Phase‐Separable Polyisobutylene Palladium‐PEPPSI Precatalysts: Synthesis and Application in Buchwald–Hartwig Amination

Abstract

This paper reports the efficient synthesis of the first class of polyisobutylene(PIB)-supported palladium-PEPPSI precatalyst (PEPPSI = pyridine-enhanced precatalyst preparation, stabilization, and initiation). The new complexes are employed in Buchwald-Hartwig amination of aryl chlorides and are found to be reasonably active in the titled cross-coupling reaction. The supported catalysts are tested in polar (1,4-dioxane and 1,2-dimethoxyethane) as well as in aliphatic reaction media (toluene and n-heptane) and display superior activity in the highly lipophilic solvent (n-heptane). The catalytic efficacy of PIB-Pd-PEPPSI precatalyst is measured to be comparable to its nonsupported analog. Pd-leaching is determined by inductively coupled plasma mass spectrometry (ICP-MS) after a simple liquid/liquid extraction and is found to be 2 ppb in the product phase, translating into a recovery of ≈99.8% of the palladium.

The Buchwald–Hartwig Amination After 25 Years

“…Modifications of the backbone of the NHC ligands in Pd‐PEPPSI precatalysts allowed for the expansion of the substrate scope and the use of milder reaction conditions . Polymer‐supported Pd‐PEPPSI precatalysts as well as a mechanochemical method based on the use of Pd‐PEPPSI‐IPent have also been recently developed for C−N couplings. In addition, the use of a NHC‐containing palladacycle enabled the amination of diaryl sulfoxides, which could be regioselectively conducted by means of steric bias …”

The Buchwald–Hartwig Amination After 25 Years

“…[77] Modifications of the backbone of the NHC ligands in Pd-PEPPSI precatalysts allowed for the expansion of the substrate scope and the use of milder reaction conditions. [78] Polymer-supported Pd-PEPPSI precatalysts [79] as well as am echanochemical method based on the use of Pd-PEP-PSI-IPent [80] have also been recently developed for CÀN couplings.I na ddition, the use of aN HC-containing palladacycle enabled the amination of diaryl sulfoxides,which could be regioselectively conducted by means of steric bias. [81]…”

Block copolymers derived from polyisobutylene oligomers

“…These materials are available with terminal alkene groups that are easily converted into functional groups such as hydroxyl, thiol, azide, ester, amide, and aryl groups – chemistry we and others have used in a variety of applications in catalysis and green chemistry . These materials’ phase selective solubility in alkane solvents like heptane and poly(α‐olefin)s (PAOs) makes these oligomeric hydrocarbon derivatives excellent phase anchors for immobilization of ligands and catalysts . Such functional polyisobutylene derivatives are also useful in that they make otherwise insoluble materials like phthallocyanines, inorganic clusters, and nanoparticles soluble in alkane solvents and in polyolefins .…”

“…PIB oligomers with better defined end group chemistry can be prepared . However, the alkene functionality on commercially available PIB oligomers has been adequate in our past work in designing alkane phase anchored species and the use of commercially available PIB facilitates use of this chemistry by others without expertise in cationic polymerization.…”