Recyclable Palladium Catalysts for the Heck/Sonogashira Reaction under Microwave‐assisted Thermomorphic Conditions

The reaction of allyl palladium(II) chloride dimer and 4,4′‐bis(R_fCH₂OCH₂)‐2,2′‐bpy, 1a–b , in the presence of AgOT_f resulted in the synthesis of cationic palladium complex, [Pd(η³‐allyl)(4,4′‐bis‐(R_fCH₂OCH₂)‐2,2′‐bpy)](OT_f), 2a–b where R_f = C₉F₁₉ ( a ), C₁₀F₂₁ ( b ), respectively. The reaction of [PdCl₂(CH₃CN)] or K₂PdCl₄ with 1b , gave rise to the synthesis of [PdCl₂(4,4′‐bis‐(C₁₀F₂₁CH₂OCH₂)‐2,2′‐bpy)], 3b . The quantitatively determined solubility curves of 2a–b and 3b in DMF indicated dramatic increase of solubility for 2a – b and 3b from ?40 to 90 °C. The catalyst‐recoverable Pd‐catalyzed Heck/Sonogashira reactions were successfully achieved in DMF with microwave‐assistance. The cationic Pd‐catalyzed Heck arylation of methyl acrylate was selected to demonstrate the feasibility of recycling 2a–b using DMF as a solvent under microwave‐assisted thermomorphic conditions. At the end of each cycle, the product mixtures were cooled, and then the catalysts were recovered by decantation. The Heck arylation catalyzed by 2b under microwave‐assisted mode exhibited good recycling results favoring the trans product. To our knowledge, this is the first example of cationic Pd‐catalyzed Heck arylation under microwave‐assisted thermomorphic conditions. Additionally, recoverable 3b ‐catalyzed Sonogashira reactions were also achieved successfully in DMF. The reactions under microwave‐assistance gave much better results in yield and in efficiency than that under conventional thermal heating.     

Synthesis,structure and reactivity of novel palladiumdichloride-2,2′-bipyridine with 4,4′-bis(fluorous-ponytail)

With the readily available fluorous alkanols R_fCH₂OH, a series of novel fluorous-ponytailed bpy ligands, 4,4′-bis(R_fCH₂OCH₂)-2,2′-bpy (1a–e), were prepared and treated with [PdCl₂(CH₃CN)₂] to result in the corresponding novel Pd complexes [PdCl₂(4,4′-bis(R_fCH₂OCH₂)-2,2′-bpy)] (2a–e) where R_f = n-C₃F₇ (a), HCF₂(CF₂)₃ (b), HCF₂(CF₂)₇ (c), n-C₈F₁₇ (d), n-C₁₀F₂₁ (e). The new ligands and Pd complexes were spectroscopically characterized by multi-nuclei NMR (¹H, ¹⁹F and ¹³C), FTIR and high resolution mass (FAB). The structure for the Pd complex 2b, the first with fluorinated ponytails on bpy and not on phosphine, was also established by a single crystal X-ray diffraction study. The TGA data of both ligands and Pd complexes indicated that the Pd-complexes were resistant to higher temperatures than the corresponding ligands. The Pd catalysts derived from 2a–c showed an almost quantitative conversion and could be reused for eight runs with Heck reactions, in that the products and unspent reactants were directly removed by distillation. With the highest fluorine content in the series, Pd complex 2e was successfully applied in the Heck reaction using the fluorous biphasic catalysis strategy.     

New bis(fluoro-ponytailed) bipyridine ligands for Pd-catalyzed Heck reactions under fluorous biphasic catalysis condition

