Phosphine-phosphonium ylides as ligands in palladium-catalysed C2-H arylation of benzoxazoles

As balanced electron-rich P,C-chelating ligands, phosphine-phosphonium-ylides are considered for their ability to in situ promote palladium-catalysed direct C(sp²)H arylation. Using methyl phosphonium salts of 2,2'-bis(diphenylphosphino)-1,1'-binaphtyl ("methyl-BINAPIUM") as ylide precursors under optimized reaction conditions, arylation of benzoxazole was found to proceed in moderate to high yield to give functional 2-aryl benzoxazoles. A strong anion effect of the non-salt free ylide was evidenced (TfO⁻ > I⁻ > PF₆⁻ ≈ salt-free). This first example of phosphonium ylides as ligands in catalytic C–H activation extends the prospect of their general implementation in homogeneous transition metal catalysis.     

The first structural characterization of a phosphonium amide: synthesis, isolation and molecular structure of (Ph3PEt)(NPh2)

The first isolation of a phosphonium amide, (Ph₃PEt)⁺(NPh₂)⁻, obtained via the deprotonation of a secondary amine (diphenylamine) with a phosphorus ylide (triphenylphosphonium ethylide), is described. An X-ray crystal structure provides the first observation of an essentially ion-separated Ph₂N⁻ anion in the solid state, though weak association with Ph₃PEt⁺ cations take plac through C---H…N hydrogen bonding. Cryoscopic and NMR spectroscopic data suggest that this association is not maintained in benzene solution.     

有机配体表面改性NiCo2O4纳米线用于水全分解

由于水分解在绿色能源领域的重要作用,能够在碱性介质中进行析氢(HER)和析氧(OER)反应的双功能电催化剂具有重要的应用价值。本文报道一种具有丰富缺陷的表面改性NiCo₂O₄纳米线(NWs),在碱性介质中作为一种高效的整体水裂解电催化剂。X射线光电子能谱(XPS)分析表明,Co²⁺/Co³⁺比值的增加是表面修饰NiCo₂O₄纳米线具有优异双功能电催化性能的重要原因。结果表明,在1.0 mol·L^-1 KOH溶液中,通过有机配体主导的表面改性,优化后的NiCo₂O₄纳米线在电流密度达到10 mA·cm^-2时的HER过电位仅为83 mV,OER过电位仅为280 mV。更重要的是,有机配体表面改性后的NiCo₂O₄纳米线表现出了出色的水分解性能,在2.1 V电压下达到了100 mA·cm^-2的电流密度。目前的工作凸显了提高NiCo₂O₄ NWs尖晶石结构中Co²⁺含量对促进整体水裂解的重要性。     

On the affinities of ammonia and water for Li, Na and K

The affinities of ammonia for Na⁺ and K⁺, recently determined experimentally, have been computed by the ab initio SCF method using ended polarized gaussian basis sets and shown to be satisfactory Furthermore, the corresponding values computed at the same level of accuracy for the three cations Li⁺, Na⁺, K⁺ and the two ligands NH₃ and H₂O are shown to yield the order Li⁺ > Na⁺ > K⁺ for each ligand and NH₃ > H₂O for each ion, in agreement with experiment. An analysis of the factors involved in the binding provides a consistent rationalization of these regularities and of some observed correlations.     

