Aryl C–H bond functionalization with diphenyldiazomethane induced by rare-earth metal alkyl complexes

Abstract

The first examples of regioselective aryl ortho-C–H functionalization with diphenyldiazomethane for the construction of C_aryl–N_hydrazinato bonds were accomplished via the activation of C–H bonds and the subsequent reaction of diphenyldiazomethane with the RE–C_aryl bond. The reactions of rare-earth metal monoalkyl complexes LRE(CH₂SiMe₃)(THF)₂ (L = 2,5-[(2-pyrrolyl)CPh₂]₂(N-Me-pyrrole)) supported by a neutral N-methylpyrrole anchored dipyrrolyl ligand with 2 equiv. of Ph₂CN₂ gave irreversibly unprecedented hydrazonato-functionalized imino rare-earth metal complexes LRE(Ph₂CNNC₆H₄-(o-CNHPh) (RE = Y (2a), Lu (2a′)) in good yields involving a rather complex process including the interaction of a diazo unit with a RE–C_alkyl bond, a β-H elimination, a N–N cleavage, 1,4-hydrogen transfer and the subsequent C–N coupling with another diphenyldiazomethane. More important is that regioselective aryl C–H bond functionalization with diphenyldiazomethane to construct the C_aryl–N_hydrazinato bonds can be easily achieved by three-component reactions of rare-earth metal monoalkyl complexes, a wide range of substituted imines (including aldimines, ketimines or analogous 2-phenylpyridine) and diphenyldiazomethane, affording various hydrazonato-functionalized phenyl, thienyl imino or pyridyl rare-earth metal complexes 2b–2j at room temperature. A further study indicated that the substituents on the phenyl ring have a great effect on the reaction pathway and governed the C_aryl–N_hydrazinato bond construction. Moreover, the experimental studies show that the formation of the C_aryl–N_hydrazinato bonds is thermodynamically facile, which could be realized at room temperature easily.