Complexes of N-hydroxyphthalimide and cobalt(II) acetate in reactions of alkylarene oxidation by molecular oxygen

The synergetic effect of the catalytic system cobalt(II) acetate-N-hydroxyphthalimide (NHPI) was studied in acetic acid during the oxidation of alkylbenzenes. The formation of complex between the components of catalytic system NHPI and Co(II) was demonstrated with the use of 1H NMR spectroscopy. It was established that N-hydroxyphthalimide is included in the complex as a ligand substituting for acetic acid in the internal coordination sphere of the metal; the reaction of NHPI with cobalt ions in the internal sphere leads to the formation of phthalimide-N-oxyl radicals that than participate in the catalytic cycle of the oxidation of organic substrates. The stability constants of complexes of NHPI with cobalt acetate were determined, as were those for the outer-sphere complexes of alkylbenzenes with metallocomplex.     

Mild and Practical Dirhodium(II)/NHPI-Mediated Allylic and Benzylic Oxidations with Air as the Oxidant

Aerobic allylic and benzylic oxidations catalyzed by dirhodium(II) complexes with N-hydroxyphthalimide (NHPI) are described. The open flask reaction occurs at mild temperature, using air as the oxidant. Mechanistic studies suggest that dirhodium(II) complexes axially coordinate with NHPI to activate the O−H bond in NHPI and decrease the bond-dissociation energy (BDE).     

A new strategy for alkane oxidation with O2 using N‐hydroxyphthalimide (NHPI) as a radical catalyst

A practical catalytic method to convert alkanes into the corresponding oxygen‐containing compounds with O₂ under mild conditions using N‐hydroxyphthalimide (NHPI) in the presence or absence of a transition metal was developed. Thus, cyclohexane was successfully converted into adipic acid in good conversion and selectivity by a combined catalytic system consisting of NHPI and Mn(acac)₂. Lower alkane such as isobutane was converted into t‐butyl alcohol (83%) under 10 atm of air by NHPI‐Co(OAc)₂ system. Alkylbenzene such as toluene was oxidized to benzoic acid in high yield (81%) under normal temperature and pressure of dioxygen in the presence of a catalytic amount of NHPI and Co(OAc)₂. ESR measurements showed that phthalimide‐N‐oxyl generated from NHPI under dioxygen atmosphere is a key species in this oxidation and functions as a radical catalyst.     

Mechanisms of reaction of aminoxyl (nitroxide), iminoxyl, and imidoxyl radicals with alkenes and evidence that in the presence of lead tetraacetate, N-hydroxyphthalimide reacts with alkenes by both radical and nonradical mechanisms

1,2-dideuterio-cyclohexene, 1,2-dideuterio-cyclooctene, and trans-3,4-dideuterio-hex-3-ene were reacted with three >NO* radicals: 4-hydroxyTempo, di-tert-butyliminoxyl, both used as the actual radicals, and phthalimide-N-oxyl (PINO) generated from N-hydroxyphthalimide (NHPI) by its reaction with tert-alkoxyl radicals (t-RO*) and with lead tetraacetate. In all cases, except the NHPI/Pb(OAc)4 system, only mono >NO-substituted alkenes were produced. The 2H NMR spectra imply that 88-92% of monoadducts were formed by the initial abstraction of an allylic H-atom, followed by capture of the allylic radical by a second >NO*, while the remaining 12-8% appear to be formed by an initial addition of >NO* to the double bond followed by H-atom abstraction by a second >NO*. A substantial and sometimes the major product formed with the NHPI/Pb(OAc)4 system has two PINO moieties added across the double bond. Since such diadducts are not formed with the NHPI/t-RO* system, a heterolytic mechanism is proposed, analogous to that known for the Pb(OAc)4-induced acetoxylation of alkenes. A detailed analysis of the NHPI/Pb(OAc)4/alkene products indicates that monosubstitution occurs by both homolytic and heterolytic processes.     