Carbon-Phosphorus Ligands with Extreme Donating Character

Carbeniophosphines [R₂C⁺−PR₂] and phosphonium ylides [R₃P⁺−CR₂⁻] are two complementary classes of carbon-phosphorus based ligands defined by their unique donor properties. Indeed, while carbeniophosphines are electron-poor P-ligands due to the positioning of a positive charge near the coordinating P-atom, phosphonium ylides are electron-rich C-ligands due to the presence of a negatively charged coordinating C-atom. Based on this knowledge, this account summarizes our recent contribution on these two classes of carbon-phosphorus ligands, and in particular the strategies developed to lower the donor character of carbeniophosphines and enhance that of phosphonium ylides. This led us to design, at both extremities of the donating scale, extremely electron-poor P-ligands exemplified by imidazoliophosphonites [R₂C⁺−P(OR)₂] and dicarbeniophosphines [(R₂C⁺)₂−PR], and extremely electron-rich C-ligands illustrated by pincer architectures exhibiting several phosphonium ylide donor extremities. In the context of carbon-phosphorus analogy, the closely related cases of ligands where the C-atom of a NHC ligand is in close proximity of two positive charges, and that of a phosphonium ylide coordinated through its P-atom are also discussed. An overview of the synthetic methods, coordinating properties, general reactivity and electronic structure of all these C,P-based species is presented here.     

Regioselective hydrophenylation of olefins catalyzed by an Ir(III) complex

The novel, anti-Markovnikov, arylation of olefins with benzene to produce straight-chain alkylbenzenes with higher selectivity than branched alkylbenzenes is catalyzed by [Ir(μ-acac-O,O′,C³)(acac-O,O′)(acac-C³)]₂ (acac=acetylacetonato), 1 [J. Am. Chem. Soc. 122 (2000) 7414]. The reaction of benzene with propylene gave n-propylbenzene and cumene in 61 and 39% selectivities, respectively. The reaction of benzene and styrene afforded 1,2-diphenylethane in 98% selectivity. Considering the anti-Markovnikov regioselectivity and lack of inhibition by water, we propose that the reaction does not proceed via a Friedel–Crafts, carbocation, mechanism. Complex 1, amongst the various transition metal complexes examined, is the most efficient for catalyzing the anti-Markovnikov olefin arylation. The crystal structure of complex 1 was solved and is consistent with a binuclear Ir(III) structure with three different types of coordinated acac ligands as reported by earlier solution IR and NMR analyses. [Ir(μ-acac-O,O′,C³)(acac-O,O′)Cl]₂, 2, was prepared by the reaction of complex 1 with benzoyl chloride, and the crystal structure was also reported.     

Cyclic (Amino)(Phosphonium Bora‐Ylide)Silanone: A Remarkable Room‐Temperature‐Persistent Silanone

A silanone substituted by bulky amino and phosphonium bora‐ylide substituents has been isolated in crystalline form. Thanks to the exceptionally strong electron‐donating phosphonium bora‐ylide substituent, the lifetime at room temperature of the silanone is dramatically extended (t _1/2=4 days) compared to the related (amino)(phosphonium ylide)silanone VI (t _1/2=5 h), allowing easier manipulation and its use as precursor of new valuable silicon compounds. The interaction of silanone with a weak Lewis acid such as MgBr₂ increases further its stability (no degradation after 3 weeks at room temperature).     

Enantioselective Hydroarylation of Olefins Using Palladium/Chiral Quinoline Oxazolines

Palladium-catalyzed arylation and alkenylation of olefins, known as the Heck reaction, is one of the most efficient catalytic methods for carbon-carbon bond formation in organic synthesis^[1]. During the last decade, asymmetric Heck reactions have attracted great attention, and a number of highly enantioselective chiral ligands have been developed to enhance chiral discrimination in these reactions^[2]. However, asymmetric Heck-type hydroarylations of olefins, addition of aryl halides or triflates to carbon-carbon double bonds, have not been well studied. In 1991, Brunner reported an asymmetric hydroarylation of norbornene and norbornadiene with aryl iodides using chiral bisphosphine ligands, and around 40% ee was achieved^[3]. Later on, Achiwa reached around 70% ee in the asymmetric hydroarylation of norbornene with phenyl triflate by using chiral P-N ligands^[4,5]. Herein, we wish to describe our investigations on chiral quinolinyl-oxazoline ligands that provide the first examples of efficient bisnitrogen ligands in Heck-type hydroarylation and the application of this reaction in the asymmetric synthesis of Epibatidine.     

