Tripyridyl Ligand Research Articles

Water-Soluble Metallo-Supramolecular Nanoreactors for Mediating Visible-Light-Promoted Cross-Dehydrogenative Coupling Reactions

Water-soluble metallo-supramolecular cages with well-defined nanosized cavities have a wide range of functions and applications. Herein, we design and synthesize two series of metallo-supramolecular octahedral cages based on the self-assembly of two congeneric truxene-derived tripyridyl ligands modified with two polyethylene glycol (PEG) chains, i.e., monodispersed tetraethylene glycol (TEG) and polydispersed PEG-1000, with four divalent transition metals (i.e., Pd, Cu, Ni, and Zn). The resulting monodispersed cages C1-C4 are fully characterized by electrospray ionization mass spectrometry (ESI-MS), nuclear magnetic resonance (NMR) spectroscopy, and single-crystal X-ray diffraction. The polydispersed cages C5-C8 display good water solubilities and can act as nanoreactors to mediate visible-light-promoted C(sp3)-C(sp2) cross-dehydrogenative coupling reactions in an aqueous phase. In particular, the most robust Pd(II)-linked water-soluble polydispersed nanoreactor C5 is characterized by ESI-MS and capable of mediating the reactions with the highest efficiencies. Detailed host-guest binding studies in conjunction with control studies suggest that these cages could encapsulate the substrates simultaneously inside its hydrophobic cavity while interacting with the photosensitizer (i.e., eosin Y).

Exploiting Supramolecular Interactions to Control Isomer Distributions in Reduced-Symmetry [Pd2L4]4+ Cages.

High-symmetry metallosupramolecular architectures (MSAs) have been exploited for a range of applications including molecular recognition, catalysis, and drug delivery. Recently, there have been increasing efforts to enhance those applications by generating reduced-symmetry MSAs. Here we report our attempts to use supramolecular (dispersion and hydrogen-bonding) forces and solvophobic effects to generate isomerically pure [Pd2(L)4]4+ cage architectures from a family of new reduced-symmetry ditopic tripyridyl ligands. The reduced-symmetry tripyridyl ligands featured either solvophilic polyether chains, solvophobic alkyl chains, or amino substituents. We show using NMR spectroscopy, high-performance liquid chromatography, X-ray diffraction data, and density functional theory calculations that the combination of dispersion forces and solvophobic effects does not provide any control of the [Pd2(L)4]4+ isomer distribution with mixtures of all four cage isomers (HHHH, HHHT, cis-HHTT, or trans-HTHT, where H = head and T = tail) obtained in each case. More control was obtained by exploiting hydrogen-bonding interactions between amino units. While the cage assembly with a 3-amino-substituted tripyridyl ligand leads to a mixture of all four possible isomers, the related 2-amino-substituted tripyridyl ligand generated a cis-HHTT cage architecture. Formation of the cis-HHTT [Pd2(L)4]4+ cage was confirmed using NMR studies and X-ray crystallography.

Nuclei DNA and mitochondria dual damages induced by thiosemicarbazone tripyridyl copper complexes with potential anti-tumor activity

In this study, we synthesised and characterised a di-nuclear complex, [Cu2(dppco)Br3] (1), and a mononuclear complex, [Cu(dppc)Br] (2), with the thiosemicarbazone tripyridyl ligand dppc = 2-(di(pyridin-2)-yl)methylene)-N-(pyridin-2-yl)hydrazine-1-carbothio-amide. The S atom of the ligand in complex 1 was replaced by an O atom in the solvothermal reaction, while only the ligand in complex 2 contains an S tom (it is therefore a thiosemicarbazone). Compared to complex 1, complex 2 has a stronger inhibitory effect on the colon cancer cell line (HCT116), human breast cancer cell line (CAOV-3) and liver cancer cell line (SMMC7721), especially being more sensitive to HCT116 cells. Fluorescence, circular dichroism and DNA cleavage experiments showed that complexes 1 and 2 have an excellent DNA binding ability, mostly binding to DNA by the intercalation mode. In contrast, the thiosemicarbazone-based complex 2 has a stronger cell uptake ability, which triggered more prominent cellular apoptosis and cell cycle arrest. Further mechanism studies revealed that complex 2 caused more serious mitochondrial damage than that for complex 1, including an increased level of reactive oxygen species (ROS) and Ca2+, decreased ATP content and mitochondrial membrane potential (Δψm), and significantly transformed the mitochondrial morphology.

Anthracene-Triphenylamine-Based Platinum(II) Metallacages as Synthetic Light-Harvesting Assembly.

