Mechanistic Insight into the Copper-Catalyzed Phosphorylation of Terminal Alkynes: A Combined Theoretical and Experimental Study.

The Journal of organic chemistry

PubMedID: 24983135

Liu L, Wu Y, Wang Z, Zhu J, Zhao Y. Mechanistic Insight into the Copper-Catalyzed Phosphorylation of Terminal Alkynes: A Combined Theoretical and Experimental Study. J Org Chem. 2014;.
The reaction mechanism of copper-catalyzed phosphorylation of terminal alkynes under different conditions has been investigated experimentally and theoretically. The important role of dioxygen has been elucidated, including the formation of ?(1)-superoxocopper (II), ?(2)-superoxocopper (III), µ-?(2):?(2)-peroxodicopper (II) and bis(µ-oxo)-dicopper (III). More importantly, the proton transfer from dialkyl phosphonates (in the form of phosphite) to the bridging oxygen atom entails the migration of the deprotonated phosphonates into the terminal alkyne, leading to the formation of a C-P bond with an activation barrier of only 1.8 kcal/mol. In addition, a particularly stable, six-centered dicopper (I) species was located with the migration of both the Ph2P(O) groups from the copper to the oxygen atom of bis(µ-oxo)-bridge, explaining experimental observation that the copper catalyst was susceptible to secondary phosphine oxides rather than dialkyl phosphonates. Thus, the diphenylphosphine oxide was added to the reaction mixture dropwise to minimize the concentration during the reaction course. Gratifyingly, it is almost quantitative to generate the coupling product without oxidation byproduct when the reaction was completed.