Access to N-Carbonyl Derivatives of Iminosydnones by Carbonylimidazolium Activation

A new methodology for N-exocyclic functionalization of iminosydnones was developed involving the addition of a large variety of nucleophiles on carbonyl-imidazolium-activated iminosydnones. This practical and highly versatile method provided access to new classes of iminosydnones and opened a straightforward synthetic route to prepare iminosydnone-based prodrugs.

Functionalized Aromatic Dicarboxylate Ligands in Uranyl-Organic Assemblies: The Cases of Carboxycinnamate and 1,2-/1,3-Phenylenedioxydiacetate

2-Carboxycinnamic acid (ccnH₂) and the isomeric 1,2- and 1,3-phenylenedioxydiacetic acids (1,2- and 1,3-pddaH₂) have been used to synthesize eight uranyl ion complexes under solvo-hydrothermal conditions. In the four complexes [PPh₄]₂[UO₂(ccn)(NO₃)]₂ (1), [PPh₄]₂[UO₂(ccn)(dibf)]₂ (2), [UO₂(ccn)(bipy)]₂ (3), and [Ni(R,S-Me₆cyclam)][UO₂(ccn)(HCOO)]₂ (4), the ccn^2- dianion retains a nearly planar geometry, which favors the formation of the centrosymmetric [UO₂(ccn)]₂ dimeric unit. Additional terminal ligands, either neutral (bipy = 2,2'-bipyridine) or anionic (nitrate, dibf^- = 1,3-dihydro-3-oxo-1-isobenzofuranacetate, and formate, the two latter formed in situ), complete the uranyl coordination sphere, leading in all cases to discrete, dinuclear species. Sodium(I) bonding to the carboxylate/ether O₄ site of the 1,2-pdda^2- dianion in the two complexes [UO₂Na(1,2-pdda)(OH)] (5) and [(UO₂)₂Na₂(1,2-pdda)₂(C₂O₄)] (6) results in this ligand being planar. Further lateral coordination to uranyl and sodium bonding to a uranyl oxo group allow formation of heterometallic diperiodic networks containing monoperiodic uranyl-only subunits. In the absence of Na⁺ cations, 1,2-pdda^2- adopts a conformation in which one carboxylate group is tilted out of the ligand plane in [UO₂(1,2-pdda)₂Ni(cyclam)] (7) and diaxial carboxylato bonding to nickel(II) unites uranyl-only monoperiodic subunits into a diperiodic network. The 1,3-pdda^2- ligand in [UO₂(1,3-pdda)(H₂O)] (8) is also nonplanar with one tilted carboxylate group, and the bridging bidentate nature of both carboxylate groups allows formation of a triperiodic framework in which both metal and ligand are four-coordinated nodes. While the emission spectra of complexes 1 and 5 display the vibronic progression considered typical of uranyl ion, those of complexes 2, 4, and 8 show broad emission bands which in the case of complex 4 completely replace the uranyl emission and which appear to be ligand-centered. The low energy of these broad bands can be rationalized in terms of the close association of certain ligand pairs within the structures.

Structure-Directing Effects of Coordinating Solvents, Ammonium and Phosphonium Counterions in Uranyl Ion Complexes with 1,2-, 1,3-, and 1,4-Phenylenediacetates