Two trigonal prismatic metallacages 1 and 2 bearing triphenylamine and anthracene moieties are designed and synthesized to fabricate artificial light-harvesting systems (LHSs). These two cages are prepared via the coordination-driven self-assembly of two anthracene-triphenylamine-based tripyridyl ligand 3, three dicarboxylates, and six 90° Pt(II) acceptors. The design of the anthracene-triphenylamine chromophore makes possible the tunable excited-state property (like the emissive transition energy and lifetime) as a function of the solvent polarity, temperature, and concentration. The synergistic photophysical footprint of these metallacages, defined by their high absorptivity and emission quantum yield (QY) relative to the free ligand 3, signifies them as a superior light sensitizer component in an LHS. In the presence of the fluorescent dye Nile Red (NR) as an energy acceptor, the metallacages display efficient (>93%) excited energy transfer to NR through an apparent static quenching mechanism in viscous dimethyl sulfoxide solvent.

Molecular ReI Cages: Structural and Luminescent Properties.

Versatile building block [{Re(CO)4 }3 (C3 N3 S3 )] (1 a; C3 N3 S3 =cyanurate trianion) reacts with linear dipyridyl ligands [i.e., pyrazine (pz), 4,4'-bipyridine (bpy), 1,2-bis(4-pyridyl)ethylene (bpe), bis(4-pyridyl)acetylene (bpa), and 1,4-bis(pyridyl-4-ylethynyl)benzene (bpb)] and a tripyridyl ligand [1,3,5-tris(4-pyridylethynyl)benzene (tpb)] to afford a series of molecular cages [{Re(CO)3 }6 (L)3 (C3 N3 S3 )2 ] [L=pz (2), bpy (3), bpe (4), bpa (5), bpb (6)] and [{Re(CO)3 }9 (tpb)3 (C3 N3 S3 )3 ] (7) under solvothermal conditions. Various structural dimensions and motifs can be systematically tuned and obtained by using different dipyridyl and tripyridyl ligands in the reactions. The molecular cages of hexanuclear complexes 2-6 containing dipyridyl ligands feature interesting trigonal-prismatic structures with different dimensions. Furthermore, nonanuclear complex 7 has a novel triangular-star structure, and three benzene rings of tpb ligands form a triple-decker arrangement with significant π⋅⋅⋅π interactions having distances of 3.490(1) and 3.528(1) Å. In addition, molecular cages 1-3 and 5-7 exhibit luminescence in the solid state, and their luminescent properties were also studied.

Octahedral [Pd6 L8 ]12+ Metallosupramolecular Cages: Synthesis, Structures and Guest-Encapsulation Studies.

Four planar tripyridyl ligands (Ltripy ), 1,3,5-tris(pyridin-3-ylethynyl)benzene 1 a, 1,3,5-tris[4-(3-pyridyl)phenyl]benzene 2 a, and the hexyloxy chain functionalized derivatives 1,3,5-tris[(3-hexyloxy-5-pyridyl)ethynyl]benzene 1 b, and 1,3,5-tris[4-(3-hexyloxy-5-pyridyl)phenyl]benzene 2 b, were synthesized and used to generate a family of [Pd6 (Ltripy )8 ](BF4 )12 octahedral cages (Ltripy =1 a, b or 2 a, b). The ligands and cages were characterized using a combination of 1 H, 13 C, and DOSY nuclear magnetic resonance (NMR) spectroscopy, high resolution electrospray mass spectrometry (HR-ESI-MS), infrared (IR) spectroscopy, elemental analysis, and in three cases, X-ray crystallography. The molecular recognition properties of the cages with neutral and anionic guests were examined, in dimethyl sulfoxide (DMSO), using NMR spectroscopy, mass spectrometry and molecular modeling. No binding was observed with simple aliphatic and aromatic guest molecules. However, anionic sulfonates were found to interact with the octahedral cages and the binding interaction was size selective. The smaller [Pd6 (1 a, b)8 ]12+ cages were able to interact with three p-toluenesulfonate guest molecules while the larger [Pd6 (2 a, b)8 ]12+ systems could host four of the anionic guest molecules. To probe the importance of the hydrophobic effect, a mixed water-DMSO (1:1) solvent system was used to reexamine the binding of the neutral organic guests adamantane, anthracene, pyrene and 1,8-naphthalimide within the cages. In this solvent system all the guests except adamantane were observed to bind within the cavities of the cages. NMR spectroscopy and molecular modeling indicated that the cages bind multiple copies of the individual guests (between 3-6 guest molecules per cage).

