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RSC Advances May 2024Friedel-Crafts benzylation/alkylation using benzylic, tertiary, and homobenzylic alcohols; aryl aldehydes, aryl ketones, and the highly challenging aryl carboxylic acids...
Friedel-Crafts benzylation/alkylation using benzylic, tertiary, and homobenzylic alcohols; aryl aldehydes, aryl ketones, and the highly challenging aryl carboxylic acids and esters as proelectrophiles has been achieved using borane-ammonia and TiCl, greatly broadening the scope of useable substrates. Incorporation of deactivated aromatic proelectrophiles and specificity for substitution at the benzylic position are demonstrated in the synthesis of various di- and triarylalkane products. Dual protocols allow for the use of standard nucleophilic solvents (benzene, toluene, ) or for stoichiometric addition of more valuable nucleophiles including furans, thiophenes, and benzodioxoles.
PubMed: 38741965
DOI: 10.1039/d4ra02213k -
Nature Communications May 2024In recent years, there has been a growing demand for drug design approaches that incorporate a higher number of sp-hybridized carbons, necessitating the development of...
In recent years, there has been a growing demand for drug design approaches that incorporate a higher number of sp-hybridized carbons, necessitating the development of innovative cross-coupling strategies to reliably introduce aliphatic fragments. Here, we present a powerful approach for the light-mediated B-alkyl Suzuki-Miyaura cross-coupling between alkyl boranes and aryl bromides. Alkyl boranes were easily generated via hydroboration from readily available alkenes, exhibiting excellent regioselectivity and enabling the selective transfer of a diverse range of primary alkyl fragments onto the arene ring under photocatalytic conditions. This methodology eliminates the need for expensive catalytic systems and sensitive organometallic compounds, operating efficiently at room temperature within just 30 min. We further demonstrate the translation of the present protocol to continuous-flow conditions, enhancing scalability, safety, and overall efficiency of the method. This versatile approach offers significant potential for accelerating drug discovery efforts by enabling the introduction of complex aliphatic fragments in a straightforward and reliable manner.
PubMed: 38740738
DOI: 10.1038/s41467-024-48212-5 -
Molecules (Basel, Switzerland) Apr 2024Borane-trimethylamine complex (MeN·BH; BTM) is the most stable of the amine-borane complexes that are commercially available, and it is cost-effective. It is a valuable... (Review)
Review
Borane-trimethylamine complex (MeN·BH; BTM) is the most stable of the amine-borane complexes that are commercially available, and it is cost-effective. It is a valuable reagent in organic chemistry with applications in the reduction of carbonyl groups and carbon-nitrogen double bond reduction, with considerable examples in the reduction of oximes, hydrazones and azines. The transfer hydrogenation of aromatic -heterocycles and the selective -monomethylation of primary anilines are further examples of recent applications, whereas the reduction of nitrobenzenes to anilines and the reductive deprotection of -tritylamines are useful tools in the organic synthesis. Moreover, BTM is the main reagent in the regioselective cleavage of cyclic acetals, a reaction of great importance for carbohydrate chemistry. Recent innovative applications of BTM, such as CO utilization as feedstock and radical chemistry by photocatalysis, have extended their usefulness in new reactions. The present review is focused on the applications of borane-trimethylamine complex as a reagent in organic synthesis and has not been covered in previous reviews regarding amine-borane complexes.
PubMed: 38731507
DOI: 10.3390/molecules29092017 -
Nature Communications May 2024Cheminformatics-based machine learning (ML) has been employed to determine optimal reaction conditions, including catalyst structures, in the field of synthetic...
Cheminformatics-based machine learning (ML) has been employed to determine optimal reaction conditions, including catalyst structures, in the field of synthetic chemistry. However, such ML-focused strategies have remained largely unexplored in the context of catalytic molecular transformations using Lewis-acidic main-group elements, probably due to the absence of a candidate library and effective guidelines (parameters) for the prediction of the activity of main-group elements. Here, the construction of a triarylborane library and its application to an ML-assisted approach for the catalytic reductive alkylation of aniline-derived amino acids and C-terminal-protected peptides with aldehydes and H is reported. A combined theoretical and experimental approach identified the optimal borane, i.e., B(2,3,5,6-Cl-CH)(2,6-F-3,5-(CF)-CH), which exhibits remarkable functional-group compatibility toward aniline derivatives in the presence of 4-methyltetrahydropyran. The present catalytic system generates HO as the sole byproduct.