多相/均相TiO2/N-羟酰亚胺混合体系中可见光诱导分子氧可控光催化氧化苄基反应

均相催化和多相催化通常被认为是独立甚至相互对立的学科.本文提出了一种新型的用于分子氧选择性氧化烷基苯的杂多酸/均相混合催化体系.该催化体系由N-羟基邻苯二甲酰亚胺(NHPI,用于自由基链式反应的均相有机催化剂)和纳米TiO2(多相紫外光活性光氧化催化剂)两种组分组成.NHPI与TiO2的协同作用使光氧化活性从紫外光转移到可见光,并产生邻苯二甲酰亚胺-N-氧基(PINO)自由基.NHPI/PINO催化的自由基链式反应能够在没有额外光输入的情况下进行,从而从根本上提高能源效率.通过控制NHPI/TiO2比率优化产物选择性,进而使烷基芳烃优先形成过氧化氢或酮.     

The radical-chain addition of aldehydes to alkenes by the use of N-hydroxyphthalimide (NHPI) as a polarity-reversal catalyst

Hydroacylation of simple alkenes with aldehydes via a radical process was successfully achieved by the use of N-hydroxyphthalimide (NHPI) as a polarity-reversal catalyst. Thus, 5-tridecanone was obtained by the reaction of oct-1-ene with pentanal in the presence of small amounts of NHPI and dibenzoyl peroxide (BPO).     

Alkane Oxidation with Molecular Oxygen Using a New Efficient Catalytic System: N-Hydroxyphthalimide (NHPI) Combined with Co(acac)(n)() (n = 2 or 3)

A novel class of catalysts for alkane oxidation with molecular oxygen was examined. N-Hydroxyphthalimide (NHPI) combined with Co(acac)(n)() (n = 2 or 3) was found to be an efficient catalytic system for the aerobic oxidation of cycloalkanes and alkylbenzenes under mild conditions. Cycloalkanes were successfully oxidized with molecular oxygen in the presence of a catalytic amount of NHPI and Co(acac)(2) in acetic acid at 100 degrees C to give the corresponding cycloalkanones and dicarboxylic acids. Alkylbenzenes were also oxidized with dioxygen using this catalytic system. For example, toluene was converted into benzoic acid in excellent yield under these conditions. Ethyl- and butylbenzenes were selectively oxidized at their alpha-positions to form the corresponding ketones, acetophenone, and 1-phenyl-1-butanone, respectively, in good yields. A key intermediate in this oxidation is believed to be the phthalimide N-oxyl radical generated from NHPI and molecular oxygen using a Co(II) species. The isotope effect (k(H)/k(D)) in the oxidation of ethylbenzene and ethylbenzene-d(10) with dioxygen using NHPI/Co(acac)(2) was 3.8.     

N- Hydroxyphthalimide and transition metal salts as catalysts of the liquid-phase oxidation of 1-methoxy-4-(1-methylethyl)benzene with oxygen

The oxidation process of 1-methoxy-4-(1-methylethyl)benzene catalysed by N-hydroxyphthalimide (NHPI) or NHPI in combination with Cu(II), Co(II), Mn(II) and Fe(II) salts was studied. The effects of the amount of catalyst and the temperature were determined. 1-Methyl-1-(4-methoxyphenyl)ethyl hydroperoxide was obtained in a yield of 73 mol% when 1-methoxy-4-(1-methylethyl)benzene was oxidised for 3 h at 60°C in acetonitrile as a solvent in the presence of NHPI. 1-(4-Methoxyphenyl)ethanone with high selectivity up to 68–75 mol%, but low yield amounting to 11 mol% was obtained when 1-methoxy-4-(1-methylethyl)benzene was oxidised in the presence of the NHPI/Cu(II) system at 120°C.      

