A convenient method of producing thiophene linked bipyridine oligomers

A series of soluble polybipyridine ligands comprising one to five bipyridine modules sandwiched between rigid carbon-carbon triple bonds substituted by 3,4-dibutylthiophene repeating units was synthesized. Two different protocols have been explored with the idea to use a divergent/convergent approach starting from bisymmetrically and symmetrically substituted bipyridine modules. At each stage of the iteration two bipy/thiophene modules are connected. The use of triethylsilylacetylene and 2-methylbut-3-yn-2-ol insures an easy entry to pivotal building blocks, which could be selectively deprotected from the TES or 2-hydroxyprop-2-yl sites. All cross-coupling reactions are promoted with palladium(0) tetrakistriphenylphosphine under mild conditions.     

Spectroscopic and redox properties of novel d6-complexes engineered from all Z-ethenylthiophene-bipyridine ligands

A series of quasilinear dinuclear complexes incorporating ruthenium(II)- and osmium(II)-tris(2,2'-bipyridine) units has been prepared in which the individual metal-containing moieties are separated by 3,4-dibutyl-2,5-diethenylthiophene spacers and end-capped by 3,4-dibutyl-2-ethenylthiophene subunits; related ruthenium(II) and osmium(II) mononuclear complexes have also been prepared where one bpy unit is likewise end-capped by 3,4-dibutyl-2-ethenylthiophene subunits [bpy = 2,2'-bipyridine]. Overall, mononuclear species, labeled here Ru and Os, and dinuclear species, RuRu, OsOs, and RuOs, have been prepared and investigated. Their electrochemical behavior has been studied in CH3CN solvent and reveals ethenylthiophene-centered oxidations (irreversible steps at > +1.37 V vs SCE), metal-centered oxidations (reversible steps at +1.30 V vs SCE for Ru(II/III) and +0.82 V vs SCE for Os(II/III)), and successive reduction steps localized at the substituted bpy subunits. The spectroscopic studies performed for the complexes in CH3CN solvent provided optical absorption spectra associated with transitions of ligand-centered nature (LC, from the bpy and ethenylthiophene subunits) and metal-to-ligand charge-transfer nature (MLCT), with the former dominating in the visible region (400-600 nm). While the constituent ethenylthiophene-bpy ligands are strong fluorophores (fluorescence efficiency in CH2Cl2 solvent, phi em = 0.49 and 0.39, for the monomer and the dimer, respectively), only weak luminescence is observed for each complex in acetonitrile at room temperature. In particular, (i) the complexes Ru and RuRu do not emit appreciably, and (ii) the complexes Os, OsOs, and RuOs exhibit triplet emission of 3Os --> L CT character, with phi em in the range from 10-3 to 10-4. These features are rationalized on the basis of the role of nonemissive triplet energy levels, 3Th, centered on the ethenylthiophene spacer. These levels appear to lie lower in energy than the 3Ru --> L CT triplet levels, and in turn higher in energy than the 3Os --> L CT triplet levels, along the sequence 3Ru --> L CT > 3Th > 3Os --> L CT.     

Further insight into the coordination of 2,5-dicarbothioamidopyrroles: the case of Cu and Co complexes

The coordination chemistry of 2,5-dicarbothioamidopyrrole ligands, namely N2,N5-dibutyl-3,4-diphenyl-1H-pyrrole-2,5-bis(carbothioamide) and N2,N5,3,4-tetraphenyl-1H-pyrrole-2,5-bis(carbothioamide), has been investigated with Cu(II) metal centres by means of X-ray crystallography. This resulted in the formation of the expected planar S,N,S' coordinated complex for the former ligand and unexpected ring-closure reactions, with formation of benzothiazole sidearms, for the latter. Both Cu(II) and Cu(I), used in large excess, were found to favour the ring-closure reaction, although the structural characterisation of the resulting complexes contained only Cu(II) cations, with varying coordination geometries ranging from square planar and square-based pyramidal to tetrahedral. By repeating the reaction using a slight excess of Cu(II) (2?:?1) two more different structures were obtained where the metal was coordinated to the original ligand, N2,N5,3,4-tetraphenyl-1H-pyrrole-2,5-bis(carbothioamide), or to the mixed ligand where only one of the thioamide substituents had converted to a benzothiazole. The essential role of Cu for the ring closure reaction was also established by comparing its complex with structural features of the analogous Co(II) complex, the latter revealing no ring closure to give benzothiazole substituents and co-crystallisation of a mixed Co(II)/Co(III) complex. Finally, the structure and photophysical properties of the corresponding 3,4-diphenyl-2,5-bis(benzothiozol-5-yl)-pyrrole ligand, obtained via treatment of the thioamide with K(3)[Fe(CN)(6)], were also investigated revealing a blue-centered emission.     

