Poly(norbornene)‐Supported N‐Heterocyclic Carbenes as Ligands in Catalysis

Abstract

In this contribution, we present the synthesis of norbornene-supported N-heterocyclic (NHC) carbenes. These functionalized norbornenes were polymerized via ring-opening metathesis polymerization in a controlled fashion either before or after metalation with a variety of palladium and ruthenium precursors resulting in the formation of polymersupported NHC-based metal catalysts. The activities of the palladium-based catalysts in the SuzukiMiyaura, Sonogashira and Heck coupling reactions were studied in detail. In all cases, the polymeric catalysts demonstrated the same activity as their small molecule analogues. Furthermore, we carried out preliminary investigations into the stability of these catalysts using poisoning studies. A clear dependence of the stability of the polymer-supported catalysts on their palladium precursor was observed with palladium acetate-based polymeric NHC catalysts being the most stable. Finally, we have studied the reactivity of our supported NHC ruthenium complexes as catalysts for ring-closing metathesis. Again, in all cases good conversions were observed with comparable activities to other supported NHC-ruthenium catalysts. Lastly, we were able to remove the ruthenium catalysts from the solution quantitatively demonstrating the possibility of metal removal.

Polymers for Green C–C Couplings

“…The catalyst could not be recycled without a serious decrease in the conversions observed. [70] Buchmeiser reported a polynorbornene with a pendant CO 2 -stabilized carbene (15, Figure 3). The reaction of this zwitterionic species with PdCl 2 afforded a catalyst that was used in the Heck reaction with good activity and recyclability without contamination of the products (Ͻ 0.1 ppm of Pd).…”

A Practical Heterogeneous Catalyst for the Suzuki, Sonogashira, and Stille Coupling Reactions of Unreactive Aryl Chlorides

“…[7][8][9] From a practical point of view, the use of aryl chlorides is highly desirable because they are readily available and inexpensive. However, they are much more difficult to activate than aryl iodides and bromides.…”

Polymer-supported macrocyclic Schiff base palladium complex: An efficient and reusable catalyst for Suzuki cross-coupling reaction under ambient condition

“…Correspondingly, palladium complexes anchored on polymers with Schiff bases [10,11], N-heterocyclic carbene groups [12][13][14][15], and dendrimers [16,17] have been described recently. In addition, a few efficient heterogeneous Pd catalysts, which are of general use for this reaction of aryl chlorides, have also been reported [18][19][20][21][22][23][24][25].…”