Controlled Formation of Heteroleptic [Pd2(La)2(Lb)2](4+) Cages.

Metallosupramolecular architectures are beginning to be exploited for a range of applications including drug delivery, catalysis, molecular recognition, and sensing. For the most part these achievements have been made with high-symmetry metallosupramolecular architectures composed of just one type of ligand and metal ion. Recently, considerable efforts have been made to generate metallosupramolecular architectures that are made up of multiple different ligands and/or metals ions in order to obtain more complex systems with new properties. Herein we show that the addition of an electron-rich 2-amino-substituted tripyridyl ligand, 2,6-bis(pyridin-3-ylethynyl)pyridine (2A-tripy), to a solution of the [Pd2(tripy)4](4+) cage resulted in the clean generation of a heteroleptic [Pd2(tripy)2(2A-tripy)2](4+) architecture. The formation of the mixed-ligand cage [Pd2(tripy)2(2A-tripy)2](4+) was confirmed using (1)H NMR spectroscopy, diffusion-ordered spectroscopy, and rotating-frame nuclear Overhauser effect spectroscopy and high-resolution electrospray ionization mass spectrometry. Density functional theory calculations suggested the cis isomer was more stable that the trans isomer. Additionally, the calculations indicated that the heteroleptic palladium(II) cages are kinetically metastable intermediates rather than the thermodynamic product of the reaction. Competition experiments supported that finding and showed the cages are long-lived in solution at room temperature. Finally, it was shown that the addition of 2A-tripy to a range of preformed [Pd2(Ltripy)4](4+) cages cleanly generated the mixed-ligand systems. Three other systems displaying different exo and endo functionalities within the cage assembly were generated, suggesting that this method could be applied to synthesize a range of highly functionalized heteroleptic cis-[Pd2(La)2(Lb)2](4+) cages.

A diaryl-linked [Pd2L4]4+ metallosupramolecular architecture: synthesis, structures and cisplatin binding studies

A diaryl-linked tripyridyl ligand (L), 2,6-bis[4-(3-pyridinyl)phenyl]-4-(hydroxymethyl)pyridine, was synthesised in good yield (57%) exploiting the Pd-catalysed Suzuki cross-coupling method and used to assemble a new [Pd2L4]4+ metallosupramolecular cage architecture. These systems have been characterised by NMR, IR and UV–vis spectroscopies, mass spectrometry, elemental analysis and by X-ray crystallography. It was shown using NMR spectroscopy and X-ray crystallography that the cage acts as a host for anions. However, efforts to bind the anticancer drug cisplatin within the central cavity of the cage were unsuccessful. This appears to be connected to steric effects caused by the aryl spacer units of the ligands forming the cage.

Flexibility is Key: Synthesis of a Tripyridylamine (TPA) Congener with a Phosphorus Apical Donor and Coordination to Cobalt(II).

Tripyridylamine (TPA), a tetradentate ligand that forms 5-membered chelate rings upon metal coordination, has demonstrated significant utility in synthetic inorganic chemistry. An analogue with a phosphorus apical donor is a desirable target for tuning electronic structure and enhancing reactivity. However, this congener has been synthetically elusive. Prior attempts have resulted in tridentate coordination to transition metal ions due to a lack of ligand flexibility. Herein, we report the successful synthesis of tris(2-pyridylmethyl)proazaphosphatrane (TPAP), a more accommodating tripyridyl ligand containing an apical phosphorus donor. The TPAP ligand forms 6-membered chelate rings upon coordination and binds in the desired tetradentate fashion to a Co(II) ion. Structural studies elucidate the importance of ligand flexibility in tripodal ligands featuring phosphorus donors. Cyclic voltammetry, UV-vis, and solution magnetic susceptibility experiments of [Co(TPAP)(CH3CN)](2+) are also reported and compared to [Co(TPA)(CH3CN)](2+). Notably, magnetic susceptibility measurements of [Co(TPAP)(CH3CN)](2+) indicate a low spin electronic configuration, in contrast to [Co(TPA)(CH3CN)](2+), which is high spin.

Single-crystal growth of coordination networks via the gas phase and dependence of iodine encapsulation on the crystal size.

Self-assembly of the tripyridyl ligand 2,4,6-tris(4-pyridyl)triazine(TPT) and ZnI2via the gas phase produced three kinds of networks: [(ZnI2)(TPT)]n; [(ZnI2)3(TPT)2]n; and [(ZnI2)(μ-I)(ZnI)(TPT)]n. [(ZnI2)3(TPT)2]n is the first example of the single crystal formation of a porous network via the gas phase and showed the dependence of iodine encapsulation on the crystal size.

