Cross-Coupling Catalysis by an Anionic Palladium Complex

Abstract

Recent studies have shown that anionic palladium complexes are viable catalysts for a range of catalytic cross-coupling reactions. We present a one-step synthesis of the anionic "ligandless" palladium complex [NBu 4 ][Pd-(DMSO)Cl 3 ] together with its crystal structure. This compound has been shown to be an active precatalyst in the Mizoroki−Heck reaction. Under Jeffery conditions, activated aryl chlorides can be coupled in yields of up to 94% without the need of an additional ligand. The presence of a small amount of water was necessary for product formation. An Amatore−Jutand-type catalytic cycle is consistent with the results presented herein. For comparison with the known mixed complex [(pym-Im-Me) 2 PdCl][Pd(DMSO)Cl 3 ], the cationic complex [(pym-Im-Me) 2 PdCl]PF 6 (pym = pyrimidyl, Im = imidazolin-2-ylidene) has been synthesized and characterized using standard techniques.

Cationic versus Anionic Palladium Species in the Suzuki–Miyaura Cross‐Coupling

“…On the contrary, the use of the anionic complex 3 leads to quick catalyst decomposition, as indicated by rapid formation of palladium black during the reaction, which in turn prevents full conversion. This is in contrast to the Mizoroki–Heck reaction, where the anion was responsible for the high activity . The presence of an induction period, the observed catalyst poisoning in the presence of CS 2 and mercury, and the SEM images indicate the participation of a heterogeneous catalyst for each of the compounds 1 – 4 .…”

“…Compound 1 was an active precatalyst in the Mizoroki–Heck reaction, as well as the oxidation of methane. Further studies assigned the high catalytic activity in the Mizoroki–Heck reaction to the palladium anion . In the Suzuki–Miyaura cross‐coupling reaction, compounds similar to the cation of 1 have been employed by Chen, as well as complexes similar to the anion of 1 by Trzeciak, Dyson, and Nolan .…”

“…In the Suzuki–Miyaura cross‐coupling reaction, compounds similar to the cation of 1 have been employed by Chen, as well as complexes similar to the anion of 1 by Trzeciak, Dyson, and Nolan . Complexes 1 – 3 have been characterized by solid‐state structures , . Thus, we chose to study the performance of complex 1 in the Suzuki–Miyaura cross‐coupling in comparison to complexes 2 – 4 , each containing only one palladium species,, to identify which of the palladium species in 1 provides the ideal precatalyst for the Suzuki–Miyaura cross‐coupling reaction.…”

“…Complexes 1 – 3 have been characterized by solid‐state structures , . Thus, we chose to study the performance of complex 1 in the Suzuki–Miyaura cross‐coupling in comparison to complexes 2 – 4 , each containing only one palladium species,, to identify which of the palladium species in 1 provides the ideal precatalyst for the Suzuki–Miyaura cross‐coupling reaction.…”

Anionische Palladium(0)‐ und Palladium(II)‐At‐Komplexe

“…Um die Auswirkungen der elektronischen Eigenschaften der Phosphanliganden auf die Stabilitätder Pd-At-Komplexe zu untersuchen, versetzten wir Lçsungen von [L 3 Pd] und LiBr mit 3 ¾quiv.L Ph1 bzw.L Ph2 .D iese Versuche ergaben gemischte Komplexe,z eigten aber auch eindeutig,d ass die elektronenreicheren Phosphane L Ph1 and L Ph2 eine geringere Affinitätz ud en Pd-At-Komplexen als La ufwiesen, was die Eingangshypothese stützt (Abbildungen S16-S20 [20] Durch zeitabhängige Messungen konnte der Aufbau dieser Spezies auf Kosten des Pd 0 -At-Komplexes [L 3 PdBr] À beobachtet und eine Halbwertszeit der Reaktion von ca. 15 min bestimmt werden (Abbildungen S47 und S48).…”