Activity In Ring-opening Metathesis Polymerization Research Articles

Ring Opening Metathesis Polymerization of Cyclooctadiene and Cyclooctene with Dihydrofuran: Influence of Ru Fischer Carbene.

Vinyl ethers are commonly used to deactivate Grubbs catalysts and terminate ring opening metathesis polymerization (ROMP) by forming Fischer carbene species with attenuated metathesis reactivity. However, we recently demonstrated that a cyclic enol ether, 2,3-dihydrofuran (DHF), can in fact be homopolymerized or copolymerized with norbornene derivatives. 1,5-Cyclooctadiene (COD) and cyclooctene (COE) consist of an important class of ROMP monomers, and we describe here a study of their copolymerization with DHF. Addition of DHF greatly suppressed the ROMP activity of COD and COE and resulted in significant alkene isomerization of COD. Chloranil was found to be an effective additive to prevent undesired isomerization and promote copolymerization. As a result, high molecular weight COD/COE and DHF copolymers were synthesized. Hydrolysis of the enol ether main chain linkages yields polyalkenamers with alcohol and aldehyde end groups. This study encourages further exploration of the in situ formed Ru Fischer carbene species in ROMP to access degradable polymers.

Syntheses and Applications of Indol-2-ylidene-Ligated Ruthenium-Based Olefin Metathesis Catalysts

Ru-based catalysts bearing ambiphilic carbenes exhibit exceptionally high turnover numbers (TONs) in olefin metathesis reactions. However, the syntheses of these catalysts are still challenging because of the strong ambiphilicities of the carbenes. Herein, we prepared a family of indol-2-ylidene (IdY)-ligated Ru-based (Ru–IdY) olefin metathesis catalysts and obtained two X-ray crystal structures of Ru–IdY complexes showing a distinct conformation of the ruthenium centers. An exceptional stability of the complexes was demonstrated by a decomposition test conducted in deuterated benzene at 40 °C, indicating that approximately 98% of the most stable Ru–IdY catalyst was retained even after 3 weeks. The catalytic activities of Ru–IdY catalysts were investigated for ring-closing metathesis, ring-opening metathesis polymerization (ROMP), and ethenolysis. The most sterically accessible Ru–IdY catalyst, 2e, exhibited the best catalytic activity for ethenolysis (TON 61200 and selectivity for methyl oleate 95%; TON 53200 and selectivity for cis-cyclooctene 70%), whereas the sterically demanding catalyst 2f demonstrated the most efficient catalytic activity for ROMP in comparison to the other Ru–IdY catalysts, achieving a complete conversion in 2 min.

Ring Opening Metathesis Polymerization (ROMP) of Norbornenes by (Arylimido)Niobium(V)–Alkylidene Catalysts, Nb(CHSiMe<sub>3</sub>)(NAr)[OC(CF<sub>3</sub>)<sub>3</sub>](PMe<sub>3</sub>)<sub>2</sub>

Effects of arylimido ligands on the ring-opening metathesis polymerization (ROMP) of norbornene (NBE), norbornadiene (NBD), and tetracyclododecene (TCD) were investigated using a series of (arylimido)niobium(V)–alkylidene complex catalysts, Nb(CHSiMe3)(NAr)[OC(CF3)3](PMe3)2 [Ar = 2,6-Me2C6H3 (1), 2-MeC6H4 (2), 2,6-Cl2C6H3 (3)]. The catalytic activity in ROMP of NBE for 1 was higher than for 2 and 3 (toluene at 25 °C, initial NBE concentration 0.44 mmol/mL), and the activity increased at 50 °C. Further increase in the activity (TOF 236 s–1) was observed using 3 with addition of 1.0 equiv. of PMe3, and activity was higher than that for the analogous vanadium(V)–alkylidene. These complexes (1-3) could also catalyze ROMP of NBD and TCD and the activities were higher than that for the ROMP of NBE. The dichlorophenylimido analogue (3) showed the highest activity for the ROMP of TCD, whereas 1 showed higher activity than 2 and 3 for the ROMP of NBD.

