Palladacycles: Efficient New Catalysts for the Heck Vinylation of Aryl Halides

Abstract

Cyclopalladated complexes of the general formula [Pd,(p-L),(P-C),] (L = bridging ligand, e.g. OAc, CI, Br, I; P-C = cyclometallated P donor, c.g. o-

The Heck reaction in the production of fine chemicals

“…Initially, reports only mentioned the use of aryl bromides and iodides as arylating agent. Later, variants were developed using aromatic triflates (11), aroyl chlorides (12), aryl sulfonyl chlorides (13), aromatic diazonium salts (14) (the Matsuda reaction), aroyl anhydrides (15), aryl chlorides (16)(17)(18)(19)(20), and arylsilanols (21). Consequently, the number of commercially available aromatic substrates is very high.…”

“…A major side product (3-11%) in these reactions is the stilbene (17), which is formed by desilylation of the initially formed monoarylated disiloxane (15) followed by Heck reaction on the vinyl group (Scheme 6). Initial results using Et 3 N as base gave much higher yields of this side product.…”

“…Another interesting, cheap, and very active class of catalysts are the palladacycles based on aromatic compounds with side chains containing N (41,46), O (47), or S (48,49). The more active catalysts also have allowed the use of chloroarenes as arylating agents, which is tremendously important because of the much wider commercial availability and the lower costs of these compounds (16)(17)(18)(19)(20).…”

σ-Alkenyl endo-palladacycle formation via regiospecific functionalisation of an unreactive NHC-tethered C(sp2)–H bond

“…1,2 Pioneered by Herrmann and coworkers in 1995, 3 palladacyclic complexes have showcased extensive utility in prolific catalytic processes such as C-C crosscoupling 4,5 and allylic substitution, 6 and have more recently emerged as promising antimicrobial agents. 7 Traditional routes to palladacyclic scaffolds involve a metal-induced C-H activation process paralleled by coordination of pendant heteroatom donors (e.g.…”

“…Initially, the deprotonation of the first imidazolium NCHN proton was considered (Figure 4 and Figure S6 in ESI). The DFT calculations illustrate that the most stable palladium acetate adduct in MeCN exists as a square planar cis-MeCN complex (4). As imidazolium 1 is introduced, the ligand initially binds via the pyridyl nitrogen atom to Pd (8).…”