(N-Heterocyclic Carbene)-Palladate Complexes in Anionic Mizoroki–Heck Coupling Cycles: A Combined Experimental and Computational Study

Abstract

The reaction of complex (SIPr)PdCl 2 (TEA) (SIPr = 1,3-bis(2,6-diisopropylphenyl)-2-imidazolidinylidene, TEA = triethylamine) with tertbutylammoniun chloride (TBAC) at room temperature affords the new ionic complex [TBA][(SIPr)-PdCl 3 ] in quantitative yield. The activity of this complex as a precatalyst for Heck coupling reactions has been explored. Experimental results and DFT calculations support a plausible anionic Amatore−Jutand-type mechanism for the Heck reaction involving anionic (NHC)-palladium(0) catalytic species.

Synthesis of N-heterocyclic carbene-palladium-PEPPSI complexes and their catalytic activity in the direct C-H bond activation

“…Palladium-catalyzed bond-forming reactions are one of the most common tools synthetic chemists employ, in industry as well as in academia [20][21][22][23]. The strong palladium-NHC bonds contribute to the high stability of the active species, even at low catalyst loading and high temperatures.…”

Theoretical study on selectivity trends in (N‐heterocyclic carbene)‐Pd catalyzed mizoroki–heck reactions: Exploring density functionals methods and molecular models

“…To investigate the use of different molecular models and DFs and to determine the selectivity of a NHC‐Pd catalyst, the MI step of the Heck coupling reaction between aryl bromine and styrene was considered. The entire mechanistic cycle for the target reaction is shown in Scheme . It is comprised by four steps: oxidative addition, MI, β‐hydride syn elimination and reductive elimination.…”

“…To gain further understanding on the selectivity properties of an NHC‐Pd catalyzed MH reaction, the present work examines the migratory insertion (MI) step using two distinct molecular models sizes and different DF approaches. The main goal is to validate a simple computational protocol that would allow to correctly predict the regioselectivity experimentally observed . Therefore, the presented outcomes provide guidance for further explorations on the current system.…”

“…Palladium‐catalyzed cross‐coupling reactions are important reactions in organic synthesis and organometallic chemistry . In this context, the Mizoroki–Heck (MH) reaction, which involves the coupling of organic halides or pseudohalides with alkenes, is one of the most explored transformations.…”

“…Their shielding steric pattern combined with strong σ‐donating properties allow these ligands to both activate and stabilize metal centers in different catalytic steps of chemical processes . In the MH reaction, for example, bulky NHC‐Pd catalysts have improved the performance of the reaction . In molecular chemistry, the use of such crowding ligands is a common procedure to influence the reactivity and the stability of different chemical systems .…”