CH Activation and CC Double Bond Formation Reactions in Iridium ortho ‐Methyl Arylphosphane Complexes

The Vaska‐type iridium(I) complex [IrCl(CO){PPh 2 (2‐MeC 6 H 4 )} 2 ] ( 1 ), characterized by an X‐ray diffraction study, was obtained from iridium(III) chloride hydrate and PPh 2 (2,6‐MeRC 6 H 3 ) with R=H in DMF, whereas for R=Me, activation of two ortho ‐methyl groups resulted in the biscyclometalated iridium(III) compound [IrCl(CO){PPh 2 (2,6‐CH 2 MeC 6 H 3 )} 2 ] ( 2 ). Conversely, for R=Me the iridium(I) compound [IrCl(CO){PPh 2 (2,6‐Me 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 CH 2 Cl 2 undergoes intramolecular CH oxidative addition, affording the cyclometalated hydride iridium(III) species [IrHCl(CO){PPh 2 (2,6‐CH 2 MeC 6 H 3 )}{PPh 2 (2,6‐Me 2 C 6 H 3 )}] ( 4 ). Treatment of 2 with Na[BAr f 4 ] (Ar f =3,5‐C 6 H 3 (CF 3 ) 2 ) gives the fluxional cationic 16‐electron complex [Ir(CO){PPh 2 (2,6‐CH 2 MeC 6 H 3 )} 2 ][BAr f 4 ] ( 5 ), which reversibly reacts with dihydrogen to afford the δ‐agostic complex [IrH(CO){PPh 2 (2,6‐CH 2 MeC 6 H 3 )}{PPh 2 (2,6‐Me 2 C 6 H 3 )}][BAr f 4 ] ( 6 ), through cleavage of an IrC bond. This species can also be formed by treatment of 4 with Na[BAr f 4 ] or of 2 with Na[BAr f 4 ] through CH oxidative addition of one ortho ‐methyl group, via a transient 14‐electron iridium(I) complex. Heating of the coordinatively unsaturated biscyclometalated species 5 in toluene gives the trans ‐dihydride iridium(III) complex [IrH 2 (CO){PPh 2 (2,6‐MeC 6 H 3 CHCHC 6 H 3 Me‐2,6)PPh 2 }][BAr f 4 ] ( 7 ), containing a trans ‐stilbene‐type terdentate ligand, as result of a dehydrogenative carboncarbon double bond coupling reaction, possibly through an iridium carbene species.