First acyclic diene metathesis polymerization under biphasic conditions using a dicationic ruthenium alkylidene: access to high-molecular-weight polymers with very low ruthenium contamination

Synthesis of High-Molecular-Weight Biobased Aliphatic Polyesters by Acyclic Diene Metathesis Polymerization in Ionic Liquids

Acyclic diene metathesis (ADMET) polymerization of an α,ω-diene monomer of bis(undec-10-enoate) with isosorbide (M1) using a RuCl₂(IMesH₂)(CH-2-O ⁱ Pr-C₆H₄) (HG2, IMesH₂ = 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene) catalyst and conducted at 50 °C (in vacuo) in ionic liquids (ILs) afforded higher-molecular-weight polymers (P1, M _n = 32 200-39 200) than those reported previously (M _n = 5600-14700). 1-n-Butyl-3-methyl imidazolium hexafluorophosphate ([Bmim]PF₆) and 1-n-hexyl-3-methyl imidazolium bis(trifluoromethanesulfonyl)imide ([Hmim]TFSI) were suitable as effective solvents among a series of imidazolium salts and the pyridinium salts. The polymerization of α,ω-diene monomers of bis(undec-10-enoate) with isomannide (M2), 1,4-cyclohexanedimethanol (M3), and 1,4-butanediol (M4) in [Bmim]PF₆ and [Hmim]TFSI also afforded the higher-molecular-weight polymers. The M _n values in the resultant polymers did not decrease even under the scale-up conditions (300 mg to 1.0 g scale, M1, M2, and M4) in the polymerizations in [Hmim]TFSI; the subsequent reaction of P1 with ethylene (0.8 MPa, 50 °C, and 5 h) gave oligomers (proceeded via depolymerization). Tandem hydrogenation of the resultant unsaturated polymers (P1) in a [Bmim]PF₆-toluene biphasic system upon the addition of Al₂O₃ (1.0 MPa H₂ at 50 °C) gave the corresponding saturated polymers (HP1), which waswere isolated by a phase separation in the toluene layer. The [Bmim]PF₆ layer containing the ruthenium catalyst could be recycled without a decrease in the activity/selectivity of the olefin hydrogenation at least eight times.

Origin and Use of Hydroxyl Group Tolerance in Cationic Molybdenum Imido Alkylidene N-Heterocyclic Carbene Catalysts

The origin of hydroxyl group tolerance in neutral and especially cationic molybdenum imido alkylidene N‐heterocyclic carbene (NHC) complexes has been investigated. A wide range of catalysts was prepared and tested. Most cationic complexes can be handled in air without difficulty and display an unprecedented stability towards water and alcohols. NHC complexes were successfully used with substrates containing the hydroxyl functionality in acyclic diene metathesis polymerization, homo‐, cross and ring‐opening cross metathesis reactions. The catalysts remain active even in 2‐PrOH and are applicable in ring‐opening metathesis polymerization and alkene homometathesis using alcohols as solvent. The use of weakly basic bidentate, hemilabile anionic ligands such as triflate or pentafluorobenzoate and weakly basic aromatic imido ligands in combination with a sterically demanding 1,3‐dimesitylimidazol‐2‐ylidene NHC ligand was found essential for reactive and yet robust catalysts.

Functional Precision Polymers via Stereo- and Regioselective Polymerization Using Group 6 Metal Alkylidene and Group 6 and 8 Metal Alkylidene N-Heterocyclic Carbene Complexes

The concepts of functional precision polymers and the latest accomplishments in their synthesis are summarized. Synthetic concepts based on chain growth polymerization are compared to iterative synthetic approaches. Here, the term "functional precision polymers" refers to polymers that are not solely hydrocarbon-based but contain functional groups and are characterized by a highly ordered primary structure. If insertion polymerization is used for their synthesis, olefin metathesis-based polymerization techniques, that is, ring-opening metathesis polymerization (ROMP), acyclic diene metathesis (ADMET) polymerization, and the regio- and stereoselective cyclopolymerization of α,ω-diynes are almost exclusively applied. Particularly with regio- and stereospecific ROMP and with cyclopolymerization, the synthesis of tactic polymers and copolymers with high regio-, stereo-, and sequence control can be accomplished; however, it requires carefully tailored transition metal catalysts. The fundamental synthetic concepts and strategies are outlined.

High-Performance Isocyanide Scavengers for Use in Low-Waste Purification of Olefin Metathesis Products

Three isocyanides containing a tertiary nitrogen atom were investigated for use as small-molecule ruthenium scavenging agents in the workup of olefin metathesis reactions. The proposed compounds are odorless, easy to obtain, and highly effective in removing metal residues, sometimes bringing the metal content below 0.0015 ppm. The most successful of the tested compounds, II, performs very well, even with challenging polar products. The performance of these scavengers is compared and contrasted with other known techniques, such as silica gel filtration and the use of self-scavenging catalysts. As a result, a new hybrid purification method is devised, which gives better results than using either a self-scavenging catalyst or a scavenger alone. Additionally, isocyanide II is shown to be a deactivating (reaction quenching) agent for olefin metathesis and superior to ethyl vinyl ether.

Grubbs-Hoveyda type catalysts bearing a dicationic N-heterocyclic carbene for biphasic olefin metathesis reactions in ionic liquids

The novel dicationic metathesis catalyst [(RuCl₂(H₂ITapMe₂)(=CH–2-(2-PrO)-C₆H₄))²⁺ (OTf⁻)₂] (Ru-2, H₂ITapMe₂ = 1,3-bis(2’,6’-dimethyl-4’-trimethylammoniumphenyl)-4,5-dihydroimidazol-2-ylidene, OTf⁻ = CF₃SO₃⁻) based on a dicationic N-heterocyclic carbene (NHC) ligand was prepared. The reactivity was tested in ring opening metathesis polymerization (ROMP) under biphasic conditions using a nonpolar organic solvent (toluene) and the ionic liquid (IL) 1-butyl-2,3-dimethylimidazolium tetrafluoroborate [BDMIM⁺][BF₄⁻]. The structure of Ru-2 was confirmed by single crystal X-ray analysis.