Robert Tuba

Ruthenium catalyzed equilibrium ring-opening metathesis polymerization of cyclopentene

Polypentenamer was synthetized by equilibrium ring-opening metathesis polymerization (ROMP) using well-defined ruthenium catalyst systems. It was found that the equilibrium time is influenced by the catalyst loading or the catalyst activity, however as expected, the overall cyclopentene conversion is determined only by the applied reaction temperature. Equilibrium of the growing chain and monomer was observed and the activation enthalpy and entropy were determined as: ΔH = −5.6 kcal mol−1; ΔS = −18.5 cal mol−1 K−1. So far these values are the lowest which are reported for cyclopentene polymerization catalyst systems. This unique feature of the equilibrium polymerization opens a way for the synthesis of durable, environmentally friendly elastomers where tires can be not only synthetized but also readily recycled by the same transition metal catalyst system.

Synthesis of Polypentenamer and Poly(Vinyl Alcohol) with a Phase-Separable Polyisobutylene-Supported Second-Generation Hoveyda-Grubbs Catalyst

Equilibrium ring‐opening metathesis polymerization (ROMP) of cyclic olefins using a soluble supported second‐generation Ru complex has been investigated. Cycloolefin homo‐ and copolymers are of great academic and industrial importance owing to their interesting applications as packaging materials, adhesives in coatings, and optoelectronics. The supported complex exhibits good chemical stability and was effective in ROMP of strained cyclic olefins. In addition, the complex is easily phase separated from the product, resulting in lower residual ruthenium in the final polymer product compared with the homogeneous complex.

Ruthenium-Catalyzed Metathesis of Conjugated Polyenes

In the past decade, numerous examples of chemical technologies based on olefin metathesis have been developed to make olefin metathesis increasingly dominant in several sustainable and green chemical processes. In spite of the wide application profile, conjugated olefin metathesis, especially conjugated polyene metathesis, is an area of great interest with little exploration. The metathesis of conjugated polyenes is often cumbersome and requires a high catalyst loading, most probably because of the formation of poorly active or inactive ruthenium η3‐vinylcarbene intermediates. A mechanistic understanding and the development of a new highly active catalytic system for olefin metathesis will open new areas for exploration, such as the utilisation of cyclopentadiene and other petrochemical by‐products or a new way to use butadiene, isoprene and conjugated electron systems that contain natural products such as terpenes and polyunsaturated fatty acids. An understanding of the mechanism of ruthenium η1–η3‐vinylcarbene interconversion may open the way to the development of a new generation of Ru‐based latent metathesis catalyst systems. This review summarises the most relevant pioneering work focused on the metathesis of conjugated polyenes to open new ideas for the development of forthcoming latent metathesis catalysts and to explore different applications.

Synthesis, structure, and reactivity of fluorous phosphorus/carbon/phosphorus pincer ligands and metal complexes

Reactions of the diphosphine 1,3-C6H4(CH2PH2)2 and fluorous alkenes H2C=CHR(fn)(R(fn)=(CF2)(n-1)CF3; n = 6, 8) at 75 degrees C in the presence of AIBN give the title ligands 1,3-C6H4(CH2P(CH2CH2R(fn))2)2(3-R(fn)) and byproducts 1,3-C6H4(CH3)(CH2P(CH2CH2R(fn))2)(4-R(fn)) in 1 : 3 to 1 : 5 ratios. Workups give -R(fn) in 4--17% yields. Similar results are obtained photochemically. Reaction of 1,3-C6H4(CH2Br)2 and HP(CH2CH2R(f8))2 (5) at 80 degrees C (neat, 1 : 2 mol ratio) gives instead of simple substitution the metacyclophane [1,3-C6H4(CH2P(CH2CH2R(f8))2 CH2-1,3-C(6)H(4)CH(2)P[lower bond 1 end](CH2CH2R(f8))2C[upper bond 1 end]H2](2+)2Br-, which upon treatment with LiAlH(4) yields 3-R(f8)(20%), 4-R(f8), and other products. Efforts to better access 3-R(f8), either by altering stoichiometry or using various combinations of the phosphine borane (H3B)PH(CH2CH2R(f8))2 and base, are unsuccessful. Reactions of 3-R(fn) with Pd(O2CCF3)2 and [IrCl(COE)2]2(COE=cyclooctene) give the palladium and iridium pincer complexes (2,6,1-C6H3(CH2 P(CH2CH2R(fn))(2)(2)Pd(O2CCF3)(10-R(fn); 80-90%) and (2,6,1-C6H3(CH2P(CH2CH2R(f8))2)2)Ir(Cl)(H)(11-R(f8); 29%), which exhibit CF3C6F(11)/toluene partition coefficients of >96 : <4. The crystal structure of 10-R(f8) shows CH2CH2R(f8) groups with all-anti conformations that extend in parallel above and below the palladium square plane to create fluorous lattice domains. NMR monitoring shows a precursor to 11-R(f8) that is believed to be a COE adduct.

