Base-promoted selective activation of benzylic carbon-hydrogen bonds of toluenes by iridium(III) porphyrin

摘要

K2CO3 and NaOPh promoted the rate of benzylic carbon-hydrogen bond activation (BnCHA) of toluenes with iridium(III) porphyrin carbonyl chloride (Ir(ttp)Cl(CO)) to give iridium porphyrin benzyls in high yields. Mechanistic studies suggested that K2CO3 initially converted Ir(ttp)Cl(CO) to Ir(ttp)X (X = OH-, KCO3-), which reacted very fast with toluenes to yield Ir(ttp)H. Ir(ttp)H then reduced the carbonyl ligand in unreacted Ir(ttp)Cl(CO) to yield Ir(ttp)Me. Ir(ttp)H also dimerized dehydrogenatively to give [Ir(ttp)](2), especially promoted in the presence of base, which further reacted with toluenes to yield iridium benzyls. Weaker base of NaOPh converted Ir(ttp)Cl(CO) to Ir(ttp)OPh, which selectively promoted BnCHA to yield iridium benzyls.