Facile Double C−H Activation of Tetrahydrofuran by an Iridium PNP Pincer Complex

The reaction of [IrCl(COE)2]2 (COE = cyclooctene) with bulky PNP amino pincer ligand HN(CH2CH2PtBu2)2, (HPNP)tBu, results in high-yield formation of iridium(III) complex [IrH(C8H13)Cl(HPNP)tBu] after oxidative addition of a vinylic COE C−H bond. Upon dissolving the product in polar solvents or chloride abstraction with TlPF6 the cationic iridium(I) complex [Ir(COE)(HPNP)tBu]+ is obtained, which is thermally unstable. This observation shows that the olefin isomer represents the thermodynamic minimum for the cationic complex, while the cyclooctenyl hydride isomer is trapped in nonpolar solvents by anion coordination. Owing to the lability of the olefin ligand, [Ir(COE)(HPNP)tBu]+ undergoes facile intermolecular C−H activation. Fischer-carbene complex [Ir(H)2(CO(CH2)3)(HPNP)tBu]BPh4 was isolated in good yield upon α,α-dehydrogenation of THF. Mechanistic examinations suggest olefin dissociation to be rate-determining.