Carbon–carbon (C–C) bond formation is a cornerstone of synthetic chemistry, relying on routes such as transition-metal mediated cross-coupling for the introduction of new carbon-based functionality. For {[M]n+–C} (M = metal) structural units, studies that offer well-defined relationships between metal oxidation state, hydrocarbon strain, and {[M]n+–C} bond thermochemistry are thus informative, providing a means to reliably access new product classes. Here, we show that one-electron oxidation of the iron tucked-in complex [(η6-C5Me4CH2)Fe(dnppe)] (dnppe = 1,2-bis(di-n-propylphosphino)ethane) results in C(sp3)–C(sp3) bond formation giving unique {Fe2} dimers. Freeze-quenched CW X-band EPR spectroscopy allowed for spectroscopic identification of the reactive [(η6-C5Me4CH2)Fe(dnppe)]+ intermediate. Density functional theory (DFT) calculations reveal a primarily Fe-centered radical and a weak {[Fe]–C} bond (BDE[Fe]–C = 24.5 kcal mol−1, c.f. BDEC–C(ethane) = 90 kcal mol−1). For comparison, a structurally analogous Fe(III) methyl complex was prepared, [Cp*Fe(dnppe)(CH3)]+ (Cp* = C5Me5−), where C(sp3)–C(sp3) coupling was not observed, consistent with a larger calculated BDE[Fe]–C value of 47.8 kcal mol−1. These data are analogized to the simple hydrocarbons ethane and cyclopropane, where a strain-induced BDEC–C decrease of 33 kcal mol−1 is witnessed on cyclization.
This article is Open Access
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