Air-Stable Single-Component Pd-Catalysts for Vinyl-Addition Polymerization of Functionalized Norbornenes

Well-defined single-component and tolerant Ru-, Mo-, and W-catalysts have been earlier developed for ring-opening metathesis polymerization of norbornene and its derivatives. Another way of norbornene polymerizationvinyl-addition polymerization (VAP)is a more thermodynamically favorable process and gives polymers with saturated and rigid main chains. Single-component catalysts for VAP are required, which combine good activity, tolerance to functional groups, resistance to oxygen, and air moisture and are capable of catalyzing living VAP of norbornenes. Herein, we have shown that cationic Pd-complexes with N-heterocyclic carbene ligands (NHC ligands) and weak coordinating anion ligands ([(NHC)Pd(allyl)L]⁺A^–, where allyl is an allyl group, L = CO, CH₃CN, CH₂Cl₂, and A^– = SbF₆^– or BARF^–) are highly efficient single-component catalysts for VAP of both norbornene and various substituted norbornenes. These complexes, being stable in the solid state and in solutions, have exhibited several important features as VAP catalysts. They are capable of catalyzing VAP of norbornenes in air and are tolerant to functional groups. The complexes have shown high catalytic activity and have allowed polymerizing monomers at very low catalyst loadings, as low as 2 ppm. The versatility of [(NHC)Pd(allyl)L]⁺A^– complexes as catalysts of VAP has been demonstrated by successful polymerization of monomers with polar and bulky groups, containing alkyl, vinyl, alkylidene, ether, ester, imide, or organosilicon motifs, affording high-molecular-weight products in good and high yields. Tuning the nature of NHC and allyl ligands in [(NHC)Pd(allyl)L]⁺A^– complexes let perform living VAP, yielding block copolymers.