Three highly fluorinated bipyridine derivatives (4,4′-bis(R_fCH₂OCH₂)-2,2′-bpy) {R_f=HCF₂(CF₂)₇ (1a), n-C₈F₁₇ (1b), n-C₁₀F₂₁ (1c)} have been synthesized using 4,4′-bis(BrCH₂)-2,2′-bpy and the corresponding fluorinated alkoxides. The fluorine contents of ligands 1a-c are 58.3, 59.8, and 62.3%, respectively. Despite its high fluorine content, the ligand 1a with a -CF₂H polar terminal group is more soluble in organic solvents. The ligand 1b is a white solid and is still moderately soluble in CH₂Cl₂. The ligand 1c has a high fluorophilicity, the partition ratio being 42:1 for the n-C₈F₁₈/CH₂Cl₂ system. The reaction of ligands 1a-c with [PdCl₂(CH₃CN)₂] results in the novel Pd complexes [PdCl₂(4,4′-bis-(R_fCH₂OCH₂)-2,2′-bpy)] where R_f=HCF₂(CF₂)₇ (2a), n-C₈F₁₇ (2b), n-C₁₀F₂₁ (2c), respectively. The Pd complex 2b is a pale yellow solid, and has been tested unsatisfactorily for FBC. Insoluble in organic solvents, the Pd complex 2c dissolves only in fluorinated solvents, for instance FC77, which is mainly n-C₈F₁₈. The novel Pd complex 2c has been tested as a catalyst in Heck reactions under a fluorous biphasic catalysis condition. It was found that the Pd complex 2c, after an easy separation, keeps its catalytic activity (>90% yield), even after seven runs. The TGA studies indicate that the Pd complexes 2a-c are stable up to 330 °C.     

Studies of two different types of intramolecular C–H···F–C interactions from polyfluorinated diiodometal(II) diimine complexes

The X‐ray crystal structures of the polyfluorinated complexes [5,5′‐bis(HCF₂CF₂CF₂CF₂CH₂OCH₂)‐2,2′‐bpy]MI₂ ( 55‐8F‐PtI ₂ and 55‐8F‐PdI ₂ where M = Pt and Pd, respectively) were obtained. These two structures are found to show not only two different types of intramolecular, six‐membered cyclic C–H···F–C interactions (F₂C–H···F–C and HC–H···F–C) as important structural features but also alternating fluorinated and non‐fluorinated layers. The F₂C–H···F–C interactions, which are close to the metal core, are much better structurally characterized in this type of complexes with fluorous ponytails at the 5,5′ positions than those previously reported at the 4,4′ positions. The molecular planes of (bpy)MI₂ are extended by self‐matching, using two C–H···I hydrogen bonds and one C–H···F–C blue‐shifting hydrogen bond. The F₂C–H···F–C hydrogen bonds interact at the supramolecular level such that one polyfluorinated ponytail of the title compounds is transoid without an intramolecular C–H···F–C interaction, while the other polyfluorinated ponytail is cisoid with an intramolecular C–H···F–C interaction. Why one ponytail is cisoidal while the other is transoidal will be explained. Furthermore, the second type of C–H···F–C interactions involving the methylene H atom has been identified for the first time. In addition, these two metal structures are studied by density functional theory (DFT).     

Side‐chain conformations in the isomorphous polyfluorinated {4,4′‐bis[(2,2‐difluoroethoxy)methyl]‐2,2′‐bipyridine‐κ2N,N′}dichloridopalladium and ‐platinum complexes

The polyfluorinated title compounds, [M Cl₂(C₁₆H₁₆F₄N₂O₂)] or [4,4′‐(HCF₂CH₂OCH₂)₂‐2,2′‐bpy]M Cl₂ [M = Pd, ( 1 ), and M = Pt, ( 2 )], have –C(H_α)₂OC(H_β)₂CF₂H side chains with H‐atom donors at the α and β sites. The structures of ( 1 ) and ( 2 ) are isomorphous, with the nearly planar (bpy)M Cl₂ molecules stacked in columns. Within one column, π‐dimer pairs alternate between a π‐dimer pair reinforced with C—H…Cl hydrogen bonds (α,α) and a π‐dimer pair reinforced with C—H_β…F(—C) interactions (abbreviated as C—H_β…F—C,C—H_β…F—C). The compounds [4,4′‐(CF₃CH₂OCH₂)₂‐2,2′‐bpy]M Cl₂ [M = Pd, ( 3 ), and M = Pt, ( 4 )] have been reported to be isomorphous [Lu et al. (2012). J. Fluorine Chem. 137 , 54–56], yet with disorder in the fluorous regions. The molecules of ( 3 ) [or ( 4 )] also form similar stacks, but with alternating π‐dimer pairs between the (α,β; α,β) and (β,β) forms. Through (C—)H…Cl hydrogen‐bond interactions, one molecule of ( 1 ) [or ( 2 )] is expanded into an aggregate of two inversion‐related π‐dimer pairs, one pair in the (α,α) form and the other pair in the (C—H_β…F—C,C—H_β…F—C) form, with the plane normals making an interplanar angle of 58.24 (3)°. Due to the demands of maintaining a high coordination number around the metal‐bound Cl atoms in molecule ( 1 ) [or ( 2 )], the ponytails of molecule ( 1 ) [or ( 2 )] bend outward; in contrast, the ponytails of molecule ( 3 ) [or ( 4 )] bend inward.     