New efficient aerobic oxidation of some alcohols with dioxygen catalysed by N-hydroxyphtalimide with vanadium co-catalysts

New efficient vanadium co-catalysts have been developed for the oxidation of some alcohols with O(2) catalysed by N-hydroxyphthalimide (NHPI). Various alcohols (primary and secondary) were selectively oxidized by O(2) under mild conditions in the presence of a catalytic amount of NHPI as a radical-producing agent combined with small amounts of vanadium complexes with or without the addition of a simple salt (e.g. LiCl) or base (e.g. pyridine).     

N-羟基邻苯二甲酰亚胺及其类似物催化下的分子氧氧化反应

本文综述了近年来N-羟基邻苯二甲酰亚胺（NHPI）及其类似物催化下分子氧氧化的各种反应,并对它们的催化机理作了简要介绍。NHPI与过渡金属离子组成的催化体系能高效的催化乙烷氧化为乙酸、环烷烃氧化为二元羧酸、甲苯氧化为苯甲酸、烯烃氧化为环氧化物、炔烃氧化为炔酮、酰胺氧化为酰亚胺;NHPI单独使用能催化金刚烷发生氧化羰基化反应、催化氧化醇制取过氧化氢;NHPI与有机助催化剂如：偶氮二异丁腈、溴化季铵盐、蒽醌、醇等也能催化分子氧氧化反应。     

介孔石墨型氮化碳/N-羟基邻苯二甲酰亚胺组合催化体系催化醇类化合物的选择性氧化

醇的氧化产品(醛和酸)是精细化工中的重要中间体.醇类的选择性氧化无论是在基础研究还是在工业应用方面都具有非常重要的意义.传统的方法是使用化学计量的氧化剂(如：高氯酸盐,重铬酸盐,高锰酸盐,过氧酸)来氧化醇.但是,这些氧化剂具有强腐蚀性,价格较昂贵,有些氧化剂还具有很强的毒性或者反应后产生大量重金属废液.而以分子氧作为氧化剂在温和条件下实现醇到醛的氧化具有更好的经济性也更环保.在过去几十年里,科学家们发展了许多催化体系来活化氧气分子.这些体系大部分是基于钌、钯、铜和钛等金属催化剂.近年,考虑成本和环境因素,越来越多的科学家把目光投向无金属催化剂来实现醇的氧化.石墨型氮化碳(g-C3N4)是二维层状类石墨结构,层内原子以共价键相连,层与层之间由于分子间作用而堆叠在一起.在g-C3N4中引入介孔(mpg-C3N4)能够提高g-C3N4的比表面积,提供更多的活性位点.由于mpg-C3N4具有半导体性质(带隙宽度为2.7 eV),在可见光照射下能够激发出一个电子给氧气,氧气得到电子后生成具有较高氧化活性的?O2–.这样我们就可以在比较温和的条件下得到活性较高的氧化剂.但是?O2–活性和产量有限、并且容易被猝灭,因此我们想通过选用一个能形成比较稳定的自由基的有机分子来“传递氧化性”.基于上述思考,我们引入mpg-C3N4和N-羟基邻苯二甲酰亚胺(NHPI)作为组合催化体系实现光催化和有机催化有效的结合来催化选择性氧化醇.以苯甲醇为模型化合物、以mpg-C3N4/NHPI作为组合型催化剂、普通的钨丝灯为光源,在25 oC下通入1 atm O2,实现了醇的选择性氧化.通过电子自旋共振测试,我们探测到?O2–自由基.在只有mpg-C3N4的体系中,产生的?O2–自由基很快被猝灭,从而不能有效地氧化苯甲醇.而加入NHPI后,?O2–自由基能够夺取NHPI中O–H键的氢,形成PINO自由基.形成的PINO自由基能够在温和的反应条件下氧化苯甲醇得到苯甲醛.(图1)通过调节mpg-C3N4和NHPI的比例,我们发现增加mpg-C3N4的比例有利于苯甲醛的生成.一方面,较低的反应温度不利于生成的醛被进一步氧化成酸.另一方面,由于苯甲醇和mpg-C3N4通过O-H...N或者O-H...π相互作用能够很好的吸附到mpg-C3N4表面,从而氧化为苯甲醛;而生成的苯甲醛与mpg-C3N4的相互作用比较弱,容易脱附到溶液中,避免被进一步的氧化.同时,我们也将mpg-C3N4/NHPI催化体系拓展到其他醇类的氧化反应,同样能够得到很好的转化率和选择性.该催化体系不需要任何金属元素,利用偶合的光催化组合进行可见光催化氧化过程,反应温度低,为醇类分子的选择性氧化制备醛或者酸提供了一条有效并且环保的策略.     