Topics: Aniline Compounds; Catalysis; Amino Acids; Peptides; Boranes; Hydrogen; Computer Simulation; Oxidation-Reduction; Alkylation; Machine Learning
PubMed: 38714662
DOI: 10.1038/s41467-024-47984-0 -
IScience May 2024Zeolite-encaged metal nanoparticles (NPs) catalysts are emerging as a new frontier owing to their superior ability to stabilize the structure and catalytic performance...
Zeolite-encaged metal nanoparticles (NPs) catalysts are emerging as a new frontier owing to their superior ability to stabilize the structure and catalytic performance in the thermal and environmental catalytic reaction. However, the pore size below 2 nm of the conventional zeolites usually limits the accessibility of metal active sites. Herein, Co-Cu NPs of about 2.5-3.5 nm were uniformly encapsulated in the intracrystalline mesoporous Silicalite-1 (S-1) through alkali-treatment ligand-assisted strategy. The obtained sample (termed CoCu@HS-1) exhibited efficient activity and stability in the ammonia borane hydrolysis with the highest TOF value of 21.46 mol·mol·min. UV-vis DRS spectra indicated that intracrystalline mesopores have greatly improved the openness and accessibility of the active sites, thus improving their catalytic performance. The introduction of Cu regulates the electronic properties of Co, further increasing hydrogen production activity. This research creates new prospects to design other high-performance hierarchical porous zeolite-confined metal/metal oxide catalysts.
PubMed: 38706839
DOI: 10.1016/j.isci.2024.109745 -
Molecules (Basel, Switzerland) Apr 2024Graphene is a good support for immobilizing catalysts, due to its large theoretical specific surface area and high electric conductivity. Solid chemical converted...
Graphene is a good support for immobilizing catalysts, due to its large theoretical specific surface area and high electric conductivity. Solid chemical converted graphene, in a form with multiple layers, decreases the practical specific surface area. Building pores in graphene can increase specific surface area and provide anchor sites for catalysts. In this study, we have prepared porous graphene (PG) via the process of equilibrium precipitation followed by carbothermal reduction of ZnO. During the equilibrium precipitation process, hydrolyzed N,N-dimethylformamide sluggishly generates hydroxyl groups which transform Zn into amorphous ZnO nanodots anchored on reduced graphene oxide. After carbothermal reduction of zinc oxide, micropores are formed in PG. When the Zn feeding amount is 0.12 mmol, the average size of the Pt nanoparticles on PG in the catalyst is 7.25 nm. The resulting Pt/PG exhibited the highest turnover frequency of 511.6 min for ammonia borane hydrolysis, which is 2.43 times that for Pt on graphene without the addition of Zn. Therefore, PG treated via equilibrium precipitation and subsequent carbothermal reduction can serve as an effective support for the catalytic hydrolysis of ammonia borane.
PubMed: 38675581
DOI: 10.3390/molecules29081761 -
International Journal of Molecular... Apr 2024A series of bench-stable Co(II) complexes containing hydrazone Schiff base ligands were evaluated in terms of their activity and selectivity in carbon-carbon multiple...
A series of bench-stable Co(II) complexes containing hydrazone Schiff base ligands were evaluated in terms of their activity and selectivity in carbon-carbon multiple bond transfer hydrogenation. These cobalt complexes, especially a Co(II) precatalyst bearing pyridine-2-yl-N(Me)N=C-(1-methyl)imidazole-2-yl ligand, activated by LiHBEt, were successfully used in the transfer hydrogenation of substituted styrenes and phenylacetylenes with ammonia borane as a hydrogen source. Key advantages of the reported catalytic system include mild reaction conditions, high selectivity and tolerance to functional groups of substrates.
Topics: Hydrogenation; Cobalt; Schiff Bases; Catalysis; Boranes; Coordination Complexes; Alkynes; Ammonia; Molecular Structure
PubMed: 38673948
DOI: 10.3390/ijms25084363 -
Materials (Basel, Switzerland) Apr 2024This work focuses on the comparison of H evolution in the hydrolysis of boron-containing hydrides (NaBH, NHBH, and (CHNHBH)) over the Co metal catalyst and the CoO-based...
