Synthesis of Open and Closed Metallacages Using Novel Tripodal Ligands: Unusually Stable Silver(I) Inclusion Compound

Synthesis of novel star-shaped molecules based on a 1,3,5-triazine core linked to different heterocyclic systems as novel hybrid molecules

The synthesis of novel star-shaped compounds based on an s-triazine core and linked to hexahydroacridinediones, pyrimido[4,5-b]quinolones, 1H-isoquinolino[2,1-a]quinolines, tetrahydro-4H-chromenes, dihydropyrano[2,3-c]pyrazoles, thiazole, or benzothiazole as new hybrid molecules through Michael and Hantzsch reactions is reported. For this purpose, 2,4,6-tris(4-formylphenoxy)benzaldehyde was used as a versatile precursor.

The synthesis of novel star-shaped compounds based on an s-triazine core and linked to different heterocycles as new hybrid molecules through Michael and Hantzsch reactions is reported.

An overview on synthetic strategies for the construction of star-shaped molecules

Strategies for the synthesis of star-shaped molecules have been in high demand in the last decades due to the importance of those compounds in various fields. The distinctly different properties of these compounds compared to their linear analogues make them versatile building blocks for the formation of mesophases of interesting mesomorphic and photophysical properties. Moreover, the applications of star-shaped molecules as building units for dendrimers as well as in supramolecular host-guest chemistry have also been recently studied. The star-shaped molecules mentioned in this review are classified according to the central core as well as the type of side arms. The properties and applications of these compounds are described in the appropriate contexts. This report summarizes the recent advances in this area.

[Ag-Ag]2+ Unit-Encapsulated Trimetallic Cages: One-Pot Syntheses and Modulation of Argentophilic Interactions by the Uncoordinated Substituents

Four [Ag-Ag]²⁺ unit-encapsulated trimetallic cages 1-4 were synthesized from one new tripodal ligand L and silver salts in different solvent systems by a one-pot method. The formation of coordination cages occurred simultaneously with the condensation of amino groups and ketone. The remarkable structural feature of cages 1-4 is their spontaneous incorporation of [Ag-Ag]²⁺ cationic units. Moreover, the argentophilic interactions are modulated by the uncoordinated amino substituents. The study herein shows that modification and subtle changes of the cage structures could be realized by a one-pot synthetic method.

Group 11 tris(pyrazolyl)methane complexes: structural features and catalytic applications

Tris(pyrazolyl)methane ligands (Tpm^x) have been for years a step behind their highly popular boron-anionic analogues, the tris(pyrazolyl)borate ligands (Tp^x).

Novel Methinic Functionalized and Dendritic C-Scorpionates

The study of chelating ligands is undoubtedly one of the most significant fields of research in chemistry. The present work is directed to the synthesis of new functionalized derivatives of tripodal C-scorpionate compounds. Tris-2,2,2-(1-pyrazolyl)ethanol, HOCH₂C(pz)₃ (1), one of the most important derivatives of hydrotris(pyrazolyl)methane, was used as a building block for the synthesis of new functionalized C-scorpionates, aiming to expand the scope of this unexplored class of compounds. The first dendritic C-scorpionate was successfully prepared and used in the important industrial catalytic reactions, Sonogashira and Heck C-C cross-couplings.

Synthesis of stable polymetalated aromatic complexes through metal-macrocycle capsule-triggered cyclization

Polymetalated aromatic compounds are of great interest because of their intermediate roles in many organic transformations. However, they are elusive and synthetically challenging. In this study, a dynamic coordination capsule constructed by a flexible macrocycle and silver(i) ions is applied to trigger one-step or cascade cyclization reactions for various alkyne substrates, finally leading to five unprecedented polysilver heteroaromatic intermediates (including indole, quinoline, benzocarbazole and 2,2'-biindole). The acquired heteroaromatic species is doubly charged, particularly at vicinal positions, and each is surrounded by a tetrasilver aggregate. The metal-macrocycle capsule holds a great potential of flexibly adjusting its conformation to adapt different polysilver heteroaromatic species. DFT calculations further reveal that metal-perturbed aromaticity and multi-centered bonding both contribute to stabilization of the polysilver heteroaromatic complexes.

