Theoretical study on the mechanism of Ni−Al bimetallic catalyzed dual C−H cyclization of amides and alkynes

Abstract

The reaction mechanism of Ni−Al bimetallic catalyzed dual C−H cyclization of amides and internal alkynes has been studied theoretically. Four reactions were considered with N-phenylformamide (S1) and (2Ph)-N,N-bis(1-phenylethyl)formamide (S2) as amides, second phosphine oxide (SPO) and PMe3 as ligands, respectively. For two reactions with SPO as ligand and the reaction of S2 with PMe3, the reaction mechanism mainly includes formyl C(sp2)−H bond activation, phenyl C(sp2)−H or benzylic methyl C(sp3)−H bond activation, release of alkene, alkyne coordination and insertion, isomerization, and reductive elimination steps generating the cyclization product. The reaction of S1 with PMe3 proceeds via formyl C(sp2)−H bond activation, isomerization, and reductive elimination steps giving the alkyne addition product. In addition, the influence of substituent in SPO on reaction mechanism and the regio-selectivity of phenylpropyne in reaction have been calculated in detail.