Mechanistic Features of Iridium Pincer Complex Catalyzed Hydrocarbon Dehydrogenation Reactions:  Inhibition upon Formation of a μ-Dinitrogen Complex

Deuterium-labeling studies show that vinyl C−H oxidative addition of tert-butylethylene (tbe) to IrH₂{C₆H₃-2,6-(CH₂PBu^t₂)₂} (1) is rapid and reversible, while the stoichiometric hydrogenation of tbe by 1 is slower and irreversible. The dinitrogen complex, [Ir{C₆H₃-2,6-(CH₂PBu^t₂)₂}]₂(μ-N₂) (3), results from the reaction of 1 with excess tbe under 1 atm of nitrogen. A single-crystal X-ray structure determination of 3 reveals a perpendicular arrangement of the P−C−P pincer ligands, which accounts for the surprising stability of 3 and the inhibiting effect of nitrogen on reactions catalyzed by 1.