Mild and Selective C(CO)–C(α) Bond Cleavage of Ketones by Rhodium(III) Porphyrins: Scope and Mechanism

Rhodium­(III) porphyrins were found to undergo selective
C­(CO)–C­(α)
bond activation (CCA) of ketones promoted by water at temperatures
as low as 50 °C. The acyl group of the ketone was transferred
to the rhodium center, and the alkyl fragment was oxidized to a carbonyl
moiety accordingly. The hydroxyl group of water is transferred to
the rhodium porphyrin through hydrolysis of the kinetic α-carbon–hydrogen
bond activation (α-CHA) product to give RhIII(ttp)­OH
(ttp = 5,10,15,20-tetratolylporphyrinato dianion), which subsequently
cleaves the C­(CO)–C­(α) bond of ketone.

研究发现，铑(III)卟啉（Rhodium(III) porphyrins）可在低至50℃的温度下，在水的促进作用下实现酮的选择性C(CO)–C(α)键活化（CCA）。反应过程中，酮的酰基会转移至铑中心，烷基片段则相应被氧化为羰基基团。通过水解动力学α-碳氢键活化（α-CHA）产物，水的羟基被转移至铑卟啉骨架上，生成RhIII(ttp)OH（其中ttp为5,10,15,20-四对甲苯基卟啉二阴离子），该配合物可进一步裂解酮的C(CO)–C(α)键。