Substituted 2,2′‐Bis(2‐oxidobenzylideneamino)‐4,4′‐dimethyl‐1,1′‐biphenyl Complexes of Zinc

The condensation reaction of 2,2′‐diamino‐4,4′‐dimethyl‐6,6'‐dibromo‐1,1′‐biphenyl with 2‐hydroxybenzaldehyde as well as 5‐methoxy‐, 4‐methoxy‐, and 3‐methoxy‐2‐hydroxybenzaldehyde yields 2,2′‐bis(salicylideneamino)‐4,4′‐dimethyl‐6,6′‐dibromo‐1,1′‐biphenyl ( 1a ) as well as the 5‐, 4‐, and 3‐methoxy‐substituted derivatives 1b , 1c , and 1d , respectively. Deprotonation of substituted 2,2′‐bis(salicylideneamino)‐4,4′‐dimethyl‐1,1′‐biphenyls with diethylzinc yields the corresponding substituted zinc 2,2′‐bis(2‐oxidobenzylideneamino)‐4,4′‐dimethyl‐1,1′‐biphenyls ( 2 ) or zinc 2,2′‐bis(2‐oxidobenzylideneamino)‐4,4′‐dimethyl‐6,6′‐dibromo‐1,1′‐biphenyls ( 3 ). Recrystallization from a mixture of CH₂Cl₂ and methanol can lead to the formation of methanol adducts. The methanol ligands can either bind as Lewis base to the central zinc atom or as Lewis acid via a weak O–H ··· O hydrogen bridge to a phenoxide moiety. Methanol‐free complexes precipitate as dimers with central Zn₂O₂ rings.     

Supramolecular Stuctures from Mononuclear,Binuclear and 2D Net of Copper(II) Complexes with 6‐Hydroxypicolinic Acid

First examples of transition metal complexes with HpicOH [Cu(picOH)₂(H₂O)₂] ( 1 ), [Cu(picO)(2,2′‐bpy)]·2H₂O ( 2 ), [Cu(picO)(4,4′‐bpy)_0.5(H₂O)]_n ( 3 ), and [Cu(picO)(bpe)_0.5(H₂O)]_n ( 4 ) (HpicOH = 6‐hydroxy‐picolinic acid; 2,2′‐bpy = 2,2′‐bipyridine; 4,4′‐bpy = 4,4′‐bipyridine; bpe = 1,2‐bis(4‐pyridyl)ethane) have been synthesized and characterized by single‐crystal X‐ray diffraction. The results show that HpicOH ligand can be in the enol or ketonic form, and adopts different coordination modes under different pH value of the reaction mixture. In complex 1 , HpicOH ligand is in the enol form and adopts a bidentate mode. While in complexes 2 – 4 , as the pH rises, HpicOH ligand becomes in the ketonic form and adopts a tridentate mode. The coordination modes in complexes 1 – 4 have not been reported before. Because of the introduction of the terminal ligands 2,2′‐bpy, complex 2 is of binuclear species; whereas in complexes 3 and 4 , picO ligands together with bridging ligands 4,4′‐bpy and bpe connect Cu^II ions to form 2D nets with (12³)₂(12)₃ topology.     

Hydrogen bonding and fluorous weak interactions in the non‐isomorphous {4,4′‐bis[(2,2,3,3‐tetrafluoropropoxy)methyl]‐2,2′‐bipyridine‐κ2N,N′}dibromidopalladium and ‐platinum complexes

