New chiral 2,2′:6′,2″-terpyridine ligands from the chiral pool: synthesis,crystal structure of a rhodium complex and uses in copper- and rhodium-catalyzed enantioselective cyclopropanation of styrene

A number of chiral C₂-symmetric 2,2′:6′,2″ terpyridines L₁–L₄ were synthesized in moderate to good yields from commercially available chiral materials. Copper(II) and rhodium(III) chloride complexes of these ligands were prepared in good yields. The Rh(L₂)Cl₃ complex was isolated as a yellow crystalline solid and characterized by X-ray crystallography. Both Cu(L)(OTf)₂ and Rh(L)(OTf)₃ were found to be active catalysts in the cyclopropanation of styrene with ethyl diazoacetate. Enantioselectivity up to 82% e.e. was observed.     

Photophysical Properties of 4′-(p-aminophenyl)-2,2′:6′,2′′-terpyridine

Spectral and photophysical investigations of 4′-(p-aminophenyl)-2,2′:6′,2′′-terpyridine (APT) have been performed in various solvents with different polarity and hydrogen-bonding ability.The emission spectra of APT are found to exhibit dual fluorescence in polar solvents, which attributes to the local excited and intramolecular charge transfer states, respectively. The two-state model is proven out for APT in polar solvent by the time-correlated single photon counting emission decay measurement. Interestingly, the linear relationships of different emission maxima and solvent polarity parameter are found for APT in protic and aprotic solvents, because of the hydrogen bond formation between APT and alcohols at the amino nitrogen N25. Furthermore, the effects of the complexation of the metal ion with tpy group of APT and the hydrogen bond formation between APT with methanol at the terpyridinenitrogen N4—N8—N14 are also presented. The appearance of new long-wave absorption and fluorescence bands indicates that a new ground state of the complexes is formed.     

Cadmium(II) complexes of 4′-tolyl-2,2′:6′,2′′-terpyridine: synthesis,structures, and antibacterial activities

A straightforward synthetic method has been developed to prepare cadmium(II) complexes of 4′-tolyl-2,2′:6′,2″-terpyridine (ttpy) in good yields. These complexes are formulated as {[Cd(ttpy)(NO₃)₂][Cd₂(ttpy)₂(NO₃)₄]} (1), [Cd₂(ttpy)₂(N₃)₄]0.5CH₃OH?·?0.125H₂O (2), and {[Cd(ttpy)(SCN)(CH₃COO)][Cd(ttpy)(SCN)₂]₂} (3). Intermolecular, intramolecular, hydrogen bonding and π–π stacking interactions were observed in the complexes, and are responsible for the arrangement of complexes in the crystal packing and play essential roles in forming different frameworks of 1–3. The antibacterial activities of the synthesized complexes were tested against three gram positive bacteria and three gram negative bacteria.     

Synthesis of a new 2,2′：6′,2″-terpyridine derivative and its coordination property

A novel compound, （E）-4′-（4-（but-1-en-3-ynyl）phenyl）-2,2′：6′,2″-terpyridine 1 was synthesized from 4′-（4-bromomethylphenyl）-2,2P：6P,2PP-terpyridine phosphonium salt 2 and propargylaldehyde via Wittig reaction, and characterized by EI-MS and ^1H NMR as well as elemental analysis. The spectral changes of the compound in the presence of transition metal ions, such as Cu（I） or Zn（ID, are investigated.     

Synthesis,molecular structure and electrochemistry of cobalt(II) complexes of 2,2′: 6′,2′′-terpyridine macrocycles

The macrocycle L, prepared by template condensation of bis-6,6′′-(α-methylhidrazino)-4′-phenyl-2,2′:6′′,2′-terpyridine with glyoxal, forms a stable crystalline complex of cobalt(II) [Co(L)(H₂O)₂][PF₆]₂ which has been used as a starting material to prepare, for electrochemical studies, a series of seven coordinate cobalt(II) complexes [Co(L)X₂][PF₆]₂ (X=pyridine, 4-cianopyridine, 4-aminopyridine, 4-dimethylaminopyridine, pirazine, imidazole, 1-methylimidazole, 2-methylimidazole, and trimethylphosphite). Cyclic voltammetry of the aquo complex in DMSO show one reversible reduction wave at −1.35 V versus Ag ∣ AgBF₄ reference electrode and controlled potential electrolysis in the presence of trimethylphosphite affords a diamagnetic species which has been assigned as a mononuclear d⁸ Co(I) species. The crystal and molecular structure of [Co(L)(imidazole)₂][PF₆]₂·Me₂CO shows the metal to be in a pentagonal-bipyramidal N₇ environment.     