Controllable Coordination Self-Assembly Based on Flexible Tripodal Ligands: From Finite Metallocages to Infinite Polycatenanes Step by Step

This article describes the developments in coordination self-assembly based on flexible tripodal ligands with different metal species. Various finite metallocages such as M3 L2 , M6 L8 , M6 L4 , M4 L4 and different catenanes based on discrete metallocages constructed from flexible tripodal ligands with suitable metal species are presented here. Many M3 L2 metallocages based on ligands L(1) -L(12) and different two-coordinated metal species have been prepared, in which various Ag(I) salts and other metal species that have been protected by suitable groups, such as Zn(OAc)2 , ZnBr2 , and PdBr2 , have been used as effective acceptors. All of the M6 L8 -type metallocages are constructed from ligands L(2) or L(12) -L(20) and different four-coordinated metal species, such as various palladium(II) salts or NiCl2 , and have similar topological structures. Only a few discrete M6 L4 -type metallocages, based on ligands L(21) -L(24) , have been reported, using different strategies such as protecting groups and steric hindrance. All of the M4 L4 -type cages have similar topological structures and are constructed from ligands L(25) -L(29) with multiple donor sites. More intriguing interlocking ensembles constructed from discrete metallocages are also described here in detail, namely, three [2]catenanes based on ligands L(30) -L(32) and four polycatenanes based on ligands L(33) -L(34) .

Synthesis, characterization and luminescent properties of lanthanide complexes with a novel multipodal ligand

Solid complexes of lanthanide nitrates with an novel multipodal ligand, 1,2,4,5-tetramethyl-3,6-bis{N,N-bis[((2'-furfurylaminoformyl)phenoxyl)ethyl]-aminomethyl}-benzene (L) have been synthesized and characterized by elemental analysis, infrared spectra and molar conductivity measurements. At the same time, the luminescent properties of the Sm(III), Eu(III), Tb(III) and Dy(III) nitrate complexes in solid state were investigated. Under the excitation of UV light, these complexes exhibited characteristic emission of central metal ions. The lowest triplet state energy level of the ligand indicates that the triplet state energy level (T1) of the ligand matches better the resonance level of Tb(III) than other lanthanide ions.

Monofluoride bridged, binuclear metallacycles of first row transition metals supported by third generation bis(1-pyrazolyl)methane ligands: unusual magnetic properties

The reaction of M(BF(4))(2).xH(2)O, where M is Fe, Co, Cu, and Zn, and the ditopic, bis(pyrazolyl)methane ligand m-[CH(pz)(2)](2)C(6)H(4), L(m), where pz is a pyrazolyl ring, yields the monofluoride bridged, binuclear [M(2)(mu-F)(mu-L(m))(2)](BF(4))(3) complexes. In contrast, a similar reaction of L(m) with Ni(BF(4))(2).6H(2)O yields dibridged [Ni(2)(mu-F)(2)(mu-L(m))(2)](BF(4))(2). The solid state structures of seven [M(2)(mu-F)(mu-L(m))(2)](BF(4))(3) complexes show that the divalent metal ion is in a five-coordinate, trigonal bipyramidal, coordination environment with either a linear or nearly linear M-F-M bridging arrangement. NMR results indicate that [Zn(2)(mu-F)(mu-L(m))(2)](BF(4))(3) retains its dimeric structure in solution. The [Ni(2)(mu-F)(2)(mu-L(m))(2)](BF(4))(2) complex has a dibridging fluoride structure that has a six-coordination environment about each nickel(II) ion. In the solid state, the [Fe(2)(mu-F)(mu-L(m))(2)](BF(4))(3) and [Co(2)(mu-F)(mu-L(m))(2)](BF(4))(3) complexes show weak intramolecular antiferromagnetic exchange coupling between the two metal(II) ions with J values of -10.4 and -0.67 cm(-1), respectively; there is no observed long-range magnetic order. Three different solvates of [Cu(2)(mu-F)(mu-L(m))(2)](BF(4))(3) are diamagnetic between 5 and 400 K, thus showing strong antiferromagnetic exchange interactions of -600 cm(-1) or more negative. Mossbauer spectra indicate that [Fe(2)(mu-F)(mu-L(m))(2)](BF(4))(3) exhibits no long-range magnetic order between 4.2 and 295 K and isomer shifts that are consistent with the presence of five-coordinate, high-spin iron(II).

