Orthopalladated and ‐platinated Bulky Triarylphosphite Complexes: Synthesis, Reactivity and Application as High‐Activity Catalysts for Suzuki and Stille Coupling Reactions

Abstract

Bulky triarylphosphite ligands undergo facile orthometallation reactions with palladium and platinum precursors. The crystal structure of an example of the resultant palladacycles has been determined. The reactivity of some of the metallacycles with HCl, monodentate and bidentate phosphines and sodium diethyldithiocarbamate has been investigated, and the crystal structure of a diethyldithiocarbamate adduct of a palladacycle is presented. The palladacyclic complexes prove to be extremely active catalysts for the Suzuki coupling of aryl bromides with aryl boronic acids. They can also be used as catalysts for the coupling of alkylboronic acids. Meanwhile di- and trialkyl phosphine adducts of one of the palladacycles shows very high activity in the Suzuki coupling of aryl chlorides and can also be used to good effect for the Stille coupling of these substrates. The role of the phosphite ligand in the Suzuki coupling of aryl chlorides seems to be one of increasing catalyst longevity by stabilisation of the Pd(0) resting state.

High‐Turnover Palladium Catalysts in Cross‐Coupling and Heck Chemistry: A Critical Overview

“…[103] More research is needed to clarify the exact nature of the catalytic species in these high-TON couplings. [104] A modification of catalysts 5a -c is constituted by the related phosphate-palladacycle 7, which reaches a new TON record in the Suzuki coupling of deactivated aryl chlorides such as 3.21 (ca. 1.3 Â 10 5 ).…”

σ‐Alkylpalladium Intermediates in Intramolecular Heck Reactions:Isolation and Catalytic Activity

“…[35] However, its coupling ability is lower than those of triaryl phosphite palladacycles, which are again shown to be the best-performing precatalysts in cross-coupling reactions. [36] It is worth noting that all palladacycles retained their activity even after being stored in air at room temperature for a few months, and demonstrated excellent thermal stability, decomposing only after being heated for more than 48 h in the presence of a base. This means that they are much more stable towards air, moisture, and heating than the [Pd-A C H T U N G T R E N N U N G (PPh 3 ) 4 ] used for their generation.…”

Pd-loaded NaY zeolite as a highly active catalyst for ligandless Suzuki–Miyaura reactions of aryl halides at low Pd loadings under aerobic conditions

“…Presently, high turnover numbers (TON) can be achieved even with the electron rich chloroarenes by the catalysis of variety of Pd complexes or Pd-ligand combinations under homogeneous and relatively mild reaction conditions [8][9][10][11][12][13][14][15][16][17]. Nevertheless, the pharmaceutical industry in particular is highly reluctant to employ the Pd catalyzed processes since there is always a risk of contamination of the end products by the transition metal and ligand residues.…”