Ring opening metathesis polymerization (ROMP) of a series of low-strain cyclic olefins and their hydroxyl derivatives using second generation Hoveyda-Grubbs catalyst has been investigated. Additionally, density functional theory (DFT) calculations were performed to evaluate the ring strain energies of the cyclic olefins and their hydroxyl derivatives, coupled with kinetic studies for the ROMP reactions. It was found that among different ring size monomers, Cy8 having a relatively moderate ring strain energy in comparison with the other cyclic olefins, exhibited the highest monomer conversion. The effect of temperature (0, 10, 15, and 25 8C) and monomer concentration (1 M; 2.5 M and 5 M for Cy5; and 1 M and 5 M for Cy7) for the cyclic olefins Cy5 and Cy7 were investigated. In general, the experimental results for the kinetic ROMP studies obtained using complex HG2 correlate really well with the DFT calculations determined for the ring strain energies of the cyclic olefins. For comparison, DFT calculations predicted the following trend for the ring strain energies Cy8 > Cy5 > Cy7 > Cy6, and the polymerizations carried out experimentally followed the same trend in terms of monomer conversion, with the exception of Cy5 and Cy7 at lower concentrations, which followed this trend Cy8 > Cy7 > Cy5 > Cy6.
ABSTRACT. Linear trans-polypentenamers are highly desired materials among the synthetic tire additives due to their comparable physical properties to natural rubber. Transpolypentenamer can be prepared by equilibrium ring-opening metathesis polymerization (ROMP) using well-defined ruthenium catalyst systems. This unique feature of the equilibrium polymerization reaction opens a way for the synthesis of durable, environmentally benign elastomers where polymers including synthetic tire additives can be synthesized and readily recycled using the same transition metal catalyst system. The addition of silica fillers significantly improves the physical properties of the composite materials in comparison to the use of polymeric material. It is also known that the structural effects and the polymer-filler surface interaction are of prime importance. Herein, we report on the synthesis of silica filler compatible recyclable polypentenamer co-polymers via equilibrium ROMP of cyclopentene 1 and 4-(triethoxy)siloxy cyclopentene 11. It has been demonstrated that polypentenamer tire additive can be synthesized via equilibrium ROMP affording polymers with high yields (> 80%) at 0 ºC and can be readily depolymerized at 40 ºC and/or under diluted condition using the same metathesis catalyst systems. Furthermore, the polypentenamer can also be synthesized in neat at room temperature and at very low (10 5 ) monomer/catalyst ratio. This methodology is based on the synthesis of polyolefins utilizing ruthenium based metathesis catalyst via equilibrium ROMP of cyclopentenes and their silylated derivatives.3
A series of studies were conducted to probe the stability and reactivity of a very sterically encumbered Nheterocyclic carbene. The X-ray structure of the NHC IPr* (IPr* = 1,3-bis(2,6-bis(diphenylmethyl)-4-methylphenyl)imidazol-2ylidene) was determined. IPr* was used as an organocatalyst in transesterification reactions. Steric and electronic parameters characterizing IPr* were determined via the synthesis of a nickel-carbonyl complex, [Ni(CO) 3 (IPr*)]. A related complex, [(Cp*)Ru(IPr*)Cl] (Cp* = η 5 -C 5 Me 5 ), was prepared and characterized by X-ray crystallography, and its catalytic performance in the racemization of chiral alcohols is reported. The catalytic performance of the NHC and of its transition metal derivatives permit establishing the standing of this uniquely bulky member among the NHC family.
The free N-heterocyclic carbene IPent (1; IPent = 1,3-bis(2,6-bis(1-ethylpropyl)phenyl)imidazol-2-ylidene) was prepared from the corresponding imidazolium chloride salt (2). The steric and electronic parameters of 1 were determined by synthesis of the gold(I) chloride complex [Au(IPent)Cl] (3) and the nickel−carbonyl complex [Ni-(IPent)(CO) 3 ] (4), respectively. 3 and 4 were fully characterized by NMR spectroscopy, elemental analysis, and X-ray diffraction studies on single crystals.
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