C-H activation of ethers by pyridine tethered PCP-type iridium complexes

Iridium PC sp3 P complexes featuring a novel bis(2-diphenylphosphinophenyl)-2-pyridylmethane ligand (PC Py HP) are reported. C-H activation reactions between the dihydride complex [(PC Py P)Ir(H) 2 ] and tetrahydrofuran or methyl tert -butyl ether in the presence of a hydrogen acceptor, norbornene (NBE), at ambient temperature led exclusively to the hydrido oxyalkyl complexes, [(PC Py P)IrH(C 4 H 7 O)] and [(PC Py P)IrH(CH 2 O t Bu)], respectively. The internal pyridine donor is important and stabilizes these species by coordination to the iridium center. The coordination of pyridine to the iridium center is labile, however, and its dissociation occurs in the presence of a suitable substrate, as demonstrated by the intramolecular nucleophilic attack of pyridine on a vinylidene intermediate generated from PhC&z.tbd;CH. An iridium complex supported by a PC Py P ligand featuring an internal pyridine tether showed selective mono-C-H activation of ethers, which represent intermediates in the synthesis of the corresponding Fischer carbenes.