This work focuses on the comparison of H evolution in the hydrolysis of boron-containing hydrides (NaBH, NHBH, and (CHNHBH)) over the Co metal catalyst and the CoO-based catalysts. The CoO catalysts were activated in the reaction medium, and a small amount of CuO was added to activate CoO under the action of weaker reducers (NHBH, (CHNHBH)). The high activity of CoO has been previously associated with its reduced states (nanosized CoB). The performed DFT modeling shows that activating water on the metal-like surface requires overcoming a higher energy barrier compared to hydride activation. The novelty of this study lies in its focus on understanding the impact of the remaining cobalt oxide phase. The XRD, TPR H, TEM, Raman, and ATR FTIR confirm the formation of oxygen vacancies in the CoO structure in the reaction medium, which increases the amount of adsorbed water. The kinetic isotopic effect measurements in DO, as well as DFT modeling, reveal differences in water activation between Co and CoO-based catalysts. It can be assumed that the oxide phase serves not only as a precursor and support for the reduced nanosized cobalt active component but also as a key catalyst component that improves water activation.
PubMed: 38673151
DOI: 10.3390/ma17081794 -
Inorganic Chemistry May 2024The borane-functionalized (BR) bis(3,5-dimethylpyrazolyl)methane () ligands (BR: 9-borabicyclo[3.3.1]nonane or 9-BBN), (BR: BCy), and (BR: B(CF)) were synthesized by...
The borane-functionalized (BR) bis(3,5-dimethylpyrazolyl)methane () ligands (BR: 9-borabicyclo[3.3.1]nonane or 9-BBN), (BR: BCy), and (BR: B(CF)) were synthesized by the allylation-hydroboration of . Metalation of with ZnCl yielded the heteroscorpionate dichloride complexes . The reaction of with ZnEt led to the formation of the zwitterionic complex . The reaction of complex with two equivalents of KHBEt under a carbon dioxide (CO) atmosphere gave rise to the formation of the dimeric bis(formate) complex , in which its borane moieties intermolecularly stabilize the formate ligands of opposite metal centers. The allylated precursor and its zinc dichloride, diethyl and bis(formate) complexes , , and were also isolated. The catalyst systems composed of 1 mol % of or and two equivalents of KHBEt hydroborated CO at 1 bar with pinacolborane (HBPin) to the methanol-level product HCOBPin (and PinBOBPin) in yields of 42 or 86%, respectively. The catalyst systems using the unfunctionalized complex and KHBEt or KHBEt/OctBR (BR: 9-BBN or BCy) hydroborated CO to HCOBPin but in 2.5- to 6-fold lower activities than those exhibited by /KHBEt. The hydroboration of CO using as a catalyst led to yields of 39-43%, comparable to those obtained with /KHBEt. The results confirmed that the catalytic intermediates benefit from the incorporated boranes' intra- or intermolecular stabilizations.
PubMed: 38656156
DOI: 10.1021/acs.inorgchem.4c00500 -
Inorganic Chemistry May 2024Diverse reactivity of the bulky tris(trimethylsilyl)silyl substituent [Si(SiMe)], also known as the hypersilyl group, was observed for amidinate-supported dichloro- and...
Diverse reactivity of the bulky tris(trimethylsilyl)silyl substituent [Si(SiMe)], also known as the hypersilyl group, was observed for amidinate-supported dichloro- and phenylchloroborane complexes. Treatment of the dichloroborane with potassium tris(trimethylsilyl)silyl led to the activation of the backbone β-carbon center and formation of saturated four-membered heterocyclic chloroboranes R'{Si(SiMe)}C(NR)BCl [R' = Ph, R = Cy (); R' = Ph, R = Pr (); R' = Bu, R = Cy ()], whereas the four-membered amidinate hypersilyl-substituted phenyl borane {PhC(NCy)B(Ph)[Si(SiMe)]} was observed for the case of an amidinate-supported phenylchloroborane. The highly deshielded B NMR spectroscopic resonance and the distinct difference in the Si NMR spectrum confirmed the presence of a σ-donating hypersilyl effect on compounds , , and . Reaction of with the Lewis acid AlCl led to the formation of complex in which an unusual cleavage of one of the C-N bonds of the amidinate backbone is observed. Nucleophilic substitution at the boron center of saturated chloroborane with phenyllithium generated the phenylborane derivative , whereas the secondary monomeric boron hydride was observed after treatment with alane (AlH). All compounds (-) have been fully characterized by NMR spectroscopy and single-crystal X-ray structure determination studies.
PubMed: 38652816
DOI: 10.1021/acs.inorgchem.4c00612