On the Relevance of Mono- and Dinuclear Iron Carbonyl Complexes to the Fixation and Stepwise Hydrogenation of N2

作者: Yu Chen , Michael Hartmann , Gernot Frenking

DOI: 10.1002/1099-0682(200106)2001:6<1441::AID-EJIC1441>3.0.CO;2-G

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摘要: Density functional theory and high-level ab initio calculations are used to evaluate the influence of mono- dinuclear iron carbonyl complexes fixation stepwise hydrogenation dinitrogen via diazene hydrazine ammonia. In comparison reaction isolated N2, only first step in this sequence (i.e. reduction N2 N2H2) experiences a significant change its thermochemistry when coordinated or tetracarbonyl fragments. The enthalpy ΔHR0 (T = 0 K) for endothermic (CO)4Fe−N2 give (CO)4Fe−N2H2 is lower than corresponding metal-free process by 16.1 kcal mol−1. analogous involving species (CO)4Fe−N2−Fe(CO4) (CO)4Fe−N2H2−Fe(CO)4 even less one complex 13.1 that, second third sequence, namely conversion (CO)4Fe−N2H4 subsequent (CO)4Fe−NH3 show relatively small thermodynamic changes compared reactions N2H2 N2H4. almost as exothermic analogue N2H2, whereas 4.0 Finally, (CO)4Fe−N2H4−Fe(CO)4 both predicted be their mononuclear analogues 1.1 mol−1, respectively. Moreover, we find that which already noticeable π-acceptor behavior with Fe(CO)4, experience important structural complexes, i.e. shortening Fe−N bonds lengthening N−N on going from (CO)4Fe−L (CO)4Fe−L−Fe(CO)4 (L N2H2). This line slightly increased ability these ligands respective complexes. Such absent N2H4, exhibits comparatively weak character (CO)4Fe−N2H4.

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