ROMP of novel hindered phenol-functionalized norbornenes and preliminary evaluation as stabilizing agents†

A series of new norbornene monomers containing sterically hindered phenol groups have been synthesized and polymerized via ring-opening metathesis polymerization (ROMP) using the Grubbs 3rd generation catalyst (G3’). ROMPs exhibit first-order kinetics and molar masses increase linearly with monomer conversion and well-controlled phenol hindered-functionalized polynorbornenes were obtained with a monomer to initiator ratio up to 1 000. The first-order rate constants show that the ROMP activity is closely associated with the norbornene monomer steric congestion. The antioxidant behavior of these hindered phenol-containing polynorbornenes with different para-bridged side groups in polypropylene (PP) was estimated by onset oxidation temperature (OOT) measurements. The ability of these hindered phenol-containing norbornenes to copolymerize by ROMP with dicyclopentadiene (DCPD) was used to bound covalently the antioxidant moiety onto a polydicyclopentadiene (PDCPD) resin whose thermal ageing has been investigated.

Preparation and activity of ruthenium catalyst based on β-cyclodextrin for ring-opening metathesis polymerization

Inspired by substrates-recognition of enzymes, we prepared supramolecular catalyst (Ru-βCD Cat) for ring-opening metathesis polymerization (ROMP) by modifying second generation Grubbs catalyst® (M204) with β-cyclodextrin (βCD) derivative (VPhe-βCD). The ROMP activity of Ru-βCD Cat was demonstrated using 7-oxanorbornene-2,3-dicarboxylic acid dimethyl ester (ONorCOOMe). The VPhe-βCD cavity recognized the ONorCOOMe monomer and attached to catalytic metal center of Ru-βCD Cat to grow poly(ONorCOOMe) with higher yield and molecular weight (Mn) in aqueous medium. The yield and Mn were higher than those of poly(ONorCOOMe) obtained by second generation Hoveyda-Grubbs catalyst® (M720). 1-Adamantanol hindered ONorCOOMe from occupying the βCD cavity, acting as a competitive guest molecule. The inhibition caused lower polymer yield and Mn. These results showed that molecular recognition of ONorCOOMe by the cavity of Ru-βCD Cat is important to increase the polymer yield and Mn of poly(ONorCOOMe).

(Arylimido)vanadium(V)-Alkylidene Complexes as Catalysts for Ring-opening Metathesis Polymerization (ROMP) of Cyclic Olefins: Ligand Design for Exhibiting the High Activity

(Imido)vanadium(V)-alkylidene complexes of type V(CHSiMe3)(NR)(OR′)(PMe3)2 [R = Ad, C6H5, 2,6-Me2C6H3, 2,6-Cl2C6H3; R′ = 2,6-Me2C6H3, 2,6-iPr2C6H3, 2,6-F2CeH3, C6F5, C6Cl5] exhibited from moderate to remarkable catalytic activities for ring-opening metathesis polymerization (ROMP) of norbornene (NBE). The catalytic activities were affected by the ligand substituents, and V(CHSiMe3)(N-2,6-Cl2C6H3)(OC6X5)(PMe3)2 (X = F, Cl) demonstrated the exceptionally high catalytic activities for ROMP of NBE. The complexes polymerized cycloheptene (CHPE) and cis-cyclooctene (COE), and ROMP of COE by the OC6Cl5 analogue proceeded in a living manner even at 80 °C, and the activity increased with increasing the temperature up to 120 °C. Highly active catalysts for ROMP of cyclic olefins (NBE, cyclopentene, and CHPE) can be generated in situ by premixing isolated V(CHSiMe3)(NC6F5)(O-2,6-iPr2C6H3)(PMe3)2 with 1.0 equiv. of C6F5OH or C6Cl5OH via immediate phenoxy exchange; the activity was affected by the kind of phenol added [TOF in the ROMPs of NBE: 4.62 × 104 min−1 (upon addition of C6F5OH) versus 37.3 min−1 (none)].

Synthesis of (Imido)niobium(V)–Alkylidene Complexes That Exhibit High Catalytic Activities for Metathesis Polymerization of Cyclic Olefins and Internal Alkynes

The (imido)niobium(V)–alkylidene complexes Nb(CHSiMe3)(NR)[OC(CF3)3](PMe3)2 (R = 2,6-Me2C6H3, 2,6-iPr2C6H3, 1-adamantyl), which could be isolated from the dialkyl analogues by α-hydrogen elimination in the presence of PMe3, exhibited remarkable catalytic activities for ring-opening metathesis polymerization (ROMP) of norbornene, and the polymerizations proceeded in a living manner. Metathesis polymerizations of (unstrained) disubstituted acetylenes also took place, affording polymers with uniform (narrow) molecular weight distributions.