Synthesis and luminescent properties of lanthanide complexes with a novel multipodal ligand

Solid complexes of lanthanide nitrates, picrates and perchlorates with a novel multipodal ligand, 1,2,4,5-tetramethyl-3,6-bis{N,N-bis[((2'-benzylaminoformyl)phenoxyl)ethyl]-aminomethyl}-benzene (L) have been synthesized and characterized by elemental analysis, infrared spectra and molar conductivity measurements. At the same time, the luminescent properties of the Eu and Tb complexes in solid state were investigated. Under the excitation of UV light, these complexes exhibited characteristic emission of central metal ions. The lowest triplet state energy level T(1) of this ligand matches better to the lowest resonance energy level of Tb(III) than to Eu(III) ion. The influence of the counter anion on the luminescent intensity was also discussed.

Janus Scorpionates: Supramolecular Tectons for the Directed Assembly of Hard−Soft Alkali Metallopolymer Chains

A new scorpionate ligand [HB(mtda)3-] containing mercaptothiadiazolyl (mtda) heterocyclic rings with both hard nitrogen donors and soft sulfur donors has been prepared. This new ligand, the Janus scorpionate, is a hybrid of a tris(pyrazolyl)borate and a tris(mercaptoimidazolyl)borate. The differential hard/soft character of the dissimilar donor groups in this bridging ligand was exploited for the controlled solid-state organization of homometallic and heterometallic alkali metal coordination polymers. Remarkably, in the case of sodium, coordination polymers with both acentric (with NaS3N3H kernels) and centric (with alternating NaN6 and NaS6H2 kernels) chains are found in the same crystal (where the centricity is defined by the relative orientations of the B-H bonds of the ligands along the lattice). For the homometallic potassium congener, the larger cation size, compared to sodium, induced significant distortions and favored a polar arrangement of ligands in the resulting coordination polymer chain. An examination of the solid-state structure of the mixed alkali metal salt system revealed that synergistic binding of smaller sodium cations to the nitrogen portion and of the larger potassium cations to the sulfur portion of the ligand minimizes the ligand distortions relative to the homometallic coordination polymer counterparts, a design feature of the ligand that likely assists in thermodynamically driving the self-assembly of the heterometallic chains. The effect of alkali metal complexation on the solution properties of the ligand was studied by comparing NMR chemical shifts, B-H stretching frequencies, and electrochemical properties with those of the noncoordinating tetrabutylammonium salt of the scorpionate. The similarity of these data regardless of cation indicates that the salts are likely dissociated in solution rather than maintaining their solid-state polymeric structures. This data is augmented by the ESI(+/-) mass spectral data for a series of mixed alkali metal tris(mercaptothiadiazolyl)borates that also indicate that dissociation occurs in solution.

Metallacycles of Iron, Zinc, and Cadmium Assembled by Polytopic Bis(pyrazolyl)methane Ligands and Fluoride Abstraction from BF4-

Reactions of the arene-linked bis(pyrazolyl)methane ligands m-bis[bis(1-pyrazolyl)methyl]benzene (m-[CH(pz)2]2C6H4, Lm) and 1,3,5-tris[bis(1-pyrazolyl)methyl]benzene (1,3,5-[CH(pz)2]3C6H3, L3) with BF4- salts of divalent iron, zinc, and cadmium result in fluoride abstraction from BF4- and formation of fluoride-bridged metallacyclic complexes. Treatment of Fe(BF4)2.6H2O and Zn(BF4)2.5H2O with Lm leads to the complexes [Fe2(mu-F)(mu-Lm)2](BF4)3 (1) and [Zn2(mu-F)(mu-Lm)2](BF4)3 (2), in which a single fluoride ligand and two Lm molecules bridge the two metal centers. The reaction of [Cd2(thf)5](BF4)4 with Lm results in the complex [Cd2(mu-F)2(mu-Lm)2](BF4)2 (3), which contains dimeric cations in which two fluoride and two Lm ligands bridge the cadmium centers. Equimolar amounts of the tritopic ligand L3 and Zn(BF4)2.5H2O react to give the related monofluoride-bridged complex [Zn2(mu-F)(mu-L3)2](BF4)3 (4), in which one bis(pyrazolyl)methane unit on each ligand remains unbound. NMR spectroscopic studies show that in acetonitrile the zinc metallacycles observed in the solid-state remain intact in solution.

