Carbonyl and Carbonyl-N-Heterocyclic Carbene-Ligated Iron Complexes as Catalysts for Markovnikov-Selective Alkyne Hydrothiolation and Hydroselenation Reactions: A Mechanistic Study.

In the present work, iron carbonyl-catalyzed hydrothiolation/hydroselenation of alkynes has been studied computationally. The catalytic efficiency of inexpensive iron carbonyls and three iron-N-heterocyclic carbene (NHC)-based complexes-Fe(NHC)(CO), Fe(NHC)(CO), and Fe(aNHC)(CO)-is evaluated. The results demonstrate significantly reduced energy barriers for the catalytic reactions compared to uncatalyzed gas-phase reactions. A high degree of regioselectivity for the Markovnikov product is observed, validating the effectiveness of these complexes in producing Markovnikov vinyl sulfides/selenides. An alternative catalytic pathway involving alkyne insertion into the MS/Se and MH bonds is also explored, and it is found that the catalyst regio- and stereoselectively leads to the formation of Markovnikov product in MS/Se insertion pathway and Z-anti-Markovnikov product in MH insertion pathway, consistent with the existing literature reports.