Latent ruthenium carbene complexes with six-membered N- and S-chelate rings

New ruthenium carbene complexes with chelating N- and S-benzylidene ligands were synthesized by the reactions of second- and third-generation Grubbs catalysts with ortho-vinylbenzyl-substituted amines or sulfides. These complexes were shown to exhibit catalytic activity in ring-opening metathesis polymerization and ring-closing metathesis.

(Arylimido)vanadium(V)-alkylidene complexes containing fluorinated aryloxo and alkoxo ligands for fast living ring-opening metathesis polymerization (ROMP) and highly cis-specific ROMP.

(Arylimido)vanadium(V)-alkylidene complexes, V(CHSiMe3)(N-2,6-X2C6H3)(OC6F5)(PMe3)2 [X = Me (2), Cl (4)], exhibited remarkable catalytic activities for ring-opening metathesis polymerization (ROMP) of norbornene, and the ROMP by 2 proceeded in a living manner, affording ultrahigh molecular weight polymers. Cis-specific ROMP was achieved with the alkoxo analogues, V(CHSiMe3)(N-2,6-X2C6H3)[OC(CH3)(CF3)2]-(PMe3)2 [X = Me (5), Cl (6)]. Both the activity and the selectivity increased upon addition of PMe3, even at 50 °C.

Comparative Reactivity of Me3Si-substituted Norbornene Derivatives in Ring-Opening Metathesis Polymerization

Silyl substituted norbornenes and their derivatives are effective monomers in the synthesis of new prospective polymer materials for gas separation membranes by metathesis and addition polymerization. Comparative activity of norbornenes (NB), norbornadienes (NBD) and tricyclononenes (TCN) with different spatial arrangement of one or two Me3Si substituents in ring-opening metathesis polymerization (ROMP) in the presence of Grubbs initiator Cl2(PCy3)2Ru =CHPh were studied by NMR and GC. It was shown that the rate of the initiation was lower than the propagation for all monomers and the highest activity was inherent to the exo-5-trimethylsilylnorbornene (5-NBSi) and 3-trimethylsilyltricyclononene (3-TCNSi). Disubstituted TCN turned out to be more active than NB having the same number and position of the substituents. The latter were more active than the corresponding NBD. It was found that syn- and anti-isomers of 3-TCNSi polymerized with close rates in contrast to exo- and endo-substituted 5-NBSi, for which polymerization rates were substantially different. Special behavior of monomers with bulky substituents in the geminal position was observed: 5,5-NBSi2 was inactive in the presence of the 1st generation Grubbs initiator, whereas it was polymerized in the presence of the 2nd generation one. Quantum-chemical calculations were in agreement with experimental data and evidenced the influence of energy, electronic and structural properties of the norbornene-type monomers studied on their activity in ROMP.

Synthesis of (Imido)vanadium(V) Alkyl and Alkylidene Complexes Containing Imidazolidin-2-iminato Ligands: Effect of Imido Ligand on ROMP and 1,2-C–H Bond Activation of Benzene

A series of (imido)vanadium(V) alkylidene complexes containing an imidazolidin-2-iminato ligand of the type V(CHSiMe3)(NR)(X)(PMe3) (R = 2,6-Me2C6H3 (Ar, 3a), 1-adamantyl (Ad, 3b), C6H5 (3c); X = 1,3-Ar′2(CH2N)2C═N; Ar′ = 2,6-iPr2C6H3) have been prepared in n-hexane in the presence of PMe3 from the corresponding dialkyl complexes V(NR)(CH2SiMe3)2(X) (2a–c). These alkylidene complexes (3a–c) exhibit catalytic activities for ring-opening metathesis polymerization (ROMP) of norbornene: the phenylimido analogue (3c) exhibits remarkable activity at 80 °C (e.g. a TOF value of 84800 h–1 (7070 turnovers after 5 min)), affording high-molecular-weight polymers with uniform molecular weight distributions. The reaction of the (arylimido)vanadium(V) dialkyl complex 2a with C6H6 afforded the phenyl complex V(NAr)(CH2SiMe3)(C6H5)(X) (4a) by 1,2-C–H activation via an alkylidene intermediate and the diphenyl complex V(NAr)(C6H5)2(X) as the final product. The activity by 3a–c for ROMP, the reactivity of 2a–c for formation ...

