Substrate-Dependent Hydridic and Radical Reactivity of Triiron Hydride Clusters

The reactivity of iron clusters with one of more μ-hydrides and in the weak field pertains to catalysis on surfaces and biological metal cluster cofactors. As a model, then, a reactivity survey of the weak-field ligated iron hydride clusters Fe₃H₃L (1) and (FeCO)₂Fe(μ₃–H)L (2) (where L^3– is a tris(β-diketiminate)cyclophanate) with Brønsted acids, organochlorides, acetyl chloride, boron trihalides, and titanium electrophiles is reported. Complex 1 reacts with Brønsted acids H₂O and [Et₃NH][Cl] to afford Fe₃(OH)₃L (3) and Fe₃H₂ClL (4), respectively, consistent with hydridic reactivity. Clusters 1 and 2 react readily with organochlorides, such as CCl₄, CHCl₃, and CH₂Cl₂, with identified intermediates supporting a radical pathway. Complex 1 reacts with trityl chloride (2 equiv) to selectively afford Fe₃HCl₂L (5) with reductive elimination of dihydrogen observed. Mixed-valent complex 2 reacts with AcCl to afford (FeCO)Fe₂HClL (9). The scope of reactivity displayed implicates possible pathways accessible to larger clusters in biology or on metal surfaces.