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Computational study of ammonia generation by iron( III ) and iron( IV ) complexes supported by trigonal bipyramidal iron
Author(s) -
Vyas Nidhi,
Sen Asmita,
Kumar Aditya,
Grover Abhinav
Publication year - 2021
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.26775
Subject(s) - reactivity (psychology) , chemistry , trigonal bipyramidal molecular geometry , protonation , nitrogenase , ammonia borane , electron deficiency , crystallography , catalysis , nitrogen , crystal structure , organic chemistry , nitrogen fixation , medicine , ion , hydrogen production , alternative medicine , pathology
High‐valent species such as terminal iron nitrides (FeN) are carried out for many organic and inorganic transformations. Simultaneously, they provide significant insight into the reactivity of various metalloenzyme as they involved in the reaction of nitrogenase enzyme. Various biomimetic model complexes were reported to understand nitrogenase enzyme's reactivity. In this framework, Peters et al. have published the facile formation of intermediate species [(TPB)Fe III/IV N] 0/1+ from the complex [(TPB)FeN 2 ] (here, TPB = tris(o‐diisopropylphosphinophenyl) borane. However, all species were thoroughly synthesized and characterized. But the mechanism is still elusive in terms of reactivity and the roles of intermediate species. In this work, we have tried to explore the mechanism of ammonia generation from these high‐valent [(TPB)Fe III/IV N] 0/1+ species employing the experimental conditions. Our computed results shows a very small energy barrier of 6.7 kJ/mol for the first transition state of protonation by the [(TPB)Fe III N] species (path1) in the NH bond activation of path1, however comparatively large energy barrier was reported for path2. From this reaction mechanism, it is established that species [(TPB)Fe III N] is more reactive than [(TPB)Fe IV N] + . The reactivity difference between these two species is mainly due to the nature of FeN bond, its basicity and electron delocalization during the NH bond activation. Comprehensive electronic structure investigation of the transition state reveals that the substrate will follow the low energy σ‐type pathway and the electron from the NH bond electron will go in the σ z 2 orbital. However, the high‐energy π‐type pathway, where the NH bond electron will go in the π * xz orbital. The spectroscopic parameters (Absorption, and Mössbauer) computed for some species, are compared to experimental observation to get belief on the computed data.