Palladaphosphacyclobutenes as catalysts in Heck and Suzuki reactions

Heck reactions of aryl halides with various olefins and Suzuki reactions of aryl halides with phenylboronic acid catalyzed by palladaphosphacyclobutene have been investigated. The scope of the Heck reaction has been investigated in N,N‐dimethylacetamide at 140 °C using NaOAc as base. Using 0.1% molar ratio of palladaphosphacyclobuyenes, aryl bromides were converted into 1,2‐substitutedethene products in good to high yields through coupling with both vinylarenes and acrylates. Actived aryl chloride reacted with styrene to afford 1,2‐substitutedethene products in moderate yields. The scope of the Suzuki reaction has been conducted in toluene at 110 °C using Cs₂CO₃ as base. Using 0.1% molar ratio of palladaphosphacyclobutene, aryl bromides reacted with phenylboronic acid to afford diaryl derivatives in excellent yield. Copyright © 2008 John Wiley & Sons, Ltd.     

Reverse atom transfer radical polymerization of methyl methacrylate initiated by p‐chlorobenzenediazonium tetrafluoroborate

The controlled polymerization of methyl methacrylate (MMA) in bulk was initiated with p‐chlorobenzenediazonium tetrafluoroborate ( 1 ) and Cu(II) or Cu(I)/Cu(II)/N,N,N′,N″,N″‐pentamethyldietylene triamine (PMDETA) complex system at various temperatures (20, 60, and 90 °C). The proposed polymerization mechanism is based on the Meerwein‐type arylation reaction followed by a reverse atom transfer radical polymerization. In this mechanism, aryl radicals formed by the reaction with 1 and Cu(I) and/or PMDETA initiated the polymerization of MMA. The polymerization is controlled up to a molecular weight of 46,000 at 90 °C. Chain extension was carried out to confirm the controlled manner of the polymerization system. In all polymerization systems, the polydispersity index and initiator efficiency ranged from 1.10–1.57 to 0.10–0.21, respectively. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2019–2025, 2003     

Editing of H2BC NMR spectra

New versions of the H2BC pulse sequence (Nyberg NT, Duus JØ, Sørensen OW. J. Am. Chem. Soc. 2005; 127: 6154) that edit into two subspectra according to the number of protons attached to ¹³C nuclei being odd or even are introduced. These sequences can be useful for resolving spectral overlap, which is demonstrated on the molecule prednisolone [(11 β)‐11,17,21‐trihydroxypregna‐1,4‐diene‐3,20‐dione] Copyright © 2005 John Wiley & Sons, Ltd.     

Base‐Free Conditions for Rhodium‐Catalyzed Asymmetric Arylation To Produce Stereochemically Labile α‐Aryl Ketones

The asymmetric arylation of 2,2‐dialkyl cyclopent‐4‐ene‐1,3‐diones with aryl boronic acids was found to be efficiently catalyzed by a chiral diene–rhodium μ‐chloro dimer, [{RhCl((R)‐diene*)}₂], in the absence of bases in toluene/H₂O to give 2,2‐dialkyl 4‐aryl cyclopentane‐1,3‐diones in high yields with high enantioselectivity. Such compounds can not be obtained with high enantiomeric purity under the standard basic conditions used for rhodium‐catalyzed asymmetric arylation because the α‐aryl ketone products undergo racemization under the basic conditions.     

Understanding the Role of Water in Aqueous Ruthenium‐Catalyzed Transfer Hydrogenation of Ketones.

We report an accurate computational study of the role of water in transfer hydrogenation of formaldehyde with a ruthenium‐based catalyst using a water‐specific model. Our results suggest that the reaction mechanism in aqueous solution is significantly different from that in the gas phase or in methanol solution. Previous theoretical studies have shown a concerted hydride and proton transfer in the gas phase (M. Yamakawa, H. Ito, R. Noyori, J. Am. Chem. Soc. 2000 , 122, 1466–1478;J.‐W. Handgraaf, J. N. H. Reek, E. J. Meijer, Organometallics 2003 , 22, 3150–3157; D. A. Alonso, P. Brandt, S. J. M. Nordin, P. G. Andersson, J. Am. Chem. Soc. 1999 , 121, 9580–9588; D. G. I. Petra, J. N. H. Reek, J.‐W. Handgraaf, E. J. Meijer, P. Dierkes, P. C. J. Kamer, J. Brussee, H. E. Schoemaker, P. W. N. M. van Leeuwen, Chem. Eur. J. 2000 , 6, 2818–2829), whereas a delayed, solvent‐mediated proton transfer has been observed in methanol solution (J.‐W. Handgraaf, E. J. Meijer, J. Am. Chem. Soc. 2007 , 129, 3099–3103). In aqueous solution, a concerted transition state is observed, as in the previous studies. However, only the hydride is transferred at that point, whereas the proton is transferred later by a water molecule instead of the catalyst.     

