Base-Promoted Selective Activation of Benzylic Carbon−Hydrogen Bonds of Toluenes by Iridium(III) Porphyrin

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.

碳酸钾（K₂CO₃）与苯氧基钠（NaOPh）可有效提升卟啉氯化羰基铱(III) [Ir(ttp)Cl(CO)] 催化甲苯发生苄基碳氢键活化（benzylic carbon−hydrogen bond activation, BnCHA）的反应速率，以高收率得到卟啉铱苄基配合物。机理研究表明，碳酸钾首先将Ir(ttp)Cl(CO)转化为Ir(ttp)X（X=OH⁻、KCO₃⁻），该中间体可与甲苯快速反应生成Ir(ttp)H。Ir(ttp)H可进一步还原未反应的Ir(ttp)Cl(CO)中的羰基配体，生成Ir(ttp)Me。Ir(ttp)H还可通过脱氢二聚生成[Ir(ttp)]₂，该过程在碱存在下会被显著促进，生成的二聚体可进一步与甲苯反应得到卟啉铱苄基配合物。碱性较弱的苯氧基钠（NaOPh）则可将Ir(ttp)Cl(CO)转化为Ir(ttp)OPh，该中间体可选择性催化苄基碳氢键活化反应，最终得到卟啉铱苄基配合物。