has led to the development of many systems (primarily based on molybdenum, tungsten, and titanium) for incorporating molecular nitrogen into organic molecules. This review will focus on the various methods for generation of nitrogen-containing organic molecules based on synthetic nitrogen fixation processes. Background Thermodynamically, the fixation of nitrogen is an exothermic process for both protonation and hydrogenation steps (Scheme 1). However, as is evident from the hydrogenation of N2 to N2H2, the