Effects of Alkyne Substituents and X-Ligands on Alkyne Insertion Reactions of RuHX(CO)(PPh ₃ ) ₃

The reactions of diaryl alkynes ArC≡CAr with RuHX(CO)(PPh 3 ) 3 (X = F, Cl, Br, I, H, N 3, NCS, CN) were investigated. The halide complexes RuHX(CO)(PPh 3 ) 3 (X = Cl, Br, I) undergo alkyne insertion reactions with the diaryl alkynes ArC≡CAr (Ar = p -C 6 H 4 OMe, Ph, p -C 6 H 4 CO 2 Me) at room temperature to afford alkenyl complexes RuX(ArC═CHAr)(CO)(PPh 3 ) 2 . A substituent effect was observed, with alkynes bearing electron-withdrawing groups displaying higher reactivity. The insertion reaction is also strongly influenced by the X-ligands. The rate of the alkyne insertion of the halide complexes follows the order of Cl < Br < I. In contrast, complexes bearing the π-donor F, the purely σ-donor H, and π-acceptors such as N 3, NCS, and CN, exhibit significantly reduced reactivity toward alkyne insertion with ArC≡CAr under ambient conditions. Density functional theory calculations reveal that phosphine dissociation, leading to the formation of a five-coordinate intermediate RuHX(CO)(PPh 3 ) 2, and subsequent alkyne coordination are two key steps governing the overall reactivity. These steps are influenced by the steric and electronic properties of the X-ligands, as well as the alkyne substituents.