Stereospecific Formation of Pentaamine Complexes of Co(III) with Terdentate 2,6-Bis(aminomethyl)pyridine

Some pentaamine complexes of Co(III) with 2,6-bis(aminomethyl)pyridine (bamp), a diamine ligand (or two ammonia ligands) and one unidentate ligand have been prepared (Table 1). In all these species, bamp remains coordinated meridionally under a variety of conditions as shown by ¹H- and ¹³C-NMR. spectroscopy and correlations by stereoretentive reaction cycles. The rates of amine proton exchange and of spontaneous aquation, Hg²⁺-induced aquation and base hydrolysis of some chloropentaamine complexes have been determined. They essentially follow the patterns observed for complexes with purely aliphatic amine ligands; the presence of a pyridine donor in these complexes does not suggest deviations from the mechanistic schemes usually proposed for the solvolytic reactions investigated.     

Recent advances in Ni−Al bimetallic catalysis for unreactive bond transformation

Ni-Al bimetallic catalysis proves to be an efficient catalytic strategy for unreactive bond transformations. Recently, chiral bifunctional ligands, especially amphoteric secondary phosphine oxide(SPO) ligand, are used for a more powerful synergistic effect in the bimetal-catalyzed reactions, providing not only milder reaction conditions and higher reactivity but also excellent reaction selectivity. Herein, we give a brief review on the development of Ni-Al bimetallic catalytic system and highlight recent advances in enantioselective Ni-Al bimetallic catalysis for unreactive bond transformation.     

General synthesis of meso-amidoporphyrins via palladium-catalyzed amidation

A series of meso-amidoporphyrins were facilely synthesized by direct reactions of meso-brominated porphyrins with amides via palladium-catalyzed amidation reaction. Using a combination of palladium precursor Pd(OAc)(2) or Pd(2)(dba)(3) and phosphine ligand Xantphos, both 5-bromo-10,20-diphenylporphyrin and 5,15-dibromo-10,20-diphenylporphyrin, as well as their zinc complexes, can be effectively coupled with a wide variety of amides to give the corresponding mono- and bis-substituted meso-amidoporphyrins in high yields under mild conditions. [reaction: see text]     

新型N-P配体的合成、表征及其在氢转移反应中的应用

利用2,3-二(二苯膦氧基)-1,3-丁二烯与胺的迈克尔加成反应,合成了单胺基及环胺基改性的有机氧化膦,经有机硅烷还原,制备出胺基取代的膦配体,所得化合物经NMR及单晶X射线衍射分析.考察了所得配体与Ru(PPh3)3Cl2组成的催化体系在苯乙酮氧转移反应中的催化活性,发现氧化膦与Ru原位形成的催化剂比其还原态的三价膦组成的催化剂催化活性还高,二胺基取代的二氧化膦配体具有较高的催化活性,TON可达273.而采用先制备催化剂再催化反应时配体6的钌络合物催化活性TON可达352.     

How bulky ligands control the chemoselectivity of Pd-catalyzed N-arylation of ammonia

Steric bulk has been recognized as a central design principle for supporting ligands in the widely utilized Buchwald–Hartwig amination. In a recent example, it was shown that a Pd-catalyst carrying a phosphine ligand can successfully aminate aryl halides using ammonia as the nitrogen source. Interestingly, the chemoselectivity of this reaction was found to depend on the steric demand of the phosphine ligand. Whereas a sterically less demanding phosphine affords diphenylamine as the major product, it was shown that the amination reaction can be stopped after the first amination to give aniline if a sterically more encumbering phosphine ligand is used. Density functional theory calculations were carried out to examine the relationship between the steric demand of the phosphine ligand and the chemoselectivity. It was found that the key feature that leads to the chemoselectivity is the ability of the phosphine ligand to rotate the biaryl moiety of the ligand away from the Pd-center upon amine addition to release some of the steric crowding from the Pd-coordination site.

Steric bulk has been recognized as a central design principle for ligands in the widely utilized Buchwald–Hartwig amination. This mechanistic study reveals how this steric effect manipulates the reaction pathway and determines the chemoselectivity.     

