Investigating the formation of metal nitride complexes employing a tetradentate bis-carbene bis-phenolate ligand.

The synthesis of Mn and Cr nitride complexes of a pro-radical tetradentate bis-phenol bis-N-heterocyclic carbene ligand H2LC2O2 was investigated. Employing either azide photolysis of the Mn precursor complex MnLC2O2(N3) or a nitride exchange reaction between MnLC2O2(Br) and the nitride exchange reagent Mnsalen(N) failed to provide a useful route to the target nitride MnLC2O2(N). Experimental results support initial formation of the target nitride MnLC2O2(N), however, the nitride rapidly inserts into a Mn-C bond.

Distorted copper(ii) radicals with sterically hindered salens: electronic structure and aerobic oxidation of alcohols.

The sterically hindered salen ligands featuring biphenyl and tetramethyl putrescine linkers were synthesized and chelated to copper. The resulting complexes CuL, CuL, CuL and CuL were structurally characterized, showing a significanty tetrahedrally distorted metal center. The complexes show two reversible oxidation waves in the range 0.

Structural and spectroscopic investigations of nine-coordinate redox active lanthanide complexes with a pincer O,N,O ligand.

The lanthanide complexes EuL3, GdL3, YbL3 and LuL3 of the N,N'-bis(2-hydroxy-di-3,5-tert-butylphenyl)amine were prepared. The X-Ray crystal structures of GdL3 and LuL3 demonstrated a nine-coordinate sphere with three ligand molecules under their anionic diamagnetic form (Cat-N-BQ)-. The complexes showed three oxidation events (Eox11/2 = 0.

Effect of Distortions on the Geometric and Electronic Structures of One-Electron Oxidized Vanadium(IV), Copper(II), and Cobalt(II)/(III) Salen Complexes.

The ligands '-bis(3--butyl-5-methoxysalicylidene)-1,2-ethanediamine and '-bis(3--butyl-5-methoxysalicylidene)-1,3-propanediamine were chelated to V(IV)═O (, ), Cu(II) (, ), Co(II) (), and Co(III) (). The X-ray crystal structures of - were solved. The vanadium center in - resides in square pyramidal geometry, with an axially bound oxo ligand, whereas the metal ion displays a tetrahedrally distorted square planar geometry in -.

Stable M(II)-Radicals and Nickel(III) Complexes of a Bis(phenol) N-Heterocyclic Carbene Chelated to Group 10 Metal Ions.

The tetradentate ligand based on (1-imidazolium-3,5-di tert-butylphenol) units was prepared and chelated to group 10 metal ions (Ni(II), Pd(II), and Pt(II)), affording complexes 1, 2, and 3, respectively. The X-ray crystal structures of 1-3 show a square planar metal ion coordinated to two N-heterocyclic carbenes and two phenolate moieties. The cyclic voltammetry curves of complexes 1-3 show two reversible oxidation waves in the range 0.

Seven-coordinate lanthanide complexes with a tripodal redox active ligand: structural, electrochemical and spectroscopic investigations.

The tripodal ligand TREN-(3,5-di-tert-butylsalicylidene) (HL) was synthesized and its tris(phenolato) lanthanide complexes L-Ln (Ln = Nd, Eu, Tb, Gd, Er, Yb and Lu) were prepared. The X-Ray crystal structures confirm that each metal ion resides in a similar monocapped octahedral geometry, excluding water molecules from the coordination sphere. The coordination bond distances are in agreement with the lanthanide contraction, with Ln-O bond lengths in the range 2.

A Structurally Characterized Cu Complex Supported by a Bis(anilido) Ligand and Its Oxidative Catalytic Activity.

Three copper(II) complexes of the (R,R)-N,N'-bis(3,5-di-tert-butyl-2-aminobenzylidene)-1,2-diaminocyclohexane ligand, namely [Cu( L)], [Cu( LH)] and [Cu( LH )] , were prepared and structurally characterized. In [Cu( LH )] the copper ion lies in an octahedral geometry with the aniline groups coordinated in equatorial positions. In [Cu( L)] the anilines are deprotonated (anilido moieties) and coordinated to an almost square-planar metal ion.