A new P-heterocyclic type of phosphonium–iodonium ylides based on dibenzophosphole

A novel mixed phosphonium–iodonium ylide was synthesized by alkylation of 5-phenyl-5H-dibenzophosphole with phenacyl bromide followed by deprotonation and oxidation of the resulting phosphonium ylide with (diacetoxyiodo)- benzene. The influence of the cyclic nature of the phosphonium moiety on the dynamic E/Z isomerism in the mixed ylide is discussed.     

Synthesis of transient and stable C-amino phosphorus ylides and their fragmentation into transient and stable carbenes

Only basic phosphines, such as tris(dimethylamino)phosphine, allow for the synthesis of a stable acyclic beta-amino phosphonium salt 1c, which upon deprotonation with butyllithium affords the corresponding stable C-amino phosphorus ylide 2c. In contrast, cyclic beta-amino phosphonium salts 5a and 5b are stable despite the presence of weakly basic triarylphosphine fragments. They are prepared by intramolecular insertion of the carbene center of (amino)(phosphonio)carbenes into the CH bond of a phosphorus substituent. Deprotonation of 5a leads to the corresponding cyclic C-amino phosphorus ylide 6a, which has been fully characterized including an X-ray diffraction study. Deprotonation of 5b affords enamine 8, probably via fragmentation of ylide 6b into transient carbene 7b and a subsequent 1,2-hydrogen shift. Transient cyclic C-amino phosphorus ylides 6c and 6d have been prepared by intramolecular addition of a carbanion generated by deprotonation of a phosphorus substituent. Three-membered heterocycle 6c rearranges into alkene 9, whereas the four-membered ring system undergoes a ring opening affording the stable carbene 7d. The latter results pave the route for the synthesis of various mixed carbene-phosphine bidentate ligands.     

金属串配合物[Ni3(L)4(NCS)2](L = dpa-, mpta-, mdpa-, mppa-)结构和磁性的理论研究

应用密度泛函理论BP86方法结合自然键轨道分析方法对具有分子导线潜在应用前景的金属串配合物[Ni₃(L)₄(NCS)₂](L = dpa^- (1), mpta^- (2), mdpa^- (3), mppa^- (4))进行研究,分析了桥联配体L对Ni―Ni相互作用和磁耦合性质的影响.结果得到: (1)配合物的基态均是对应于五重态(HS)的反铁磁(AF)单重态, HS的能量和结构与AF态相近, Ni₃⁶⁺链形成了三中心四电子σ键(σ₂σ_nb¹σ^*1). (2) dpa^-引入甲基成为mdpa^-,对Ni―Ni、Ni―N距离影响不大; 3H-吡咯环和噻唑环取代吡啶环后, N1―N2、Ni―Ni距离增大, Ni2―N2键长缩短,但噻唑环的影响较小;故Ni―Ni相互作用强度为1 ≈ 3 > 2 > 4. (3)预测了3和4的J_ab值为-103和-88 cm^-1,随Ni―Ni相互作用增强磁耦合效应增大. Ni―Ni相互作用越大,通过Ni₃⁶⁺链σ型轨道的直接磁耦合越强; Ni2―N2键越强,通过涉及桥联配体的间接磁耦合越强,直接磁耦合比间接磁耦合更强.     

Synthese und reaktivität von dienylmetall-verbindungen : XXVII. Ein einfacher weg zur synthese von cyclopentadienylcobalt(III)-dikationen