Utilization of photocatalysts in decarboxylative coupling of carboxylic N-hydroxyphthalimide (NHPI) esters

Recently, the visible-light photoredox decarboxylative couplings of N-(acyloxy)phthalimides (NHPI esters) and its derivatives have become an efficient chemical transformation. Under visible light, the NHPI esters undergo a single-electron transfer (SET) process to afford the corresponding carbon or nitrogen radicals that participate in many chemical transformations. The photoredox decarboxylative couplings have been applied to achieve construction of an array of carbon–carbon and carbon–heteroatom bonds as well as the synthesis of carbocycles and heterocycles. This review categorises photocatalysts, discusses the application and catalysis mechanisms of NHPI esters, and details recent progress in this field.     

N-hydroxyphthalimide incorporated onto Cu-BTC metal organic frameworks: An novel catalyst for aerobic oxidation of toluene

Research on Chemical Intermediates - N-hydroxyphthalimide (NHPI) incorporated onto a Cu-based metal–organic framework [NHPI/Cu-BTC (BTC:1,3,5-benzenetricarboxylate)] was prepared and used as...     

On the mechanism of oxidation process initiation by the N-hydroxyphthalimide-cobalt (II) acetate system

The effect of the structure of radical catalysts, N-hydroxyphthalimides (NHPI), on the oxidation process initiation in the presence of cobalt (II) acetate is studied. It is shown that the magnitude of the synergic effect of the system NHPI-Co(OAc)₂ depends on the structure of NHPI molecule. The proposed mechanism is confirmed according to which of the NHPI molecules in the inner sphere of the metal are catalytically active.     

Efficient oxidation of alcohols to carbonyl compounds with molecular oxygen catalyzed by N-hydroxyphthalimide combined with a Co species

Highly efficient catalytic oxidation of alcohols with molecular oxygen by N-hydroxyphthalimide (NHPI) combined with a Co species was developed. The oxidation of 2-octanol in the presence of catalytic amounts of NHPI and Co(OAc)2 under atmospheric dioxygen in AcOEt at 70 degrees C gave 2-octanone in 93% yield. The oxidation was significantly enhanced by adding a small amount of benzoic acid to proceed smoothly even at room temperature. Primary alcohols were oxidized by NHPI in the absence of any metal catalyst to form the corresponding carboxylic acids in good yields. In the oxidation of terminal vic-diols such as 1,2-butanediol, carbon-carbon bond cleavage was induced to give one carbon less carboxylic acids such as propionic acid, while internal vic-diols were selectively oxidized to 1,2-diketones.     

Kinetic and Product Study of the S-oxidation vs HAT Chemoselectivity in Reactions Promoted by Nonheme Iron(IV)-oxo Complex/NHPI Mediator System