Crystal structure of a hydroxo-bridged dimeric uranyl complex with a 2,2′:6′,2″-terpyridine ligand

A new dimeric compound [{UO₂(μ-OH)(terpy)}₂](ClO₄)₂·0.67CH₃CN, containing an uranyl cation and a tridentate 2,2′:6′,2″-terpyridine (terpy) ligand, is synthesized from an acetonitrile solution of uranyl perchlorate and terpy. The crystal structure of the compound is determined by single crystal X-ray diffraction. The crystal structure shows the formation of symmetric and asymmetric cationic hydroxo-bridged uranyl dimers. The uranium atoms adopt a distorted pentagonal bipyramidal configuration with a UO₄N₃ coordination environment formed by two uranyl O atoms, three N atoms from the terpy ligand, and two O atoms from the hydroxide anions.     

Effect of solvent on the crystal structures of copper(II) complexes based on 4′-(4-methoxyphenyl)-2,2′:6′,2″-terpyridine and 4′-(3-chlorophenyl)-2,2′:6′,2″-terpyridine

Four homoleptic copper(II) complexes, [Cu(Meophtpy)₂](ClO₄)₂ (Meophtpy = 4′-(4-methoxylphenyl)- 2,2′:6′,2″-terpyridine) (I), [Cu(Meophtpy)₂](ClO₄)₂ · 2H₂O (II), [Cu₂(m-Clphtpy)₄](ClO₄)₄ (m-ClPhtpy = 4′-(3-chlorophenyl)-2,2′:6′,2″-terpyridine) (III), and [Cu₂(m-ClPhtpy)₄](ClO₄)₄ (IV) have been synthesized by hydrothermal methods and characterized by IR, elemental analysis and single crystal X-ray diffraction (CIF files CCDC nos. 963375 (I), 885457 (II), 963377 (III), and 963376 (IV)). Complex II is a polymorph of I and complex IV is a polymorph of III. All these complexes are obtained with 95% ethanol solution or 50% ethanol solution and the solvent control on the crystallization are obviously found. In all complexes, the face-to-face interactions between pyridyl rings or phenyl rings facilitate the construction of 3D network in the crystal in addition to hydrogen bonds. The fluorescence properties of these complexes have been investigated.     

Crystal Structures of Molecular Adducts between Uranyl Nitrate and 2,2′ : 6′,2′′-Terpyridine or 2,2′-Bipyridyl

Complexes of uranyl nitrate with aromatic molecular ligands : [UO₂Terpy(NO₃)₂] and (H₂Terpy)₂[UO₂(NO₃)₂(H₂O)₂](NO₃)₄ · 4H₂O (Terpy 2,2:6,2-terpyridine), (Hbipy)[UO₂(NO₃)₃] and [(UO₂)₂(Bipy)₂O₂(NO₃)₂] (Bipy—2,2-bipyridyl) and (HPy)₄[(UO₂)₂(NO₃)₄(OH)₂](NO₃)₂ (Py—pyridine) were characterized by X-ray diffraction analysis. In all these compounds, the U(VI) atom has the hexagonal bipyramidal environment. The U–O bond lengths in the UO₂ ²⁺ have close values. In the equatorial planes, the U–N bond lengths with the Bipy and Terpy ligands are identical, whereas the U–O bond lengths depend on the type of the ligand. The lengths of the equatorial bonds increase in the sequence U–N > U–O_nitr > U–O_hydr > U–O_perox. The geometric characteristics of the coordinated and solvate Terpy and Bipy molecules are different. The lengths of the N–O bonds in the NO₃ ^– groups depend on the participation of the O atom in the coordination of the central atom, the coordination mode, and the formation of hydrogen bonds.     