Room temperature polymerization of norbornene with a hydride-bridged dinuclear ruthenium complex system

A two-component system, [Ru(p-cymene)Cl2]2 (C1)/BH3•NMe3, allows for the catalytic ring-opening metathesis polymerization (ROMP) of norbornene at 60°C. A hydride-bridged complex isolated from the two-component system, [RuCl(p-cymene)]2(μ-H)(μ-Cl) (C2), is also active in the ROMP reaction, albeit at a reduced rate. Abstraction of one chloride ligand from C2, by the reaction with 1equiv of either AgPF6 or AgSbF6, leads to the generation of either [{Ru(p-cymene)}2(μ-H)(μ-Cl)2]PF6 (C3) or [{Ru(p-cymene)}2(μ-H)(μ-Cl)2]SbF6 (C4) and further reduction of ROMP activity. Importantly, a reaction of C2 with 2equiv each of AgSbF6 and BH3•NMe3 provides the ability to achieve room temperature ROMP of norbornene. Various hydride-bridged dinuclear ruthenium complexes have been observed in the room temperature system based on 1H NMR analysis. An independent synthesis of a complex mixture containing [{Ru(p-cymene)}2(μ-H)3]PF6 (C5) and a single-component complex [{Ru(η6-C6Me6)}2(μ-H)3]PF6 (C6) rules out the catalytic capacity of this tri-μ-hydrido species. A di-μ-hydrido complex, [{Ru(p-cymene)}2(μ-H)2(μ-Cl)]PF6 (C7), is therefore postulated to act as the ROMP reaction center at room temperature.

Influence of ruthenium alkylidene complexes bearing tricyclohexylphosphine or 3-bromopyridine ligand on the properties of fluorine containing polymers

The catalytic performance of ruthenium alkylidene complexes bearing tricyclohexylphosphine or 3-bromopyridine ligand in the ring opening metathesis polymerization (ROMP) of fluorine containing monomers, exo-N-4-fluorophenyl-7-oxanorbornene-5,6-dicarboximide (FPhONDI) and exo-N-4-fluorophenyl-norbornene-5,6-dicarboximide (FPhNDI) was investigated. Pure monomers were subjected to ROMP with RuCl2(PCy3)2(CHPh) (I), RuCl2(PCy3)(H2IMes)(CHPh) (II), RuCl2(3-Br-py)2(PCy3)(CHPh) (III) and RuCl2(3-Br-py)2(H2IMes)(CHPh) (IV). The polymers were fully characterized using NMR, DSC, SEM and GPC. Catalysts I–IV displayed significant ROMP activity, allowing for the synthesis of the corresponding polymers with polydispersity indices (PDIs) in the range of 1.4–4.0. High molecular weight polymers (Mw up to 4.95 x105) were prepared in yields up to 90 %, depending on the initiator and monomer used.

Ring-Opening Metathesis Polymerization by a Ru Phosphine Derivative of Cyclodextrin in Water

Trimethylated cyclodextrins with a phosphine ligand and ruthenium (PCy2Ru-CDs) realize supramolecular polymerization catalysts for ring-opening metathesis polymerization (ROMP). Although PCy2Ru-βCD shows a low polymerization activity for 7-oxanorbornene dimethanol (7-ONorOH2) in organic solvents, it exhibits a high ROMP activity for 7-ONorOH2 in aqueous solutions. The ROMP activity of PCy2Ru-βCD is higher than that of PCy2Ru-αCD. The addition of competitive guest molecules decreases the polymer yield, indicating that complexation between PCy2Ru-CD and 7-ONorOH2 in water plays an important role in the increased polymer yield.

