Stereoinvertive C–C Bond Formation at the Boron-Bound Stereogenic Centers through Copper-Bipyridine-Catalyzed Intramolecular Coupling of α-Aminobenzylboronic Esters

Enantiospecific intramolecular Suzuki–Miyaura-type coupling with α-(2-halobenzoylamino)benzylboronic esters to give 3-substituted isoindolinones is achieved by using copper catalysts with 2,2′-bipyridine-based achiral ligands. Enantioenriched α-aminobenzylboron reactants bearing a hydrogen atom at the boron-bound stereogenic carbons undergo stereoinvertive coupling in the presence of a 6-phenyl-2,2′-bipyridine ligand with high enantiospecificity. α-Aminobenzylboronates bearing fully substituted boron-bound stereogenic centers also gave the 3,3-disubstituted isoindolinones with stereospecific stereochemical inversion in the presence of simple 2,2′-bipyridine as a ligand.     

Bipyridine‐Modulated Palladium‐Catalyzed Oxidative Heck‐Type Reactions of Arylboronic Acids with Olefins

We have demonstrated that 4,4′‐dimethyl 2,2′‐bipyridine as ligand for Pd(II) catalysts was very efficient for oxidative Heck‐type coupling reaction of arylboronic acids with olefins in DMA or CH₃CN under atm air at 80 °C. The presence of chelated bipyridine ligand isindispensable to achieve high reaction yields and to suppress the formation of biphenyl as homocoupled byproduct.     

Synthesis and photophysical properties of novel amphiphilic ruthenium (II) complexes containing 4,4′‐dialkylaminomethyl‐2,2′‐bipyridyl ligands

The synthesis of a number of new 2,2′‐bipyridine ligands functionalized with bulky amino side groups is reported. Three homoleptic polypyridyl ruthenium (II) complexes, [Ru(L)₃]²⁺ 2(PF₆^?), where L is 4,4′‐dioctylaminomethyl‐2,2′‐bipyridine (Ru4a), 4,4′‐didodecylaminomethyl‐2,2′‐bipyridine (Ru4b) and 4,4′‐dioctadodecylaminomethyl‐2,2′‐bipyridine (Ru4c), have been synthesized. These compounds were characterized and their photophysical properties examined. The electronic spectra of three complexes show pyridyl π → π* transitions in the UV region and metal‐to‐ligand charge transfer bands in the visible region. Copyright © 2005 John Wiley & Sons, Ltd.     

Copper‐Catalyzed γ‐Selective and Stereospecific Allylic Cross‐Coupling with Secondary Alkylboranes

The scope of the copper‐catalyzed coupling reactions between organoboron compounds and allylic phosphates is expanded significantly by employing triphenylphosphine as a ligand for copper, allowing the use of secondary alkylboron compounds. The reaction proceeds with complete γ‐E‐selectivity and preferential 1,3‐syn stereoselectivity. The reaction of γ‐silicon‐substituted allylic phosphates affords enantioenriched α‐stereogenic allylsilanes.     

Dimethyl 2,2′‐bipyridine‐6,6′‐dicarboxylate and bis(dimethyl 2,2′‐bipyridine‐6,6′‐dicarboxylato‐κ2N,N′)copper(I) tetrafluoroborate

The single‐crystal X‐ray structures of dimethyl 2,2′‐bipyridine‐6,6′‐dicarboxylate, C₁₄H₁₂N₂O₄, and the copper(I) coordination complex bis(dimethyl 2,2′‐bipyridine‐6,6′‐dicarboxylato‐κ²N,N′)copper(I) tetrafluoroborate, [Cu(C₁₄H₁₂N₂O₄)₂]BF₄, are reported. The uncoordinated ligand crystallizes across an inversion centre and adopts the anticipated anti pyridyl arrangement with coplanar pyridyl rings. In contrast, upon coordination of copper(I), the ligand adopts an arrangement of pyridyl donors facilitating chelating metal coordination and an increased inter‐pyridyl twisting within each ligand. The distortion of each ligand contrasts with comparable copper(I) complexes of unfunctionalized 2,2′‐bipyridine.     