CpCo(CO)₂ is oxidised by [Cp₂Fe]BF₄ (Cp = C₅H₅) in the presence of neutral ligands L to give the dications [CpCoL₃]²⁺ (L = SMe₂, S(n-C₄H₉)₂, PMe₃, C₅H₅N, MeCN; Me = CH₃). In [CpCo(SMe₂)₃]²⁺, sulfane ligands are substituted by neutral ligands L, L---L and L---L---L, to give the complexes [CpCoL₃]²⁺ (L = SeMe₂, TeMe₂, PMe₃, P(OMe)₃, AsMe₃, SbMe₃, t-C₄H₉NC, C₅H₅N, MeCN), [Cp-Co(L---L)SMe₂]²⁺ (L---L = R₂P(CH₂)_nPR₂, n = 1, 2, R = C₆H₅; bipyridine, o-phenanthroline, neocuproin) and [CpCo(L---L---L)]²⁺ (L---L---L = RP(CH₂CH₂PR₂)₂, R = C₆H₅). The dications react with iodide resulting in the monocations [CpCoL₂I]⁺ and [CpCo(L---L)I]⁺. Azacobaltocinium cations [CpCo(C₄R₂H₂N)]⁺ (R = H, CH₃) are obtained by reaction of [CpCo(SMe₂)₃]²⁺ with metal pyrrolides.     

Diaminocarbene and phosphonium ylide ligands: a systematic comparison of their donor character

The coordinating properties of the diaminocarbene (A) and phosphonium ylide (B) ligand types have been investigated systematically through a test family of C,C-chelating ligands containing two moieties of either kind. The overall character of o-C6H4A(a)B(b) ligands (a + b = 2) has been analyzed from the IR CO stretching frequencies of isostructural complexes [(eta(2)-C6H4A(a)B(b))Rh(CO)2][TfO]. The test moieties A = NC2H2N(+)(Me)C(-) and B = Ph2P(+)CH2(-) were first considered. While the ligands bearing at least one diaminocarbene end (AA, a = 2 and AB, a = 1) could be generated (and trapped by complexation), the bis-ylide case BB (a = 0) proved to be awkward: treatment of the dication C6H4(P(+)Ph2Me)2 with n-BuLi indeed lead to the Schmidbaur's carbodiphosphorane Ph3PCPPh2Me, through an unprecendented ylido-pentacoordinated phosphorane which could be fully characterized by NMR techniques. The bis-ylide ligand type C6H4B2 could however be generated by bridging the phosphonium methyl groups by a methylene link (B2 = (P(+)Ph2CH(-))2CH2), preventing the formation of the analogous highly strained carbodiphosphorane. The three complexes [(eta(2)-C6H4A(a)B(b))Rh(CO)2][TfO] were fully characterized, including by X-ray diffraction analysis and (103)Rh NMR spectroscopy. Comparison of their IR spectra indicated that the A2 type bis-NHC ligand is less donating than the hybrid AB type, which is itself less donating than the B2 type bis-ylide ligand. The excellent linear variation of the nu(CO) frequencies vs a (= 0, 1, 2) shows that the coordinating moieties act in a pseudoindependent way. This was confirmed by DFT calculations at the B3PW91/6-31G**/LANL2DZ*(Rh) level. It is therefore demonstrated that a phosphonium ylide ligand is a stronger donor than a diaminocarbene ligand.     

Role of axial ligation on potentiometric response of Co(III) tetraphenylporphyrin-doped polymeric membranes to nitrite ions

Two types of Co(III) tetraphenylporphyrins, Co(III)TPPX (I) and Co(III)(N)TPPX (II), where X = C1⁻ or NO⁻₂ and N = C₅H₅N or C₆H₅CH₂C₅H₄N, are used as ionophores to prepare nitrite responsive polymeric membrane electrodes. The influence of the initial axial ligand (X⁻ and N) on the operative ionophore mechanism of these metalloporphyrins within the solvent polymeric membranes is examined. Results from potentiometric and electrodialysis experiments suggest that in the presence of nitrite in the test sample and internal solution, both types of Co (III) porphyrins studied (I and II) act as neutral carriers and that the addition of lipophilic cationic sites (e.g., tridodecylmethylammonium ions (TDMA⁺)) to the organic membrane is essential to improve the selectivity and long term stability of sensors prepared with these species. Membranes formulated with (I) or (II) in the nitrite form along with TDMACl in plasticized PVC films exhibit the following selectivity sequence: SCN⁻ > NO⁻₂ ˜ C1O⁻₄ > Sal⁻ > NO⁻₃ > Br⁻ > C1⁻. Membrane electrodes with added lipophilic cationic sites are shown to exhibit rapid, fully reversible and Nernstian response towards nitrite ions in the concentration range of 10⁻¹–10⁻⁵ M, with good long term stability.     