The three isomers 1,2-, 1,3-, and 1,4-phenylenediacetic acids (1,2-, 1,3-, and 1,4-pdaH₂) have been used to synthesize 16 uranyl ion complexes under solvo-hydrothermal conditions and in the presence of various coligands and organic counterions. The two neutral and homoleptic complexes [UO₂(1,2-pda)]·CH₃CN (1) and [UO₂(1,3-pda)] (2) crystallize as diperiodic assemblies with slightly different coordination modes of the ligands, but the same sql topology. Introduction of the coordinating solvents N-methyl-2-pyrrolidone (NMP) or N,N'-dimethylpropyleneurea (DMPU) in the uranyl coordination sphere produces the four complexes [UO₂(1,2-pda)(DMPU)] (3), [UO₂(1,3-pda)(NMP)] (4), [UO₂(1,4-pda)(NMP)] (5), and [UO₂(1,4-pda)(DMPU)] (6), which are either monoperiodic (4) or diperiodic species with the fes (3 and 5) or 3,4L13 (6) topology. The presence of dimethylammonium cations is associated with the formation of ladder-like monoperiodic polymers with the 1,2 isomer in the complexes [H₂NMe₂]₂[(UO₂)₂(1,2-pda)₃]·H₂O (7) and [H₂NMe₂]₂[(UO₂)₂(1,2-pda)₃]·3H₂O (8), while a conformational change giving the 1,3 and 1,4 isomers a pincer-like geometry favors the formation of dinuclear ring subunits assembled into daisy-chain-like monoperiodic polymers in [H₂NMe₂]₂[(UO₂)₂(1,3-pda)₃]·0.5H₂O (9), [H₂NMe₂]₂[(UO₂)₂(1,4-pda)₃] (10), and the mixed-ligand species [H₂NMe₂]₂[(UO₂)₂(1,2-pda)(1,4-pda)₂] (11). The unique complex including guanidinium cations, [C(NH₂)₃]₂[(UO₂)₂(1,2-pda)₃]·0.5H₂O·CH₃CN (12), crystallizes as a diperiodic polymer with the hcb topology. Due to differences in ligand conformations, the phosphonium-containing complexes [PPh₃Me]₂[(UO₂)₂(1,3-pda)₃] (13) and [PPh₄]₂[(UO₂)₂(1,4-pda)₃] (14) contain ladder-like and daisy-chain-like monoperiodic polymers, respectively, while only the latter geometry is found in the mixed-cation complexes [PPh₃Me][H₂NMe₂][(UO₂)₂(1,4-pda)₃]·H₂O (15) and [PPh₃Me][H₂NMe₂][(UO₂)₂(1,2-pda)(1,4-pda)₂] (16). The influence of ligand conformation and the structure-directing effects of coligands and counterions throughout the series are discussed. The uranyl emission spectra of 14 of the complexes display the usual vibronic fine structure, the peak positions being dependent on the number of equatorial donors.

Structural Systematics of Lanthanide(III) Picrate Solvates: Neutral, Mononuclear Ln(pic)3(dimethylsulfoxide)3 Arrays

Adducts of dimethylsulfoxide, dmso=Me2SO, with lanthanide(iii) picrates (picrate=2,4,6-trinitrophenoxide, pic) of stoichiometry Ln(pic)3·3dmso have been prepared and characterised by single-crystal X-ray structure determinations as discrete, neutral, mononuclear molecular species. Such complexes have been obtained across the gamut of Ln, specifically for Ln=La, Pr, Nd, Sm, Gd, Dy, Yb, Lu, and Y, presumably also accessible for other intermediate members, the series being isomorphous (monoclinic, C2/c, Z=8); a second triclinic P form has also been identified for Ln=La, Pr. In both forms, the metal atom coordination environments are nine-coordinate, tricapped trigonal prismatic, [Ln(dmso-O)3(pic-O,O′)3], two of the three unidentate ligands lying in one of the trigonal planes and one in the other (an isomer we have termed meridional, mer). A hydrated form of Ln(pic)3·2dmso·H2O stoichiometry has also been defined for Ln=Sm, Gd, Lu, the metal atom environment again nine-coordinate, [Ln(dmso-O)2(H2O)(pic-O,O′)3], but now fac, with the three unidentate ligands occupying one triangular face of the tricapped trigonal prism and involved in a centrosymmetric H-bonding array with the three similar ligands of an adjacent complex; the three capping atoms are nitro-oxygen atoms, the phenoxy-O triad occupying the other face.

Zero-, mono- and diperiodic uranyl ion complexes with the diphenate dianion: influences of transition metal ion coordination and differential UVI chelation

Diphenate complexes with uranyl cations are generally of low periodicity (0 or 1), but for one 2-periodic uranyl–Cu^II species.

The sulfonate group as a ligand: a fine balance between hydrogen bonding and metal ion coordination in uranyl ion complexes