Giant macrocycles composed of thiophene, acetylene, and ethylene building blocks

Fully conjugated giant macrocyclic oligothiophenes with 60pi, 90pi,120pi, 150pi, and 180pi frames (1, 2, 3, 4 and 5) have been designed, and their butyl-substituted derivatives (1a, 2a, 3a, 4a, and 5a) have been synthesized using modified Sonogashira and McMurry coupling reactions as key steps. The 60-180pi systems 1-5 are circular with 1.8-6 nm inner cavities and 3.3-7.5 nm outside molecular diameters. Compound 1a containing ten 3,4-dibutyl-2,5-thienylene, eight ethynylene, and two vinylene units has been converted into macrocyclic oligo(3,4-dibutyl-2,5-thienylene-ethynylene) 6a using bromination/dehydrobromination procedure. Giant macrocycles 1a-6a exhibit a red shift of their absorption spectra and a fairly strong fluorescence with a large Stokes shift as compared to a linear conjugated counterpart having five thiophene rings. Compounds 1a-6a exhibit multistep reversible redox behaviors with fairly low first oxidation potentials, reflecting their cyclic conjugation. Furthermore, chemical oxidation of 1a-6a with FeCl3 shows drastic changes of spectroscopic properties due to intramolecular and intermolecular pi-pi interactions. Doping of 1a-3a with iodine forms semiconductor due to its pi-donor properties and pi-pi stacking ability. X-ray analysis of 1a confirmed a round, planar structure with nanoscale inner cavity, and revealed host ability for alkanes and unique packing structure. Interestingly, 2a and 3a self-aggregate in the solid state to form "molecular wires," which are about 200 nm thick and more than 1 mm long. The internal structures of fibrous aggregates have been investigated by optical microscope, scanning electron microscopy, atomic force microscopy, and X-ray diffraction analyses.     

Energy transfer in hybrids based on a thiophene-substituted ethynylbipyridine dimer decorated with Re(I), Ru(II), and Os(II) units

The preparation, structural features, electrochemical behavior, and optical properties (at room temperature and at 77 K) are reported for a series of thiophene-containing hybrids based on the bent conjugated backbone of a rigid ditopic ligand, the dimeric moiety 3,4-dibutyl-2,5-bis{5'-[(3,4-dibutylthien-2-ylethynyl)-2,2'-bipyridin-5-yl]ethynyl}thiophene (TBTBT). Within the dimer, the diethynyl-2,2'-bipyridine units (bpy, the coordination sites) alternate with three 3,4-dibuthylthiophene units and coordination of the [Re(CO)3Cl], [Ru(bpy)2]2+, and [Os(bpy)2]2+ centers results in the mononuclear species RuTBTBT and OsTBTBT and the binuclear species RuTBTBTRu, OsTBTBTOs, RuTBTBTOs, and ReTBTBTOs. At room temperature, the emitting states obtained by photoexcitation are of 3MLCT nature, and vibronic analysis of the emission spectra indicates that they are largely delocalized over the TBTBT ligand. In the binuclear species, the intermetal separation is ca. 17 A, and for RuTBTBTOs, an efficient Ru --> Os excitation transfer takes place, resulting solely in an Os-based emission. The process is ascribed to double-electron transfer (Dexter), as mediated by the TBTBT ligand; a similar conclusion holds for the case of ReTBTBTOs. For RuTBTBTOs, the process is discussed in some detail also with regard to the possibility of disentangling the constituent hole and electron-transfer events.     