Stimuli-responsive Pd2L4metallosupramolecular cages: towards targeted cisplatin drug delivery

Metallosupramolecular cages are an emerging, but as of yet relativity unexplored, drug delivery vector. Herein we show that discrete dipalladium(II) molecular cages of the formula [Pd2L4](X)4 can be quantatively self-assembled from a simple tripyridyl ligand (2,6-bis(pyridin-3-ylethynyl)pyridine) and [Pd(CH3CN)4](X)2 (X = BF4− or SbF6−). The cages have been fully characterised using 1H, 13C and DOSY NMR spectroscopy, elemental analysis, IR spectroscopy, and high resolution electrospray mass spectrometry (HR-ESMS). Additionally, the molecular structure of the [Pd2L4](SbF6)4 cage was confirmed unequivocally using X-ray diffraction. These [Pd2L4](X)4 cages are stimuli-responsive and can be reversibly disassembled/reassembled upon the addition/removal of suitable competing ligands. The central cavities of the [Pd2L4](X)4 cages are lined with four hydrogen bond accepting pyridine units which enable the encapsulation of two cisplatin molecules within the metallosupramolecular architecture through hydrogen bonding interactions between the cage and the amine ligands of the cisplatin guest. The structure of the [Pd2L4⊃(cisplatin)2](BF4)4 host–guest adduct has been confirmed by 1H NMR spectroscopy, HR-ESMS and X-ray crystallography. Additionally we have demonstrated that the cage–cisplatin host–guest adduct can be quantatively disassembled upon the addition of a competing ligand, releasing the cisplatin guest. This is the first crystallographically characterised example of a discrete metallosupramolecular cage encapsulating an FDA-approved inorganic drug molecule. This host–guest chemistry could open the way to relatively unexplored methods of drug delivery, which circumvent the malicious side effects and drug resistance associated with cisplatin and other anticancer therapeutics.

Two new coordination polymers constructed by angular tripyridyl ligand: syntheses, structures, and properties

U-shaped tripyridyl ligand 2,6-bis(pyridine-4-carboxamido)pyridine (L) was synthesized and used to assemble metal complexes. The resulting new complexes [Mn(L)3(SCN)2] n (1) and [Co(L)3(SCN)2] n (2) are isostructural, crystallizing in the monoclinic C2/c space group. In compounds 1 and 2, each metal is in a slightly distorted octahedron ligated by six nitrogens from four L and two SCN−. Complexes 1 and 2 possess infinite 1-D zigzag polymeric chain structures where L adopts bridge and terminal coordination. These 1-D coordination polymers assemble into 3-D supermolecules of compounds 1 and 2 through hydrogen bonds. Fluorescence measurements and thermal analysis show that 1 emits strong fluorescence with a single broad band centered at 410 nm upon excitation at 357 nm and the polymeric chain structure is stable up to 340°C.

Thermodynamics and Selectivity of Two-Dimensional Metallo-supramolecular Self-Assembly Resolved at Molecular Scale

We investigated the thermodynamic processes of two-dimensional (2D) metallo-supramolecular self-assembly at molecular resolution using scanning tunneling microscopy and variable-temperature low-energy electron diffraction. On a Au(111) substrate, tripyridyl ligands coordinated with Cu in a twofold Cu-pyridyl binding mode or with Fe in a threefold Fe-pyridyl binding mode, forming a 2D open network structure in each case. The network structures exhibited remarkable thermal stability (600 K for the Cu-coordinated network and 680 K for the Fe-coordinated network). The Fe-pyridyl binding was selected thermodynamically as well as kinetically in self-assembly involving both modes. The selectivity can be effectively suppressed in a specifically designed self-assembly route.

Synthesis and Magnetic Study of μ1,1‐Azido‐Bridged Dinuclear Manganese(II) Complexes Based on Tripyridyl Ligands

