Synthesis of megadalton stereoregular ring-substituted poly(phenylacetylene)s by a rhodium(i) catalyst with a N-functionalized hemilabile phosphine ligand

Abstract

The cationic compound [Rh(nbd){κ²P,N-Ph₂P(CH₂)₃NMe₂}][BF₄] efficiently catalyzes the polymerization of a series of ring-substituted phenylacetylene derivatives, R-C₆H₄–CCH with groups of different electronic and steric properties at the para (R = F, CF₃, Me, Bu, ^tBu, OMe, OBu) and meta (R = OMe) positions to give highly stereoregular ring-substituted poly(phenylacetylene)s with a cis-transoidal configuration of very high molar mass and moderate dispersities. The polymers have been characterized by size exclusion chromatography (SEC-MALS), NMR, DSC and TGA. The polymerization of phenylacetylene and 1-ethynyl-3-methoxybenzene gives megadalton poly(phenylacetylene)s, while the polymerization of 1-ethynyl-4-methoxybenzene and 1-(tert-butyl)-4-ethynylbenzene gives ultra-high molecular weight poly(phenylacetylene)s with M_n of 1.70 × 10⁶ and 2.72 × 10⁶, respectively. The electronic effect of the substituent strongly influences the catalytic activity. Phenylacetylene derivatives with an electron-withdrawing substituent in para position polymerize faster than those with an electron-donating substituent.