Aryl-alkyl Bond Research Articles

Nickel‐Catalyzed Electrochemical Cross‐Electrophile C(sp2)−C(sp3) Coupling via a NiII Aryl Amido Intermediate

AbstractCross‐electrophile coupling (XEC) between aryl halides and alkyl halides is a streamlined approach for C(sp2)−C(sp3) bond construction, which is highly valuable in medicinal chemistry. Based on a key NiII aryl amido intermediate, we developed a highly selective and scalable Ni‐catalyzed electrochemical XEC reaction between (hetero)aryl halides and primary and secondary alkyl halides. Experimental and computational mechanistic studies indicate that an amine secondary ligand slows down the oxidative addition process of the Ni‐polypyridine catalyst to the aryl bromide and a NiII aryl amido intermediate is formed in situ during the reaction process. The relatively slow oxidative addition is beneficial for enhancing the selectivity of the XEC reaction. The NiII aryl amido intermediate stabilizes the NiII–aryl species to prevent the aryl–aryl homo‐coupling side reactions and acts as a catalyst to activate the alkyl bromide substrates. This electrosynthesis system provides a facile, practical, and scalable platform for the formation of (hetero)aryl–alkyl bonds using standard Ni catalysts under mild conditions. The mechanistic insights from this work could serve as a great foundation for future studies on Ni‐catalyzed cross‐couplings.

Nickel-Catalyzed Electrochemical Cross-Electrophile C(sp2)-C(sp3) Coupling via a NiII Aryl Amido Intermediate.

Cross-electrophile coupling (XEC) between aryl halides and alkyl halides is a streamlined approach for C(sp2)-C(sp3) bond construction, which is highly valuable in medicinal chemistry. Based on a key NiII aryl amido intermediate, we developed a highly selective and scalable Ni-catalyzed electrochemical XEC reaction between (hetero)aryl halides and primary and secondary alkyl halides. Experimental and computational mechanistic studies indicate that an amine secondary ligand slows down the oxidative addition process of the Ni-polypyridine catalyst to the aryl bromide and a NiII aryl amido intermediate is formed in situ during the reaction process. The relatively slow oxidative addition is beneficial for enhancing the selectivity of the XEC reaction. The NiII aryl amido intermediate stabilizes the NiII-aryl species to prevent the aryl-aryl homo-coupling side reactions and acts as a catalyst to activate the alkyl bromide substrates. This electrosynthesis system provides a facile, practical, and scalable platform for the formation of (hetero)aryl-alkyl bonds using standard Ni catalysts under mild conditions. The mechanistic insights from this work could serve as a great foundation for future studies on Ni-catalyzed cross-couplings.

Engineering a mild and site-selective Ru-catalyzed C(sp2)–H alkylation protocol

In this issue of Chem Catalysis , the Larrosa research group develops a synthetic methodology that enables the formation of aryl–alkyl bonds, via C–H activation, by the use of a p -cymene-free mono-cyclometalated Ru(II) catalyst and primary alkyl bromides as coupling partners. In this issue of Chem Catalysis , the Larrosa research group develops a synthetic methodology that enables the formation of aryl–alkyl bonds, via C–H activation, by the use of a p -cymene-free mono-cyclometalated Ru(II) catalyst and primary alkyl bromides as coupling partners.

Transformation of aromatic structure of vitrinite with different coal ranks by HRTEM in situ heating

Three vitrinite samples of different rank, denoted as V-YJL, V-AW, and V-J15, were investigated by in situ heating while in a High resolution transmission electron microscope (HRTEM) to study the aromatic structural transformations from 200 to 800 °C. Thermogravimetry coupled with Fourier transform infrared spectroscopy and mass spectrometry (TG-FTIR-MS) was employed to measure gaseous release from 30 to 900 °C. The relationships between aromatic structural transformations and gaseous release were also discussed in this work. The results showed that the rank of coal influenced the changes of aromatic layers. The change of naphthalene of low-rank coal (V-YJL, R = 0.61%) had four stages. For higher rank coals with R = 1.09% (V-AW) and R = 2.22% (V-J15), the changes of naphthalene had three and two stages, respectively. The increase in naphthalene content occurred at the same temperature with the release of CO2 and H2O, suggesting the increase of naphthalene probably caused by the decomposing of oxygen-containing functional groups. The noticeable change in 4 × 4 aromatic layers is from 650 to 750 °C, accompanying CH4 release, suggesting the increase of 4 × 4 aromatic layers may result from the break of bonds like aryl-methyl bonds or aryl-alkyl bonds.

Hydrogenolysis of lignosulfonate into phenols over heterogeneous nickel catalysts

We report a strategy for the catalytic conversion of lignosulfonate into phenols over heterogeneous nickel catalysts. Aryl-alkyl bonds (C-O-C) and hydroxyl groups (-OH) are hydrogenated to phenols and alkanes, respectively, without disturbing the arenes. The catalyst is based on a naturally abundant element, and is recyclable and reusable.

Coarsening of nanodomains by reorganization of polysiloxane segments at high temperature in polyurethane/α,ω-aminopropyl polydimethylsiloxane blends

The reaction in bulk at high temperature of α,ω-aminopropyl oligodimethylsiloxane and thermoplastic polyurethane (TPU) allowed observing interesting behavior. Mixing at 200 °C first involved dissociation of urethanes and splitting of polyurethane chains followed by reaction of the released isocyanates with amino end-groups of the oligosiloxane. At this stage, a copolymer was formed which morphology consisted of a very fine dispersion of the polysiloxane domains at the nanoscale (20 nm) with a narrow size dispersity. The polymer blend was perfectly transparent. Increasing the reaction time resulted in a significant coarsening of the morphology and a consequent loss of transparency. The reason for such a morphology evolution has been elucidated. The progressive formation of alkyl–alkyl urea linkages at the expense of aryl–alkyl bonds obtained earlier in the process caused an increase in the average number of successive polydimethylsiloxane (PDMS) blocks that organized in larger domains. The average number of consecutive polysiloxane segments was found to evolve from ∼1.5 in the first 10–15 min to a value of 3–5 at the end of the reactive process.

