1197-01-9Relevant academic research and scientific papers
Single-Site Cobalt-Catalyst Ligated with Pyridylimine-Functionalized Metal-Organic Frameworks for Arene and Benzylic Borylation
Akhtar, Naved,Antil, Neha,Balendra,Begum, Wahida,Kumar, Ajay,Manna, Kuntal,Newar, Rajashree,Shukla, Sakshi
, p. 10473 - 10481 (2020)
We report a highly active single-site heterogeneous cobalt-catalyst based on a porous and robust pyridylimine-functionalized metal-organic frameworks (pyrim-MOF) for chemoselective borylation of arene and benzylic C-H bonds. The pyrim-MOF having UiO-68 topology, constructed from zirconium-cluster secondary building units and pyridylimine-functionalized dicarboxylate bridging linkers, was metalated with CoCl2 followed by treatment of NaEt3BH to give the cobalt-functionalized MOF-catalyst (pyrim-MOF-Co). Pyrim-MOF-Co has a broad substrate scope, allowing the C-H borylation of halogen-, alkoxy-, alkyl-substituted arenes as well as heterocyclic ring systems using B2pin2 or HBpin (pin = pinacolate) as the borylating agent to afford the corresponding arene- or alkyl-boronate esters in good yields. Pyrim-MOF-Co gave a turnover number (TON) of up to 2500 and could be recycled and reused at least 9 times. Pyrim-MOF-Co was also significantly more robust and active than its homogeneous control, highlighting the beneficial effect of active-site isolation within the MOF framework that prevents intermolecular decomposition. The experimental and computational studies suggested (pyrim?-)CoI(THF) as the active catalytic species within the MOF, which undergoes a mechanistic pathway of oxidative addition, turnover limiting σ-bond metathesis, followed by reductive elimination to afford the boronate ester.
The efficient and selective biocatalytic oxidation of norisoprenoid and aromatic substrates by CYP101B1 from Novosphingobium aromaticivorans DSM12444
Hall, Emma A.,Bell, Stephen G.
, p. 5762 - 5773 (2015)
CYP101B1 from Novosphingobium aromaticivorans DSM12444 is a homologue of CYP101A1 (P450cam) from Pseudomonas putida and the CYP101D1, CYP101D2 and CYP101C1 enzymes from the same bacterium. CYP101B1 binds norisoprenoids more tightly than camphor and efficiently hydroxylates substrates in combination with ferredoxin reductase, ArR, and [2Fe-2S] ferredoxin, Arx, electron transfer partners. The norisoprenoids, α-ionone and β-damascone are both oxidised by CYP101B1 with high product formation activity, >500 min-1. α-Ionone oxidation occurred regioselectively at the allylic C3 position while β-damascone was hydroxylated predominantly at C3, 86%, with the main competing minor product arising from oxidation at the allylic C4 position (11%). When incorporated into a whole-cell oxidation system, with ArR and Arx, CYP101B1 is also capable of oxidising the aromatic compound indole. Other aromatic molecules including phenylcyclohexane and p-cymene were tested and both were hydroxylated by CYP101B1. Phenylcyclohexane was selectively oxidised to trans-4-phenylcyclohexanol while p-cymene was hydroxylated at the benzylic carbons to yield a mixture of isopropylbenzyl alcohol and p-α,α-trimethylbenzylalcohol. Trans-4-Phenylcyclohexanol was formed with a product formation rate of 141 min-1 and was five times more active than the oxidation of p-cymene. This journal is
Ruthenium(III)-catalysed Hydrogen Peroxide Oxidation of Alkyl Aromatic Compounds under Phase-Transfer Conditions
Barak, Gabriela,Sasson, Yoel
, p. 637 - 638 (1988)
The side chain of alkyl aromatic derivatives is oxidized to aldehydes, ketones, or alcohols by hydrogen peroxide in the presence of a ruthenium(III) salt and a quaternary ammonium phase-transfer catalyst.
Allylic oxidation of cyclic alkenes with molecular oxygen and tert-butyl hydroperoxide over copper-manganese oxides
Zhang, Wu,Wei, Qiuyu,Lan, Lingling,Wu, Aiqun,Yin, Xiuju,Shen, Liqun
, p. 357 - 365 (2017)
Abstract: An efficient and mild method for the allylic oxidation of cyclic alkenes employing molecular oxygen and tert-butyl hydroperoxide as the oxidant, copper-manganese oxides as heterogeneous catalyst under ambient temperature is proposed. The catalyst, which was prepared by co-precipitation and characterized, was evaluated oxidation of isolongifolene as a typical mode substrate. The catalyst showed a good catalytic activity and remained nearly the same after four cycles. The scope of the reaction was investigated with a variety of cyclic alkenes compounds. Graphical abstract: [Figure not available: see fulltext.]