Nine uranyl ion complexes have been synthesized using two kinds of sulfonate-containing ligands, i.e. 2-, 3- and 4-sulfobenzoic acids (2-, 3- and 4-SBH₂), which include additional carboxylic donors, and p-sulfonatocalix[4]arene (H₈C4S), with additional phenolic groups, and [Ni(cyclam)]²⁺, [Cu(R,S-Me₆cyclam)]²⁺ or PPh₄⁺ as counterions. [Ni(cyclam)][UO₂(4-SB)₂(H₂O)₂]·2CH₃CN (1) and [Ni(cyclam)][UO₂(3-SB)₂(H₂O)₂] (2) are molecular species in which only the carboxylate groups are coordinated to uranyl, the sulfonate groups being essentially hydrogen bond acceptors. In contrast, uranyl κ¹-O(S);κ¹-O(C)-chelation is found in the four complexes involving 2-SB^2-, different bridging interactions producing diverse geometries. [UO₂(2-SB)₂Ni(cyclam)]·H₂O (3) crystallizes as a two-dimensional (2D) assembly with fes topology, in which uranyl ion dimeric subunits are bridged by six-coordinate Ni^II cations. Complexes [UO₂(2-SB)₂Cu(R,S-Me₆cyclam)]₂·2H₂O (4) and [(UO₂)₂(2-SB)₂(C₂O₄)Cu(R,S-Me₆cyclam)] (5), obtained together from the same solution, are a molecular tetranuclear complex and a 2D species with fes topology, respectively, depending on the coordination number, 5 or 6, of the Cu^II cation. The complex [PPh₄]₂[(UO₂)₂(2-SB)₃(H₂O)]·H₂O (6) is a one-dimensional (1D), ribbon-like coordination polymer with a layered packing of alternate cationic and anionic sheets. No heterometallic complex was obtained with H₈C4S, but the copper-only compound [{Cu(R,S-Me₆cyclam)}₅(H₃C4S)₂]·17H₂O (7) displays mixed coordination/hydrogen bonding association of the copper azamacrocycle complex with the phenolic groups. The complexes [PPh₄]₅[UO₂(H₄C4S)(H₂O)₄][UO₂(H₃C4S)(H₂O)₄]·14H₂O (8) and [PPh₄]₃[UO₂(H₃C4S)(H₂O)₃]·9H₂O (9) were crystallized from the same solution and are a molecular complex and a 1D polymer, respectively, with monodentate sulfonate coordination to uranyl, while [PPh₄]₂[UO₂(H₄C4S)(H₂O)₃]·11H₂O (10) is also a 1D polymer. The anionic complexes in the last three complexes form layers (9) or double layers (8 and 10) separated from one another by hydrophobic layers of PPh₄⁺ cations. The balance between coordination and hydrogen bonding interactions with the macrocyclic ligands provides an indication of the energy of the sulfonate coordinate bond. Complex 6 is the only luminescent species in this series, albeit with a low quantum yield of 3%, and its emission spectrum is typical of a uranyl complex with five equatorial donors.

Tubelike Uranyl-Phenylenediacetate Assemblies from Screening of Ligand Isomers and Structure-Directing Counterions

Reaction of 1,2-, 1,3-, or 1,4-phenylenediacetic acids (1,2-, 1,3-, or 1,4-H₂PDA) with uranyl ions under solvo-hydrothermal conditions and in the presence of [M(L) _n] ^q+ cations, in which M = transition metal cation, L = 2,2'-bipyridine (bipy) or 1,10-phenanthroline (phen), n = 2 or 3, and q = 1 or 2, gave 10 complexes which have been crystallographically characterized. The diacetate ligands are bis-chelating and the uranyl cations are tris-chelated in all cases. [UO₂(1,2-PDA)₂Zn(phen)₂]·2H₂O (1) and [UO₂(1,4-PDA)₂Mn(bipy)₂]·H₂O (2) are heterometallic, neutral one-dimensional (1D) coordination polymers in which the carboxylate-coordinated 3d block metal cation is either decorating only (1) or participates in polymer building (2). [Zn(phen)₃][(UO₂)₂(1,3-PDA)₃] (3) and [Ni(phen)₃][(UO₂)₂(1,4-PDA)₃]·H₂O (4), with separate counterions, crystallize as anionic two-dimensional (2D) networks, as does [Cu(bipy)₂][H₂NMe₂][(UO₂)₂(1,4-PDA)₃] (5), which displays parallel 2D interpenetration. The complex [Zn(phen)₃][(UO₂)₂(1,2-PDA)₃]·7H₂O (6) crystallizes as a ladderlike, slightly inflated ribbon. The same topology is found in [Zn(bipy)₃][(UO₂)₂(1,3-PDA)₃] (7), but the larger separation between coordination sites and the coexistence of curved and divergent ligand conformations produce a tubelike assembly. An analogous but more regular and spacious tubular geometry is found in [M(bipy)₃][(UO₂)₂(1,4-PDA)₃], with M = Co (8) or Ni (9), and {Λ-[Ru(bipy)₃]}[(UO₂)₂(1,4-PDA)₃] (10). The disordered counterions in 8 and 9 are replaced by well-ordered, enantiomerically pure chiral counterions in 10. The tubular assemblies formed in 7-10 are characterized by an oblong section and the presence of gaps in the walls, which enable the inclusion of two rows of counterions in the cavity.