Synthesis of polymers possessing tetraphenylethylene units by three‐component coupling reactions of poly(p‐phenylene ethynylene) derivative with aryl halides and phenylboronic acid

A derivative of poly(p‐phenylene ethynylene) was subjected to the palladium‐catalyzed three‐component coupling reactions with aryl halides and phenylboronic acid to obtain polymers having tetrasubstituted cis‐vinylene units. For example, 69% of the acetylene units in the prepolymer were converted to cis‐vinylene (i.e., tetrasubstituted cis‐vinylene) units using iodobenzene and phenylboronic acid (5 equiv each with respect to acetylene units). In the UV–vis absorption spectra of the resulting polymers, clear hypsochromic shifts of the absorption maxima were observed, while bathochromic shifts and suppression of the efficiency were observed in their photoluminescence spectra. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 787–791     

Gold‐Catalyzed Suzuki Coupling of ortho‐Substituted Hindered Aryl Substrates

A method that allows hindered ortho ‐substituted aryl iodides to be efficiently coupled to phenylboronic acid using a gold‐catalyzed C−C bond formation is presented. The use of a molecularly‐defined dinuclear gold chloride catalytic precursor that is stabilized by a new tetradentate (N ,N′ )‐diamino‐(P,P′ )‐diphosphino ferrocene hybrid ligand in a Suzuki‐type reaction is described for the first time. Electron‐rich isopropyl groups on phosphorus were found essential for a superior activity, while the performances of a set of analogous gold dinuclear complexes that were fully characterized by multinuclear NMR spectroscopy and XRD analysis, were investigated. Therefore, arylation of para and ortho ‐substituted iodoarenes bearing electron‐rich, electron‐poor functional groups, and even hindered polycyclic aromatic compounds is described.     

Behavior of 3(2‐pyridinylmethylene)‐5‐aryl‐2(3H)‐furanones and 3(3‐pyridinylmethylene)‐5‐aryl‐2(3H)‐furanones as alkylating agents: A comparative study

3(2‐pyridinylmethylene)‐5‐aryl‐2(3H)‐furanones and 3(3‐pyridinylmethylene)‐5‐aryl‐2(3H)‐furanones were prepared as a mixture of (E) and (Z) stereoisomers by condensing pyridine‐2‐carboxaldehyde and pyridine‐3‐carboxaldehyde with 3‐aroylpropionic acids. The reaction of the furanones 6 and 7 with anhydrous aluminium chloride in benzene led to the formation of 4,4‐diaryl‐1‐(2‐pyridinyl)but‐1,3‐diene ( 8 ) and 4,4‐diaryl‐1‐(3‐pyridinyl)but‐1,3‐diene ( 9 ) as mixtures of geometrical (E,E‐ and E,Z‐) stereoisomers via an intermolecular alkylation mode. When the reaction was carried out in tetrachloroethane as a solvent, the reaction of 6 gave 5‐arylquinoline‐7‐carboxylic acid via intramolecular alkylation mode. This may be considered as a novel method for the synthesis of quinoline derivatives. J. Heterocyclic Chem., (2011).     

N‐methyliminodiacetic acid as a simple and highly efficient ligand for palladium‐catalyzed Suzuki–Miyaura cross‐coupling of aryl chlorides

A simple, air‐stable, inexpensive and easily prepared molecule, N‐methyliminodiacetic acid (MIDA), is reported as a ligand for palladium‐catalyzed Suzuki–Miyaura cross‐coupling reaction of phenylboronic acid with aryl chlorides. The yield of the corresponding Suzuki coupling reaction is up to around 90% at both high temperature of 80°C and room temperature under ambient atmosphere. Copyright © 2015 John Wiley & Sons, Ltd.     

The Suzuki cross‐coupling reaction in pure water catalyzed by ligandless palladium using polyethylene glycol derivatives as surfactant

The results of a ligandless Pd(OAc)₂‐catalyzed Suzuki–Miyaura coupling experiment are presented. It was found that the use of polyethylene glycol phosphonium salts (PEG‐quat) as surfactant resulted in very rapid reactions of aryl halides with phenylboronic acids in pure water. Moreover, aryl chlorides such as 4‐nitrochlorobenezene reacted quantitatively with phenylboronic acid under optimized conditions. Copyright © 2013 John Wiley & Sons, Ltd.     