Template-Mediated Stabilization of a DNA G-Quadruplex formed in the HIV-1 Promoter and Comparative Binding Studies.

G-rich DNA oligonucleotides derived from the promoter region of the HIV-1 long terminal repeat (LTR) were assembled onto an addressable cyclopeptide platform through sequential oxime ligation, a thiol-iodoacetamide SN2 reaction, and copper-catalyzed azide-alkyne cycloaddition reactions. The resulting conjugate was shown to fold into a highly stable antiparallel G4 architecture as demonstrated by UV, circular dichroism (CD), and NMR spectroscopic analysis. The binding affinities of six state-of-the-art G4-binding ligands toward the HIV-G4 structure were compared to those obtained with a telomeric G4 structure and a hairpin structure.

A redox active switch for lanthanide luminescence in phenolate complexes.

The reversible oxidation of coordinated phenolates into phenoxyl radicals results in a dramatic quenching (>95%) of the luminescence of the f metal ion.

The structure of a one-electron oxidized Mn(iii)-bis(phenolate)dipyrrin radical complex and oxidation catalysis control via ligand-centered redox activity.

The tetradentate ligand dppH3, which features a half-porphyrin and two electron-rich phenol moieties, was prepared and chelated to manganese. The mononuclear Mn(iii)-dipyrrophenolate complex 1 was structurally characterized. The metal ion lies in a square pyramidal environment, the apical position being occupied by a methanol molecule.

Efficient Inhibition of Telomerase by Nickel-Salophen Complexes.

Four nickel(II)-salophen complexes containing alkyl-imidazolium chains connected at the ortho or meta positions were prepared: N,N'-bis(2-hydroxy-4-methyl-3H-imidazol-1-iumbenzylideneamino)phenylenediamine (1), N,N'-bis(2-hydroxy-3-methyl-3H-imidazol-1-iumbenzylideneamino)phenylenediamine (2), N,N'-bis(2-hydroxy-3-methyl-3H-imidazol-1-iumbenzylideneamino)methyl-3H-imidazol-1-iumphenylenediamine (3), and N,N'-bis(2-hydroxy-4-methyl-3H-imidazol-1-iumbenzylideneamino)methyl-3H-imidazol-1-iumphenylenediamine (4). They protect G-quadruplex DNA (G4 -DNA) against thermal denaturation and show KA values in the range of 7.4×10(5) to 4×10(7)  m(-1) for G4 -DNA models.

Templated Formation of Discrete RNA and DNA:RNA Hybrid G-Quadruplexes and Their Interactions with Targeting Ligands.

G-rich RNA and DNA oligonucleotides derived from the human telomeric sequence were assembled onto addressable cyclopeptide platforms through oxime ligations and copper-catalyzed azide-alkyne cycloaddition (CuAAc) reactions. The resulting conjugates were able to fold into highly stable RNA and DNA:RNA hybrid G-quadruplex (G4) architectures as demonstrated by UV, circular dichroism (CD), and NMR spectroscopic analysis. Whereas rationally designed parallel RNA and DNA:RNA hybrid G4 topologies could be obtained, we could not force the formation of an antiparallel RNA G4 structure, thus supporting the idea that this topology is strongly disfavored.

Nickel(ii) radical complexes of thiosemicarbazone ligands appended by salicylidene, aminophenol and aminothiophenol moieties.

The nickel(ii) complexes of three unsymmetrical thiosemicarbazone-based ligands featuring a sterically hindered salicylidene (1), aminophenol (2) or thiophenol (3) moiety were synthesized and structurally characterized. The metal ion lies in an almost square planar geometry in all the complexes. The cyclic voltammetry (CV) curve of 1 shows an irreversible oxidation wave at E = 0.

Interaction of polycationic Ni(II)-salophen complexes with G-quadruplex DNA.

A series of nine Ni(II) salophen complexes involving one, two, or three alkyl-imidazolium side-chains was prepared. The lengths of the side-chains were varied from one to three carbons. The crystal structure of one complex revealed a square planar geometry of the nickel ion.

A singlet ground state for a cobalt(II)-anilinosalen radical complex.

The cobalt(II) anilinosalen complex [Co(II)(L)] was prepared and subsequently oxidized by one electron. The resulting cation comprises a square planar low spin Co(II) ion anti-ferromagnetically exchange coupled to an anilinyl radical.