Structural diversity in the first metal complexes of 2,5-dicarboxamidopyrroles and 2,5-dicarbothioamidopyrroles

Metal complexes of 2,5-dicarboxamidopyrroles and 2,5-dicarbothioamidopyrroles have been structurally characterised for the first time, complementing the significant amount of work that has been reported for the analogous pyridine ligands. N,N'-Bis(3,5-dinitrophenyl)-3,4-diphenyl-1H-pyrrole-2,5-dicarboxamide forms octahedral bis(tridentate) complexes with cobalt(iii) and nickel(ii), where the ligands are bound to the metal centres through deprotonated pyrrole and amide N atoms. N,N'-Dibutyl-3,4-diphenyl-1H-pyrrole-2,5-dicarboxthioamide and N,N'-diphenyl-3,4-diphenyl-1H-pyrrole-2,5-dicarboxthioamide also form bis(tridentate) cobalt complexes but are only deprotonated at the pyrrole N atom, the remainder of the coordination sphere comprising the thioamide S atoms. The dibutyl derivative was isolated as a Co(ii) complex, whereas the diphenyl system deposited a Co(iii) complex. In contrast, N,N'-dibutyl-3,4-dichloro-1H-pyrrole-2,5-dicarboxamide was found to act as a bidentate ligand, in an octahedral cobalt(ii) complex comprising of two bidentate pyrrole ligands, and two aqua ligands. Synthesis of N,N-bis(pyridin-2-ylmethyl)-3,4-diphenyl-1H-pyrrole-2,5-carboxamide gave a pyrrole ligand with increased denticity. Reaction with cobalt(ii) chloride resulted in the isolation of a dinuclear helicate complex. The ligand was found to have undergone addition of a methoxy group to one of the linking methylene carbons, presumably as a result of the oxidative addition of solvent methanol.     

Synthesis of derivatives of cyclobuteno[c]thiophen and attempts to synthesise thiophen analogues of biphenylene

Starting from 2,5-dichlorothiophen many new 3,4-disubstituted thiophens have been made including the dialdehyde. Treatment of this with phosphorus pentabromide could be made to give 2,5-dichloro-3- dibromomethylthiophen-4-aldehyde, 2,5-dichloro- or 2-bromo-5-chloro-3,4-bisdibromomethylthiophen. the latter two compounds reacted with sodium iodide to give the corresponding cis- and trans-3,4-dibromo cyclobuteno[c]thiophen derivatives (18–21). Reaction of trans-3,4-dibromo-2,5-dichlorocyclobuteno[c]thiophen with N-bromosuccinimide resulted in fission of the 4-membered ring regenerating 2,5-dichloro-3,4-bisdibromomethylthiophen.When 2,5-dichloro-3,4-di-iodothiophen was treated with butyl-lithium followed by dimethylsulphate it gave 2,5- dichloro-3,4-dimethylthiophen together with a low yield of a red compound which is considered to be a dichloro dimethyl derivative (11) of bisthiophenindigo.Several unsuccessful approaches to the synthesis of dithiophen analogues of biphenylene are outlined. These included heating various 3,4-di-iodothiophens and 4,4′-di-iodo-3,3′-bithienyls with copper as well as the flash vacuum pyrolysis of the latter compounds, of thiophen-3,4-dicar?ylic anhydrides and of 2,5-dichloro-3-iodothiophen-4-car?ylic acid.     

A concise modular synthesis of 2,5-diethynyl-3,4-dibutyl-thiophene-bridged back-to-back terpyridine ligands

The efficient synthesis of soluble and rigid terpyridine-based ditopic ligands bearing an increasing number of 2,5-diethynyl-3,4-dibutylthiophene (DEDBT) modules has demonstrated the advantages of a single convergent strategy based on a double coupling in a final step of monoterpyridine building blocks carrying the adequate number of thiophene modules with a diiodo-substituted thiophene subunit. This protocol enjoys the advantages of both efficiency and versatility and requires pivotal intermediates, which were produced by a step-by-step implementation of monoterpyridine fragments with a key thiophene intermediate carrying an iodo function, a propargylic-protecting group, and two butyl-solubilizing fragments. One set of experimental conditions is required to produce all the intermediates and the final ligands. Oxidative dimerization of monosubstituted terpyridine skeletons bearing one or two thiophene substituents and a terminal alkyne function, in the presence of cupric salts and oxygen, afforded the homotopic ligands with a central dithienylbutadiyne spacer. Optical properties for the new oligomers have been investigated and are discussed in terms of effective conjugation length and pi-electron conjugation. Upon increasing the number of interspersed DEDBT units, a significant lowering in energy of absorption and fluorescence transitions as well as of the quantum yields is observed.     

