An Examination of C−H Bond Activation by Cationic TpMe₂Ir(III) Complexes

Synthesis and characterization of a set of iridium(III) compounds utilizing the sterically encumbering hydridotris(3,5-dimethylpyrazolyl)borate ligand (Tp Me 2 ) has been performed, and a comparison with the corresponding Cp* complexes is presented. Tp Me 2 (PMe 3 )Ir(Me)OTf ( 7, OTf = O 3 SCF 3 ) was synthesized and found to be unreactive toward a variety of C−H bonds, in contrast to the behavior of Cp*(PMe 3 )Ir(Me)OTf ( 1 ). We have rationalized this lack of reactivity in terms of an electronic effect rather than a steric effect imposed by the Tp Me 2 ligand. Metathesis of the triflate ligand with the BAr f (BAr f = B[3,5-C 6 H 3 (CF 3 ) 2 ] 4 ) anion under a N 2 atmosphere produces the dinitrogen complex [Tp Me 2 (PMe 3 )Ir(N 2 )(Me)][BAr f ] ( 3-N 2 ). Compound 3-N 2 is indeed reactive toward dative ligands, H 2, and hydrocarbons, activating the C−H bonds of benzene and aldehydes but not those of saturated hydrocarbons. A rationale for the difference in behavior between the Cp* and Tp Me 2 systems with respect to C−H activation is presented.