Corrado Rizzoli

Radical annulations and cyclisations with isonitriles: the fate of the intermediate imidoyl and cyclohexadienyl radicals

Abstract The reaction of 4-methoxyphenylisonitrile with phenylacetylene and AIBN produces a novel cyclopenta-fused quinoxaline through addition of 2-cyanoprop-2-yl radical to the alkyne; the resulting vinyl radical attacks isonitrile to afford an imidoyl radical, which gives rise to a tandem 5-exo, 6-endo cyclisation. The whole process entails a new example of a rare 4 + 1 radical annulation. The cyanopropyl radical can also attack isonitrile to yield small amounts of quinolines deriving from 4 + 2 and 3 + 2 annulation between the resulting imidoyl radicals and phenylacetylene. The oxidation step leading to the final aromatic products involves the starting isonitrile, which is converted to an α-unsubstituted imidoyl radical and affords 2-unsubstituted quinolines. This behaviour was also found in cyclisations of biphenyl-2-ylisonitrile under various radical conditions. Finally, the title reaction gives small amounts of an α,β-unsaturated nitrile, which can arise from a spirocyclohexadienyl radical through fragmentation and subsequent β-scission of the resulting iminyl. This could be the first, direct evidence of the intermediacy of iminyl radicals in the rearrangements of the spirocyclohexadienyls obtained by 3 + 2 annulation between imidoyl radicals and alkynes.

Titanium-carbon functionalities on an oxo surface defined by a calix [4] arene moiety and its redox chemistry

Abstract Lithiation of [ p -Bu t -calix[4]-(OMe) 2 (OH) 2 ] ( 1 ), followed by reaction with TiCl 3 (thf) 3 or TiCl 4 (thf) 2 , led to the corresponding titanium-calix[4]arene complexes [ p -Bu t -calix[4]-(OMe) 2 (O) 2 ]TiCl] ( 2 ) and [ p -Bu t -calix[4]-(OMe) 2 (O) 2 ]TiCl 2 ] ( 3 ), respectively. Reaction of 1 with TiCl 4 (thf) 2 results in demethylation of the calix[4]arene and the obtention of [ p -Bu t -calix[4]-(OMe) 2 (O) 3 ]TiCl] ( 4 ), whose hydrolysis led to [ p -Bu t -calix[4]-(OMe)(OH) 3 ] ( 6 ). The preparation of 6 can be carried out as a one-pot synthesis. Both 2 and 4 undergo alkylation reactions using conventional procedures, thus forming surprisingly stable organometallic species, namely [ p -Bu t -calix[4]-(OMe) 2 (O) 2 Ti(R)] (R = Me ( 7 ); CH 2 Ph ( 8 ), p -MeC 6 H 4 ( 9 ) and [ p -Bu t -calix[4]-(OMe)(O) 3 Ti(R)] (R = Me ( 10 ); CH 2 Ph ( 11 ); p -MeC 6 H 4 ( 12 )). Complexes 7 and 9 undergo a thermal oxidative conversion into 10 and 12 , occurring with the demethylation of one of the methoxy groups. A solid state structural property of 9 and 12 has been revealed by X-ray analysis showing a self-assembly of the monomeric units into a columnar polymer, where the p -tolyl substituent at the metal functions as a guest group for an adjacent titanium-calixarene. Reductive alkylation of 3 with Mg(CH 2 Ph) 2 gave 8 instead of forming the corresponding dialkyl derivative. Two synthetic routes have been devised for the synthesis of the Ti(III)-Ti(III) dimer [ p -Bu t -calix[4]-(OMe)(O) 3 Ti] 2 ] ( 13 ): the reduction of 4 and the reaction of TiCl 3 (thf) 3 with the lithiated form of 6 . A very strong antiferromagnetic coupling is responsible for the peculiar magnetic behavior of 13 . The proposed structures have been supported by the X-ray analyses of 4, 9, 12 and 13 .