Ring-Opening Polymerization of THF by Aryloxo-Modified (Imido)vanadium(V)-alkyl Complexes and Ring-Opening Metathesis Polymerization by Highly Active V(CHSiMe3)(NAd)(OC6F5)(PMe3)2

Ring-opening polymerizations of THF using V(NR)(CH2SiMe3)(OAr)2 [R = 2,6-Me2C6H3, 1-adamantyl (Ad), Ph; Ar = 2,6-Me2C6H3, C6F5] proceeded in a living manner in the presence of [Ph3C][B(C6F5)4], affording high molecular weight polymers with low PDI (Mw/Mn) values: the observed activity (initiation efficiency) was affected by the arylimido and aryloxo ligands employed. A new vanadium(V)-alkylidene, V(CHSiMe3)(NAd)(OC6F5)(PMe3)2, prepared from V(NAd)(CH2SiMe3)2(OC6F5) by α-hydrogen elimination in n-hexane in the presence of PMe3 at 25 °C, exhibited remarkable catalytic activity for ring-opening metathesis polymerization of norbornene: the activity at 25 °C was higher than those by the reported vanadium(V)-alkylidenes and ordinary Mo(CHCMe2Ph)(N-2,6-iPr2-C6H3)(OtBu)2.

A Set of Olefin Metathesis Catalysts with Extraordinary Stickiness to Silica

We report on a series of six new pyridinealkoxide-bridged first and second generation ruthenium carbenes with similar or even higher activity in ring-opening metathesis polymerization (ROMP), cross metathesis (CM), and ring closing metathesis (RCM) reactions than state-of-the-art catalysts. The new precatalysts show an extraordinarily high stickiness to commercially available silica, which significantly enhances their adsorptive separation from unprocessed reaction mixtures.

(Imido)vanadium Complexes as Efficient Catalyst Precursors for Olefin Polymerization/Oligomerization

(Arylimido)vanadium(V) complexes containing anionic ancillary donor ligands of type, V(NAr)Cl2(L) (Ar = 2,6-Me2C6H3, L = aryloxo, ketimide phenoxyimine, etc.) exhibited high catalytic activities for ethylene polymerization in the presence of Al cocatalyst; V(NAr)Cl2(O-2,6-Me2C6H3) showed the exceptionally high activities in the presence of halogenated Al alkyls such as Et2AlCl, EtAlCl2, etc. (Arylimido)vanadium(V)-alkylidene complexes, V(CHSiMe3)(NAr)(L′) (L′ = N=C t Bu2, O-2,6- i Pr2C6H3) exhibited the remarkable catalytic activities for ring-opening metathesis polymerization of norbornene. (Imido)vanadium(V) complexes containing the (2-anilidomethyl)pyridine ligand, V(NR)Cl2[2-Ar′NCH2(C5H4N)] (R = 1-adamantyl, cyclohexyl, phenyl, Ar′ = 2,6-Me2C6H3, 2,6- i Pr2C6H3), exhibit the remarkable activities for ethylene dimerization in the presence of MAO, affording 1-butene exclusively (selectivity 90.4 to >99%). The steric bulk of the imido ligand plays an important role in the selectivity, and the electronic nature directly affects the activity.

Cationic versus Neutral RuIIN‐Heterocyclic Carbene Complexes as Latent Precatalysts for the UV‐Induced Ring‐Opening Metathesis Polymerization

A series of cationic and neutral Ru(II) complexes of the general formula [Ru(L)(X) (tBuCN)(4)](+)X(-) and [Ru(L)(X)(2)(tBuCN)(3))], that is, [Ru(CF(3)SO(3)){NCC(CH(3))(3)}(4)(IMesH(2))](+)[CF(3)SO(3)](-) (1), [Ru(CF(3)SO(3)){NCC(CH(3))(3)}(4)(IMes)](+)[CF(3)SO(3)](-) (2), [RuCl{NCC(CH(3))(3)}(4)(IMes)](+)Cl(-) (3), [RuCl{NCC(CH(3))(3)}(4)(IMesH(2))(+)Cl(-)]/[RuCl(2){NCC(CH(3))(3)}(3)(IMesH(2))] (4), and [Ru(NCO)(2){NCC(CH(3))(3)}(3)(IMesH(2))] (5) (IMes=1,3-dimesitylimidazol-2-ylidene, IMesH(2)=1,3-dimesityl-imidazolin-2-ylidene) have been synthesized and used as UV-triggered precatalysts for the ring-opening metathesis polymerization (ROMP) of different norborn-2-ene- and cis-cyclooctene-based monomers. The absorption maxima of complexes 1-5 were in the range of 245-255 nm and thus perfectly fit the emission band of the 254 nm UV source that was used for activation. Only the cationic Ru(II)-complexes based on ligands capable of forming μ(2)-complexes such as 1 and 2 were found to be truly photolatent in ROMP. In contrast, complexes 3-5 could be activated by UV light; however, they also showed a low but significant ROMP activity in the absence of UV light. As evidenced by (1)H and (13)C NMR spectroscopy, the structure of the polymers obtained with either 1 or 2 are similar to those found in the corresponding polymers prepared by the action of [Ru(CF(3)SO(3))(2)(IMesH(2))(CH-2-(2-PrO)-C(6)H(4))], which strongly suggest the formation of Ru-based Grubbs-type initiators in the course of the UV-based activation process. Precatalysts that have the IMesH(2) ligand showed significantly enhanced reactivity as compared with those based on the IMes ligand, which is in accordance with reports on the superior reactivity of IMesH(2)-based Grubbs-type catalysts compared with IMes-based systems.

