Cationic Rhodium Complexes with Hemilabile Phosphine Ligands as Polymerization Catalyst for High Molecular Weight Stereoregular Poly(phenylacetylene)

Abstract

A series of cationic complexes [Rh(diene){Ph 2 P(CH 2 ) n Z}] [BF 4 ] (diene = 1,5-cyclooctadiene (cod), tetrafluorobenzobarralene (tfb) or 2,5-norbonadiene (nbd)) containing functionalized phosphine ligands of the type Ph 2 P(CH 2 ) n Z (n = 2, or 3; Z = OMe, NMe 2 , SMe) have been prepared and characterized. These complexes have shown a great catalytic activity for phenylacetylene (PA) polymerization. Catalyst screening and optimization have determined the superior performance of complexes containing a P,N-functionalyzed phosphine ligand, [Rh(diene){Ph 2 P(CH 2 ) 3 NMe 2 }][BF 4 ] (diene = cod 5, tfb 6, nbd 7), and tetrahydrofuran as solvent. The influence of the diene ligand and the effect of temperature, PA to rhodium molar ratio, addition of water or a co-catalyst, DMAP (4-(dimethylamino)pyridine), have been studied. Diene ligands strongly influence the catalytic activity and complexes 6 and 7 are far more active than 5. Both complexes gave polyphenylacetylene (PPA) with very high number-average molecular weights (M n ) of 970 000 (6) and 1 420 000 (7). The addition of DMAP resulted in a dramatic drop in the PPA molecular weight, 106 000 (6) and 233 000 (7,). The PPA obtained with the system 6/DMAP showed a narrow molecular weight distribution (M w /M n = 1.20) and incremental monomer addition experiments have demonstrated the quasi-living nature of the polymerization reaction under these conditions. The PPA obtained with these catalytic systems has been characterized by 1 H and 13 C{ 1 H} NMR spectroscopy and shows a cis-transoidal configuration with a high level of steroregularity (cis content superior to 99%). TGA, DSC, and IR analysis have revealed a thermal cis↔trans

Synthesis of polyarylacetylenes by γ‐ray‐induced polymerization of terminal alkynes. Nanostructures of ortho‐substituted derivatives

“…The antisymmetric deformation of methyl groups gave rise to strong bands at 1490 and 1463 cm −1 in P5 , and 1488 and 1458 cm −1 in P6 . Absorptions of medium intensity found at 1265 ( P4 ), 1291 ( P5 ) and 1261 ( P6 ) cm −1 may be attributed to vibrational CC bond stretching coupled with the CH bond of trans ‐vinyl groups, according to previous structural studies of poly( o ‐OMePA)28 and polyPA 29…”

Rhodium(I) Complexes with Hemilabile Phosphines: Rational Design for Efficient Oxidative Amination Catalysts

“…Alkylamino‐functionalized phosphines with hemilabile character have been very effective for the design of rhodium catalysts for the stereoregular polymerization of phenylacetylene 23. In light of the active role of the hemilabile fragment in the generation of the alkynyl catalytically active species, we also explored their potential use in the design of efficient hydroamination catalysts.…”

Asymmetric polymerisation of substituted phenylacetylene using chiral Rh(2,5-norbornadiene)(L-proline) catalyst

“…The chiral ligand of the catalyst is not dissociated in the initiation stage and it remains a part of the propagating species. The O atom has stronger donating and acceptor capacities than the N atom; on the other hand, the Rh-N bond length is greater than Rh-O, the proton transfer from the NH group to the coordinated monomer (Hetterscheid et al, 2006;Jellema et al, 2007;Victoria Jiménez et al, 2009). Hence, it is proposed that the Rh-O bond can be kept, but the Rh-N bond can dissociate to enable the monomer triple-bond coordination to Rh in the polymerisation of DoDHPA.…”