Silica-Supported Oligomeric Benzyl Phosphate (Si-OBP) and Triazole Phosphate (Si-OTP) Alkylating Reagents

The syntheses of silica-supported oligomeric benzyl phosphates (Si-OBPn) and triazole phosphates (Si-OTPn) using ring-opening metathesis polymerization (ROMP) for use as efficient alkylating reagents is reported. Ease of synthesis and grafting onto the surface of norbornenyl-tagged (Nb-tagged) silica particles has been demonstrated for benzyl phosphate and triazole phosphate monomers. It is shown that these silica polymer hybrid reagents, Si-OBPn and Si-OTPn, can be used to carry out alkylation reactions with an array of different nucleophiles to afford the corresponding benzylated and (triazolyl)methylated products in good yield and high purity

Rapid Ring-Opening Metathesis Polymerization of Monomers Obtained from Biomass-Derived Furfuryl Amines and Maleic Anhydride

Well-controlled and extremely rapid ring-opening metathesis polymerization of unusual oxanorbornene lactam esters by Grubbs third-generation catalyst is used to prepare a range of bio-based homo- and copolymers. Bio-derived oxanorbornene lactam monomers were prepared at room temperature from maleic anhydride and secondary furfuryl amines by using a 100 % atom economical, tandem Diels–Alder lactamization reaction, followed by esterification. Several of the resulting homo- and copolymers show good control over polymer molecular weight and have narrow molecular weight distributions

Catalytic living ring-opening metathesis polymerization

In living ring-opening metathesis polymerization (ROMP), a transition-metal–carbene complex polymerizes ring-strained olefins with very good control of the molecular weight of the resulting polymers. Because one molecule of the initiator is required for each polymer chain, however, this type of polymerization is expensive for widespread use. We have now designed a chain-transfer agent (CTA) capable of reducing the required amount of metal complex while still maintaining full control over the living polymerization process. This new method introduces a degenerative transfer process to ROMP. We demonstrate that substituted cyclohexene rings are good CTAs, and thereby preserve the ‘living’ character of the polymerization using catalytic quantities of the metal complex. The resulting polymers show characteristics of a living polymerization, namely narrow molecular-weight distribution, controlled molecular weights and block copolymer formation. This new technique provides access to well- defined polymers for industrial, biomedical and academic use at a fraction of the current costs and significantly reduced levels of residual ruthenium catalyst

Regioselectivity of Insertion and Role of the Anionic Ligands in the Ruthenium Alkylidene Catalyzed Cyclopolymerization of 1,6-Heptadiynes

The experimentally observed high α-addition selectivity of 1,6-heptadiynes to modified Grubbs–Hoveyda initiators was elucidated with quantum chemical calculations. For these purposes, the two possible pathways of initiation in the Ru alkylidene triggered cyclopolymerization (CP) of 1,6-heptadiynes, resulting in either five-membered (α insertion) or six-membered (β insertion) repeat units, were treated as a multistep process. The first reaction cascade entails the activation of the precatalyst RuX₂(IMesH₂)­(CH-2-(2-PrO-C₆H₄)) (<b>1</b>: X = F, Cl, Br, I, CF₃COO; IMesH₂ = 1,3-dimesitylimidazolin-2-ylidene), reaction with a 1,6-heptadiyne (π-1 complex formation), and further transformation into the first metallacyclobutene (MCB-1) followed by ring opening. The second reaction cascade entails again the formation of a π complex (π-2) through binding of the second alkyne moiety of the 1,6-heptadiyne and further transformation into MCB-2 followed by ring opening of MCB-2. The energies of the transition structures for both MCB-1 and MCB-2 formation (TS-1 and TS-2), which are considered the rate-determining steps in CP, are systematically lower for an α insertion of a monomer than for a β insertion. In addition, the geometrical parameters of the most stable structure of the βπ-2 complex are systematically less favorable for MCB-2 formation than in the case of an απ-2 complex, resulting in very high activation energies for βMCB-2 formation. Finally, the formation of βMCB-2 needs an additional step: namely, the endergonic formation of the intermediate βMCB-2*. Since a halogen exchange to pseudohalides in Grubbs–Hoveyda initiators is required to turn them into active initiators in CP, the effect of electronegativity (EN) of the X ligands on the stability of the π-1 complex was calculated for X = I, Br, Cl, CF₃COO, F. There, an increase in EN results in lower energies for the α-insertion-derived π-1 complexes. For α insertion, the barriers to the MCB-1 intermediate formation, i.e. the energies of the transition states (TS-1­(α)) for MCB-1 formation, decrease in the order I > Br > Cl > CF₃COO < F. All findings are consistent with the experimentally observed preference for α insertion in the cyclopolymerization of 1,6-heptadiynes with modified Grubbs–Hoveyda initiators and with the necessity for using pseudohalide variations of the Grubbs–Hoveyda initiator