Stable anilinyl radicals coordinated to nickel: X-ray crystal structure and characterization.

Two anilinosalen and a mixed phenol-anilinosalen ligands involving sterically hindered anilines moieties were synthesized. Their nickel(II) complexes 1, 2, and 3 were prepared and characterized. They could be readily one-electron oxidized (E(1/2)=-0.

Structural and spectroscopic investigation of an anilinosalen cobalt complex with relevance to hydrogen production.

A Co(II) anilinosalen catalyst containing proton relays in the first coordination sphere has been synthesized that catalyzes the electrochemical production of hydrogen from acid in dichloromethane and acetonitrile solutions. The complex has been spectroscopically and theoretically characterized in different protonation and redox states. We show that both coordinated anilido groups of the neutral Co(II) complex can be protonated into aniline form.

Ligand-centered redox activity in cobalt(II) and nickel(II) bis(phenolate)-dipyrrin complexes.

One for all: a trianionic ligand containing the biologically relevant moieties phenolate and porphyrin was designed and synthesized. One-electron oxidation of the nickel and cobalt complexes of these ligands affords an unprecedented and highly stable hybrid porphyrinyl-phenoxyl radical bound to the metal center. Two-electron oxidation of these complexes leads to the M(2+) -(close-shell two-electron oxidized ligand) species.

Ligand contributions to the electronic structures of the oxidized cobalt(II) salen complexes.

Square planar cobalt(II) complexes of salen ligands N,N'-bis(3-tert-butyl-5R-salicylidene)-1,2-cyclohexanediamine), where R = OMe (1) and tert-butyl (2), were prepared. 1 and 2 were electrochemically reversibly oxidized into cations [1-H(2)O](+) and [2-H(2)O](+) in CH(2)Cl(2). The chemically generated [1-H(2)O](SbF(6))·0.

Radical localization in a series of symmetric Ni(II) complexes with oxidized salen ligands.

Square-planar nickel(II) complexes of salen ligands, N,N'-bis(3-tert-butyl-(5R)-salicylidene)-1,2-cyclohexanediamine), in which R=tert-butyl (1), OMe (2), and NMe(2) (3), were prepared and the electronic structure of the one-electron-oxidized species [1-3](+·) was investigated in solution. Cyclic voltammograms of [1-3] showed two quasi-reversible redox waves that were assigned to the oxidation of the phenolate moieties to phenoxyl radicals. From the difference between the first and second redox potentials, the trend of electronic delocalization 1(+·) >2(+·) >3(+·) was obtained.

Geometric and electronic structures of phenoxyl radicals hydrogen bonded to neutral and cationic partners.

Two di-tert-butylphenols incorporating an N-methylbenzimidazole moiety in the ortho or para position have been synthesised ((Me)OH and (pMe)OH, respectively). Their X-ray structures evidence a hydrogen bond between the phenolic proton and the iminic nitrogen atom, whose nature is intra- and intermolecular, respectively. The present studies demonstrate that (Me)OH is readily oxidised by an intramolecular PET mechanism to form the hydrogen-bonded phenoxyl-N-methylbenzimidazolium system ((Me)OH)(.

Co(II), Ni(II), Cu(II) and Zn(II) complexes of a bipyridine bis-phenol conjugate: generation and properties of coordinated radical species.

Four bis-phenolate complexes [Zn(II)L], [Ni(II)L], [Cu(II)L] and [Co(II)L] (where [H(2)L = 2,2'-[2,2']bipyridinyl-6-yl-bis-4,6-di-tert-butylphenol] have been synthesized. The copper(II) and nickel(II) complexes have been characterized by X-ray diffraction, showing a metal ion within a square planar geometry, slightly distorted towards tetrahedral. The cyclic voltametry (CV) curve of [Zn(II)L] consists of a single bi-electronic reversible wave at 0.

Unsymmetrical one-electron oxidized Ni(II)-bis(salicylidene) complexes: a protonation-induced shift of the oxidation site.

The spin density in the nickel(II) radical salen complex (2*)(+) could be localized on a specific ring by controlling the acidity of the medium.