Reaction of octacarbonyldicobalt with the free radicals galvinoxyl and 2,2-diphenyl-1-picrylhydrazyl. Attempts to scavenge the tetracarbonylcobalt radical

Abstract The addition of galvinoxyl or 2,2-diphenyl-1-picrylhydrazyl to octacarbonyldicobalt in n-octane solution results in the loss of all carbon monoxide ligands and the formation of Co(II)-containing products.

Kinetic Investigation of the Reaction of Octacarbonyl Dicobalt with 2,2,6,6-Tetramethylpiperidin-1-oxyl

The initial rate of carbon monoxide evolution in the reaction of Octacarbonyl dicobalt with 2,2,6,6-tetramethylpiperidin-1-oxyl free radical (TEMPO) at 15°C in n-octane solution leading to the 16e complex (TEMPO)Co(CO)2 was found to be first order with respect to the TEMPO concentration, 0.5 order with respect to the Co2(CO)8 concentration, and negative 0.5 order with respect to the CO concentration. Scavenging ·Co(CO)4 and ·Co(CO)3 by the free radical TEMPO in the rate-determining steps are in accord with the kinetic observation. The observed rate constant is kobs = 6.4 × 10−5 s−1.

One-pot Synthesis of 1,3-Butadiene and 1,6-Hexanediol Derivatives from Cyclopentadiene (CPD) via Tandem Olefin Metathesis Reactions

A novel tandem reaction of cyclopentadiene leading to high value linear chemicals via ruthenium catalyzed ring opening cross metathesis (ROCM), followed by cross metathesis (CM) is reported. The ROCM of cyclopentadiene (CPD) with ethylene using commercially available 2nd gen. Grubbs metathesis catalysts (1‐G2) gives 1,3‐butadiene (BD) and 1,4‐pentadiene (2) (and 1,4‐cyclohexadiene (3)) with reasonable yields (up to 24 % (BD) and 67 % (2+3) at 73 % CPD conversion) at 1–5 mol % catalyst loading in toluene solution (5 V% CPD, 10 bar, RT) in an equilibrium reaction. The ROCM of CPD with cis‐butene diol diacetate (4) using 1.00 ‐ 0.05 mol % of 3rd gen. Grubbs (1‐G3) or 2nd gen. Hoveyda‐Grubbs (1‐HG2) catalysts loading gives hexa‐2,4‐diene‐1,6‐diyl diacetate (5), which is a precursor of 1,6‐hexanediol (an intermediate in polyurethane, polyester and polyol synthesis) and hepta‐2,5‐diene‐1,7‐diyl diacetate (6) in good yield (up to 68 % or TON: 1180). Thus, convenient and selective synthetic procedures are revealed by ROCM of CPD with ethylene and 4 leading to BD and 1,6‐hexanediol precursor, respectively, as key components of commercial intermediates of high‐performance materials.

Development of Highly Active Ring Opening Metathesis Polymerization Catalyst Systems - A New Approach for Green Catalyst Design

Abstract The aim of the green chemistry is to develop chemical products and processes having minimal use and generation of hazardous chemicals and low energy requirement. Catalytic reagents are considered to be green tools to synthesize organic molecules as they basically open an alternative synthetic route to target molecules by lowering the energy barriers of the reactions while keeping the selectivity and the yield of the reactions high. Polynorbornene - which can be synthesized by ring opening methathesis polymerization (ROMP) with Grubbs’ catalyst - is used in the automotive and appliance industries mainly as vibration and noise isolators and produced thousands of tons per year scale. It is well known that during the catalytic cycle the reverse phosphine reassociation step competes with the subsequent alkene binding step on the coordination sphere of the catalyst, slowing the observed rate constant. One option to improve the activity of the catalyst system is rolling back the reassociation step by th...