Ring opening metathesis polymerization-derived block copolymers bearing chelating ligands: synthesis, metal immobilization and use in hydroformylation under micellar conditions

Norborn-5-ene-(N,N-dipyrid-2-yl)carbamide (M1) was copolymerized with exo,exo-[2-(3-ethoxycarbonyl-7-oxabicyclo[2.2.1]hept-5-en-2-carbonyloxy)ethyl]trimethylammonium iodide (M2) using the Schrock catalyst Mo(N-2,6-Me2-C6H3)(CHCMe2Ph)(OCMe(CF3)2)2 [Mo] to yield poly(M1-b-M2). In water, poly(M1-b-M2) forms micelles with a critical micelle-forming concentration (cmc) of 2.8 × 10−6 mol L−1; Reaction of poly(M1-b-M2) with [Rh(COD)Cl]2 (COD = cycloocta-1,5-diene) yields the Rh(I)-loaded block copolymer poly(M1-b-M2)-Rh containing 18 mg of Rh(I)/g of block copolymer with a cmc of 2.2 × 10−6 mol L−1. The Rh-loaded polymer was used for the hydroformylation of 1-octene under micellar conditions. The data obtained were compared to those obtained with a monomeric analogue, i.e. CH3CON(Py)2RhCl(COD) (C1, Py = 2-pyridyl). Using the polymer-supported catalyst under micellar conditions, a significant increase in selectivity, i.e. an increase in the n:iso ratio was accomplished, which could be further enhanced by the addition of excess ligand, e.g., triphenylphosphite. Special features of the micellar catalytic set up are discussed

Terpyridinebased silica supports prepared by ring-opening methathesis polymerization for the selective extraction of noble metals

The synthesis of a terpyridine-based sorbent for solid-phase extraction (SPE) of noble metal ions is described. For this purpose, 4'-(norborn-2-en-5-ylmethylenoxy)terpyridine was copolymerized with norborn-2-ene via Mo(N-2,6-i-Pr2-C6H3)(=CHCMe2Ph)(OC(CH3)(CF3)2)2-catalyzed ring-opening metathesis polymerization (ROMP) to give a poly(norbornene900-b-4'-(norborn-2-en-5-ylmethylenoxy)terpyridine60) block-copolymer. This block-copolymer was used for the preparation of polymer-coated silica 60 (4.8 wt.% coating), which was investigated for its extraction capabilities for Cr(III), Mn(II), Re(II), Fe(III), Ru(III), Co(II), Rh(III), Ir(III), Ni(II), Pd(II), Pt(II), Cu(II), Ag(I), Au(III), Zn(II), Cd(II) and Hg(II), at different pH. Under competitive conditions and at pH Re > Ir > Rh > Ru > Fe > Cr ˜ Mn ˜ Cd ˜ Zn. Enhanced selectivity was observed at pH = 3.5, the order was Au > Hg > Pd ˜ Ag > Rh > Pt > Ir ˜ Re > Cu > Co ˜ Zn ˜ Cd ˜ Ni > Cr > Mn. The maximum metal loading that was achieved under non-competitive conditions was >6 mg/g for Au(III), Hg(II), Pd(II) and Ag(I). Even under competitive conditions, loadings of >6 mg/g were realized for Au(III) and Hg(II). Quantitative recoveries >97% were observed for all metals in case loading was stopped before reaching the point of breakthrough