Synthesis of bipyridine and terpyridine based ruthenium metallosynthons for grafting of multiple pyrene auxiliaries

The synthesis of novel ruthenium(II) bipyridine or terpyridine complexes bearing an increasing number of pyrene or toluyl moieties is described. The ruthenium complexes are constructed in a first step with ligands bearing the required bromine functions, followed in a second step by stepwise grafting of 1-ethynylpyrene or 4-ethynyltoluene promoted by Pd(0). A complex bearing a protected triethylsilylacetylene function was also prepared. In situ deprotection of this function with K₂CO₃ and cross-coupling with 1-bromopyrene afforded a soluble complex in which two pyrene moieties are linearly linked via ethynyl spacers to one of the bipyridine ligands. These highly coloured complexes exhibit well defined absorption and emission properties in solution at both rt and 77 K.     

Elastic and inelastic electron tunneling spectroscopy of a new rectifying monolayer

Rectification of electrical current was observed in a Langmuir-Schaefer monolayer of fullerene-bis[ethylthio-tetrakis(3,4-dibutyl-2-thiophene-5-ethenyl)-5-bromo-3,4-dibutyl-2-thiophene] malonate, Au electrodes at room temperature (there are two regimes of asymmetry, at lower bias, i.e., between 0 and +/-2 V, and at higher bias), and also between Pb and Al electrodes at 4.2 K. The latter experiment was coupled with second harmonic detection of the second derivative of the current with respect to voltage (d2I/dV2). The d2I/dV2 spectrum shows intramolecular vibrations, and also two antisymmetric broad bands, centered at +/-0.65 V, due to resonant electron tunneling between the Fermi level(s) of the electrodes and the lowest unoccupied molecular orbital of the molecule.     

Weak Antiferromagnetism in Carboxylato Copper(II) Complexes of Bipyridines

Three new members of the copper/carboxylato/heterocyclic diimine family, namely [Cu(GLYO)(2, 2′‐bipy)]₂ · nH₂O (n = 4 ( 1 ) or 6 ( 2 ), H₂GLYO = glycolic acid, 2, 2′‐bipy = 2, 2′‐bipyridine) and {[Cu(AcO)₂(4, 4′‐bipy)] · 3H₂O}_n ( 3 ) (AcO = acetato, 4, 4′‐bipy = 4, 4‐bipyridine), have been synthesized and characterized by IR and electronic absorption spectroscopy, and the crystal structures have been determined by single crystal X‐ray analysis. 1 and 2 are composed of discrete dinuclear units in which each Cu^II atom is coordinated in a square pyramidal arrangement to the two nitrogen atoms of a bipyridine ligand, to bridging non‐carboxy oxygen atoms belonging to two glycolato ligands, and to one of the carboxy oxygen atoms of one of these glycolato ligands. The Cu··Cu distance is 3.0666(5)Å. Compound 3 consists of linear chains of dinuclear units in which each Cu^II is coordinated to one non‐bridging monodentate acetato ligand, to two acetato ligands that each bridge via a single oxygen atom, and to one nitrogen atom of each of two mutually trans bis‐monodentate 4, 4′‐bipyridine ligands that link the repeat units of the polymer. The coordination polyhedra are square pyramids, and the Cu··Cu distance within each dimeric repeat unit is 3.502(2)Å. The temperature dependence of their magnetic susceptibilities shows there to be weak antiferromagnetic interaction between the metal atoms of each dimer in all three complexes, with fitting parameter values of —2J = 1.3 cm^—1 and g = 2.09 for 1 and 2 , and —2J = 1.4 cm^—1 and g = 2.15 for 3 . The X‐band EPR spectra show signals corresponding to the dinuclear units.     

Synthesis and michael reaction of 3,4-dimethylpyrrole

A two step synthesis of 3,4-dimethylpyrrole via the reduction of 3-carboethoxy-4-methyl-pyrrole is described. Michael addition of methyl vinyl ketone and butyn-2-one to 3,4-dimethylpyrrole gives the bisadducts, 2,5-bis(3-oxobutyl)-3,4-dimethylpyrrole and 2,5-bis(3-oxobutenyl)-3,4-dimethylpyrrole, respectively, while ethyl propiolate affords only the monoadduct, ethyl 3-(3,4-dimethylpyrrol-2-yl)propenoate. Catalytic reduction of the latter ester gives ethyl 3-(3,4-dimethylpyrrol-2-yl)propanoate which with ethyl propiolate gives ethyl 3-(5-carbethoxyethyl-3,4-dimethyl-2-yl)propenoate.     