Structure and C-S bond cleavage in aryl 1-methyl-1-arylethyl sulfide radical cations
Baciocchi, Enrico,Bettoni, Marta,Del Giacco, Tiziana,Lanzalunga, Osvaldo,Mazzonna, Marco,Mencarelli, Paolo
, p. 573 - 582 (2011)
Steady state and laser flash photolysis (LFP) of a series of p-X-cumyl phenyl sulfides (4-X-C6H4C(CH3) 2SC6H5: 1, X = Br; 2, X = H; 3, X = CH 3; 4, X = OCH3) and p-X-cumyl p-methoxyphenyl sulfides (4-X-C6H4C(CH3)2SC6H 4OCH3: 5, X = H; 6, X = CH3; 7, X = OCH 3) has been carried out in the presence of N-methoxy phenanthridinium hexafluorophosphate (MeOP+PF6-) under nitrogen in MeCN. Steady state photolysis showed the formation of products deriving from the C-S bond cleavage in the radical cations 1+?-7 +? (2-aryl-2-propanols and diaryl disulfides). Formation of 1+?-7+? was also demonstrated by LFP experiments evidencing the absorption bands of the radical cations 1+?- 3+? (λmax = 530 nm) and 5+?- 7+? (λmax = 570 nm) mainly localized in the arylsulfenyl group and radical cation 4+? (λ max = 410, 700 nm) probably mainly localized in the cumyl ring. The radical cations decayed by first-order kinetics with a process attributable to the C-S bond cleavage. On the basis of DFT calculations it has been suggested that the conformations most suitable for C-S bond cleavage in 1 +?-4+? and 7+? are characterized by having the C-S bond almost collinear with the π system of the cumyl ring and by a significant charge and spin delocalization from the ArS ring to the cumyl ring. Such a delocalization is probably at the origin of the observation that the rates of C-S bond cleavage result in very little sensitivity to changes in the C-S bond dissociation free energy (BDFE). A quite large reorganization energy value (λ = 43.7 kcal mol-1) has been calculated for the C-S bond scission reaction in the radical cation. This value is much larger than that (λ = 12 kcal mol-1) found for the C-C bond cleavage in bicumyl radical cations, a reaction that also leads to cumyl carbocations.
Linear Free Energy Relationship Studies of the Dimethyldioxirane C-H Bond Insertion Reaction
Murray, Robert W.,Gu, Hong
, p. 5673 - 5677 (1995)
The relative rates of reaction of a series of p-substituted cumenes with dimethyldioxirane have been studied.The products are the corresponding cumyl alcohols.Treatment of the rate data with the Hammett substituent constants reveals that the insertion reaction is an electrophilic process with ρ = -2.76.Similar tretment of the data with the Brown-Okamoto substituent constants gives ρ+ = -1.61.The second-order rate constants for the reaction of a series of substituted adamantanes with dimethyldioxirane were also determined.Again, the products are the corresponding adamantanols.The rate constants were correlated with several types of substituent constants.The best correlations were obtained with the Taft ?* and ?I constants which gave ρ* = -1.08 and ρI = -2.39, respectively.Thus, the insertion reaction in this aliphatic system is also electrophilic.
To Rebound or...Rebound? Evidence for the "alternative Rebound" mechanism in Ca'H Oxidations by the systems nonheme Mn Complex/H2O2/carboxylic acid
Ottenbacher, Roman V.,Bryliakova, Anna A.,Shashkov, Mikhail V.,Talsi, Evgenii P.,Bryliakov, Konstantin P.