The chemoselectivity between S-oxidation and hydrogen atom transfer (HAT) from C−H bonds has been investigated in the oxidations of a series of aryl sulfides, alkyl aromatic compounds and benzylic alcohols promoted by the iron(IV)-oxo complex [(N4Py)Fe^IV(O)]²⁺ (N4Py: N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)-methylamine) either alone or in the presence of the N-hydroxyphthalimide (NHPI) mediator via kinetic and product studies. Kinetic analyses indicate a generally higher reactivity of [(N4Py)Fe^IV(O)]²⁺ for S-oxidation process while HAT is favored in the reactions promoted by phthalimide-N-oxyl radical (PINO) deriving from NHPI oxidation. Product analysis in intermolecular competitive oxidations confirms the kinetic results with sulfoxides obtained as major products in the oxidation promoted by [(N4Py)Fe^IV(O)]²⁺. Conversely, when NHPI is employed as a mediator, significant differences in terms of chemoselectivity are observed, and HAT-derived products are obtained in higher yields which translate into an inversion of selectivity in the case of the substrates containing activated C−H bonds like diphenylmethane, triphenylmethane and benzylic alcohols. A similar change of chemoselectivity is also observed in the oxidation of aromatic substrates containing both a sulfur atom and α to OH benzylic C−H bonds, with the sulfoxide product more abundant in the absence of NHPI and carbonyl products prevailing with the [(N4Py)Fe^IV(O)]²⁺/NHPI system.     

Aerobic oxidation with N-hydroxyphthalimide catalysts in ionic liquid

N-Hydroxyphthalimide (NHPI)-catalyzed aerobic oxidations in the ionic liquids were examined for the first time. Both NHPI and its ionic derivative, 3-pyridinylmethyl-N-hydroxyphthalimide (Py-NHPI), were found to have better performance in the ionic liquid than in the conventional organic solvents for the aerobic oxidation of N-alkylamides to imides. On the other hand, Py-NHPI was found to be a much better catalyst than NHPI for the aerobic oxidation of benzylic compounds in the ionic liquid.     

Kinetic Studies of Acenaphthene Oxidation Catalyzed by N‐Hydroxyphthalimide

The acenaphthene oxidation with molecular oxygen in the presence of N‐hydroxyphthalimide (NHPI) has been investigated. It is shown that the main oxidation product is acenaphthene hydroperoxide. The phthalimide‐N‐oxyl (PINO) radical has been generated in situ from its hydroxyimide parent, NHPI, by oxidation with iodobenzenediacetate. The rate constant of H‐abstraction (k_H) from acenaphthene by PINO has been determined spectroscopically in acetonitrile. The kinetic isotope effect and the activation parameters have also been measured. On the basis of the results of our studies and available published literature data, a plausible mechanism for the oxidation process of acenaphthene with dioxygen catalyzed by NHPI was discussed.     

An efficient nitration of light alkanes and the alkyl side-chain of aromatic compounds with nitrogen dioxide and nitric acid catalyzed by N-hydroxyphthalimide

Nitration of light alkanes and the alkyl side-chain of aromatic compounds with NO(2) and HNO(3) was successfully achieved by the use of N-hydroxyphthalimide (NHPI) as a catalyst under relatively mild conditions. For example, the nitration of propane with NO(2) catalyzed by NHPI at 100 degrees C for 14 h gave 2-nitropropane in good yield without formation of 1-nitropropane and cleaved products such as nitroethane and nitromethane. Various aliphatic nitroalkanes, which are difficult to prepare by conventional methods, could be selectively obtained by means of the present methodology by using NHPI as the key catalyst. In addition, the side-chain nitration of alkylbenzenes such as toluene was selectively carried out to lead to alpha-nitrotoluene without the ring nitration. The present reaction provides an efficient selective method for the nitration of light alkanes and alkylbenzenes, which has been very difficult to carry out so far.     

Action of N-hydroxyphthalimide on chain stereoregularity in the radical polymerization of methyl methacrylate

N-Hydroxyphthalimide (NHPI) has a dual function in the radical polymerization of methyl methacrylate (MMA): this compound acts as an initiator and also provides for stereochemical control of the polymer chain. Lowering the polymerization temperature leads to increased syndiotactic specificity in the polymethyl methacrylate molecule. The action of NHPI as an initiator and stereoregulator is attributed to the capacity of this compound to form a hydrogen bond with the monomer molecule and growing macroradical.