Preparation of N‐alkylpyridinium aryl ketone derivatives via the surfactant promoted cross‐coupling reaction of N‐alkylpyridiniumboronic acids with carboxylic anhydride in water at room temperature

The palladium (II) chloride catalyzed coupling reaction of N‐alkylpyridiniumboronic acids with benzoic anhydride was carried out smoothly in water to give high yields of ketones without the use of a phosphine ligand. The reaction was conducted under mild conditions at room temperature. In this article, by focusing on the Suzuki reaction, it is shown how this method can impact modern synthetic chemistry, making reactions faster, easier and cleaner. Copyright © 2009 John Wiley & Sons, Ltd.     

Versatile synthesis of meso-aryloxy- and alkoxy-substituted porphyrins via palladium-catalyzed C-O cross-coupling reactions

[reaction: see text] meso-Aryloxy- and alkoxy-substituted porphyrins were conveniently synthesized by direct reactions of meso-halogenated porphyrins with alcohols via palladium-catalyzed C-O cross-coupling reactions. Using a combination of palladium precursor Pd(OAc)(2) or Pd(2)(dba)(3) and phosphine ligand DPEphos or Xantphos allowed both 5-bromo-10,20-diarylporphyrin and 5,15-dibromo-10,20-diarylporphyrin, as well as their zinc complexes, to be effectively coupled with a variety of alcohols to give the corresponding mono- and bis-substituted meso-aryloxy/alkoxyporphyrins in moderate to high yields under mild conditions.     

Palladium-catalyzed cross-coupling reactions of 2-iodo-4-(phenylchalcogenyl)-1-butenes

[reaction: see text] 2-Iodo-4-(phenylchalcogenyl)-1-butenes 2 or 3, which are derived from the ring-opening reaction of methylenecyclopropanes (MCPs) 1 by iodine, can be applied to some palladium-catalyzed cross-coupling reactions such as the Sonogashira, Heck, Kumada, Suzuki, and Negishi reactions under mild conditions to give the corresponding coupling products in good yields. These reactions proceeded smoothly at room temperature (20 degrees C) in most cases without any phosphine ligand and additive. The phenylchalcogenyl group plays an important role in the reactions and a plausible reaction mechanism has been proposed.     

Reactions and crystal structures of heterodinuclear complexes R3Sn-M（CO）5 （M = Mn, Re） with some nitrogen ligands

Some reactions of R_3SnM(CO)_5(M = Mn,Re) with CH_3CN or pyridine were investigated to give complexes R_3SnMn(CO)_3LL′or R_3SnMn(CO)_4L by a facile mild method.X-ray diffractions analyses show that,in contrast to the phosphine ligand occupying in axial position,nitrogen ligands occupy equatorial position.     

Room temperature asymmetric Pd-catalyzed methoxycarbonylation of norbornene: highly selective catalysis and HP-NMR studies

Palladium complexes bearing monodentate and bidentate phosphine ligands (1-7) were synthesised and used as catalyst precursors in the methoxycarbonylation of norbornene. The catalytic systems bearing ligands 1, 3 and 4 afforded excellent conversions (>99%) and selectivity of the ester (>99%). NMR investigations showed that using complex 1a as the precursor resulted in the protonated phosphine, 1-H(+), being formed under catalytic conditions and thus the addition of acid is not required for the activation of this system since the reaction involving the precursor with methanol under CO pressure produces 2 equivalents of HCl and leads to the formation of the active species. The protonation of ligand 4 under methoxycarbonylation conditions was also observed and the diprotonated diphosphine was isolated and characterised. This compound was tested as a ligand and acid source in a catalysis and provided excellent conversion and high selectivity to the ester.     

Chiral induction effects in ruthenium(II) amino alcohol catalysed asymmetric transfer hydrogenation of ketones: an experimental and theoretical approach

The enantioselective outcome of transfer hydrogenation reactions that are catalysed by ruthenium(II) amino alcohol complexes was studied by means of a systematically varied series of ligands. It was found that both the substituent at the 1-position in the 2-amino-1-alcohol ligand and the substituent at the amine functionality influence the enantioselectivity of the reaction to a large extent: enantioselectivities (ee values) of up to 95% were obtained for the reduction of acetophenone. The catalytic cycle of ruthenium(II) amino alcohol catalysed transfer hydrogenation was examined at the density functional theory level. The formation of a hydrogen bond between the carbonyl functionality of the substrate and the amine proton of the ligand, as well as the formation of an intramolecular H...H bond and a planar H-Ru-N-H moiety are crucially important for the reaction mechanism. The enantioselective outcome of the reaction can be illustrated with the aid of molecular modelling by the visualisation of the steric interactions between the ketone and the ligand backbone in the ruthenium(II) catalysts.     