Metallomacrocycles with a Difference: Macrocyclic Complexes with Exocyclic Ruthenium(II)‐Containing Domains

The templated synthesis of organic macrocycles containing rings of up to 96 atoms and three 2,2′‐bipyridine (bpy) units is described. Starting with the bpy‐centred ligands 5,5′‐bis[3‐(1,4‐dioxahept‐6‐enylphenyl)]‐2,2′‐bipyridine and 5,5′‐bis[3‐(1,4,7‐trioxadec‐9‐enylphenyl)]‐2,2′‐bipyridine, we have applied Grubbs’ methodology to couple the terminal alkene units of the coordinated ligands in [FeL₃]²⁺ complexes. Hydrogenation and demetallation of the iron(II)‐containing macrocyclic complexes results in the isolation of large organic macrocycles. The latter bind {Ru(bpy)₂} units to give macrocyclic complexes with exocyclic ruthenium(II)‐containing domains. The complex [Ru(bpy)₂(L)]²⁺ (isolated as the hexafluorophosphate salt), in which L=5,5′‐bis[3‐(1,4,7,10‐tetraoxatridec‐12‐enylphenyl)]‐2,2′‐bipyridine, undergoes intramolecular ring‐closing metathesis to yield a macrocycle which retains the exocyclic {Ru(bpy)₂} unit. The poly(ethyleneoxy) domains in the latter macrocycle readily scavenge sodium ions, as proven by single‐crystal X‐ray diffraction and atomic absorption spectroscopy data for the bulk sample. In addition to the new compounds, a series of model complexes have been fully characterized, and representative single‐crystal X‐ray structural data are presented for iron(II) and ruthenium(II) acyclic and macrocyclic species.     

Chiral and extended π-conjugated bis(2-pyridyl)phospholes as assembling N,P,N pincers for coordination-driven synthesis of supramolecular [2,2]paracyclophane analogues

Chiral, π-conjugated 3,4-butano-1-phenyl-2,5-bis(2-pyridyl)phosphole derivatives 1a(2,2') and 1a(3) with chiral trans-1,2-diol moieties and fused pinene derivatives, respectively, were prepared from the corresponding chiral diynes by using the Fagan-Nugent method. Their UV/Vis absorption and chiroptical properties (optical rotation and circular dichroism) were studied. Their behavior as N,P,N chelates towards coordination of Cu(I) and formation of chiral supramolecular assemblies with π-conjugated ditopic dicyano ligands was investigated. Chiral C(2)-symmetric rectangles that are [2,2]paracyclophane analogues were obtained, as demonstrated by X-ray crystallography. During the course of this study, the first stable water-soluble phosphole derivative (1a(2)·2 HCl) was prepared. Furthermore, achiral 3,4-butano-1-phenyl-2,5-bis(aza[4]helicene)phosphole 1a(4) was synthesized and displays extended π conjugation. A supramolecular rectangle was obtained by coordination to Cu(I) and assembly with a dicyano stilbene. This coordination-driven supramolecular assembly contains a total of four aza[4]helicene moieties and displays two types of π-π stacking interactions in the solid state, that is, between two helicene moieties and between one helicene and a bridging dicyano ligand. All the supramolecular arrangements are discussed by comparing them with previous work on the parent 3,4-butano-1-phenyl-2,5-bis(2-pyridyl)phosphole.     

Mechanism and selectivity of radical alkylation of 3,4-Dichloro-2,5-dihydrofuran-2,5-dione

The mechanism of radical alkylation of 3,4-dichloro-2,5-dihydrofuran-2,5-dione with cyclohexane and 2,3-dimethylbutane follows an addition-elimination pattern with reversible formation of alkyl radicals. The proposed kinetic scheme takes into account the possibility for isomerization of primary 2,3-dimethylbutane radicals into tertiary and is consistent with the experimental data. The regioselectivity of the process is linearly related to the concentration of hydrogen chloride, so that the rate constant for the addition of primary 2,3-dimethylbutane radical to 3,4-dichloro-2,5-dihydrofuran-2,5-dione may be estimated. Effective procedures for the synthesis of 3-chloro-4-(2,3-dimethylbut-2-yl)-, 3-chloro-4-cyclohexyl-, and 3,4-dicyclohexyl-2,5-dihydrofuran-2,5-diones have been proposed.     

