1,4- and 1,3-Metal Migration in a Cp*IrIII Complex: Experimental Evidence of Direct 1,3-Metal Migration

Reactions of the phenyliridium­(III) complex [Cp*IrCl­(Ph)­(PMe3)] with internal alkynes (RCCR, R = Ph or Me) in the presence of NaBArF4 give rise to the formation of the (o-vinylaryl)iridium complexes [Cp*Ir­{o-C6H4C­(R)CHR}­(PMe3)]­[BArF4] (2a, R = Ph; 2b, R = Me) via the alkyne insertion and the subsequent vinyl-to-aryl 1,4-miration of the Ir­(III) center, while a similar reaction of PhCCMe affords the π-allyl complex [Cp*Ir­{η3-CH­(Ph)­C­(Ph)­CH2}­(PMe3)]­[BArF4] (4) in high yield. The latter is the formal 1,3-Ir migration product formed from the vinyliridium complex [Cp*Ir­{C­(Ph)C­(Me)­Ph}­(PMe3)]­[BArF4] (3c). Deuterium labeling experiments have revealed that this π-allyl complex is produced by two distinct mechanisms, (1) CC bond rotation in 3c, followed by direct 1,3-Ir migration, and (2) successive vinyl-to-aryl and aryl-to-allyl 1,4-Ir migrations by way of the o-vinylaryl complex [Cp*Ir­{o-C6H4C­(Me)CHPh}­(PMe3)]­[BArF4] (2c). This reaction provides the first experimental evidence of the direct 1,3-metal migration accompanied by the C–H bond activation. In addition, detailed analysis of the reaction system has demonstrated that a cyclometalated carbene complex 5, which is formed from 2c or 3c through the intramolecular C–H oxidative addition and the subsequent 1,3-hydrido migration, is involved in the isomerization process.