Double Activation of the Geminal Carbon−Hydrogen Bonds in 1,3-Butadiene by a Diiridium Complex

The binuclear complex [Ir 2 (CH 3 )(CO) 2 (dppm) 2 ][CF 3 SO 3 ] ( 1 ) (dppm = Ph 2 PCH 2 PPh 2 ) reacts with 1,3-butadiene at ambient temperature over a 48 h period to give the vinylvinylidene-bridged product [Ir 2 (CH 3 )(H)(CO) 2 (μ-H)(μ-CC(H)C(H)CH 2 )(dppm) 2 ][CF 3 SO 3 ] ( 2 ). At −55 °C the same reactants yield the 1,3-butadiene adduct [Ir 2 (CH 3 )(CO) 2 (μ-η 2:η 2 -H 2 C C(H)C(H) CH 2 )(dppm) 2 ][CF 3 SO 3 ] ( 3 ), in which the diolefin binds in an s-trans geometry on one face of the complex. A proposal is advanced rationalizing the conversion of 3 to 2 upon warming.