A novel entry into a new class of spiroheterocyclic framework: regioselective synthesis of dispiro[oxindole-cyclohexanone]pyrrolidines and dispiro[oxindole-hexahydroindazole]pyrrolidines

2,6-Bis(arylmethylidene)cyclohexanones undergo a regioselective 1,3-dipolar cycloaddition reaction with the azomethine ylide derived from isatin and sarcosine by a decarboxylative route affording a series of 1-N-methyl-spiro[2.3¹]oxindole-spiro[3.2¹¹]6¹¹-arylmethylidenecyclohexanone-4-aryl-pyrrolidines which were further annulated to give a series of novel 1-N-methyl-spiro[2.3¹]oxindole-spiro[3.7¹¹](3¹¹-aryl)Δ^111,711a-hexahydro-2H-indazole-4-aryl-pyrrolidines. The structures of which were established by spectroscopic techniques as well as single crystal X-ray analysis.     

Asymmetric Borohydride Reduction of Acetophenone Catalyzed by Chiral Salen-Co(Ⅱ) Complex Using Sodium Borohydride

Development of efficient catalytic asymmetric reactions is the most challenging task in current synthetic chemistry; much effort has been devoted to create the chiral metal complexes of asymmetric catalysis. In the last two decades' many brand-new ligands had been synthesized and their combination with various metal ions has been applied in asymmetric catalysis. However, most ligands have only narrow applications and their use is limited to some reactions. Exceptionally, a few ligands and their metal complexes such as binaphthol, semicollin,and binap show wide applicability. Chiral salen ligand is one of such ligands and their metal complexes are now used as the catalysts for a variety of asymmetric reactions such as epoxidation^[1], aziridination^[2], cyclopropanation^[3], Diels-Alder reaction^[4], asymmetric transfer hydrogenation of aromatic ketones^[5] and kinetic resolution of racemic epoxides^[6] and so on.     

Exploring the Coordination Properties of Phosphonium-Functionalized N-Heterocyclic Carbenes Towards Gold

Gold(I) complexes with N-heterocyclic carbene ligands functionalized with a pendant phosphonium moiety were synthesized by simple procedures. In particular, the simple addition of LiBr salt in the reaction media allows the formation of the NHC gold(I) mononuclear complexes, whilst in the absence of excess bromide ions the deprotonation of the methylene group in alpha position to the phosphonium group occurs, allowing the isolation of the dinuclear complexes with two C,C-bridging NHC-phosphonium ylide ligands. The complexes were characterized in solution with NMR spectroscopy and ESI-MS spectrometry, as well as in the solid state by means of single crystal X-ray diffraction analysis. Mononuclear gold(III) species were also isolated by Br₂ oxidative addition to the mononuclear gold(I) species and fully characterized. Preliminary results of the biological effects on MCF7 cancer cells are also reported.     

Novel Oxidative Coupling of 2-Naphthols to 1,1'-Bi-2-naphthols Catalysed by Solid Lewis Acids Using Atmospheric Oxygen as Oxidant

