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

Abstract

The reaction of [IrCl(COE)2]2 (1, COE = cyclooctene) with pincer ligand HN(CH2CH2PiPr2)2 ((PNP)H) and AgPF6 gives iridium(I) amino olefin complex [Ir(COE)(PNP)H]PF6 (3COE-PF6). Without anion exchange, the stability of 3COE-Cl is highly solvent dependent. In benzene or THF a mixture of amido complex [Ir(COE)(PNP)] (4COE), [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. 3L-PF6 (L = C2H4, C3H6, CO) are prepared by olefin substitution. Deprotonation with KOtBu gives the corresponding amido complexes [IrL(PNP)] (4L; L = COE, C2H4, CO). Reversible COE C−H activation is proposed to account for the fluxional behavior of 3COE-PF6 in solution as compared with the structural rigidity of 4COE, which points toward strong N→Ir π-donation in the amido complexes.