Switching of molecular insertion in a cyclic molecule via photo- and thermal isomerization

Two new cyclic ligands were synthesized: a ligand with two trans-azobenzene moieties and one bipyridine moiety, trans(2)-oAB-O13, and a ligand with two trans-azobenzene moieties and two bipyridine moieties, trans(2)-oAB-bpy. Both ligands underwent reversible trans-cis isomerization at the azobenzene moieties. The mole ratios of the trans(2) form:trans-cis form:cis(2) form, evaluated by (1)H NMR spectroscopy of the photostationary states prepared by 1 h illumination, were 0.13:0.27:0.60 (365 nm irradiation) and 0.41:0.47:0.12 (436 nm irradiation) for oAB-O13, and 0.18:0.12:0.70 (365 nm irradiation) and 0.36:0.43:0.21 (436 nm irradiation) for oAB-bpy. When trans(2)-oAB-O13 was mixed with Cu(I), both the bipyridine units and the polyether chains coordinated to the copper center. Addition of a noncyclic bipyridine ligand, trans(2)-oAB-2OH, afforded a bis(bipyridine)copper(I) complex, [Cu(trans(2)-oAB-O13)(trans(2)-oAB-2OH)]BF(4). The bis(bipyridine) ligand, trans(2)-oAB-bpy, formed a 1:1 complex with Cu(I), [Cu(trans(2)-oAB-bpy)]BF(4). [Cu(cis(2)-oAB-bpy)]BF(4) did not undergo the ligand substitution reaction with a noncyclic ligand with two azobenzene moieties and one bipyridine moiety, oAB, whereas its thermal isomerization in the presence of oAB caused the formation of [Cu(trans(2)-oAB-bpy)(trans(2)-oAB)]BF(4), indicating that the isomerization and ligand exchange reactions synchronized via a conformational change of the cyclic ligand.     

Electron Localization Dynamics in the Triplet Excited State of [Ru(bpy)3]2+ in Aqueous Solution

Hybrid DFT/classical molecular dynamics of the long‐lived triplet excited state of [Ru(bpy)₃]²⁺ (bpy=2,2′‐bipyridine) in aqueous solution is used to investigate the solvent‐mediated electron localization and dynamics in the triplet metal‐to‐ligand charge‐transfer (MLCT) state. Our studies reveal a solvent‐induced breaking of the coordination symmetry with consequent localization of the photoexcited electron on one or two bipyridine units for the entire length of our simulation, which amounts to several picoseconds. Frequent electronic “hops” between the ligands constituting the pair are observed with a characteristic time of approximately half a picosecond.     

Synthesis and several transformations of sulfides of the thiophene series

Several new N-substituted 2,5-bis(mercapto)-3,4-bis(iminomethyl)thiophenes, which are new tetradentate ligands of the thiophene series, were obtained by the reaction of primary amines with the product formed during the successive action of four equivalents of sodium in liquid ammonia and HCl on the tetraethylacetal of 2,5-bis(methylmercapto)-3,4-thiophenedialdehyde.For Communication XXII, see [4].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1323–1325, October, 1970.     

Synthesis of Polyaza Macrocyclic Ligands Incorporating Pyridine Units

The synthesis of nine macrocyclic polyamines 2-10 containing pyridine units is described. These compounds are 22- ( 9 ), 24- ( 2-4,6,8,10 ), or 26- ( 5 , 7 ) membered hexaaza ( 2,3,9,10 ) or octaaza ( 4–7 ) macrocycles in which one to four pyridine units are incorporated. Compounds 3,4,9 , and 10 are homoditopic ligands, whereas 2 and 5 are heteroditopic and 6?8 multitopic receptors. Compounds 2-10 are potential ligands for metal cations as well as, in their protonated forms, for anions. Protonated macrocycles 2?10 are also potential catalysts for the hydrolysis of nucleotides and polyphosphates.     

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.