An Easy One‐Pot Synthesis of Diverse 2,5‐Di(2‐pyridyl)pyrroles: A Versatile Entry Point to Metal Complexes of Functionalised,Meridial and Tridentate 2,5‐Di(2‐pyridyl)pyrrolato Ligands

A wide variety of 2,5‐di(2‐pyridyl)pyrroles (dppHs) substituted at the C3 and C4 positions of the pyrrole core were obtained by direct condensation of a 2‐pyridylcarboxaldehyde (2 equiv), an α‐methylene ketone with at least one electron‐withdrawing substituent and ammonium acetate. A novel 2,5‐di(1,10‐phenanthrolin‐2‐yl)pyrrole was also characterised. The dppHs provide a direct, quick entry to dipyridylpyrrolato (dpp^?)–metal complexes. The meridial tridentate dpp^? ligand is a useful anionic analogue of the terpyridyl ligand. The first (dpp)Ru complexes are described; the 3,4‐substitution of the central pyrrole significantly perturbs the potentials of the redox processes of these complexes. A [(dpp)Ru(bpy)(MeCN)]⁺ (bpy=2,2′‐bipyridine) complex is an electrocatalyst for the reductive disproportionation of carbon dioxide to carbon monoxide and the carbonate ion.     

Synthesis,Coordination, and Spectroscopic Properties of 2,2′‐Bipyridyldimesitylpalladium(II) and 6‐Mesityl‐2,2′‐bipyridyldimesitylpalladium(II)

The synthetic route to the dimesitylpalladium(II) complex [(bpy)PdMes₂] ( 1 ) (Mes = mesityl = 2,4,6‐trimethyl phenyl) does not only give the desired compound but also the 6‐mesityl‐2,2′bipyridyldimesitylpalladium [(6‐Mes‐bpy)PdMes₂] ( 2 ) complex and the free ligand 6,6′‐dimesityl‐2,2′‐bipyridine in reasonable yields. Single crystals of 2 were examined by X‐Ray diffraction. The compound reveals a sterically crowded molecular structure. An intramolecular π‐stacking interaction was found between the mesityl substituent on the bipyridine ligand and the adjacent mesityl ligand. The electrochemical behaviour of 1 and 2 together with a related compound was examined at various temperatures showing two reversible reduction reactions and reversible one‐electron oxidation steps at low temperatures. The latter are assigned to Pd^II/Pd^III couples.     

Shielding of Electron Acceptors Coordinated to Rhenium(I) by Carboxylato Groups. Intraligand and Charge‐Transfer Excited‐State Properties of fac‐(‘Anthraquinone‐2‐carboxylato')(2,2′‐bipyridine)tricarbonylrhenium (fac‐[ReI(aq‐2‐CO2)(2,2′‐bipy)(CO)3])

The photophysical and photochemical properties of (OC‐6‐33)‐(2,2′‐bipyridine‐κN¹,κN¹′)tricarbonyl(9,10‐dihydro‐9,10‐dioxoanthracene‐2‐carboxylato‐κO)rhenium (fac‐[Re^I(aq‐2‐CO₂)(2,2′‐bipy)(CO)₃]) were investigated and compared to those of the free ligand 9,10‐dihydro‐9,10‐dioxoanthracene‐2‐carboxylate (=anthraquinone‐2‐carboxylate) and other carboxylato complexes containing the (2,2′‐bipyridine)tricarbonylrhenium ([Re(2,2′‐bipy)(CO)₃]) moiety. Flash and steady‐state irradiations of the anthraquinone‐derived ligand (λ_exc 337 or 351 nm) and of its complex reveal that the photophysics of the latter is dominated by processes initiated in the Re‐to‐(2,2′‐bipyridine) charge‐transfer excited state and 2,2′‐bipyridine‐ and (anthraquinone‐2‐carboxylato)‐centered intraligand excited states. In the reductive quenching by N,N‐diethylethanamine (TEA) or 2,2′,2″‐nitrilotris[ethanol] TEOA, the reactive states are the 2,2′‐bipyridine‐centered and/or the charge‐transfer excited states. The species with a reduced anthraquinone moiety is formed by the following intramolecular electron transfer, after the redox quenching of the excited state: [Re^I(aq−2−CO₂)(2,2′‐bipy^.)(CO)₃]⁻⇌[Re^I(aq−2−CO₂^.)(2,2′‐bipy)(CO)₃]⁻ The photophysics, particularly the absence of a Re^I‐to‐anthraquinone charge‐transfer excited state photochemistry, is discussed in terms of the electrochemical and photochemical results.     