Synthesis and Structural Properties of Novel Calixarene Analogues having Schiff Base Units

Novel calixarene analogues having Schiff base units have been synthesised by condensation reaction of the bisaldehyde with o-phenylenediamines in the presence of boric acid. The present calixarene analogues form hydrogen bonds between imine nitrogen and phenol hydrogen with 1,2-alternate conformation, confirmed by X-ray crystallography.

Sydnone-Based Approach to Heterohelicenes through 1,3-Dipolar-Cycloadditions

The first approach to pyrazole-containing helicenes via sydnone-aryne [3 + 2]-cycloaddition is described. An unprecedented regioselectivity in the cycloaddition step toward the more sterically constrained product was observed in the presence of extended aromatic scaffolds. DFT calculations enabled understanding the origin of this unexpected selectivity.

Chiral Discrete and Polymeric Uranyl Ion Complexes with (1 R,3 S)-(+)-Camphorate Ligands: Counterion-Dependent Formation of a Hexanuclear Cage

Reaction of (1 R,3 S)-(+)-camphoric acid (H₂cam) with uranyl ions under solvo-hydrothermal conditions and in the presence of bulky countercations gave five chiral complexes of varying dimensionality. [Cu( R,S-Me₆cyclam)][UO₂(Hcam)₂(HCOO)₂] (1) and [Ni( R,S-Me₆cyclam)][UO₂(cam)(HCOO)₂] (2), in which the formate coligand is formed in situ, involve very similar countercations, but 1 is a discrete, mononuclear complex, whereas 2 crystallizes as a one-dimensional (1D) coordination polymer, and NH-bond donation by the macrocyclic ligand of the countercation complexes is present in both. [Co(en)₃][(UO₂)₄(cam)( R,R-tart)₂(OH)]·3H₂O (3), in which en is ethylenediamine and H₄ R,R-tart is R,R-tartaric acid, contains three enantiomerically pure chiral species, and it displays a two-dimensional (2D) arrangement, with the countercation again involved in NH-bond donation. While [PPh₄][UO₂(cam)(NO₃)] (4) is a 1D polymer, [PPh₃Me]₃[NH₄]₃[(UO₂)₆(cam)₉] (5) is a discrete, homochiral, and homoleptic hexanuclear cage with C₃ point symmetry and a trigonal prismatic arrangement of the uranium atoms. This cage differs from the octanuclear, pseudocubic uranyl camphorate species previously described, thus providing an example of modulation of the cage size through variation of the structure-directing counterions. The cage in 5 is closely associated with three PPh₃Me⁺ cations, two of them outside and with their methyl group directed toward the prism basis center, and one inside the cage cavity. While complex 5 is nonluminescent, complexes 1 and 4 have emission spectra in the solid state typical of equatorially hexacoordinated uranyl complexes. Solid-state photoluminescence quantum yields of 2 and 23% have been measured for complexes 1 and 4, respectively.

Structure-Directing Effects of Counterions in Uranyl Ion Complexes with Long-Chain Aliphatic α,ω-Dicarboxylates: 1D to Polycatenated 3D Species