Theoretical studies on the electronic structures and spectroscopic properties for a series of Osmium(II)-2,2′,6′,2′′-terpyridine complexes

A series of Osmium(II) complexes [Os (trpy-R)₂]²⁺(trpy=2,2′,6′,2′′-terpyridine and R=H (1), OH (2), and C₆H₅(3)) have been investigated by the density functional (DF) and ab initio calculations. The structures of 1–3 in the ground and excited states were fully optimized at the B3LYP and CIS level, respectively, and their absorption and emission spectra in the acetonitrile solution were obtained using the TD-DFT (B3LYP) method associated with the PCM model. The calculations indicated that, for 1–3, the variation of the substituents on the terpyridine ligand only slightly changes their geometrical structures in the ground and excited states but leads to a sizable difference in the electronic structures. The results show that the low-lying MLCT/ILCT transitions (at 446 (1), 465 (2), and 499 nm (3)) are red-shifted according to the electron-donating ability of substituents on the terpyridine ligand, but blue-shift trend of the high-lying ILCT transitions (at 301 (1), 297 (2), and 272 nm (3)). It also reveals that the lowest energy emissions of 1–3 at 649 nm, 656 nm, and 676 nm have the character of mixing ³[π*(trpy) → d(Os)] and ³ ππ* (³MLCT/³ILCT) transitions localized on the terpyridine ligand, which are identical to the transition properties of the lowest-energy absorptions.     

1,1′-Spirobiindane-7,7′-diol: a novel,C2-symmetric chiral ligand

A novel, C₂-symmetric chiral diol (16) was prepared in six steps from m-anisaldehyde and resolved via its bis-l-menthoxycarboxylate.     

Synthesis and application of C2-symmetric diamino FERRIPHOS as ligands for enantioselective Rh-catalyzed preparation of chiral α-amino acids

C₂-Symmetrical ferrocenyl diamino diphosphines (diamino FERRIPHOS ligands) proved to be excellent ligands for the rhodium-catalyzed enantioselective reduction of methyl α-acetamidoacrylates. The straightforward synthesis, their air stability and the easy modification of their structure makes these ligands especially interesting for transition metal-catalyzed hydrogenations. α-Amino acids with enantioselectivities greater than 95% (and up to 99.3% ee) were obtained with no need of further recrystallization.     

Isosteric expansion of the structural diversity of chiral ligands: Design and application of proline-based N,N′-dioxide ligands for copper-catalyzed enantioselective Henry reactions

Chiral N,N′-dioxide catalysts were designed based on isosteric approach. Using l-Proline as the starting material, a variety of chiral N,N′-dioxide ligands were obtained via conventional functional group transformations and were utilized in asymmetric Henry reactions between nitromethane and aromatic aldehydes. Using the N,N′-dioxide-copper(II) complexes as the catalysts, asymmetric Henry reaction produced the corresponding β-nitroalcohols in up to 66% yields and up to 83% ee's under mild conditions. The reactions were easy to carry out, and special care such as air or moisture-free conditions was not required.     

Understanding the role of flexible 4′-functionalized polyethylene glycoxy chains on the behavior of platinum(II) (4′-(ethylene glycoxy)-2,2′:6′,2′′-terpyridine: a kinetic and a mechanistic study

The ligand substitution kinetics of 4′-functionalized mononuclear Pt(II) (4′-(ethylene glycoxy)-2,2′:6′,2′′-terpyridine complexes, [Pt(nY-tpy)Cl)Cl] (where Y = ethylene glycoxy, n = number of ethylene, glycoxy units = 1, 2, 3, and 4, and tpy = 2,2′:6′,2′′-terpyridine), with thiourea, 1,3-dimethyl-2-thiourea, 1,1,3,3-tetramethyl-2-thiourea, and iodide were investigated under pseudo-first-order conditions as a function of concentration and temperature by conventional stopped-flow technique. The observed first-order rate constants followed the simple rate law k_obs = k₂[Nu]. The data obtained show that the ethylene glycoxy pendant, trans to the leaving group, acts as a σ-donor into the terpyridine ligand and is effective only up to n = 1, beyond which the substitution reactivity of the complexes are controlled by the steric influence of the appended ethylene glycoxy pendant units, which decreases with increase in the number of ethylene glycoxy units. The activation parameters obtained support an associative mechanism, where bond formation in the transition state is favored. The observed reactivity trends were supported by density functional theory calculations.     

Studies on the asymmetric synthesis of huperzine A. Part 2: Highly enantioselective palladium-catalyzed bicycloannulation of the β-keto-ester using new chiral ferrocenylphosphine ligands

New chiral ferrocenylphosphine ligands were designed and tested in the enantioselective bicycloannulation of β-keto-ester 2 with bifunctional allylic agent 4. A range of e.e. values from 80 to 90% of the bicyclic intermediate 6 was achieved. Subsequently, enantiopure (−)-huperzine A was prepared in ca. 40% yield from β-keto-ester 2.     