Synthesis and characterization of alt‐bipyridinylene‐phenylene copolymers containing ruthenium(II) complexes

Poly{bis(4,4′‐tert‐butyl‐2,2′‐bipyridine)–(2,2′‐bipyridine‐5,5′‐diyl‐[1,4‐phenylene])–ruthenium(II)bishexafluorophosphate} ( 3a ), poly{bis(4,4′‐tert‐butyl‐2,2′‐bipyridine)–(2,2′‐bipyridine‐4,4′‐diyl‐[1,4‐phenylene])–ruthenium(II)bishexafluorophosphate} ( 3b ), and poly{bis(2,2′‐bipyridine)–(2,2′‐bipyridine‐5,5′‐diyl‐[1,4‐phenylene])–ruthenium(II)bishexafluorophosphate} ( 3c ) were synthesized by the Suzuki coupling reaction. The alternating structure of the copolymers was confirmed by ¹H and ¹³C NMR and elemental analysis. The polymers showed, by ultraviolet–visible, the π–π* absorption of the polymer backbone (320–380 nm) and at a lower energy attributed to the d–π* metal‐to‐ligand charge‐transfer absorption (450 nm for linear 3a and 480 nm for angular 3b ). The polymers were characterized by a monomodal molecular weight distribution. The degree of polymerization was approximately 8 for polymer 3b and 28 for polymer 3d . © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2911–2919, 2004     

Synthesis, Characterization, Spectroscopic and Electrochemical Properties of New Mono- and Binuclear Copper（Ⅰ） Complexes with Substituted 2,2′-Bipyridine

The mono- and binuclear Cu(Ⅰ) complexes with substituted 2,2′-bipyridine and iodide ligands, [CuL2]BF4(L=4-methoxycarbonyl-6-(4-methylphenyl)-2,2′-bipyridine (a), 6-(4-hydroxymethylphenyl)-2,2′-bipyridine (b) and 6-(4-methoxylphenyl)-2,2′-bipyridine (c)) and [Cu2(μ-I)2L2] were prepared, and the crystal structures of the complexes were obtained from signal-crystal X-ray diffractional analysis. The spectroscopic properties of the complexes in dichloromethane are dominated by low energy MLCT bands from 360 to 650 nrn. The electrochemical studies of mononuclear complexes reveal that the complexes have stable copper(Ⅰ) state.     

High‐throughput experimentation in atom transfer radical polymerization: A general approach toward a directed design and understanding of optimal catalytic systems

High‐throughput experimentation (HTE) was successfully applied in atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) for the rapid screening and optimization of different reaction conditions. A library of 108 different reactions was designed for this purpose, which used four different initiators [ethyl 2‐bromoisobutyrate, methyl 2‐bromopropionate, (1‐bromoethyl)benzene, and p‐toluenesulfonyl chloride], five metal salts (CuBr, CuCl, CuSCN, FeBr₂, and FeCl₂), and nine ligands (2,2′‐bipyridine and its derivatives). The optimal reaction conditions for Cu(I) halide, CuSCN, and Fe(II) halide‐mediated ATRP systems with 2,2′‐bipyridine and its 4,4′‐dialkyl‐substituted derivatives as ligands were determined. Cu(I)‐mediated systems were better controlled than Fe(II)‐mediated ones under the examined conditions. A bipyridine‐type ligand with a critical length of the substituted alkyl group (i.e., 4,4′‐dihexyl 2,2′‐bipyridine) exhibited the best performance in Cu(I)‐mediated systems, and p‐toluenesulfonyl chloride and ethyl 2‐bromoisobutyrate could effectively initiate Cu(I)‐mediated ATRP of MMA, resulting in polymers with low polydispersities in most cases. Besides, Cu(I) halide‐mediated ATRP with 4,5′‐dimethyl 2,2′‐bipyridine as the ligand and p‐toluenesulfonyl chloride as the initiator proved to be better controlled than those with 4,4′‐dimethyl 2,2′‐bipyridine as the ligand, and polymers with much lower polydispersities were obtained in the former cases. This successful HTE example opens up a way to significantly accelerate the development of new catalytic systems for ATRP and to improve the understanding of structure–property relationships of the reaction systems. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1876–1885, 2004     

Stereoselective Synthesis of cis‐2,5‐Disubstituted Pyrrolidines via Copper‐Catalyzed Cyclization of Alkenes

An efficient methodology for the stereoselective synthesis of cis‐2,5‐disubstituted pyrrolidines using copper catalyst was developed. The corresponding cis‐2,5‐disubstituted pyrrolidines could be obtained in reasonable yields and with good stereoselectivities in the presence of 4,4′‐di‐tert‐butyl‐2,2′‐bipyridine as ligand and 1‐methyl‐2‐pyrrolidinone as solvent.     

