The direct oxidative addition of strong, unstrained C–C σ-bonds to transition metals is a challenging transformation that holds promise as an efficient and atom-economical strategy for molecular engineering. Activation of the alkynyl-aryl C(sp)–C(sp2) bond has been of particular interest for direct and selective C–C functionalization. While Pt(0) systems have been reported to activate the C(sp)–C(sp2) bond of diphenylacetylene, they require photochemical conditions to see conversion, due, at least in part, to the endergonic nature of the oxidative addition reaction. Herein, we report the first thermodynamically-favorable oxidative addition of C(sp)–C(sp2) σ-bonds by way of diphenylacetylene activation at a diiron bridging dinitrogen ([Fe2N2]0) complex. It was found that treatment of [Fe2N2]0 with diphenylacetylene resulted in conversion to a C–C activation product, [Fe2(C≡CPh)(Ph)]0 . The product is stable at room temperature and no back conversion to free diphenylacetylene was detected under thermal conditions. Experimental and computational mechanistic studies revealed the initial formation of a diacetylene adduct, which transforms into a transient monoacetylene adduct prior to C–C bond activation. Interestingly, when mixed aryl/alkyl-substituted acetylenes were used, the regioselectivity of the C–C bond activation was found to depend on the identity of the alkyl group. Finally, treatment of various [Fe2(C≡CR1)R2]0 complexes with H2 was found to generate R1H and R2CH2CH3 products in high yields, with the fate of the diiron cluster identified as a diiron dihydride species [Fe2H2]0. A stepwise catalytic C–C σ-bond borylation reaction was also achieved by treating [Fe2(C≡CPh)Me]0 with HBpin, which generated PhCH=CHBpin and MeBpin as the hydroboration products, while returning the cluster to [Fe2N2]0.

Direct oxidative addition and functionalization of unactivated C(sp)–C(sp2) σ-bonds at a diiron cluster complex

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