Iridium Olefin Complexes Bearing Dialkylamino/amido PNP Pincer Ligands: Synthesis, Reactivity, and Solution Dynamics

The reaction of [IrCl(COE)(2)](2) (1, COE = cyclooctene) with pincer ligand HN((CH2CH2PPr2)-Pr-i)(2) ((PNP)(H)) and AgPF6 gives iridium(I) amino olefin complex [Ir(COE)(PNP)(H)]PF6 (3(COE)-PF6). Without anion exchange, the stability of 3(COE)-Cl is highly solvent dependent. In benzene or THF a mixture of amido complex [Ir(COE)(PNP)] (4(COE)), [IrHCl2(PNP)(H)] (5), and [IrHCl(C8H13)(PNP)(H)] (6) with a vinylic cyclooctenyl ligand is obtained. A pathway is proposed that includes concurrent trapping of intramolecular C-H versus intermolecular N-H activation products. 3(L)-PF6 (L = C2H4, C3H6, CO) are prepared by olefin substitution. Deprotonation with (KOBu)-Bu-t gives the corresponding amido complexes [IrL(PNP)] (4(L); L = COE, C2H4, CO). Reversible COE C-H activation is proposed to account for the fluxional behavior of 3(COE)-PF6 in solution as compared with the structural rigidity of 4(COE), which points toward strong N -> Ir pi-donation in the amido complexes.