C-H activation and C=C double bond formation reactions in iridium ortho-methyl arylphosphane complexes

The Vaska-type iridium(I) complex [IrCl(CO){PPh2((2)-MeC6H4)}(2)] (1), characterized by an X-ray diffraction study, was obtained from iridium(111) chloride hydrate and PPh2(2,6-MeRC6H3) with R=H in DMF, whereas for R=Me, activation of two orthomethyl groups resulted in the biscyclometalated iridium(III) compound [IrCl(CO){PPh2(2,6-CH2MeC6H3)}(2)] (2). Conversely, for R=Me the iridium(I) compound [IrCL(CO){PPh2(2,6Me(2)C(6)H(3))}(2)] (3) can be obtained by treatment of [IrCl(COE)(2)](2) (COE=cyclooctene) with carbon monoxide and the phosphane in acetonitrile. Compound 3 in CH2Cl2 undergoes intramolecular C-H oxidative addition, affording the cyclometalated hydride iridium(111) species [IrHCl(CO){PPh2(2,6-CH2MeC6H3)}{PPh2(2,6-Me2C6H3)}] (4). Treatment of 2 with Na[BAr'(4)] (Ar'=3,5-C6H3(CF3)(2)) gives the fluxional cationic 16-electron complex [Ir(CO){PPh2(2,6-CH2MeC6H3)}2]-[BAr'(4)] (5), which reversibly reacts with dihydrogen to afford the delta-agostic complex [IrH(CO){PPh2(2,6CH(2)MeC(6)H(3))}{PPh2(2,6-Me2C6H3)}]- [BAr'4] (6), through cleavage of an Ir-C bond. This species can also be formed by treatment of 4 with Na[BAr4f] or of 2 with Na[BAr'4] through C-H oxidative addition of one orthomethyl group, via a transient 14-electron iridium(l) complex. Heating of the coordinatively unsaturated biscyclometalated species 5 in toluene gives the trans-dihydride iridium(111) complex [IrH2(CO){PPh2(2,6-MeC6H3CH= CHC6H3Me-2,6)PPh2}][BAr4f] (7), containing a trans-stilbene-type terdentate ligand, as result of a dehydrogenative carbon-carbon double bond coupling reaction, possibly through an iridium carbene species.