Direct Synthesis of Fluorescent Oxazolo-phenoxazines by Copper-Catalyzed/Hypervalent Iodine(III)-Mediated Dimerization/Cyclization of 2-Benzylamino-phenols.

A dimerization/cyclization reaction of 2-benzylamino-phenols for the direct synthesis of the oxazolo-phenoxazine skeleton is reported. The reaction occurs under copper catalysis in the presence of hypervalent iodine(III), giving selectively the 5H-oxazolo[4,5-b]phenoxazine compounds. The cascade process, which allows the conversion of the substrates into the tetracyclic products, involves three C-H functionalization steps. Initial oxidation of electron-rich arenes by the hypervalent iodine is essential for the dimerization of substrates, whereas the formation of the five-membered rings is promoted by the copper species. 1-Benzyl-2-phenyl-6-(aryl-benzyl)amino-benzimidazoles are regioselectively obtained using N,N'-dibenzyl-phenylenediamines as starting substrates. The fluorescence emission properties of these classes of products have been evaluated.

Driving the Emission Towards Blue by Controlling the HOMO-LUMO Energy Gap in BF2 -Functionalized 2-(Imidazo[1,5-a]pyridin-3-yl)phenols.

Several boron compounds with 2-(imidazo[1,5-a]pyridin-3-yl)phenols, differentiated by the nature of the substituent (R) in the para position of the hydroxy group, have been synthesized and thoroughly characterized both in solution (1 H, 13 C, 11 B, 19 F NMR) and in the solid state (X-ray). All derivatives displayed attractive photophysical properties like very high Stokes shift, high fluorescence quantum yields and a good photostability in solution. Time-Dependent Density Functional Theory (TD-DFT) calculations allowed to define the main electronic transitions as intra ligand transitions (1 ILT), which was corroborated by the Natural Transition Orbitals (NTOs) shapes. The HOMO-LUMO energy gap was correlated to the electronic properties of the substituent R on the phenolic ring, as quantified by its σp Hammett constant.

Interpretation of Tolman electronic parameters in the light of natural orbitals for chemical valence.

Understanding the nature and the strength of metal-ligand interactions in d- and f-block metal complexes has always been a central issue for both synthetic and theoretical chemists. These interactions are usually described according to the well accepted Dewar-Chatt-Duncanson model, and thus over the years numerous research groups directed their efforts to shed light on the role of σ- and π-contributions. Among others, the electronic parameter introduced by Tolman in the 1970s represents a milestone in this field. Herein we present a quantitative description of the nickel-phosphine bond in Tolman's nickel(0) carbonyl complexes. The combination of Natural Orbitals for Chemical Valence with Energy Decomposition Analysis resulted in the definition of a new parameter (Tphos) which comprises all the energetic contributions needed to describe the nickel-phosphine bond and thus stands as a reliable descriptor of the electronic properties of phosphines. Moreover, steric effects of phosphines (i.e. Tolman's cone angles) have been considered too, and a linear relation including Ni-P bond distances, Tphos and cone angle has been found.

Imidazo-pyridine-based zinc(II) complexes as fluorescent hydrogen sulfide probes.

In this work we explore the interaction of HS- with a family of fluorescent zinc complexes. In particular we selected a family of complexes with N,O-bidentate ligands aiming at assessing whether the zinc-chelating ligand plays a role in influencing the reactivity of HS- with the complexes under investigation. Different experiments, performed by diverse spectroscopic techniques, provide evidence that HS- binds the zinc center of all the complexes included in this study. The results highlight the potential of the devised systems to be used as HS-/H2S fluorescent sensors via a coordinative-based approach. To shed light on the species formed in solution when HS-/H2S interacts with the title complexes and aiming to rationalize the photophysical properties of the sensing constructs, we performed a computational analysis based on the time dependent density functional theory (TD-DFT). Preliminary bio-imaging experiments were also performed and the results indicate the potential of this class of compounds as probes for the detection of H2S in living cells.

Sigma-alkylpalladium intermediates in intramolecular Heck reactions:isolation and catalytic activity.

