An immobilized symmetrical bis-(NHC) palladium complex as a highly efficient and recyclable Suzuki–Miyaura catalyst in aerobic aqueous media

Abstract

A bis-N-heterocyclic carbene (NHC) functionalized with chloropropyltriethoxysilane over silica was used to synthesize a well-defined immobilized palladium complex. This complex is a suitable and easily retrievable catalyst for Suzuki-Miyaura cross-coupling reactions under mild aqueous conditions. Excellent yields and conversions were obtained with low palladium loadings (down to 0.03 mol% Pd). The catalyst can be reused up to six cycles without the loss of its activity. The catalytic role of the NHC complex of palladium during coupling between bromobenzene and phenylboronic acid was investigated theoretically. The oxidative addition step is predicted to be endothermic in agreement with the experimental conditions.

Magnetic nanoparticle‐tethered Schiff base–palladium(II): Highly active and reusable heterogeneous catalyst for Suzuki–Miyaura cross‐coupling and reduction of nitroarenes in aqueous medium at room temperature

“…The biphenyl homocoupled product obtained was in a trace amount, which indicated that the SB‐Pd@MNPs nanomagnetic catalyst is highly selective . A plausible mechanism for our newly investigated SB‐Pd@MNPs nanomagnetic catalyst is illustrated in Scheme which delivers the C‐C coupling products via possible mechanistic intermediates ( I – III ) …”

“…The Suzuki–Miyaura cross‐coupling reactions are some of the most extensively used C‐C bond forming reactions in synthetic chemistry and have been utilized as an efficient method to obtain pharmaceutical drugs, complex natural products, engineering materials such as liquid crystals, molecular wires and conducting polymers . Numerous catalysts have been developed for Suzuki–Miyaura cross‐coupling reactions . Among these, Schiff base–transition metal complexes have exhibited superior catalytic activities and several homogeneous catalysts have been developed .…”

Highly efficient polymer‐stabilized palladium heterogeneous catalyst: Synthesis, characterization and application for Suzuki–Miyaura and Mizoroki–Heck coupling reactions

“…The generally accepted mechanisms for Pd‐catalyzed Suzuki–Miyaura and Mizoroki–Heck reactions are shown in Scheme . Both the mechanisms start with oxidative addition of the organohalide (R 1 ‐X) to the Pd (0) to form a Pd (II) complex …”

N‐heterocyclic carbene–palladium(II) complex supported on magnetic mesoporous silica for Heck cross‐coupling reaction

“…As can be seen, MNP@SiO 2 -SBA exhibits a typical type-IV curve with an H2 hysteresis loop. [47,48] Appearance and increase in intensity of Pd 3d doublet corresponding to Pd(0) were observed from XPS measurements followed by a decrease in Pd(II) doublet intensity. The obtained results indicate that MNPs do not block the intrachannel space, allowing molecules to enter the channels for subsequent modifications.…”