Mild and room temperature C-C bond forming reactions of nucleoside C-6 arylsulfonates

[reaction: see text] Palladium catalyzed cross coupling of nucleoside arylsulfonates and arylboronic acids has been accomplished under mild conditions and at room temperature. Among three structurally similar ligands that differ in their steric and electronic properties, one yielded an effective catalyst in conjunction with Pd(OAc)2. Of the nucleoside arylsulfonates evaluated, the O6-(2,4,6-trimethylphenyl)sulfonate proved optimal, but other alkyl and alkoxy derivatives were also reasonably reactive. On the other hand, a 2-nitrophenyl and a 2-thienyl derivative were ineffective substrates. PhMe and THP were suitable as solvents, yielding good results in several cases, although reactions of some arylboronic acids were faster in PhMe. In contrast, reactions of arylboronic acids bearing strongly electron-withdrawing groups proceeded more successfully in THP. Interplay between several factors that include substituents on the nucleoside arylsulfonate, ligand substituents, and solvent is responsible for successful cross coupling. Using 31P NMR, an initial investigation has been conducted to study the interaction of Pd(OAc)2 with the ligand. At a 1:1 stoichiometry of ligand and Pd(OAc)2, a predominant species, likely a cyclopalladation product, was obtained. At a 2:1 ratio of ligand and Pd(OAc)2, a different species bearing chemically distinct phosphine ligands was observed. Both complexes display catalytic activity, although the 2:1 species may be superior.     

Synthesis and characterization of a polymer-anchored palladium(II) Schiff base complex and its catalytic efficiency in phosphine-free Sonogashira coupling reactions

A polymer-anchored Pd(II) Schiff base complex has been synthesized by reacting a polymeric amine with 2-pyridinecarboxaldehyde to get the polymer-anchored Schiff base, which was then reacted with palladium acetate. The catalyst was characterized by physicochemical and spectroscopic methods. It shows excellent catalytic activity in the Sonogashira coupling of phenylacetylene with aryl halides using triethylamine as a base and copper iodide as a co-catalyst in water under open air at 70 °C. We have also studied the effects of base and solvent on the coupling reaction. Sonogashira reactions of phenylacetylene with a variety of functionalized aryl halides were performed under the optimized reaction conditions. This catalyst gives excellent yields without the use of phosphine ligands. Further experiments showed that the catalyst can be used five times without much loss in the catalytic activity.     

A highly modular and convergent approach for the synthesis of stimulant-responsive heteroligated cofacial porphyrin tweezer complexes

The synthesis of new hemilabile phosphine ligands and their reaction with [Rh(COE)2Cl]2 to form dissymmetric heteroligated tweezer complexes using a halide-induced ligand rearrangement reaction are reported. These complexes can undergo reactions with small-molecule ligands and elemental anions quantitatively in situ, which serve to regulate the porphyrin-porphyrin distances and interactions within the assembly.     

Insights into the origin of high activity and stability of catalysts derived from bulky, electron-rich monophosphinobiaryl ligands in the Pd-catalyzed C-N bond formation

A comparative kinetic examination of catalyst systems based on several monophosphinobiaryl ligands is reported. The bulk of the phosphine ligand controls the catalytic activity and the rate of catalyst activation with the catalyst based on 2-dicyclohexylphosphino-2',4',6'-triisopropylbiphenyl providing the greatest activity and fastest activation. In the case where catalyst activation is slow (i.e., use of the smaller ligands such as 2-dicyclohexylphosphino-2'-methylbiphenyl in combination with Pd(OAc)2) stirring the amine with the catalyst/base mixture prior to the commencement of the reaction increases the reaction rate along with the rate of catalyst activation. Kinetic isotope effects established that the catalyst activation process occurs through a beta-hydride elimination pathway.     

