The recently discovered cyanide bridge between a 4Fe4S cluster of HydF maturation hydrogenase protein and a synthetic diiron complex has inspired research of significance to hybrid enzymes.1 Interestingly, conversion of [FeFe]-HydF to [FeFe]-HydA, allows the N-bound diiron site of the cyanide to be flipped leading to a C-bound isomer of the latter, an example of classic organometallic linkage isomerism. Moreover, synthetic efforts are aimed at unmasking presumed multiple roles of cyanide in hydrogenase enzyme active sites such as H-bonding and electronic tuning in bioorganometallic chemistry.2 As an ambivalent ligand, the possibility for linkage isomers was explored in a biomimetic series of CN-bridged tri-iron clusters.3 In the current study, we connect the redox non-innocent {Fe(NO)2}9/10 unit, as a surrogate for 4Fe4S cluster, to a redox innocent FeII via cyanide bridge, see figure. The redox potential of the latter is tuned by ancillary (η5-C5R5) ligands, where R = H or Me. Various spectroscopic techniques (IR, EPR, and Mossbauer) are utilized to probe the extent of communication between the iron centers, as well as the possibility of cyanide linkage isomerism. Substituting 12C14N with 13C15N would allow us to measure the extent of hyperfine coupling of the latter on the paramagnetic {Fe(NO)2}9 center.

Cyanide ligands as docking agents in [FeFe]-hydrogenase biomimetics

254th National Meeting (2017)

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