Highly Activated Terminal Carbon Monoxide Ligand in an Iron–Sulfur Cluster Model of FeMco with Intermediate Local Spin State at Fe

Abstract

Nitrogenases, the enzymes that convert N 2 to NH 3 , also catalyze the reductive coupling of CO to yield hydrocarbons. CO-coordinated species of nitrogenase clusters have been isolated and used to infer mechanistic information. However, synthetic FeS clusters displaying CO ligands remain rare, which limits benchmarking. Starting from a synthetic cluster that models a cubane portion of the FeMo cofactor (FeMoco), including a bridging carbyne ligand, we report a heterometallic tungsten−iron−sulfur cluster with a single terminal CO coordination in two oxidation states with a high level of CO activation (ν CO = 1851 and 1751 cm −1 ). The local Fe coordination environment (2S, 1C, 1CO) is identical to that in the protein making this system a suitable benchmark. Computational studies find an unusual intermediate spin electronic configuration at the Fe sites promoted by the presence the carbyne ligand. This electronic feature is partly responsible for the high degree of CO activation in the reduced cluster.

Ditopic ligand effects on solution-phase equilibria and electrochemistry of atomically precise copper chalcogenide nanoclusters

“…[10][11][12] APNCs capture the essential features of bulk metal chalcogenide catalysts including their highly delocalized electronic structures and flexible configuration of multimetallic sulfide active sites, both of which contribute to lowering activation energy barriers through cooperative multimetallic pathways. [13][14][15][16][17][18][19][20][21][22][23][24][25] Additionally, their discrete, atomically precise structures confer some distinct advantages. First, APNCs feature a well-defined arrangement of surface ligands that can be tuned to manipulate active site steric environment and electronic character.…”

Multi-phosphine-chelated iron-carbide clusters via redox-promoted ligand exchange on an inert hexa-iron-carbide carbonyl cluster, [Fe6(μ6-C)(μ2-CO)4(CO)12]2−

“…27 A report by Agapie et al employing a multidentate bis(diisopropylamino)cyclopropenylidene (BAC) ligand to give a carbyne FeS cluster is also notable. 28,29 This approach has yet to be applied to iron clusters that contain the authentic inorganic carbide, in large part due to the challenges in controlling CO substitution (and prevention of cluster disproportionation) as discussed above. Instead, some of the most biologically relevant models to date have approached FeMoco models with a 'carbide-like' motif bound to iron centers.…”