Easy access to esters with a benzylic quaternary carbon center from diallyl malonates by palladium-catalyzed decarboxylative allylation

Diallyl 2-alkyl-2-arylmalonates underwent palladium-catalyzed decarboxylative allylation quickly under mild conditions. In contrast, no reaction took place with diallyl 2,2-dialkylmalonates under the same conditions. Electron-donating phosphine ligands were found to be vital for this reaction. Most of the solvents used did not affect the catalytic cycle. Catalysis in [bmim][BF4], a well-known ionic liquid, was inhibited as a result of formation of a hydrogen bond between a carboxylate anion and a [bmim]+ cation; however, the reaction in [bdmim][BF4], in which the acidic proton of [bmim][BF4] was replaced with a methyl group, proceeded smoothly. The catalytic mechanism was investigated using a tetradeuterated substrate and an enzymatically synthesized enantio-enriched allyl methyl 2-methyl-2-phenylmalonate. Even the electron-deficient phosphite ligand was found to be active for catalysis of diallyl 2-methyl-2-(2- or 4-nitrophenyl)malonates.     

One-step multi-electron transfer mechanism of polynuclear copper complexes for molecular conversions

The oxidative coupling reaction of 2,6-dimethylphenol may result in either a desired polymeric substance (i.e. the polyphenylene ether, PPE) or the undesired “dimeric” species diphenoquinone, DPQ. The relative amounts of each product depend on the experimental conditions and the used catalytic system. Usually copper amine compounds are used as a catalyst for the oxidative coupling reactions. They have the advantage of easy access and produce high yields of high molecular PPE; however, other metal coordination compounds, like those of Mn, may also be used as catalysts. The present paper focuses on mechanistic studies with various copper (aliphatic and aromatic) amine compounds as catalysts. Owing to the steric constraints of the amine ligands, dinuclear Cu(II) compounds, with small bridging anionic ligands, are easily formed. Such species are believed to be the catalyst precursors. Upon addition of a base (1:1 on copper) and excess phenol, phenolate ligands coordinate as bridging ligands to copper. After a two-electron transfer reaction, the resulting phenoxonium ligand, which is a rather poor ligand, remains attached to the Cu(I), probably coordinating via its aromatic ring. Nucleophilic attack by a phenol to the phenoxonium ion at the 4-position is likey to be most important to the coupling reaction. In the beginning of the reaction the undesired side product DPQ is also formed via a C–C coupling reaction. With copper(II) compounds containing imidazole-type chelating ligands, good activity was obtained; in the case of pyrazole-based and bridging S-donor chelating ligands, that no or very weak activity was found. In a study of the mechanism of the propagation reaction the rate-determining reaction was thought to be probably a one-step, two-electron transfer, during which the two Cu(II) ions in the dinuclear complex oxidize the phenolate to phenoxonium. After the phenoxium ion is formed the bonding with the (then) Cu(I) species is weakened and the reactions with phenolic end groups can take place. The effect of the amine ligands appears to be both steric and electronic. With certain ligands the reoxidationof the reduced catalyst is not possible.     

Facile and efficient synthesis of meso-arylamino- and alkylamino-substituted porphyrins via palladium-catalyzed amination

meso-Arylamino- and alkylamino-substituted porphyrins were efficiently synthesized by reactions of meso-halogenated porphyrins with amines via palladium-catalyzed amination. The combination of palladium acetate and the commercially available phosphine ligand bis(2-diphenylphosphinophenyl) ether (DPEphos) is effective for catalyzing the couplings of both [5-bromo-10,20-diphenyl porphyrino]zinc(II) and [5,15-dibromo-10,20-diphenylporphyrino]zinc(II) with amines to give the corresponding monoamino- and diamino-substituted porphyrins in high yields under mild conditions. The corresponding halogenated free-base porphyrins also underwent the cross-coupling reactions efficiently under similar catalytic conditions.     

The Different,but Interesting Behaviors of Benzyl Systems in the Willgerodt-Kindler Reaction under Solvent-Free Conditions

On the benzyl system, bearing various functional groups, have been carried out the Willgerodt-Kindler reaction to obtain thiobenzmorpholide ( 1 ). The reactions, under solvent-free conditions, were performed in both classical (reflux, room temperature) and nonclassical (microwave) conditions to attempt our elucidation of the reactions pathways. Unlike benzylamine and benzyl mercaptan, benzyl halides give poor result due to the type of amine. The experimental results suggest that the proposed reaction pathway involves the oxidation coupling of benzylic substrates, followed by a thiolation step and an attack of the amine on the thiolated product to give ( 1 ).