DFT Studies on Cu-Catalyzed Cross-Coupling of Diazo Compounds with Trimethylsilylethyne and <i>tert</i>-Butylethyne: Formation of Alkynes for Trimethylsilylethyne while Allenes for <i>tert</i>-Butylethyne

The detailed reaction mechanism for the Cu­(I)-catalyzed cross-coupling of (diazomethyl)­benzene with trimethylsilylethyne and tert-butylethyne was studied with the aid of density functional theory calculations. For both reactions, two catalytic cycles were considered. In one catalytic cycle, the active species reacts first with trimethylsilylethyne or tert-butylethyne, whereas, in the other one, the active species reacts first with (diazomethyl)­benzene. In both catalytic cycles, the copper acetylide formation, copper carbene migratory insertion, and protonation steps are involved. The calculation results show that the protonation step is crucial for the product selectivity. In addition, the reaction of diazoethane with tert-butylethyne and the reaction of (diazomethyl)­benzene with phenylacetylene were also considered theoretically.