Effect of Phosphines on the Thermodynamics of the Cobalt-Catalyzed Hydroformylation System

Klingler, R. J.; Chen, Michael; Rathke, J. W.; Kramarz, Kurt W.

doi:10.1021/om060768d

Cited by 24 publications

(18 citation statements)

References 54 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…To demonstrate the applicability of this method, we undertook a total synthesis of vasicoline (Scheme 10). Cyclization of 15 proved to be particularly challenging, but a conformationally rigid cyclohexyl-phoban ligand, which had previously provided ruthenium alkylidene catalysts with enhanced stability,31 proved to be an effective ligand to facilitate the desired reaction.…”

Section: Intermolecular Alkylation Of Heterocyclesmentioning

confidence: 99%

Direct Functionalization of Nitrogen Heterocycles via Rh-Catalyzed C−H Bond Activation

2008

View full text Add to dashboard Cite

Conspectus Nitrogen heterocycles are present in many compounds of enormous practical importance, ranging from pharmaceutical agents and biological probes to electroactive materials. Direct functionalization of nitrogen heterocycles through C-H bond activation constitutes a powerful means of regioselectively introducing a variety of substituents with diverse functional groups onto the heterocycle scaffold. Working together, our two groups have developed a family of Rh-catalyzed heterocycle alkylation and arylation reactions that are notable for their high level of functional-group compatibility. This Account describes our work in this area, emphasizing the relevant mechanistic insights that enabled synthetic advances and distinguished the resulting transformations from other methods. We initially discovered an intramolecular Rh-catalyzed C-2-alkylation of azoles by alkenyl groups. That reaction provided access to a number of di-, tri-, and tetracyclic azole derivatives. We then developed conditions that exploited microwave heating to expedite these reactions. While investigating the mechanism of this transformation, we discovered that a novel substrate-derived Rh-N-heterocyclic carbene (NHC) complex was involved as an intermediate. We then synthesized analogous Rh–NHC complexes directly by treating precursors to the intermediate [RhCl(PCy3)2] with N-methylbenzimidazole, 3-methyl-3,4-dihydroquinazoline, and 1-methyl-1,4-benzodiazepine-2-one. Extensive kinetic analysis and DFT calculations supported a mechanism for carbene formation in which the catalytically active RhCl(PCy3)2 fragment coordinates to the heterocycle before intramolecular activation of the C-H bond occurs. The resulting Rh-H intermediate ultimately tautomerizes to the observed carbene complex. With this mechanistic information and the discovery that acid co-catalysts accelerate the alkylation, we developed conditions that efficiently and intermolecularly alkylate a variety of heterocycles, including azoles, azolines, dihydroquinazolines, pyridines, and quinolines, with a wide range of functionalized olefins. We demonstrated the utility of this methodology in the synthesis of natural products, drug candidates, and other biologically active molecules. In addition, we developed conditions to directly arylate these heterocycles with aryl halides. Our initial conditions that used PCy3 as a ligand were successful only for aryl iodides. However, efforts designed to avoid catalyst decomposition led to the development of ligands based on 9-phosphabicyclo[4.2.1]nonane (Phoban) that also facilitated the coupling of aryl bromides. We then replicated the unique coordination environment, stability, and catalytic activity of this complex using the much simpler tetrahydrophosphepine ligands and developed conditions that coupled aryl bromides bearing diverse functional groups without the use of a glovebox or purified reagents. With further mechanistic inquiry, we anticipate that researchers will better understand the details of the aforementioned Rh-catalyzed C-H b...

show abstract

Section: Intermolecular Alkylation Of Heterocyclesmentioning

confidence: 99%

Direct Functionalization of Nitrogen Heterocycles via Rh-Catalyzed C−H Bond Activation

2008

View full text Add to dashboard Cite

show abstract

“…23 kcal=mol and Co--H ! 60 kcal=molÞ relative to the previously reported values for the case of L ¼ CO (CoÀCo ¼ 19 AE 2 kcal mol À1 and CoÀH 59 AE 1 kcal mol À1 ) [9].…”

mentioning

confidence: 51%

“…All anticipated major and minor component spectra were reconstructed using band-target entropy minimization (BTEM) without spectral preconditioning. Beside Rh 4 (s-CO) 9 (m-CO) 3 , RC(O)Rh (CO) 4 , and Rh 6 (CO) 16 , the presence of a previously unknown complex Rh 4 (s-CO) 12 was identified [59]. The same technique has led to the reconstruction of the purecomponent spectra of RhH(CO) 4 and RhD(CO) 4 for the first time [60].…”