Synthesis of (Arylimido)vanadium(V) Complexes Containing (2-Anilidomethyl)pyridine Ligands and Their Use as the Catalyst Precursors for Olefin Polymerization

A series of (arylimido)vanadium(V) dichloride complexes containing (2-anilidomethyl)pyridine ligands of the type V(NAr)Cl2[2-Ar′NCH2(C5H4N)] [Ar = 2,6-Me2C6H3; Ar′ = 2,6-Me2C6H3 (1a), 2,6-iPr2C6H3 (1b), 2,6-F2C6H3 (1c)] have been prepared from V(NAr)Cl3 by treating with Li[2-Ar′NCH2(C5H4N)], and the structures of 1b,c have been determined by X-ray crystallography. These complexes are effective catalyst precursors for ethylene polymerization in the presence of Al cocatalysts: 1b showed the highest catalytic activities in the presence of Et2AlCl (6000 kg PE/mol V·h), and the observed activities of 1a,b in the presence of Et2AlCl were much higher than those in the presence of MAO. V(NAr)(CH2SiMe3)2[2-Ar′NCH2(C5H4N)] (2a,b) have been prepared by treating 1a,b with 2.0 equiv of LiCH2SiMe3, and their structures have been determined by X-ray crystallography. The dialkyl complex 2b cleanly reacted with 2.0 equiv of (CF3)2CHOH in C6D6 at 25 °C to afford V(NAr)(CH2SiMe3)[OCH(CF3)2][2-Ar′NCH2(C5H4N)] (3), and the reaction with 3.0 equiv of (CF3)2CHOH eventually afforded V(NAr)[OCH(CF3)2]2[2-Ar′NCH2(C5H4N)] (4) from 3 after 3 days. The dialkyl complexes 2a,b showed catalytic activities for ring-opening metathesis polymerization (ROMP) of norbornene in benzene at 80 °C in the presence of PMe3. The ROMP did not occur in the absence of PMe3 under the same conditions, suggesting that an additional coordination of PMe3 may be required to induce the α-hydrogen elimination.

Synthesis, Characterization and Radical Scavenging Ability of 3,5-di-tert-Butyl-4-hydroxyphenoxy-Functionalized Polynorbornenes Synthesized Using Ring-Opening Metathesis Polymerization

Novel norbornene derivatives bearing a 3,5-di-tert-butyl-4-hydroxyphenoxy (DBHO) group were synthesized and used as sterically hindered phenol functionalized norbornene monomers (1–4). The ring-opening metathesis polymerization (ROMP) of these functional monomers was carried out with a typical ruthenium catalyst (bis(tricyclohexylphosphine)benzylidene ruthenium (IV) dichloride, a Grubbs first-generation catalyst) to prepare sterically-hindered phenol-functionalized polymers possessing radical scavenging function. The resulting polymers bearing a DBHO side-chain were characterized by means of gel-permeation chromatography, 1H-NMR and 13C-NMR. The radical scavenging ability of polymers was determined using the α,α-diphenyl-β-picrylhydrazyl (DPPH⋅) free radical. Due to the electron-donating effect of the oxygen atom located in the para-position of phenol, the resulting polymers showed high efficiency to scavenge DPPH⋅free radical. The molecular weight of polymers was dependent on the molar ratio of monomer to catalyst ([M]/[C]), and the ROMP activity was dependent on the stereostructure of monomers themselves.