The polyfluorinated title compounds, [MBr₂(C₁₈H₁₆F₈N₂O₂)] or [4,4′‐(HCF₂CF₂CH₂OCH₂)₂‐2,2′‐bpy]MBr₂, ( 1 ) (M = Pd and bpy is bipyridine) and ( 2 ) (M = Pt), have –CH_(α)2OCH_(β)2CF₂CF₂H side chains with methylene H‐atom donors at the α and β sites, and methine H‐atom donors at the terminal sites, in addition to aromatic H‐atom donors. In contrast to the original expectation of isomorphous structures, ( 1 ) crystallizes in the space group C2/c and ( 2 ) in P2₁/n, with similar unit‐cell volumes and Z = 4. The asymmetric unit of ( 1 ) is one half of the molecule, which resides on a crystallographic twofold axis. Both ( 1 ) and ( 2 ) display stacking of the molecules, indicating a planar (bpy)MBr₂ skeleton in each case. The structure of ( 1 ) exhibits columns with C—H_(β)…Br hydrogen bonds between consecutive layers which conforms to a static (β,β) linkage between layers. In the molecular plane, ( 1 ) shows double C—H_(α)…Br hydrogen bonds self‐repeating along the b axis, the planar molecules being connected into infinite belts. Compound ( 2 ) has no crystallographic symmetry and forms π‐dimer pairs as supermolecules, which then stack parallel to the a axis. The π‐dimer‐pair supermolecules exhibit (Pt—)Br…Br(—Pt) contacts [3.6937 (7) Å] to neighbouring π‐dimer pairs crosslinking the columns. The structure of ( 2 ) reveals many C—H…F(—C) interactions between F atoms and aromatic C—H groups, in addition to those between F atoms and methylene C—H groups.     

Synthesis and Characterization of Monomeric Aryloxo Palladium Complexes of the Type [Pd(N–N)(OAr)(C6F5)]. Crystal Structure of [Pd(tmeda)(C6F5)(OC6H4NO2‐p)]

Mononuclear palladium‐hydroxo complexes of the type [Pd(N–N)(C₆F₅)(OH)][(N–N) = 2,2′‐bipyridine (bipy), 4,4′‐dimethyl‐2,2′‐bipyridine (Me₂bipy), 1,10‐phenantroline (phen) or N,N,N′,N′‐tetramethylethylenediamine (tmeda) react with phenols ArOH in tetrahydrofuran giving the corresponding aryloxo complexes [Pd(N–N)(C₆F₅)(OAr)]. Elemental analyses and spectroscopic (IR, ¹H and ¹⁹F) methods have been used to characterize the new complexes. The X‐ray crystal structure of [Pd(tmeda)(C₆F₅)(OC₆H₄NO₂‐p)] has been determined. In the crystal packing the planes defined by two C₆H₄ rings show a parallel orientation. There are also intermolecular C–H···F and C‐H···O hydrogen bonds.     

Effect of Metal Ions on the Structures of Coordination Polymers Based on Biphenyl‐2,2′,4,4′‐Tetracarboxylate

Two new coordination polymers, {[Cd₂(btc)(2,2′‐bpy)₂] · H₂O}_n ( 1 ) and [Zn₂(btc)(2,2′‐bpy)(H₂O)]_n ( 2 ) (H₄btc = biphenyl‐2,2′,4,4′‐tetracarboxylic acid, 2,2′‐bpy = 2,2′‐bipyridine), were synthesized hydrothermally under similar conditions and characterized by elemental analysis, IR spectra, TGA, and single‐crystal X‐ray diffraction analysis. In complexes 1 and 2 , the (btc)^4– ligand acts as connectors to link metal ions to give a 2D bilayer network of 1 and a 3D metal‐organic framework of 2 , respectively. The differences in the structures are induced by diverging coordination modes of the (btc)^4– ligand, which can be attributed to the difference metal ions in sizes. The results indicate that metal ions have significant effects on the formation and structures of the final complexes. Additionally, the fluorescent properties of the two complexes were also studied in the solid state at room temperature.     

A new route for the synthesis of phosphate esters: 2,2′‐[benzene‐1,2‐diylbis(oxy)]bis(5,5‐dimethyl‐1,3,2‐dioxaphosphinane) 2,2′‐dioxide

