Pyridine Wingtip in [Pd(Py-tzNHC)₂]²⁺ Complex Is a Proton Shuttle in the Catalytic Hydroamination of Alkynes

Abstract

The cationic palladium(II) complex 1 of pyridylmesoionic carbene ligand catalyzes Markovnikov-selective intermolecular hydroamination between anilines and terminal alkynes into the corresponding imines. The reaction proceeds at room temperature, in the absence of additives, with exquisite selectivity and diverse functional group tolerance. The key intrinsic feature of the catalyst is the pyridine wingtip confined to the proximity of the alkynophilic metal active site, which mimics the function of enzymelike architectures by assisting entropically favored proton transfers.

Pincer‐Type Mesoionic Carbene Nickel(II) Complexes: Synthesis, Properties, Reactions, and Catalytic Application to the Suzuki–Miyaura Coupling Reaction of Aryl Bromides

“…[53] Among several methods used to prepare late-transition metal MIC complexes, the most accessible and common protocol is the use of their silver MIC analogues as intermediates. [15-34,54À 55] However, the [39][40][41][42][43][44][45] www.eurjic.org silver method has not been applied to previously reported nickel MIC complexes, [35][36][37][38][39][40] although the similar nickel imidazolylidene complexes can be made by the silver method. [56][57] Herein, we developed an efficient synthetic procedure used for the preparation of pincer-type complexes of nickel(II) bearing an MIC ligand via their silver analogues.…”

“…[10][11][12][13][14][15][16] In particular, 1,2,3-triazol-5-ylidene (triazolylidene) is the most attractive ligand motif and has been well established because it can be easily synthesized via the [3 + 2] Huisgen reaction between alkynes and azides. [17][18] Although several reports have been published on the palladium chemistry of MIC complexes, [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] examples of MICs bound to nickel centers are rare, as shown in Figure 1. [39][40][41][42][43][44][45] Among these complexes, there are several examples of complexes prepared using monodentate and bidentate MIC ligands, [39][40][41][42] but only a few complexes in which the MIC moiety is incorporated into a tridentate ligand.…”

“…Among several methods used to prepare late‐transition metal MIC complexes, the most accessible and common protocol is the use of their silver MIC analogues as intermediates [15–34,54−55] . However, the silver method has not been applied to previously reported nickel MIC complexes, [35–40] although the similar nickel imidazolylidene complexes can be made by the silver method [56–57] …”

Metal–ligand–Lewis acid multi-cooperative catalysis: a step forward in the Conia-ene reaction

“…Our group introduced a few years ago an SCS pincer framework featuring an electron-rich indenediide back-bone. 6 The paucity of MLC behavior reported for Pd and Pt complexes, 7 despite the prominent role of these metals in homogeneous catalysis, led us to study complexes of type I (Fig. 1).…”

Designing Homogeneous Copper-Free Sonogashira Reaction through a Prism of Pd–Pd Transmetalation

“…Although their ability to activate terminal alkynes into acetylides of type B is well-established, 10b,23 the propensity of phosphines to dissociate and exchange 24 could lead to undesired scrambling between the reactive palladium species from both cycles, leading to uncontrolled side reactions or even termination of the process. Instead, we selected N-heterocyclic carbene (NHC) ligand of a pyridine (Py) functionalized mesoionic (MIC) structure (PyMIC), 19,25 possessing coordination abilities to a metal beyond phosphines and even NHCs. B-like NHC acetylide Pd 2+ complexes are well-documented, 26 and their formation is also evident from many Pd-NHC promoted copper-free and copper cocatalyzed alkynylations.…”