l,l'-Bi-2-naphthol derivatives have wide applications as chiral inducing agents for asymmetric synthesis.¹ There are many good methods for resolution of racemic binaphthols to give enantiomeric binaphthols.² Therefore, it is essential to established simple, convenient, economically and environmental-friendly methods for preparation of racemic l,l'-binaphthol derivatives. A number of methods have been developed for the oxidative coupling of 2-naphthols usually by using Fe³⁺, Cu²⁺ or Mn³⁺ as oxidants. The reaction were carried out in organic solvent,^3a in solid state^3b and in aqueous Fe³⁺ solution.^3c However, all those cases by employing excess, usually 2 equivalents of oxidant. The excess Fe³⁺, Cu²⁺ and the resulted Fe²⁺, Cu⁺ and HCl were not acceptable from a view point of environmental protection. Recently, Sakamoto et at⁴ and Kantam et at⁵ independently reported two catalytic oxidative coupling procedure for preparation of l,l'-binaphthols using aerial oxygen as oxidant and Cu²⁺-exchanged montmorillonite as catalysts. However, both procedures were by using some toxic chlorobenzene as solvent and long reaction time (>2 h) and high temperature(>140℃) were needed. Consquently, there is still a great demand for catalytic oxidative coupling 2-naphthols to generate binaphthols under mild conditions, environmentally friendly procedure and rapid process. Herein we report novel oxidative coupling of to 1,1-bi-2-naphthols (2a, 2b) catalysed by a number of supported reagents using aerial oxygen as oxidant. The results are listed in Table 1.     

A localized molecular orbital study on the bonding of> Mo3S4]2Mo> and> Mo3S4]CuI> versus (C6H6)2Cr and C6H6Cr(CO)3

The energy-localized CNDO/2 molecular orbitais have been calculated for the clusters containing molybdenum, > {Mo₃S₄₂Mo}⁸⁺ and> Mo₃S₄]CuI> ⁴⁺, versus the prototype arene-metal sandwich (C₆H₆)₂Cr and half-sandwich complexes C₆H₆Cr(CO)₃. The bonding characteristics of these compounds are described from a localization bonding viewpoint. There are two typical M-arene and M-[Mo₃S₄] bondings. One is formed by electron donation from the three-center two-electron π-bonds in the arene or [Mo₃S₄]⁴⁺ ligands into the vacant hybrid orbitais of the “stranger” metal atom. In the other M-arene or M-[Mo₃S₄] bond there is very little donation by the lone electron pair occupying the d AOs of the “stranger” metal atom to the arene or [Mo₃S₄]⁴⁺ ligands. The analogy of the ligand [Mo₃S₄]⁴⁺ in the clusters studied with the ligand benzene is also briefly discussed.     

Highly Uniform Alkali Doped Cobalt Oxide Derived from Anionic Metal-Organic Framework: Improving Activity and Water Tolerance for CO Oxidation

A sequence of alkali metal cation-exchanged Co metal-organic frameworks(Co-MOFs), therein after denoted as M@Co-MOF, M=Na⁺, K⁺, Rb⁺, and Cs⁺, was prepared and used as the precursors to obtain the corresponding alkali doped cobalt oxide(defined as M/Co₃O₄, M=Na⁺, K⁺, Rb⁺, and Cs⁺) through calcination under air atmosphere. The cobalt oxide modified by uniform alkali metals exhibited a significant promotion of catalytic activity for CO oxidation. The activity of M/Co₃O₄ decreased in the order of Cs⁺ > Na⁺ > K⁺ > Rb⁺. Experimental and theoretical results revealed that the anionic skeleton of Co-MOF could facilely adsorb alkali metal cations and play a crucial role in the formation of highly uniform alkali doped cobalt oxide. The further characterizations, such as temperature-programmed reduction of H₂(H₂-TPR), oxygen temperature-programmed desorption(O₂-TPD), X-ray photoelectron spectroscopy(XPS), and in situ diffuse reflectance infrared Fourier transform(DRIFT) spectra demonstrated that the enhanced catalytic activity is originated from the interfacial electron transfer as well as weakened the Co-O bond strength, which promoted oxygen desorption from Co₃O₄ and formation of cobalt species with the lower valence state. The Cs/Co₃O₄ catalyst was maintained for 60 h without deactivation and still showed a high activity in the presence of water.