Podand‐type ligands are an interesting class of acyclic ligands which can form host–guest complexes with many transition metals and can undergo conformational changes. Organic phosphates are components of many biological molecules. A new route for the synthesis of phosphate esters with a retained six‐membered ring has been used to prepare 2,2′‐[benzene‐1,2‐diylbis(oxy)]bis(5,5‐dimethyl‐1,3,2‐dioxaphosphinane) 2,2′‐dioxide, C₆H₄{O[cyclo‐P(O)OCH₂CMe₂CH₂O]}₂ or C₁₆H₂₄O₈P₂, (1), 2‐[(2′‐hydroxybiphenyl‐2‐yl)oxy]‐5,5‐dimethyl‐1,3,2‐dioxaphosphinane 2‐oxide, [cyclo‐P(O)OCH₂CMe₂CH₂O](2,2′‐OC₆H₄–C₆H₄OH), (2), and oxybis(5,5‐dimethyl‐1,3,2‐dioxaphosphinane) 2,2′‐dioxide, O[cyclo‐P(O)OCH₂CMe₂CH₂O]₂, (3). Compound (1) is novel, whereas the results for compounds (2) and (3) have been reported previously, but we record here our results for compound (3), which we find are more precise and accurate than those currently reported in the literature. In (1), two cyclo‐P(O)OCH₂CMe₂CH₂O groups are linked through a catechol group. The conformations about the two catechol O atoms are quite different, viz. one C—C—O—P torsion angle is −169.11 (11)° and indicates a trans arrangement, whereas the other C—C—O—P torsion angle is 92.48 (16)°, showing a gauche conformation. Both six‐membered POCCCO rings have good chair‐shape conformations. In both the trans and gauche conformations, the catechol O atoms are in the axial sites and the short P=O bonds are equatorially bound.     

Chiral Bis(oxazoline) Ruthenium Complexes with Bipyridyl‐Type N‐Heteroaromatics: Comparative Stereochemical and Photochemical Characterization of their Λ‐ and Δ‐Diastereomeric Geminate Isomers

Diastereomeric geminate pairs of chiral bis(2‐oxazoline) ruthenium complexes with bipyridyl‐type N‐heteroaromatics, Λ‐ and Δ‐[Ru(L‐ L)₂(iPr‐biox)]²⁺ (iPr‐biox=(4S,4′S)‐4,4′‐diisopropyl‐2,2′‐bis(2‐oxazoline); L‐ L=2,2′‐bipyridyl (bpy) for 1 Λ and 1 Δ, 4,4′‐dimethyl‐2,2′‐bipyridyl (dmbpy) for 2 Λ and 2 Δ, and 1,10‐phenanthroline (phen) for 3 Λ and 3 Δ), were separated as BF₄ and PF₆ salts and were subjected to the comparative studies of their stereochemical and photochemical characterization. DFT calculations of 1 Λ and 1 Δ electronic configurations for the lowest triplet excited state revealed that their MO‐149 (HOMO) and MO‐150 (lower SOMO) characters are interchanged between them and that the phosphorescence‐emissive states are an admixture of a Ru‐to‐biox charge‐transfer state and an intraligand excited state within the iPr‐biox. Furthermore, photoluminescence properties of the two Λ,Δ‐diastereomeric series are discussed with reference to [Ru(bpy)₃]²⁺.     

Supramolecular Assembly of Double‐Stranded Chains,Helical Chains and Catenane‐like Layers with Flexible Ligands

Four new transition metal coordination polymers, [Co(bpndc)(phen)(H₂O)]_n ( 1 ), [Co₃(bpndc)₃(2,2′‐bpy)₂]_n·0.5n(i‐C₃H₇OH) ( 2 ), and [M(bpndc)(2,2′‐bpy)₂]_n (M = Zn, 3 ; Cu, 4 ; H₂bpndc = benzophenone ‐4,4′‐dicarboxylic acid; phen = 1,10‐phenanthroline; 2,2′‐bpy = 2,2′‐bipyridine) have been synthesized by the hydrothermal reactions and characterized by single crystal X‐ray diffraction, elemental analysis, and IR spectrum. Because of the introduction of different terminal auxiliary ligands, bpndc ligands in complexes 1 and 2 adopt different coordination modes. In complex 1 , bpndc ligands act as tridentate ligand and bridge Co^II ions into 1D double‐stranded chains; while complex 2 possesses 2D (4,4) grids, where bpndc ligands adopt tetradente and pentadentate modes. Two such grids interpenetrate to form a novel catenane‐like layer. Complexes 3 and 4 are isostructural. Bpndc ligands adopt tetradentate mode and bridge metal ions forming 1D helical chains.     

