Symmetrical and unsymmetrical pincer complexes with group 10 metals: synthesis via aryl C–H activation and some catalytic applications

Abstract

Aryl-based pincer metal complexes with anionic terdentate ligands have been widely applied in organic synthesis, organometallic catalysis and other related areas. Synthetically, the most simple and convenient method for the construction of these complexes is the direct metal-induced C(aryl)-H bond activation, which can be fulfilled by choosing the appropriate functional donor groups in the two side arms of the aryl-based pincer preligands. In this perspective, we wish to summarize some results achieved by our group in this context. Successful examples include symmetrical chiral bis(imidazoline) NCN pincer complexes with Ni(II), Pd(II) and Pt(II), bis(phosphinite) and bis(phosphoramidite) PCP pincer Pd(II) complexes, unsymmetrical (pyrazolyl)phosphinite, (amino)phosphinite and (imino)phosphinite PCN pincer Pd(II) complexes, chiral (imidazolinyl)phosphinite and (imidazolinyl)phosphoramidite PCN pincer complexes with Ni(II) and Pd(II) as well as unsymmetrical (oxazolinyl)amine and (oxazolinyl)pyrazole NCN' pincer Pd(II) complexes. Among them, the P-donor containing complexes are efficiently synthesized by the "one-pot phosphorylation/metalation" method. The obtained symmetrical and unsymmetrical pincer complexes have been used as catalysts in Suzuki-Miyaura reaction (Pd), asymmetric Friedel-Crafts alkylation of indole with trans-β-nitrostyrene (Pt) as well as in asymmetric allylation of aldehyde and sulfonimine (Pd). In the Suzuki couplings conducted at 40-50 °C, some unsymmetrical Pd complexes exhibit much higher activity than the related symmetrical ones which can be attributed to their faster release of active Pd(0) species resulting from the hemilabile coordination of the ligands. Literature results on the synthesis of some related pincer complexes as well as their activities in the above catalytic reactions are also presented.

The Trans Influence in Unsymmetrical Pincer Palladacycles: An Experimental and Computational Study

“…Their reactivity and other properties are influenced by the donor group around the metal [3]. The attractive feature of pincer palladacycles is the possibility for fine-tuning the catalytic activity by varying the two side arms to modify the palladium environment, by changing the donor atoms and their substituents, providing the opportunity to alter hard/soft acid base properties, or by changing the ring size, giving rise to varying steric hindrance [12].…”

“…They have been widely used as catalysts or pre-catalysts in organic reactions, such as in Heck and Suzuki-Miyaura cross-couplings [2][3][4][5]. Pincer palladacycles are an interesting type of palladacycle, of which there are two different types.…”

Pincer Complexes with Thione Sulfur Donors

“…Nowadays, hybrid systems bearing donor groups of different nature are of particular interest since they offer additional possibilities for fine-tuning electronic and steric properties. Pincer metallacycles based on such unsymmetrical ligands were shown to combine characteristics of several symmetrical prototypes or manifest unique properties [8,12,[74][75][76][77]. Despite an increasing number of publications devoted to the hybrid pincer complexes, only several examples containing thione sulfur donors have been described to date.…”

“…Since the pioneering work of B. Shaw in 1976 [1], pincer complexes have emerged as a privileged class of organometallic compounds, finding extensive use in organic synthesis, catalysis, materials science, and so on. A series of excellent reviews [2][3][4][5][6][7][8][9][10][11][12] and two recently published special treatises [13,14] cover synthetic aspects, structural features, as well as different applications of pincer complexes, showing rapid development of this area of organometallic chemistry.…”

New types of bi- and tri-dentate pyrrole-piperazine ligands and related zinc compounds: Synthesis, characterization, reaction study, and ring-opening polymerization of ε-caprolactone

“…1 All of the crystals were mounted on a glass fiber using epoxy resin and transferred to a goniostat. The data were collected on a Bruker SMART CCD diffractometer using graphite monochromated Mo-K a radiation.…”