The isolation of sigma-alkylpalladium Heck intermediates, possible when beta-hydride elimination is inhibited, is a rather rare event. Performing intramolecular Heck reactions on N-allyl-2-halobenzylamines in the presence of [Pd(PPh(3))(4)], we isolated and characterized a series of stable bridged palladacycles containing an iodine or bromine atom on the palladium atom. Indolyl substrates were also tested for isolation of the corresponding complexes. X-ray crystallographic analysis of one of the indolyl derivatives revealed the presence of a five-membered palladacycle with the metal center bearing a PPh(3) ligand and an iodine atom in a cis position with respect to the nitrogen atom. The stability of the sigma-alkylpalladium complexes is probably a consequence of the strong constraint resulting from the bridged junction that hampers the cisoid conformation essential for beta-hydride elimination. Subsequently, the thus obtained bridged five-membered palladacycles were proven to be effective precatalysts in Heck reactions as well as in cross-coupling processes such as Suzuki and Stille reactions.

Phosphorescence enhancement by close metal-metal interaction in T1 excited state in a dinuclear copper(i) complex.

The dinuclear copper(i) complex [Cu2(µ-dppm)2(lact)(µ-lact)] (1) (dppm = bis(diphenylphosphino)methane; lact = l-(+)-lactate) was synthesized and fully characterized both in solution and solid state. Variable temperature NMR experiments (1H and 31P), conductivity measurements and infrared spectroscopy, suggest the occurrence of a fluxional behavior in solution involving the lactate anion. The crystal structure shows the presence of both monodentate and bridged lactate in the complex. In the solid state, 1 shows green phosphorescent emission characterized by a very large Stokes shift (161 nm, 1.09 eV) and a good absolute quantum yield (0.43). Calculations performed at the Density Functional Theory level demonstrate that the electronic transition responsible for the emission originates from a triplet excited state where the shortening of the CuCu distance plays a crucial role.

Synthesis and ab-initio XRPD structure of group 12 imidazolato polymers.

Two new 3D homoleptic binary imidazolates, Cd(im)2 and Hg(im)2 (Him = imidazole), as well as [Hg(im)]NO3, containing 1D polycations of [Hg(im)]n(n+) formulation, have been prepared and characterized by ab-initio XRPD methods.

Surface electromyography recording of spontaneous eyeblinks: applications in neuroprosthetics.

OBJECTIVE: We are designing an implantable neuroprosthesis for the treatment of unilateral facial paralysis. The envisioned biomimetic device paces artificial blinks in the paretic eyelid when activity in the healthy orbicularis oculi (orbicularis) muscle is detected. The present article focuses on electromyography (EMG)-based eyeblink detection. STUDY DESIGN: A pilot clinical study was performed in healthy volunteers who were intended to represent individuals with facial paralysis. Spontaneous eyeblinks were detected by a surface EMG recording. Blink detection accuracy was tested at rest and during voluntary smiling and chewing. SETTING: Fifteen participants were asked to wear surface recording electrodes on the left side of their face, detecting the orbicularis oculi, the masseter, and the zygomatic muscle EMG activity. SUBJECTS AND METHODS: Participants were asked to look ahead, voluntarily smile, and chew according to an experimental protocol. Custom software was designed with the purpose of selectively filtering the multichannel EMG recordings and triggering a digital output. RESULTS: The software filter allowed elimination of spurious artificial eyeblinks and thus increased the accuracy of the EMG recording apparatus for the spontaneous blinking. CONCLUSION: Orbicularis oculi EMG recording worked as a real-time eyeblink-detecting system. Moreover, the multichannel EMG recording coupled to a proper digital signal processing was very effective in specifically detecting the spontaneous blinking during other facial muscle activities. With regard to closed-loop biomimetic devices for the pacing of the eyeblink, the EMG signal represents a valid option for the recording side.

The Goldilocks principle in action: synthesis and structural characterization of a novel {Cu4(µ3-OH)4} cubane stabilized by monodentate ligands.

