Mimicking the Constrained Geometry of a Nitrogen-Fixation Intermediate

作者：Tianchang Liu, Michael R. Gau, Neil C. Tomson · 发表于：Journal of the American Chemical Society · 年份：2020 · DOI：10.1021/jacs.0c01861 · 被引用次数：58 · 研究领域：Ammonia Synthesis and Nitrogen Reduction、Metalloenzymes and iron-sulfur proteins、Catalytic Processes in Materials Science

Both biological and industrial nitrogen reduction catalysts activate N 2 at multinuclear binding sites with constrained Fe–Fe distances. This contrasts with molecular diiron systems, which routinely form linear N 2 bridges to minimize steric interactions. Model compounds that capture the salient geometric features of N 2 binding by the nitrogenase enzymes and Mittasch catalysts would contribute to understanding their high N 2 -reduction activity. It is shown in the present study that use of a geometrically flexible, dinucleating macrocycle allows for the formation of a bridging N 2 ligand with an unusual Fe–Ct N2 –Fe angle of 150° (Ct N2 = centroid of N 2 ), a geometry that approximates the α-N 2 binding mode on Fe(111) surfaces that precedes N 2 bond cleavage. The cavity size of the macrocycle prevents the formation of a linear Fe–N 2 –Fe unit and leads to orbital interactions that are distinct from those available to the linear configuration.