Aryl Cation Chemistry as an Emerging Versatile Tool for Metal-Free Arylations

The development of transition-metal-free arylation procedures represents a key goal in modern organic synthesis. A green arylation can be obtained by having recourse to light as a ‘clean’ reagent in place of toxic metals. In particular, a new method based upon the photoheterolytic fragmentation of substituted aryl halides or esters, with the formation of aryl cations has recently emerged. The peculiar reactivity of these cations with carbon nucleophiles allows several straightforward photo-arylations, which compare favorably with other thermal or photochemical metal-free analogues. 1 Introduction 2 Aryl Cation Chemistry 3 Metal-Free Formation of Aryl-Carbon Bonds 3.1 Formation of Aryl-Alkyl Bonds 3.1.1 Arylation of Carbonyl Compounds 3.1.2 Formation of Aryl-Allyl Bonds 3.1.3 Formation of Other Aryl-Alkyl Bonds 3.2 Formation of Aryl-Vinyl Bonds 3.3 Formation of Aryl-Alkynyl Bonds 3.4 Formation of Aryl-Aryl Bonds 3.5 Cyanation 4 Conclusions

Synthesis and Structure of (π-Arene)titanium(II) Haloaluminate Complexes with Diarylmethane Ligands

Novel (arene)titanium(II) haloaluminate complexes (η6-arene)Ti[(μ-X)2AlX2]2 (X = Cl, Br) were obtained from (η6-benzene)Ti[(μ-X)2AlX2]2 (X = Cl, Br) complexes by ligand exchange reactions with bis(pentamethylphenyl)methane and dimesitylmethane. The [η6-1,2,3,4,5- pentamethyl-6-(2,3,4,5,6-pentamethylbenzyl)benzene]Ti[(μ-X)2AlX2]2 (X = Cl, Br) and [η6-1,3,5- trimethyl-2-(2,4,6-trimethylbenzyl)benzene]Ti[(μ-Br)2AlBr2]2 complexes containing titanium coordinated to only one of the two phenyl rings were obtained and their crystal structures were determined. (η6-Benzene)Ti[(μ-Cl)2AlCl2]2 and dimesitylmethane afforded the (η6-mesi- tylene)Ti[(μ-Cl)2AlCl2]2 complex which is isotypic with the known bromo analogue. This product shows that Friedel-Crafts scission of aryl-alkyl bonds occurs in such systems even under mild conditions.

Reactions of polycyclic alkylaromatics—VI. Detailed chemical kinetic modeling

We developed a detailed chemical kinetics model for the pyrolysis of long-chain polycyclic n-alkylarenes based on a general free-radical mechanism. The model accounts for the two major primary pathways in the pyrolysis network of polycyclic alkylaromatics. Using 1-dodecylpyrene (DDP) as an example, we show that the model qualitatively predicted the effects of time, temperature, and concentration on the product molar yields and the reaction kinetics. The model also predicted the autocatalytic kinetics associated with the cleavage of the arylalkyl bond. The model results showed that radical hydrogen transfer was the dominant hydrogenolysis mechanism during all but the very initial stages of the reaction when reverse radical disproportionation dominated. A sensitivity analysis revealed that reactions involving α-DDP radicals where the most important in determining the reaction kinetics and the product selectivities.

Reactions of polycyclic alkylaromatics. 1. Pathways, kinetics, and mechanisms for 1-dodecylpyrene pyrolysis

1-Dodecylpyrene (DDP) was pyrolyzed at concentrations between 0.0007 and 0.47 M in a benzene diluent, at temperatures from 375 to 450°C. Product yields and selectivities were functions of both the conversion and the initial concentration. DDP pyrolysis at low conversions (<25%) and low initial concentrations (<0.14 M) yielded primary products analogous to those observed for alkylbenzene pyrolysis, whereas experiments at higher conversions and concentrations yielded n-dodecane and pyrene as the major products through the cleavage of the strong aryl-alkyl C-C bond. Kinetics analysis showed that this concentration-dependent behavior could be modeled by using the rate law previously derived for alkylbenzene pyrolysis plus an additional term accounting for the apparently autocatalytic decomposition of the strong aryl-alkyl bond

Autocatalysis and aryl-alkyl bond cleavage in 1-dodecylpyrene pyrolysis

Autocatalysis and aryl-alkyl bond cleavage in 1-dodecylpyrene pyrolysis

New chemical structural features of coal. A comparison of several coals

Structural features of several coals of different ranks are compared using an adaptation of the transalkylation reaction. In the present application of this method, trifluoromethanesulphonic acid is used as catalyst and toluene is used in excess as acceptor and solvent. The process can be visualized as a disproportionation reaction in which intermolecular alkyl transfers occur. Under the influence of the acid catalyst, aryl-alkyl bonds in coal are cleaved and alkyl-aryl bonds are formed with the excess toluene solvent. Thus, a large number of substituted toluene derivatives are formed by transfer of groups from coal. Concentrations of ≈ 20 substituent groups and connecting groups are estimated and compared for a range of coals and numerous other compounds are present in small amounts. These compounds are tabulated for two coals and the possible significance and origin of some of them are discussed. The mechanism of the transalkylation reaction as it applies to coal and the reactions of a limited number of relevant model systems are also discussed.