1,4- and 1,3-Metal Migration in a Cp*Ir^III 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 NaBAr^F₄ give rise to the formation of the (<i>o</i>-vinylaryl)iridium complexes [Cp*Ir­{<i>o</i>-C₆H₄C­(R)CHR}­(PMe₃)]­[BAr^F₄] (<b>2a</b>, R = Ph; <b>2b</b>, 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)]­[BAr^F₄] (<b>4</b>) 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)]­[BAr^F₄] (<b>3c</b>). Deuterium labeling experiments have revealed that this π-allyl complex is produced by two distinct mechanisms, (1) CC bond rotation in <b>3c</b>, 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 <i>o</i>-vinylaryl complex [Cp*Ir­{<i>o</i>-C₆H₄C­(Me)CHPh}­(PMe₃)]­[BAr^F₄] (<b>2c</b>). 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 <b>5</b>, which is formed from <b>2c</b> or <b>3c</b> through the intramolecular C–H oxidative addition and the subsequent 1,3-hydrido migration, is involved in the isomerization process