A {Cu4(µ3-OH)4} compound, where four copper(II) and four µ3-bridging oxygen atoms occupy alternate corners of a slightly distorted cube, has been prepared and structurally characterized. This species, formulated as [Cu4(µ3-OH)4(Htmpz)8](ClO4)4·1.5Et2O (Htmpz = 3,4,5-1H-trimethyl pyrazole), can be classified as belonging to type I Cu4O4 cubane complexes, and is better described as two Cu(II)-(µ-OH)2-Cu(II) units held together by four long Cu-O bonds. The central distorted cubane core is stabilized by neutral monodentate ligands (Htmpz) and perchlorate anions, as demonstrated by single-crystal X-ray structure analysis. The title compound was obtained by hydrolysis of a dinuclear methoxo-bridged species, [Cu(µ-OCH3)(Htmpz)2]2(ClO4)2, which was prepared by reaction of [Cu(Htmpz)4(ClO4)2] with methanol. All these reactions represent a nice example of the Goldilocks principle in action in coordination chemistry, since each single actor (solvent, counteranion, and ligand) has the "just right" electronic, steric or coordinative properties which determine the fate of the final products.

Ni(II) and Pd(II) pyridinyloxazolidine-compounds: synthesis, X-ray characterisation and catalytic activities in the aza-Michael reaction.

The 3-phenyl-2-(pyridin-2-yl)oxazolidine ligand (ppo) was synthesised and its coordination behaviour regarding Ni(II) and Pd(II) centres was studied. The reaction with K(2)PdCl(4) affords [Pd(N,N'-ppo)Cl(2)] (1), in which ppo binds to palladium via the pyridyl nitrogen and the oxazolyl nitrogen atoms. On the contrary, reaction with NiCl(2)·6H(2)O produces [Ni(N,O-ppo)(2)Cl(2)] (2), in which two ppo ligands are coordinated via the pyridyl nitrogen and the oxygen atom of the oxazolidine ring. The X-ray diffraction analysis of the complexes confirms a square planar geometry for Pd(II) in 1 and an octahedral configuration around Ni(II) in 2, which, to the best of our knowledge, represents the first reported example of a structurally characterised nickel-oxazolidine compound. In addition, both complexes prove to be active catalysts under mild conditions in the aza-Michael reaction of (E)-4-phenylbut-3-en-2-one (benzalacetone) with aliphatic amines.

(14)N NMR and two-dimensional suspension (1)H and (13)C HRMAS NMR spectroscopy of ionic liquids immobilized on silica.

A variety of popular ionic liquids have been synthesized and characterized, including by optimized (14)N NMR spectroscopy of the neat and dissolved ionic liquids. Ionic liquids incorporating Si(OEt)(3) groups have been immobilized on silica in a well-defined manner with the imidazolium moiety remaining intact. This has been proved by optimized one- and two-dimensional (1)H and (13)C HRMAS NMR spectroscopy of the materials suspended in suitable solvents.

One-dimensional polymers containing strictly collinear metal ions: synthesis and XRPD characterization of homoleptic binary metal pyrazolates.

The synthesis of a number of 3d transition metal binary pyrazolates in microcrystalline form, thus suitable for a full XRPD characterization, has been pursued. The crystal and molecular structures of the Fe(pz)3, Co(pz)2, Co(pz)3, and Ni(pz)2 polymers, together with the few congeners reported in the recent literature, show that these species tend to afford highly crystalline materials where strictly collinear chains of metal atoms are present. Depending on the synthetic strategy used, Ni(pz)2 has been found to crystallize as two different alpha (orthorhombic) and beta (monoclinic) phases, possessing nearly identical intramolecular features. Data for each compound follow. Fe(pz)3: C9H9FeN6, hexagonal, P63/m, a = 9.1745(3) A, c = 7.2191(4) A, Z = 2. Co(pz)2: C6H6CoN4, orthorhombic, Ibam, a = 7.5239(5) A, b = 14.3461(9) A, c = 7.4331(5) A, Z = 4. Co(pz)3: C9H9CoN6, hexagonal, P63/m, a = 9.1966(3) A, c = 7.1051(3) A, Z = 2. Alpha-Ni(pz)2: C6H6N4Ni, orthorhombic, Cmcm, a = 16.6758(11) A, b = 6.4872(4) A, c = 6.9423(6) A, Z = 4. Beta-Ni(pz)2: C6H6N4Ni, monoclinic, P21/m, a = 9.967(2) A, b = 6.975(1) A, c = 6.016(1), A, beta = 98.50(1)degrees, Z = 2. The thermal stability and the detailed structural properties of these model compounds have been evaluated, in the light of the technologically relevant crystal phases (the well-known metal-diazolates showing reversible spin-crossover or spin-transition behavior) obtainable upon doping, magnetic dilution, and ring substitution (in the 4-position).