mentioning

confidence: 99%

Carbonylation of Alkenes and Dienes

Kégl

2008

Modern Carbonylation Methods

View full text Add to dashboard Cite

In the beginning, only cobalt catalysts were utilized for hydroformylation under relatively vigorous conditions. The moderate selectivity of the generally more desired linear isomers, the substantial formation of by-products, and the low stability of the catalysts forced more appropriate catalytic systems to be developed. Using donor ligands such as phosphanes resulted in an increase in the linear selectivity. Rhodium-containing catalysts, however, permitted the use of much milder conditions in combination with suitable ligands. Other transition metals such as ruthenium, palladium, platinum, and iridium also tended to show activity for hydroformylation, albeit a vast majority of works on hydroformylation still concentrated on rhodium-containing systems. Cobalt CatalystsThe initial rate of Co 2 (CO) 8 -catalyzed cyclohexene hydroformylation, triethyl orthoformate carbonylation, and CoH(CO) 4 formation from Co 2 (CO) 8 and H 2 is reduced by the addition of dinitrogen, argon, or xenon. It is assumed that the additional gas competes with one or more reactants for a coordinatively unsaturated site responsible for their activation, thus affecting the reaction rate [1].The carbonylation reaction of propylene oxide in the presence of various [Lewis acid] þ [Co(CO) 4 ] À salts was investigated using in situ attenuated total reflection infrared (ATR-IR) spectroscopy. b-Alkoxy-acyl-cobalttetracarbonyl species were found to be key intermediates from which two reaction routes start depending on the applied Lewis acid. Labile Lewis acid-alkoxy combinations primarily favor the production of lactone products [2].The reaction of olefins (1-octene, 3,3-dimethylbutene, cyclohexene) introduced into a preequilibrated Co 2 (CO) 8 þ H 2 system was investigated by high-pressure infrared spectroscopy. Based on the observed induction period for the formation of the corresponding aldehyde, the decrease in HCo(CO) 4 concentration and increase in Co 2 (CO) 8 concentration during the induction period, the active catalytic species of the type H x Co y (CO) z was proposed [3]. Experiments with isotope mixtures of H 2 /D 2 in the gas phase during the various steps of the reaction showed that the ratio of H/D isotopes in the hydrocarbon portion of the aldehyde product correlates with the HCo(CO) 4 /DCo(CO) 4 ratio in solution, whereas the RC(¼O)H/RC(¼O)D product ratio correlates with the H 2 /D 2 in the gas phase. It was concluded that the dominant pathway for the hydrogenolysis step in this type of hydroformylation is the direct reaction of hydrogen or deuterium with the acyl complex intermediate [4].The effect of argon (280 bar) on the rate of aldehyde formation in 1-hexene hydroformylation catalyzed by Co 2 (CO) 8 at 50 C, 70 bar P(CO) and 85 bar P(H 2 ) in toluene was investigated by high-pressure FT-IR spectroscopy. The initial rate of the reaction was found to be reduced by the presence of argon. A similar effect was observed in the RhH(CO)(PPh 3 ) 3 -catalyzed cyclohexene hydroformylation reaction [5]. 162j 7 Carbonylation of Alkenes and D...

show abstract

“…78 Promoters can be present in diff erent chemical species, for example, CH 3 I, phosphine. 79,80 Additives, mainly oxygenate compounds, aff ect product distribution since most are products of the secondary reactions during homologation. [81][82][83][84][85] Th ese additives shift secondary reactions, which are in equilibrium, at operating conditions of methanol homologation.…”

Section: Methanol Hom Ologation To Ethanolmentioning

confidence: 99%

Potential routes for thermochemical biorefineries

Haro

Ollero

Perales

et al. 2013

Biofuels Bioprod Bioref

View full text Add to dashboard Cite

This critical review focuses on potential routes for the multi-production of chemicals and fuels in the framework of thermochemical biorefineries. The up-to-date research and development in this field has been limited to BTL/G (biomass-to-liquids/gases) studies, where biomass-derived synthesis gas (syngas) is converted into a single product with/without the co-production of electricity and heat. Simultaneously, the interest on biorefineries is growing but mostly refers to the biochemical processing of biomass. However, thermochemical biorefineries (multi-product plants using thermo-chemical processing of biomass) are still the subject of few studies. This scarcity of studies could be attributed to the limitations of current designs of BTL/G for multi-production and the limited number of considered routes for syngas conversion. The use of a platform chemical (an intermediate) brings new opportunities to the design of process concepts, since unlike BTL/G processes they are not restricted to the conversion of syngas in a single-reaction system.Most of the routes presented here are based on old-fashioned and new routes for the processing of coaland natural-gas-derived syngas, but they have been re-thought for the use of biomass and the multiproduction plants (thermochemical biorefinery). The considered platform chemicals are methanol, DME, and ethanol, which are the common products from syngas in BTL/G studies. Important keys are given for the integration of reviewed routes into the design of thermochemical biorefineries, in particular for the selection of the mix of co-products, as well as for the sustainability (co-feeding, CO2 capture, and negative emissions).

show abstract

Effect of Phosphines on the Thermodynamics of the Cobalt-Catalyzed Hydroformylation System

Cited by 24 publications

References 54 publications

Direct Functionalization of Nitrogen Heterocycles via Rh-Catalyzed C−H Bond Activation

Direct Functionalization of Nitrogen Heterocycles via Rh-Catalyzed C−H Bond Activation

Carbonylation of Alkenes and Dienes

Potential routes for thermochemical biorefineries

Contact Info

Product

Resources

About