μ‐2,2′,6,6′‐Tetramethyl‐4,4′‐bipyridine‐κ2N1:N1′‐bis[(diethylenetriamine‐κ3N,N′,N′′)palladium(II)] tetranitrate

The title compound, [Pd₂(C₄H₁₃N₃)₂(C₁₄H₁₆N₂)](NO₃)₄, comprises discrete tetracationic dumbbell‐type dinuclear complex molecules and noncoordinating nitrate anions. Two Pd(dien)²⁺ moieties (dien is diethylenetriamine) are joined by the rigid linear exo‐bidentate bridging 2,2′,6,6′‐tetramethyl‐4,4′‐bipyridine ligand to form the dinuclear complex, which lies across a centre of inversion in the space group P2₁/n, so that the rings in the 2,2′,6,6′‐tetramethyl‐4,4′‐bipyridine bridging ligand are parallel. In the crystal, the primary and secondary amino groups of the dien ligand act as hydrogen‐bond donors towards the nitrate anions to form a three‐dimensional hydrogen‐bond network.     

Synthesis and Characterization of Heteroleptic Ru(II) Complexes Based on 4,4′‐Bis((E)‐styryl)‐2,2′‐bipyridine as Ancillary Ligand and Application for Dye‐Sensitized Solar Cells

Heteroleptic Ru(II) complexes were designed based on 4,4′‐bis((E)‐styryl)‐2,2′‐bipyridine (bsbpy) as an ancillary ligand for dye‐sensitized solar cells (DSSCs), and those Ru(II) sensitizers, [Ru(L)(bsbpy)(NCS)₂][TBA] (TBA; tetrabutylammonium), were synthesized according to a typical one‐pot reaction of [RuCl₂(p‐cymene)]₂ with the corresponding anchoring ligands (where L = 4,4′‐dicarboxy‐2,2′‐bipyridine (dcbpy), 4,4′‐bis((E)‐carboxyvinyl)‐2,2′‐bipyridine (dcvbpy), 4,7‐dicarboxy‐1,10‐phenanthroline (dcphen), or 4,7‐bis((E)‐carboxyvinyl)‐1,10‐phenanthroline (dcvphen)). The new Ru(II) dyes, [Ru(L)(bsbpy)(NCS)₂][TBA] that incorporated vinyl spacer(s) into ancillary and/or anchoring ligand displayed red‐shifted bands over the overall UV/VIS region relative to the absorption spectra of N719 . A combination of bsbpy ancillary and dcphen anchoring ligand showed the best result for the overall power conversion efficiency (η); i.e., a DSSC fabricated with [Ru(dcphen)(bsbpy)(NCS)₂][TBA] exhibited a power conversion efficiency (η) of 2.98% (compare to N719 , 4.82%).     

Bis(3‐amino­pyridine‐κN)(4,4′‐di­methyl‐2,2′‐bipyridine‐κ2N,N′)(per­chlorato‐κO)copper(II) per­chlorate

The title compound, [Cu(ClO₄)(C₅H₆N₂)₂(C₁₂H₁₂N₂)]ClO₄, was prepared by in situ partial ligand substitution between 3‐amino­pyridine and 4,4′‐dimethyl‐2,2′‐bipyridine at room temperature. The central copper(II) ion is five‐coordinated by one bidentate 4,4′‐dimethyl‐2,2′‐bipyridine mol­ecule, two monodentate pyridine‐coordinated 3‐amino­pyridine mol­ecules and one apical O atom from the perchlorate counter‐ion. Inter­molecular N—H⋯O and C—H⋯O hydrogen‐bonding inter­actions form a hydrogen‐bond‐sustained network.     

