Chemical fixation of dinitrogen under mild conditions

Abstract

Chemical fixation of dinitrogen has been performed under mild conditions in homogeneous and heterogeneous systems. In heterogeneous system electron donor-acceptor complexes of iron phthalocyanine, ruthenium phthalocyanine, osium phthalocyanine, poly-iron phthalocyanine, and iron tetraphenylporphin have been used as catalysts for ammonia synthesis from dinitrogen and dihydrogen. These EDA complexes have been found to be active at temperatures lower than 200° C. EDA complex of iron phthalocyanine gives the best results among them. A new efficient, homogeneous system based on the combination of titanium (IV) complexes and sodium-potassium alloy has been developed. The system gives high yield of ammonia without hydrolysis of dinitrogen titanium complexes. The best yield has been obtained by using hydro-carbon solvent such as methylcyclohexan and toluene. The hydrogen source for ammonia production has been found not to be the solvents but the organic ligands of the titanium complexes such as cyclopentadienyl and isoproproxy groups. Introduction of dihydrogen to the system together with dinitrogen resulted in decrease of ammonia yield. A new class of metallophtalocyanine complexes with carbonyl ligand has been found during the synthesis of the catalysts for the heterogeneous reactions. The carbonyl complexes of ruthenium and osium phthalocyanine have also been prepared in high yield by several new methods.