Bulky Terphenyl Phosphines Stabilize Otherwise Highly Reactive Iridium Fragments, Key in C–H Activation Reactions

High Resolution Image Download MS PowerPoint Slide The photogenerated Ir(I) compound [Cp*Ir(PMe 3 )] and its Ir(III) derivative [Cp*IrMe(PMe 3 )(solvent)] + [Cp* = η 5 -(C 5 Me 5 )] have tamed the field of C–H bond activation chemistry; however, analogues using bulkier phosphines have been barely investigated. We report the synthesis and characterization of their congested versions using sterically demanding terphenyl (C 6 H 3 -2,6-Ar 2 ) phosphine ligands. Two Ir(I) species, [Cp*Ir(PMe 2 ArDtbp2 )] ( 3, Ar Dtbp2 = C 6 H 3 -2,6-(C 6 H 3 -3,5- t Bu 2 ) 2 ) and [Cp*Ir(PMe 2 ArDipp2 )] ( 3′, Ar Dipp2 = C 6 H 3 -2,6-(C 6 H 3 -2,6- i Pr 2 ) 2 ), were isolated and structurally authenticated, revealing strong metal–arene interactions that confer remarkable stability to these otherwise highly unsaturated species. Despite their apparent similarity, these complexes exhibit sharply contrasting reactivity toward methyl triflate: only the PMe 2 Ar Dtbp2 derivative undergoes clean formal oxidative addition to form the targeted cationic methyl complex [Cp*IrMe(PMe 2 ArDtbp2 )] + ( 4 ). Computational studies rationalize this divergent behavior in terms of steric effects beyond conventional metrics. Besides, compound 4 displays rich chemistry, including intramolecular activation of a tert -butyl group and selective intermolecular functionalization of 1,2-difluorobenzene, as well as reactions with H 2 and phenylsilane. These findings evince the role of terphenyl phosphines in stabilizing reactive iridium fragments and highlight their potential for selective C–H activation under sterically congested environments.