Supramolecular Architectures with Open Frameworks Constructed by Transitional Metal Ions,Linear Dicarboxylic Acid,and 2,2′‐Bipyridine

Four new transitional metal supramolecular architectures, [Zn(cca)(2,2′‐bpy)]_n · n(2,2′‐bpy) ( 1 ), [Cu(cca)(2,2′‐bpy)]_n ( 2 ), [Zn(bpdc)(2,2′‐bpy)(H₂O)]_n · 0.5nDMF · 1.5nH₂O ( 3 ), and [Co(bpdc)(2,2′‐bpy)(H₂O)]_n · nH₂O ( 4 ) (H₂cca = p‐carboxycinnamic acid; H₂bpdc = 4,4′‐biphenyldicarboxylic acid; 2,2′‐bpy = 2,2′‐bipyridine) were synthesized by hydrothermal reactions and characterized by single crystal X‐ray diffraction, elemental analyses, and IR spectroscopy. Although the metal ions in these four compounds are bridged by linear dicarboxylic acid into 1D infinite chains, there are different π–π stacking interactions between the chains, which results in the formation of different 3D supramolecular networks. Compound 1 is of a 3D open‐framework with free 2,2′‐bpy molecules in the channels, whereas compound 2 is of a complicated 3D supramolecular network. Compounds 3 and 4 are isostructural. Both compounds have open‐frameworks.     

Spectroscopic,Thermal and Structural Studies of Aza‐aromatic Base Adducts of Cadmium Furoyltrifluoroacetonate

Three aza‐aromatic base adducts of cadmium(II) furoyltrifluoroacetonate, [Cd(4,4′‐bpy)(ftfa)₂]_n ( 1 ), [Cd(2,2′‐bpy)(ftfa)₂] ( 2 ) and [Cd(dmp)(ftfa)₂] ( 3 ) (“4,4′‐bpy”, “2,2′‐bpy”, “dmp” and “ftfa” are the abbreviations of 4,4′‐bipyridine, 2,2′‐bipyridine, 2,9‐dimethyl‐1,10‐phenanthroline and furoyltrifluoroacetonate, respectively) have been synthesized and characterized by elemental analysis and IR, ¹H NMR and ¹³C NMR spectroscopy and studied by thermal as well as X‐ray crystallography. The single‐crystal structure of these complexes shows that the coordination number of the Cd^II ions are six with two N‐donor atoms from aza‐aromatic base ligands and four O‐donors from two the furoyltrifluoroacetonates. The supramolecular features in these complexes are guided/controlled by weak directional intermolecular interactions.     

Palladium‐MOP Chemistry: Pseudo‐cis‐Allyl MOP Complexes and Flexible Olefin Bonding. Preliminary Communication

We show that both palladium(0) and palladium(II) metal centers are capable of coordinating two monodentate MOP (=(R)‐2‐(diarylphosphino)‐1,1′‐binaphthalene) ligands in a pseudo‐cis orientation, despite published statements to the contrary. In addition to [Pd(η³‐C₃H₅)(MeO? MOP)₂]BF₄ (MeO? MOP=(R)‐2‐(diphenylphosphino)‐2′‐methoxy‐1,1′‐binaphthalene), the first examples of chiral bis κC¹‐prop‐2‐enyl (η¹‐CH₂CH?CH₂) complexes [cis‐Pd(κC¹‐C₃H₅)₂(MeO? MOP or MOP)₂], are shown to be relatively stable. Further, coordinated MOP and MeO? MOP both show stronger propensity towards novel intramolecular π‐olefin complexation than the CN? MOP analogue. The solid‐state structure of [Pd(fumaronitrile)(MOP)₂] is reported.     

Tris(2,2′‐bipyridine)ruthenium Derivatives with Multiple Viologen Acceptors: Quadratic Dependence of Photocatalytic H2 Evolution Rate on the Local Concentration of the Acceptor Site