Role of electronic structure of ruthenium polypyridyl dyes in the photoconversion efficiency of dye‐sensitized solar cells: Semiempirical investigation

ZINDO/S calculations on cis‐Ru(4,4′‐dicarboxy‐2,2′‐bipyridine)₂(X)₂ and cis‐Ru(5,5′‐dicarboxy‐2,2′‐bipyridine)₂(X)₂ complexes where X = Cl^?, CN^?, and NCS^? reveal that the highest occupied molecular orbital (HOMO) of these complexes has a large amplitude on both the nonchromophoric ligand X and the central ruthenium atom. The lowest‐energy metal to ligand charge transfer (MLCT) transition in these complexes involves electron transfer from ruthenium as well as the halide/pseudohalide ligand to the polypyridyl ligand. The contribution of the halide/pseudohalide ligand(X) to the HOMO affects the total amount of charge transferred to the polypyridyl ligand and hence the photoconversion efficiency. The virtual orbitals involved in the second MLCT transition in 4,4′‐dicarboxy‐2,2′‐bipyridine complexes have higher electron density on the ? COOH group compared to the lowest unoccupied molecular orbital and hence a stronger electronic coupling with the TiO₂ surface and higher injection efficiency at shorter wavelengths. In comparison, the virtual orbitals involved in the second MLCT transition in 5,5′‐dicarboxy‐2,2′‐bipyridine complexes have lesser electron density on the ? COOH group, leading to a weaker electronic coupling with the TiO₂ surface and therefore lower efficiency for electron injection at shorter wavelengths for these complexes. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Crystal Structure and Characterization of a Double‐helical‐chain Coordination Polymer Zinc Complex Constructed by Flexible Dicarboxylate Ligand 2‐Nitro‐benzene‐1,4‐di(oxyacetate) and Rigid 2,2′‐Bipyridine Ligand

A novel double‐helical‐chain coordination polymer [Zn(nbdoa)(2,2′‐bipy)(H₂O)]_n constructed by flexible 2‐nitro‐benzene‐1,4‐di(oxyacetate) ligand and rigid 2,2′‐bipyridine ligand was obtained by hydrothermal reaction. The crystal structure demonstrates that there is a double‐helical chain with an inner channel running parallel to the helix axis without any interpenetration, which is connected to network via π‐π stacking and hydrogen bond interactions. The thermal analysis shows that the infinite helical structure is stable up to 536 K. The luminescence property is investigated and the complex shows photoluminescence in the solid state at room temperature.     

Electronic Coupling between Two Amine Redox Sites through the 5,5′‐Positions of Metal‐Chelating 2,2′‐Bipyridines

Electron delocalization of new mixed‐valent (MV) systems with the aid of lateral metal chelation is reported. 2,2′‐Bipyridine (bpy) derivatives with one or two appended di‐p‐anisylamino groups on the 5,5′‐positions and a coordinated [Ru(bpy)₂] (bpy=2,2′‐bipyridine), [Re(CO)₃Cl], or [Ir(ppy)₂] (ppy=2‐phenylpyridine) component were prepared. The single‐crystal molecular structure of the bis‐amine ligand without metal chelation is presented. The electronic properties of these complexes were studied and compared by electrochemical and spectroscopic techniques and DFT/TDDFT calculations. Compounds with two di‐p‐anisylamino groups were oxidized by a chemical or electrochemical method and monitored by near‐infrared (NIR) absorption spectral changes. Marcus–Hush analysis of the resulting intervalence charge‐transfer transitions indicated that electron coupling of these mixed‐valent systems is enhanced by metal chelation and that the iridium complex has the largest coupling. TDDFT calculations were employed to interpret the NIR transitions of these MV systems.     

[Re(CO)3Cl]‐Chelation‐Mediated Electronic Coupling between Two Amine Redox Sites through the 5,5′‐Positions of 2,2′‐Bipyridine

The electronic coupling between two amine redox sites bridged through the 5,5′‐positions of the [Re(CO)₃Cl]‐chelated 2,2′‐bipyridine was studied by the electrochemical, spectroscopic, and EPR analysis. Interestingly, multiple near‐infrared bands were observed in this new organic mixed‐valent system. The results are interpreted with the aid of DFT and TDDFT calculations.     

A Typical Metal‐Ion‐Responsive Color‐Tunable Emitting Insulated π‐Conjugated Polymer Film

We report the synthesis of an insulated π‐conjugated polymer containing 2,2′‐bipyridine moieties as metal coordination sites. Metal coordination to the polymer enabled easy and reversible tuning of the luminescent color without changes to the main chain skeleton. The permethylated α‐cyclodextrin (PM α‐CD)‐based insulation structure allowed the metalated polymers to demonstrate efficient emission even in the solid state, with identical spectral shapes to the dilute solutions. In addition, the coordination ability of the metal‐free polymer was maintained in the solid state, resulting in reversible changes in the luminescent color in response to the metal ions. The synthesized polymer is expected to be suitable for application in recyclable luminescent sensors to distinguish different metal ions.