Diels–Alder adducts of maleic ­anhydride and dienes: new compounds by crystallization

We have determined the crystal structures of bi­cyclo­[2.2.1]­hept‐2‐ene‐endo‐cis‐5,6‐di­carboxyl­ic anhydride, C₉H₈O₃, (I), 1,2,3,4,7,7‐hexa­chloro­bi­cyclo­[2.2.1]­hept‐2‐ene‐endo‐cis‐5,6‐di­carboxyl­ic anhydride diethyl ether solvate, C₉H₂Cl₆O₃·0.16­C₄H₁₀O, (II), bi­cyclo­[2.2.1]­hept‐2‐ene‐endo‐cis‐5,6‐di­carboxyl­ic acid, C₉H₁₀O₄, (III), 1,2,3,4,7,7‐hexa­chloro­bi­cyclo­[2.2.1]­hept‐2‐ene‐endo‐cis‐5,6‐di­carboxyl­ic acid, C₉H₄Cl₆O₄, (IVa) and (IVb), and ethyl 1,2,3,4,7,7‐hexa­chloro‐6‐carboxybi­cyclo­[2.2.1]­hept‐2‐ene‐endo‐cis‐5‐carboxyl­ate monohydrate, C₁₁H₈Cl₆O₄·H₂O, (V). Compounds (I) and (II) were prepared by a standard Diels–Alder reaction from maleic anhydride and cyclo­penta­diene or hexa­chloro­cyclo­penta­diene, respectively. The crystal‐growing processes of these compounds led to surprising results: rapid recrystallization of (I) from diethyl ether and (II) from petroleum ether gave crystals of these compounds, however, crystallization by slow evaporation techniques using common solvents yielded new compounds in which the five‐membered heterocycle has been cleaved.     

Redox initiated cationic polymerization: Silane‐N‐aryl heteroaromatic onium salt redox couples

In this article, a new route for the synthesis of N‐aryl heteroaromatic onium salts by the direct copper catalyzed arylation of pyridine, substituted pyridines, isoquinoline, and acridine with diaryliodonium salts is described. It was demonstrated that these N‐aryl heteroaromatic onium salts undergo facile platinum or rhodium‐catalyzed reduction by silanes bearing Si? H groups. The reduction of N‐aryl heteroaromatic onium salts generates Brønsted acids. When this redox reaction was carried out in situ in the presence of an appropriate monomer, cationic polymerization was observed. Using this approach, the cationic polymerizations of epoxides, oxetanes, 1,3,5‐trioxane, styrene, and vinyl ethers were carried out. The use of optical pyrometry to monitor the redox initiated cationic polymerizations of some representative multifunctional monomers is described. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

PdII‐Catalyzed Mild CH ortho Arylation and Intramolecular Amination Oriented by a Phosphinamide Group

A novel protocol for the Pd‐catalyzed ortho‐arylation of aryl phosphinamide with boronic acid is reported. By using phosphinamide as a new directing group, the reaction proceeds efficiently under mild conditions at 40 °C. Mechanistic studies reveal that the reaction proceeds via a Pd^II to Pd⁰ cycle. The phosphinamide group is also shown to be an effective orienting group for direct C?H amination.     

Suzuki–Miyaura coupling reactions of aryl chlorides catalyzed by a new nickel(II) σ‐aryl complex

A new nickel(II) σ‐aryl complex, trans‐chloro(9‐phenanthrenyl)bis(triphenylphosphine)nickel(II), was used as a precatalyst for the Suzuki–Miyaura coupling reactions of aryl chlorides. The catalytic conditions were optimized by investigating the cross‐coupling of p‐chloroanisole with phenylboronic acid. The results show that this complex is efficient for both electron‐rich and electron‐deficient aryl chlorides, though it gives better yields for activated arylboronic acids than deactivated ones. All isolated cross‐coupled biaryl products have been characterized by ¹H and ¹³C NMR, and their spectral data are consistent with those reported. Side products from the coupling of arylboronic acid with the precatalyst complex have also been isolated and characterized, which is helpful for understanding the coupling mechanism. Copyright © 2013 John Wiley & Sons, Ltd.     

Revealing noncovalent interactions in quantum crystallography: Taurine revisited

The charge density distribution in taurine (2‐aminoethane‐sulfonic acid) is further studied with the molecular orbital occupation number refinement scheme. The recently proposed NCIPLOT scheme (Johnson et al., J. Am. Chem. Soc. 2010, 132, 6498) is applied to visualize the noncovalent interactions from experimentally refined charge densities. Herein, we demonstrate the evolution of the reduced density gradient isosurface during the charge density refinement process. © 2012 Wiley Periodicals, Inc.     