, p. 5517 - 5524 (2021/05/31)
In this work, it has been shown that aliphatic Ca'H oxidations by bioinspired catalyst systems Mn aminopyridine complex/H2O2/carboxylic acid in acetonitrile afford predominantly a mixture of the corresponding alcohol and the ester. The alcohol/ester ratio is higher for catalysts bearing electron-donating groups at the aminopyridine core. Isotopic labeling studies witness that the oxygen atom of the alcohol originates from the H2O2molecule, while the ester oxygen comes exclusively from the acid. Oxidation of ethylbenzene in the presence of acetic acid affords enantiomerically enriched 1-phenylethanol and 1-phenyl acetate, with close enantioselectivities and the same sign of absolute chirality. Experimental data and density functional theory calculations provide evidence in favor of the rate-limiting benzylic H atom abstraction by the high-spin (S = 1) [LMnV(O)OAc]2+active species followed by competitive OH/OC(O)R rebound. This mechanism has been unprecedented for Ca'H oxidations catalyzed by bioinspired Mn complexes. The trends governing the alcohol/ester ratios have been rationalized in terms of steric properties of the catalyst, acid, and substrate. copy; 2021 American Chemical Society.
Palladium-Aminopyridine Catalyzed C?H Oxygenation: Probing the Nature of Metal Based Oxidant
Lubov, Dmitry P.,Bryliakova, Anna A.,Samsonenko, Denis G.,Sheven, Dmitriy G.,Talsi, Evgenii P.,Bryliakov, Konstantin P.
, p. 5109 - 5120 (2021/11/10)
A mechanistic study of direct selective oxidation of benzylic C(sp3)?H groups with peracetic acid, catalyzed by palladium complexes with tripodal amino-tris(pyriylmethyl) ligands, is presented. The oxidation of arylalkanes having secondary and tertiary benzylic C?H groups, predominantly yields, depending on the substrate and conditions, either the corresponding ketones or alcohols. One of the three 2-pyriylmethyl moieties, which is pending in the starting catalyst, apparently, facilitates the active species formation and takes part in stabilization of the high-valent Pd center in the active species, occupying the axial coordination site of palladium. The catalytic, as well as isotopic labeling experiments, in combination with ESI-MS data and DFT calculations, point out palladium oxyl species as possible catalytically active sites, operating essentially via C?H abstraction/oxygen rebound pathway. For the ketones formation, O?H abstraction/в-scission mechanism has been proposed.
Method for synthesizing tertiary alcohol by catalytically oxidizing benzyl tertiary C-H bonds of aromatic hydrocarbon through metalloporphyrin
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Paragraph 0072-0073, (2020/09/30)
The invention discloses a method for synthesizing tertiary alcohol by catalytically oxidizing benzyl tertiary C-H bonds of aromatic hydrocarbon through metalloporphyrin. The method comprises the following steps: dispersing metalloporphyrin (1*10-1%, mol/mol) into aromatic hydrocarbon; sealing the reaction system, heating to 40-120 DEG C while stirring, introducing an oxidant (0.10-1.0 MPa), keeping the set temperature and pressure, carrying out reactions for 3.0-24.0 hours under stirring, and carrying out after-treatment on the reaction solution to obtain the product aromatic benzyl tertiary alcohol. The method has the advantages of shortest conversion path, highest atom economy, lower reaction temperature, lower environmental influence and the like, and the selectivity of aromatic benzyl tertiary alcohol is high. In addition, the content of aromatic hydrocarbon hydroperoxide is low, and the safety coefficient is high. The invention provides an efficient, feasible and safe method for synthesizing aromatic benzyl tertiary alcohol through selective catalytic oxidation of benzyl tertiary C-H bonds of aromatic hydrocarbon.
Efficient and selective oxidation of tertiary benzylic C[sbnd]H bonds with O2 catalyzed by metalloporphyrins under mild and solvent-free conditions
Hu, Meng-Yun,Liu, Lei,Qi, Bei,She, Yuan-Bin,Shen, Hai-Min,Ye, Hong-Liang
, (2020/05/19)
The direct and efficient oxidation of tertiary benzylic C[sbnd]H bonds to alcohols with O2 was accomplished in the presence of metalloporphyrins as catalysts under solvent-free and additive-free conditions. Based on effective inhibition on the unselective autoxidation and deep oxidation, systematical investigation on the effects of porphyrin ligands and metal centers, and apparent kinetics study, the oxidation system employing porphyrin manganese(II) (T(2,3,6-triCl)PPMn) with bulkier substituents as catalyst, was regarded as the most promising and efficient one. For the typical substrate, the conversion of cumene could reach up to 57.6% with the selectivity of 70.5% toward alcohol, both of them being higher than the current documents under similar conditions. The superiority of T(2,3,6-triCl)PPMn was mainly attributed to its bulkier substituent groups preventing metalloporphyrins from oxidative degradation, its planar structure favoring the interaction between central metal with reactants, and the high efficiency of Mn(II) in the catalytic transformation of hydroperoxides to alcohols.
