Alkane Dehydrogenation by Sequential, Double C−H Bond Activation by TpBr3Ir(C₂H₄)₂ (TpBr3 = hydrotris(3,4,5-tribromo)pyrazolylborate)

The new complex Tp Br3 Ir(C 2 H 4 ) 2, 1, photochemically activates the C−H bonds of n -pentane in a two-step process, the first one being the formation of an isolable alkyl-hydride intermediate of composition Tp Br3 Ir(H)(C 2 H 4 )(C 5 H 11 ), 3a, that subsequently undergoes β-hydride elimination to generate a terminal olefin complex, Tp Br3 Ir(H) 2 (C 5 H 10 ), 4a . The reaction can also be extended to diethyl ether. In this case, the reaction proceeds by the activation of one of the β-C−H bonds (with respect to the O-ether atom) with formation of the alkyl-hydride 3b and the dehydrogenation product 4b . These processes also compete with the intramolecular C−H activation of one of the coordinated ethylene ligand by the Ir(I) center in 1, which affords the hydride-vinyl complex Tp Br3 Ir(H)(CH CH 2 )(C 2 H 4 ), 2 . Attempts to thermally induce the above transformations has led to the exclusive formation of a mixture of the hydride-α,ω-butenyl complex Tp Br3 Ir(H)(CH 2 CH 2 CH CH 2 ), 5, and the hydride-crotyl complex Tp Br3 Ir(H)(C 4 H 7 ), 6 .