Three Ru(bpy)₃²⁺ derivatives tethered to multiple viologen acceptors, [Ru(bpy)₂(4,4′‐MV2)]⁶⁺, [Ru(bpy)₂(4,4′‐MV4)]¹⁰⁺, and [Ru(bpy)(4,4′‐MV4)₂]¹⁸⁺ [bpy=2,2′‐bipyridine, 4,4′‐MV2=4‐ethoxycarbonyl‐4′‐(N‐G₁‐carbamoyl)‐2,2′‐bipyridine, and 4,4′‐MV4=4,4′‐bis(N‐G₁‐carbamoyl)‐2,2′‐bipyridine, where G₁=Asp(NHG₂)‐NHG₂ and G₂=‐(CH₂)₂‐N⁺C₅H₄‐C₅H₄N⁺‐CH₃] were prepared as “photo‐charge separators (PCSs)”. Photoirradiation of these complexes in the presence of a sacrificial electron donor (EDTA) results in storage of electrons per PCS values of 1.3, 2.7, and 4.6, respectively. Their applications in the photochemical H₂ evolution from water in the presence of a colloidal Pt H₂‐evolving catalyst were investigated, and are discussed along with those reported for [Ru(bpy)₂(5,5′‐MV4)]¹⁰⁺, [Ru(4,4′‐MV4)₃]²⁶⁺, and [Ru(5,5′‐MV4)₃]²⁶⁺ (Inorg. Chem. Front. 2016 , 3, 671–680). The PCSs with high dimerization constants (K_d=10⁵–10⁶ m ^?1) are superior in driving H₂ evolution at pH 5.0, whereas those with lower K_d values (10³–10⁴ m ^?1) are superior at pH 7.0, where K_d=[(MV⁺)₂]/[MV^{+ .} ]². The (MV⁺)₂ site can drive H₂ evolution only at pH 5.0 as a result of its 0.15 eV lower driving force for H₂ evolution relative to MV^{+ .} , whereas the PCSs with lower K_d values exhibit higher performance at pH 7.0 owing to the higher population of free MV^{+ .} . Importantly, the rate of electron charging over the PCSs is linear to the apparent H₂ evolution rate, and shows an intriguing quadratic dependence on the number of MV²⁺ units per PCS.     

Poly[diaqua(μ‐4,4′‐bipyridine‐κ2N:N′)bis(μ‐cyanido‐κ2C:N)bis(cyanido‐κC)nickel(II)copper(II)]: a metal–organic cyanide‐bridged framework

The structure of the title compound, [NiCu(CN)₄(C₁₀H₈N₂)(H₂O)₂]_n or [{Cu(H₂O)₂}(μ‐C₁₀H₈N₂)(μ‐CN)₂{Ni(CN)₂}]_n, was shown to be a metal–organic cyanide‐bridged framework, composed essentially of –Cu–4,4′‐bpy–Cu–4,4′‐bpy–Cu– chains (4,4′‐bpy is 4,4′‐bipyridine) linked by [Ni(CN)₄]²⁻ anions. Both metal atoms sit on special positions; the Cu^II atom occupies an inversion center, while the Ni^II atom of the cyanometallate sits on a twofold axis. The 4,4′‐bpy ligand is also situated about a center of symmetry, located at the center of the bridging C—C bond. The scientific impact of this structure lies in the unique manner in which the framework is built up. The arrangement of the –Cu–4,4′‐bpy–Cu–4,4′‐bpy–Cu– chains, which are mutually perpendicular and non‐intersecting, creates large channels running parallel to the c axis. Within these channels, the [Ni(CN)₄]²⁻ anions coordinate to successive Cu^II atoms, forming zigzag –Cu—N[triple‐bond]C—Ni—C[triple‐bond]N—Cu– chains. In this manner, a three‐dimensional framework structure is constructed. To the authors' knowledge, this arrangement has not been observed in any of the many copper(II)–4,4′‐bipyridine framework complexes synthesized to date. The coordination environment of the Cu^II atom is completed by two water molecules. The framework is further strengthened by O—H...N hydrogen bonds involving the water molecules and the symmetry‐equivalent nonbridging cyanide N atoms.     

A novel cadmium(II) coordination polymer with biphenyl‐3,3′,4,4′‐tetra­carboxylic acid and 4,4′‐bipyridine

A novel cadmium(II) coordination polymer, poly[[[bis­(4,4′‐bipyridine)cadmium(II)]‐μ₃‐4,4′‐dicarboxy­biphenyl‐3,3′‐di­carboxyl­ato] 0.35‐hydrate], {[Cd(C₁₆H₈O₈)(C₁₀H₈N₂)₂]·0.35H₂O}_n, was obtained by reaction of Cd(CH₃COO)₂·3H₂O, 4,4′‐bipyridine (4,4′‐bpy) and biphenyl‐3,3′,4,4′‐tetra­car­boxylic acid (H₄L) under hydro­thermal conditions. Each Cd^II atom lies at the centre of a distorted octa­hedron, coordinated by four O atoms from three H₂L²⁻ ligands and N atoms from two monodentate 4,4′‐bpy ligands. Each H₂L²⁻ ligand coordinates to three Cd^II atoms through two carboxyl­ate groups, one acting as a bridging bidentate ligand and the other in a chelating bidentate fashion. Two Cd atoms, two H₂L²⁻ anions and four 4,4′‐bpy ligands form a ring dimer node, which links into an extended broad zonal one‐dimensional chain along the c axis.     

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.