Nine uranyl ion complexes were synthesized under (solvo-)hydrothermal conditions using α,ω-dicarboxylic acids HOOC-(CH₂) _n-2-COOH (H₂C n, n = 6-9) and diverse counterions. Complexes [PPh₄][UO₂(C6)(NO₃)] (1) and [PPh₄][UO₂(C8)(NO₃)] (2) contain zigzag one-dimensional (1D) chains, with further polymerization being prevented by the terminal nitrate ligands. [PPh₃Me][UO₂(C7)(HC7)] (3) crystallizes as a 1D polymer with a curved section, with hydrogen bonding of the uncomplexed carboxylic groups giving rise to formation of 3-fold interpenetrated two-dimensional (2D) networks. [PPh₄][H₂NMe₂][(UO₂)₂(C7)₃] (4) and [PPh₃Me]₂[(UO₂)₂(C8)₃] (5) contain 1D chains, either ladder-like or containing doubly bridged dimers, while [PPh₃Me]₂[(UO₂)₂(C9)₃]·2H₂O (6) displays interdigitated, strongly corrugated honeycomb 2D nets. Ladder-like 1D polymers in [Cu( R,S-Me₆cyclam)][(UO₂)₂(C7)₂(C₂O₄)]·4H₂O (7) are associated into layers by the hydrogen bonded counterions, whereas the [Ni(cyclam)]²⁺ moieties are part of the 2D polymeric arrangement in [(UO₂)₂(C7)₂(HC7)₂Ni(cyclam)]·2H₂O (8) because of axial coordination of the nickel(II) center, with hydrogen bonding mediated by water molecules generating a three-dimensional (3D) net. [(UO₂)₂K₂(C7)₃(H₂O)]·0.5H₂O (9) contains convoluted uranyl dicarboxylate 2D subunits, which generate a 3D framework through 2D → 3D parallel polycatenation similar to that previously found in [NH₄]₂[(UO₂)₂(C7)₃]·2H₂O; further linking of these subunits is provided by bonding of the potassium cations to carboxylate and uranyl oxido groups. The solid-state emission spectra of complexes 1-6 and 9 display maxima positions typical of hexacoordinated uranyl carboxylate complexes, but uranyl luminescence is quenched in 7. A solid-state photoluminescence quantum yield of 11.5% has been measured for complex 1, while those for compounds 3-6 and 9 are in the range of 2.0-3.5%.

Element 92 – Uranium

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Synthesis and Suzuki-Miyaura cross coupling reactions for post-synthetic modification of a tetrabromo-anthracenyl porphyrin

The outstanding properties of porphyrins and the extreme versatility of their synthesis and their functionalisation constitute real assets for the fabrication of opto- and electroactive materials or for biological applications. In the large collection of porphyrinic structures, meso-substituted anthracenylporphyrins are among the less studied. Here, we synthesised the 5,10,15,20-tetra-bromoanthracenylporphyrin (BrTAP) and we investigated its chemical reactivity by post-synthetic modification using Suzuki-Miyaura cross coupling reactions with a series of boronic acids to generate a collection of original tetra-anthracenyl porphyrin based molecules: tetraphenylanthracenylporphyrin (TPAP), tetratolylanthracenylporphyrin (TTAP), tetramethoxyphenylanthracenylporphyrin (TMPAP), tetranaphthylanthracenylporphyrin (TNAP) and tetrapyrenylanthracenylporphyrin (TPyAP). Optical characterisations of these modified porphyrins showed, in most cases, only emission of the porphyrin in the visible region with extinction of the fluorescence of PAHs in the UV or visible region.

Closed Uranyl-Dicarboxylate Oligomers: A Tetranuclear Metallatricycle with Uranyl Bridgeheads and 1,3-Adamantanediacetate Linkers

In the presence of NH₄⁺ and either PPh₄⁺ or PPh₃Me⁺ cations, 1,3-adamantanediacetic acid (H₂ADA) reacts with uranyl ions under solvo-hydrothermal conditions to give the complexes [NH₄]₂[PPh₄]₂[(UO₂)₄(ADA)₆] (1) and [NH₄]₂[PPh₃Me]₂[(UO₂)₄(ADA)₆] (2), both of which contain a tetranuclear metallatricycle built from two 2:2 rings including convergent ligands, linked by two additional ligands in an extended conformation defining a third, larger ring. While the ammonium cations are closely associated with the 2:2 rings through triple hydrogen bonding, the large PPh₄⁺ or PPh₃Me⁺ cations are more loosely bound to each of the two faces of the larger ring. In contrast, the complex [H₂NMe₂][PPh₃Me][(UO₂)₂(ADA)₃]·H₂O (3), in which dimethylammonium replaces ammonium cations, crystallizes as a two-dimensional network with honeycomb {6³} topology, albeit with very distorted, elongated hexagonal cells. These and previous results show that both NH₄⁺ and PPh₄⁺ or PPh₃Me⁺ cations are essential to the formation of the metallatricycle. The role of the flexibility imparted to ADA^2- by the acetate arms, in comparison to the more rigid 1,3-adamantanedicarboxylate (ADC^2-), is also discussed. All three complexes are luminescent, with quantum yields of 0.06, 0.06, and 0.09 for 1-3, respectively. The vibronic fine structure apparent on the emission spectra gives peak positions typical of species in which the uranyl ion is chelated by three carboxylate groups.