Tetrametallic rectangular box complexes assembled from heteroligated macrocycles

The reaction of a heteroligated Rh(I) bimetallic macrocycle with rigid ditopic ligands (1,4-dicyanobenzene, 4-4'-dicyanobiphenyl, or dipyridyl terminated salen ligand 5) results in the formation of tetrametallic rectangular box complexes.

Crystal Retro-Engineering: Structural Impact on Silver(I) Complexes with Changing Complexity of Tris(pyrazolyl)methane Ligands

The preparation and structures of seven new silver(I) complexes involving the parent tris(pyrazolyl)methane unit, [C(pz)(3)], as the donor set, {[C6H5CH2OCH2C(pz)3]Ag}(BF4), {[C6H5CH2OCH2C(pz)3]2Ag3}(CF3SO3)3, {[HOCH2C(pz)3]Ag}(BF4), {[HOCH2C(pz)3]Ag}(CF3SO3), {[HC(pz)3]2Ag2(CH3CN)}(BF4)2, {[HC(pz)3]Ag}(PF6), and {[HC(pz)3]Ag}(CF3SO3), are reported. This project is based on a retro-design of our multitopic C6H(6-n)[CH2OCH2C(pz)3]n (pz = pyrazolyl ring, n = 2, 3, 4, and 6) family of ligands in such a way that each new ligand has one fewer organizational feature. The kappa2-kappa1 bonding mode of the [C(pz)3] units to two silvers, also observed with the multitopic ligands, is the dominant structural feature in all cases. Changing the counterion has important effects on the local structures and on crystal packing. When these structures are compared to similar ones based on the multitopic C6H(6-n)[CH2OCH2C(pz)3]n ligands, it has been shown that the presence of the rigid parts (central arene core and the [C(pz)3] units) are important in order to observe highly organized supramolecular structures. The presence of the flexible ether linkage is also crucial, allowing all noncovalent forces to manifest themselves in a cumulative and complementary manner.

New N,N,N-Heteroscorpionates Based on 2,2‘-Bis(pyrazolyl)ethanamine and Its Derivatives. Ligands Designed for Probing Supramolecular Interactions

The successful design and synthesis of the new bis(pyrazolyl)ethanamine ligand and its copper(I) triphenylphosphine complex is reported. The ligand coordinates to the copper(I) center in a fac tridentate fashion, through both the pyrazolyl rings and the nitrogen atom from the NH2 group. In the solid state, the compound is organized in a 2D noncovalent network by N-H...pi and C-H...pi interactions and hydrogen bonds. The analogous ligand with a benzyl group substituted on the amine forms a complex with the same copper(I) center that has a similar 2D supramolecular structure and, in addition, is organized by the benzyl synthon into a 3D architecture.

Synthesis and infrared and luminescence spectra of rare earth complexes with a new hexapodal ligand

Solid complexes of rare earth nitrates and picrates with a new hexapodal ligand, 1,2,3,4,5,6-hexa{[(2'-benzylamino-formyl)phenoxyl]methyl}-benzene (L) have been prepared. These complexes were characterized by elemental analysis, IR and molar conductivity. At the same time, the luminescence properties of the Eu(III) and Tb(III) nitrates and picrates complexes in solid state were also investigated. Under the excitation of UV light, these complexes exhibited characteristic emission of europium and terbium ions. The influence of the counter anion on the luminescent intensity was also discussed.

Coinage metal complexes of tris(pyrazolyl)methanide [C(3,5-Me2pz)3]−: κ3-coordination vs. backbone functionalisation

Tris(pyrazolyl)methanides, [C(3,5-R2pz)3]-, contain an unassociated tetrahedral carbanionic centre in the bridgehead position. In addition to nitrogen donor centres for transition metal coordination, an accessible reactive site for further manipulations is available in the backbone of the ligand. The coordination variability of the ambidental C-/N ligand [C(3,5-Me2pz)3]- was elucidated by investigating its coinage metal complexes. Two principle coordination modes were found for complexes of general formula [LMPR3] (with M = Cu(I), Ag(I), Au(I); L =[C(3,5-Me2pz)3]-; R = Ph, OMe). While for Cu(I) (2,3) and Ag(I) (4) complexes the anionic ligand acts as a face-capping, six electron N3-donor, gold(I) (5) is coordinated by the bridging carbanion yielding a two coordinate Au(I) complex comprising a covalent Au-C bond. The complexes featuring the kappa3-coordinated N3-donor ligand were investigated by 31P CP (MAS) NMR in the solid state.