Highly efficient orthopalladated complexes of second and third benzyl amine for catalyzing the Suzuki cross‐coupling reaction

In this work, ortho‐palladated complexes [Pd(µ‐Cl)(C₆H₄CH₂ NRR′‐κ²‐C,N)]₂ and [Pd(C₆H₄CH₂NH₂‐2‐C,N)Cl(Y)] were tested in the Suzuki–Miyaura cross‐coupling reaction. Cyclopalladated Pd(II) complexes as thermally stable catalysts can activate aryl bromides and chlorides. These complexes were active and efficient catalysts for the Suzuki–Miyaura reaction of aryl bromides and even less reactive aryl chlorides. The cross‐coupled products of a variety of aryl bromides and aryl chloride with phenylboronic acid in methanol as solvent at 60 °C were produced in excellent yields. Copyright © 2010 John Wiley & Sons, Ltd.     

Dimethyl‐ and diethyl­dithio­cyanato­tin(IV)

The structures of dimethyl­dithio­cyanato­tin(IV), [Sn(CH₃)₂(NCS)₂], and diethyl­dithio­cyanato­tin(IV), [Sn(C₂H₅)₂(NCS)₂], have been determined. The dimethyl derivative has 2mm crystallographic symmetry and the diethyl derivative has twofold crystallographic symmetry. The experimental differences in the distances and angles around the Sn atom between the two structures agree reasonably well with the differences expected from the reaction path mapped previously [Britton & Dunitz (1981). J. Am. Chem. Soc. 103 , 2971–2979].     

Water‐Soluble and Recyclable Cyclopalladated Ferrocenylimine for Suzuki Coupling Reaction

A series of new water‐soluble cyclopalladated ferrocenylimines were designed and prepared. They were efficient catalyst for Suzuki coupling reactions of aryl bromides and phenylboronic acid in neat water under ambient atmosphere. Among of these catalysts, the catalyst ( C₂D ) could be reused for 6 times for the Suzuki coupling reaction of 4‐bromotoluene with phenylboronic acid in EtOH/H₂O under ambient atmosphere, in which no significant loss activity of C₂D was observed.     

Ligand‐Enabled Auxiliary‐Free meta‐C−H Arylation of Phenylacetic Acids

The meta ‐C−H arylation of free phenylacetic acid was realized using 2‐carbomethoxynorbornene (NBE‐CO₂Me) as a transient mediator. Both the modified norbornene and the mono‐protected 3‐amino‐2‐hydroxypyridine type ligand are crucial for this auxiliary‐free meta ‐C−H arylation reaction. A series of phenylacetic acids, including mandelic acid and phenylglycine, react smoothly with various aryl iodides to provide the meta ‐arylated products in high yields.     

Cavity‐Shaped Ligands: Calix[4]arene‐Based Monophosphanes for Fast Suzuki–Miyaura Cross‐Coupling

Five conical calix[4]arenes that have a PPh₂ group as the sole functional group anchored at their upper rim were assessed in palladium‐catalysed cross‐coupling reactions of phenylboronic acid with aryl halides (dioxane, 100 °C, NaH). With arylbromides, remarkably high activities were obtained with the catalytic systems remaining stable for several days. The performance of the ligands is comparable to a Buchwald‐type triarylphosphane, namely, (2′‐methyl[1,1′‐biphenyl]‐2‐yl)diphenylphosphane, which in contrast to the calixarenyl phosphanes tested may display chelating behaviour in solution. With the fastest ligand, 5‐diphenylphosphanyl‐25,26,27,28‐tetra(p‐methoxy)benzyloxy‐calix[4]arene ( 8 ), the reaction turnover frequency for the arylation of 4‐bromotoluene was 321 000 versus 214 000 mol(ArBr).mol(Pd)^?1. h^?1 for the reference ligand. The calixarene ligands were also efficient in Suzuki cross‐coupling reactions with aryl chlorides. Thus, by using 1 mol % of [Pd(OAc)₂] associated with one of the phosphanes, full conversion of the deactivated arenes 4‐chloroanisole and 4‐chlorotoluene was observed after 16 h. The high performance of the calixarenyl–phosphanes in Suzuki–Miyaura coupling of aryl bromides possibly relies on their ability to stabilise a monoligand [Pd⁰L(ArBr)] species through supramolecular binding of the Pd‐bound arene inside the calixarene cavity.