Preparation and resolution of 2,2′-dimercapto-6,6′-dimethoxy-1,1′-biphenyl: a C2-symmetric sulfur building block

The preparation of the title dimercaptan 1 starting from 2,2′-dihydroxy-6,6′-dimethoxy-1,1′-biphenyl 2 is described. Resolution of dimercaptan 1 was performed using (−)-(1R,2S,5R)-menthyl chloroformate as a chiral resolving agent. The procedure affords dimercaptan (+)-1 and (−)-1 in 98% ee and 93% ee, respectively. A new and direct intermolecular Ullmann coupling resulting in an improved preparation of diol 2 is also reported.     

New cobalt and iron pivalate complexes with 2,2′:6′,2″-terpyridine: synthesis, structure, and magnetic properties

The mononuclear complexes (η³-terpy)M(Piv)²·MeCN (M = Fe ⁱⁱ (3) and Co ⁱⁱ (4), and Piv is the pivalate anion) were synthesized by the reactions of polymeric iron(ii) and cobalt(ii) pivalates with 2,2′:6′,2″-terpyridine (terpy). The oxidation of compound 3 affords the pentanuclear heterospin iron(ii,iii) complex (η³-terpy)Fe₅(μ₄-O)(μ₃-OH)(μ-OH)₂(μ-Piv)₇(η¹-Piv)₂ (5). All compounds were characterized by X-ray diffraction. Dedicated to the 90th anniversary of the L. Ya. Karpov Institute of Physical Chemistry. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1186–1190, June, 2008.     

Effect of the Counter Anion and Solvate on the Structure,Stability and Spectral Properties of a Ruthenium(II) Complex Containing Group 15 Donors and 2,2′ :6′,2′′-terpyridine

Ruthenium complexes [Ru(κ³−tpy)(AsPh₃)₂C1]PF₆ · 0.42H₂O (tpy =2,2′:6′,2′′-terpyridine) (1) and a new crystal form of [Ru(κ³−tpy)(AsPh₃)₂Cl]BF₄ (2), which crystallized without water solvate, and their comparative studies on spectral, structure and stability aspects are reported. The complexes have been characterized by elemental analyses, FAB-MS, i.r., ¹H n.m.r. and electronic spectral studies. In these complexes weak C—H···Fπ and face-to-face π–π interactions lead to a single helical motif while, C—H···FX (X=F, Cl) interactions result in linear chains. Various studies on the stability of the complexes suggested that the compound containing the counter anion PF₆^- is more stable than the other containing BF₄^- as the counterpart.     

Selective formation of thecis isomer of the nitridotechnetium(V) complex with 2,2′:6′,2″-terpyridine

The reaction of [TcNCl₂(PPh₃)₂] with 2,2′:6′,2″-terpyridine producedcis-[TcNCl₂(terpy)] selectively. The resulting complexes were characterized by¹H NMR and IR spectroscopy. The geometries of thecis andtrans isomers were estimated by theoretical calculations following a density functional method. Thecis isomer is likely more stable than thetrans one with respect to thetrans influence of the nitrido ligand. Furthermore, the behavior of nitridotechnetium complexes in polar solvents was compared to Os-analogues.     

Syntheses,characterizations of copper compounds containing a series of S-, N-containing aromatic heterocyclic 2,2′:6′,2″-terpyridine derivatives

A series of 2,2′:6′,2″-terpyridine (TPY) based aromatic heterocyclic compounds, extended by thiophene, 4-dibenzothiophene, and thiazole units at the para position of the central pyridine ring in TPY, are described in this paper. A new compound, 4′-(4′-dibenbenzothiophene-5-thiophene-2-yl)-2,2′:6′,2″-terpyridine (L_a), serves as a tridentate ligand to react with Cu(NO₃)₂·3H₂O and CuCl₂·2H₂O, respectively, to produce two different Cu(II) complexes [Cu(L_a)₂](NO₃)₂ and [CuL_aCl₂] with 1?:?2 and 1?:?1 metal/ligand ratios. Dibenzothiophene is first introduced to TPY via the thiophene bridge. The alterations in cis and trans configuration, dihedral angles between adjacent aromatic rings, and photophysical properties have been observed before and after Cu(II) complexation, which has been verified by their crystal structures, UV–vis and fluorescence spectra.