C-C σ-Bond Oxidative Addition and Hydrofunctionalization by a Macrocycle-Supported Diiron Complex.

This report describes the first examples of unassisted C(sp)-C(sp 2 ) and C(sp)-C(sp 3 ) bond oxidative addition reactions to give thermodynamically favorable products. Treatment of a diiron complex supported by a geometrically and electronically flexible macrocyclic ligand, ( 3 PDI 2 )Fe 2 (μ-N 2 )(PPh 3 ) 2 ( [Fe 2 N 2 ] 0 ), with stoichiometric amounts of various 4,4'-disubstituted diphenylacetylenes (Ar X -C≡C-Ar X ; X = OMe, H, F, CF 3 ) yielded C(sp)-C(sp 2 ) bond oxidative addition products. When Ph-C≡C-R substrates were used as substrates (R = Me, Et, i Pr, t Bu), products of either C(sp)-C(sp 2 ) or C(sp)-C(sp 3 ) bond activation were obtained, with the less sterically encumbering alkynes exclusively undergoing C(sp)-C(sp 3 ) bond activation. Treatment of the C-C activation species with either H 2 or HBpin was found to form products of C-C σ-bond hydrofunctionalization. In both the hydrogenation and hydroboration schemes, the diiron species was observed to return to [Fe 2 N 2 ] 0 , thereby completing synthetic cycles for C-C σ-bond functionalization.