Poly(norbornene)-Supported N-Heterocyclic Carbenes

Significance

Poly(norbornene)-supported N-heterocyclic carbene (NHC) and its palladium complex were prepared (eq. 1). Thus, reaction of the norbornene derivative 1 with the N-mesitylimidazole 2 gave the imidazolinium salt 3. Treatment of 3 with Ag₂O afforded silver complex 4. The resulting complex 4 was then treated with Pd(OAc)₂ to afford the NHC-Pd complex 5. Ring-opening metathesis polymerization of 5 with the Grubbs catalyst 6 provided the poly(norbornene)-supported NHC-Pd complex 7. Catalytic activity of 7 for the Suzuki-Miyaura coupling reaction was comparable to its small-molecule analogues, such as IMes. Thus, the reaction of the aryl chlorides 8 with phenylboronic acid 9 took place in the presence of 1 mol% of 7 to give the corresponding biphenyls 10 in 92-100% yield (eq. 2).