AbstractThree azido‐bridged MnII complexes of formulas [Mn2(N3)4(ttp)2] (1), [Mn2(N3)4(ttp‐N3)2] (2) and [Mn2(N3)4(ttp‐N3)2]3[MnIII(ttp‐N3)(N3)3]2 (3), where ttp and ttp‐N3 represent 4′‐p‐tolyl‐2,2′:6′,2″‐terpyridine and 4′‐p‐azidomethylphenyl‐2,2′:6′,2″‐terpyridine, were synthesized and characterized by single‐crystal X‐ray diffraction analysis and magnetic studies. The Mn ions in complexes 1 and 2 are coordinated by three N atoms of the ttp or ttp‐N3 ligands, and they are connected by double end‐on (EO) azide ligands; this forms a dinuclear MnII system with Mn–N–Mn bridging angles of 103.5 and 103.1°. The Br atoms of the –CH2Br ligands were replaced by azido groups during the formation of complexes 2 and 3. The structure of complex 3 comprises two structurally similar MnII dimers with double end‐on bridging azide groups and one mononuclear MnIII structure. The bridging Mn–N–Mn angles in 3 are 104.2, 105.1, and 106.73°. Magnetic studies indicate the presence of intramolecular ferromagnetic superexchange. The strength of ferromagnetic coupling within the Mn2 cores in 1–3 is dependent on the Mn–N–Mn bridging angles. The magnetic coupling constants for intermolecular exchange are 2.46(4), 2.25(2), and 1.92(4) cm–1 for 1, 2, and 3, respectively, on the basis ofHamiltonian Ĥ = –2JŜ1Ŝ2.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Synthesis and structure of dimeric [(cis-Py3Im)M]2 complexes [M = Ni, Cu, Zn; (cis-Py3Im) = cis-2,4,5-tri(2-pyridyl)imidazoline

A series of dinuclear complexes of the new tetradentate tripyridyl ligand, cis-2,4,5-tri(2-pyridyl)imidazoline, (cis-Py3Im), 1, with Ni(II), Cu(II), and Zn(II) is reported. The complexes introduced here are the first prepared of the (cis−Py3Im) ligand system and illustrate the preferred binding mode of this ligand to M(II) for M = Ni, Cu, and Zn. Each metal is bonded to two ligands, one through the cis-4,5-(2-pyridyl) groups and the other through the 2(2-pyridyl) and imidazoline nitrogens.

Structure of chlorohydroxonitrosyl(terpyridine)ruthenium(II) hexafluorophosphate

The title complex has the NO grouptrans to the hydroxyl ligand and the chloride ion in the plane of the tripyridyl ligand. The Ru−O and Ru−N(O) distances are 1.939(5) A and 1.764(6) A, respectively; the Ru−N−O bond angle is 171.7(6)0. These values are consistent with previously reported shortening of Ru−O distances whentrans to a linear NO ligand. The space group of the structure isP21/c, witha=9.7213(9) A,b=13.9318(11) A,c=14.523(4) A, and β=105.820(13)0.

Ambidentate coordination of the tripyridyl ligands 2,2′:6′,2″‐terpyridyl, tris(2‐pyridyl)‐amine, tris(2‐pyridyl)methane and tris(2‐pyridyl)phosphine to carbonylrhenium centres: Structural and spectroscopic studies

AbstractThe reactions of [Re(CO)5Cl] with the ligands tpy (2,2′:6′,2″‐terpyridine), py3N {tris(2‐pyridyl)‐amine}, py3CH {tris(2‐pyridyl)methane}, and py3P {tris(2‐pyridyl)phosphine} in toluene solution realize compounds with the general formulation [Re(ligand)(CO)3Cl] in which the tripyridyl ligands are bidentate. X‐ray structural determinations of fac‐[Re(typ)(CO)3Cl].H2O and fac‐[Re(py3N)(CO)3Cl] confirm these assignments. [Re(tpy)(CO)3Cl].H2O (C18H13ClN3O4Re) is monoclinic, space group P21/n, with cell dimensions a = 7.432(2) Å, b = 17.016(4) Å, c = 14.466(2) Å, β = 93.51(2)°, and Z = 4; full‐matrix least‐squares refinement on 2435 reflections with I ⩾ 2.5σ(I) converged to a final R = 0.028 and Rw = 0.029. [Re(py3N)(CO)3Cl] (C18H12ClN4O3Re) is triclinic, space group P1 with cell dimensions a = 13.761(2) Å, b = 14.636(6)Å, c = 11.110(2) Å, α = 110.70(2)°, β = 102.45(2)°, γ = 107.48(2)°, and Z = 4; full‐matrix least‐squares refinement on 3459 reflections with I ⩾ 2.5σ(I) converged to a final R = 0.038 and Rw = 0.039. If the synthetic procedure is undertaken under irradiation by visible light, for the ligand py3N a species [Re(py3N)(CO)2Cl] (characterized by infrared spectroscopy and conductance measurements) is also formed, in which the ligand py3N is tridentate. No analogous tridentate species is formed with the ligands tpy or py3P, although there is evidence that it also forms for py3CH.