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Mechanisms for the Formation of NH 3 , N 2 H 4 , and N 2 H 2 in the Protonation Reaction of Fe(DMeOPrPE) 2 N 2 {DMeOPrPE = 1,2‐bis[bis(methoxypropyl)phosphino]ethane}
Author(s) -
Tyler David R.
Publication year - 2015
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/zaac.201400126
Subject(s) - protonation , chemistry , deprotonation , ammonia , reaction mechanism , reactive intermediate , denticity , hydrazine (antidepressant) , reaction intermediate , photochemistry , medicinal chemistry , stereochemistry , computational chemistry , catalysis , crystallography , organic chemistry , crystal structure , ion , chromatography
Research from the author's laboratory is reviewed on the reaction of Fe(DMeOPrPE) 2 N 2 with acid to form ammonia and hydrazine {DMeOPrPE is the water‐soluble, bidentate phosphine 1,2‐bis[bis(methoxypropyl)phosphino]ethane}. DFT calculations suggested that a symmetric protonation mechanism was more favorable than either an asymmetric protonation mechanism or a dinuclear mechanism. Two symmetric protonation pathways were investigated by synthesizing or generating reaction intermediates. Among the various species synthesized or spectroscopically observed were hydrazine complexes, diazene complexes, and their deprotonated conjugate bases. A relatively long‐lived intermediate in the protonation reaction, identified as [((DMeOPrPE) 2 Fe) 2 (μ‐N 2 )] 2+ , hints that a dinuclear pathway might be operating, but further mechanistic investigations suggested this species is likely forming in a side‐reaction and is not involved in the formation of ammonia. The only source of electrons for the reduction of N 2 in the reaction is the Fe(DMeOPrPE) 2 N 2 complex. As discussed in this review, this feature will ultimately limit the yields of ammonia and hydrazine that can form in the reaction. The reactions pathways uncovered by this research are symmetric protonation pathways, and as such they are different from the “asymmetric” protonation pathway proposed for some Mo‐N 2 complexes that protonate to form ammonia. Recent studies suggest a symmetric protonation pathway for nitrogenase (which has Fe in its active site), and it may well be a general conclusion that Fe‐N 2 species produce ammonia via the symmetric protonation mechanism.