Probing the C-H Activation of Linear and Cyclic Ethers at (PNP)Ir

Interaction of the amido/bis(phosphine)supported (PNP)Ir fragment with a series of linear and cyclic ethers is shown to afford, depending on substrate, products of alpha,alpha-dehydrogenation (carbenes), alpha,beta-dehydrogenation (vinyl ethers). or decarbonylation. While carbenes are exclusively obtained from tert-amylmethylether, sec-butyl methyl ether (SBME), n-butyl methyl ether (NBME), and tetrahydrofuran (THF), vinyl others or their adducts are observed upon reaction with diethyl ether and 1,4-dioxane. Decarbonylation occurs upon interaction of (PNP)Ir with benzyl methyl ether, and a mechanism is proposed for this unusual transformation, which occurs via a series of C-H, C-O, and C-C bond eleavege events. The intermediates characterized for serveral of these reactions as well as the alpha,alpha-dehydrogenation of tert-butyl methyl ether (MTBE) are used to outline a reaction pathway for the gernation of PNP-supported iriidium(1) carbene complexes, and it is shown that the long-lived, observable intermediates are substrate-dependent and differ for the related cases of MTBE and THF. Taken together, these findings highlight the variety of pathways utilized by the electron-rich, unsaturated (PNP)Ir fragment to stabilize itself by transferring electron density to ethereal substrates through exidative addition and/or the formation of pi-acidic ligands.