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(CH 2 CH 2 P i Pr 2 ) 2 ((PNP) H ) and AgPF 6 gives iridium(I) amino olefin complex [Ir(COE)(PNP) H ]PF 6 ( 3 COE -PF 6 ). 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 ), [IrHCl 2 (PNP) H ] ( 5 ), and [IrHCl(C 8 H 13 )(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 -PF 6 (L = C 2 H 4, C 3 H 6, CO) are prepared by olefin substitution. Deprotonation with KO t Bu gives the corresponding amido complexes [IrL(PNP)] ( 4 L; L = COE, C 2 H 4, CO). Reversible COE C−H activation is proposed to account for the fluxional behavior of 3 COE -PF 6 in solution as compared with the structural rigidity of 4 COE, which points toward strong N→Ir π-donation in the amido complexes.