Alkali and Alkaline‐Earth‐Metalated Forms of Calix[4]arenes: Synthons in the Synthesis of Transition Metal Complexes

This is the first coherent report on the metalation of calix[4]arene by alkali and alkaline-earth metals, thus providing a high-yield production of appropriate synthons for the synthesis of transition metal calix[4]arenes. In addition, various facets of the coordination chemistry by calix[4]arene anions of alkali and alkaline-earth metal ions have been singled out. Among them: 1) the exo and endo coordination of metal ions by the calix[4]arene skeleton; 2) the pi solvation of the ions by the phenyl rings; 3) the ion-carrier properties of metallacalix[4]arenes; 4) the simulation of the kinetically labile coordination sphere of alkali and alkaline-earth metal ions by a polyoxo rigid skeleton. The peculiarities of the complexation of alkali and alkaline-earth metal ions by calix[4]arenes outlined are deduced from the synthesis and the structural characterization both in solution ((1)H NMR) and in the solid state (X-ray structure analysis) of the following classes of compounds: 1) [p-tBu-calix[4](OMS(n))(4)](2) (M=Li, Na, K); 2) [p-tBu-calix[4](OR)(2)(O)(2)ML] (M=Mg, L=THF, R=C(5)H(9); M=Ca, L=TMEDA (tetramethylethylenediamine), R=C(5)H(9); M=Ca, L=DME (dimethoxyethane), R=C(5)H(9); M=Ba, L=TMEDA, R=C(5)H(9); M=Ba, L=none, R=C(5)H(9)); 3) [p-tBu-calix[4](OC(5)H(9))(2)(O)(2)Ca(2)I(2)(MeCN)(2)]; 4) [(p-tBu-calix[4](OR)(2)(O)(2))(2)BaNa(2)].

Weak Interactions Modulating the Dimensionality in Supramolecular Architectures in Three New Nickel(II)-Hydrazone Complexes, Magnetostructural Correlation, and Catalytic Potential for Epoxidation of Alkenes under Phase Transfer Conditions

Three different ONO donor acetyl hydrazone Schiff bases have been synthesized from the condensation of acetic hydrazide with three different carbonyl compounds: salicylaldehyde (HL(1)), 2-hydroxyacetophenone (HL(2)), and 2, 3-dihydroxybenzaldehyde (HL(3)). These tridentate ligands are reacted with Ni(OOCCF(3))(2)·xH(2)O to yield three new Ni(II) complexes having distorted octahedral geometry at each Ni center: [Ni(L(1))(OOCCF(3))(CH(3)OH)](2) (1), [Ni(L(2))(OOCCF(3))(H(2)O)](2) (2), and [Ni(L(3))(L(3)H)](OOCCF(3))(H(2)O)(1.65)(CH(3)OH)(0.35) (3). The ligands and the complexes have been characterized by elemental analysis and IR and UV-vis spectroscopy, and the structures of the complexes have been established by single crystal X-ray diffraction (XRD) study. 1 and 2 are centrosymmetric dinuclear complexes and are structural isomers whereas 3 is a bis chelated cationic monomer coordinated by one neutral and one monoanionic ligand. O-H···O hydrogen bonds in 3 lead to the formation of a dimer. Slight steric and electronic modifications in the ligand backbone provoke differences in the supramolecular architectures of the complexes, leading to a variety of one, two, and three-dimensional hydrogen bonded networks in complexes 1-3 respectively. Variable temperature magnetic susceptibility measurements reveal that moderate antiferromagnetic interactions operate between phenoxo bridged Ni(II) dimers in 1 and 2 whereas very weak antiferromagnetic exchange occurs through hydrogen bonding and π-π stacking interactions in 3. All complexes are proved to be efficient catalysts for the epoxidation of alkenes by NaOCl under phase transfer condition. The efficiency of alkene epoxidation is dramatically enhanced by lowering the pH, and the reactions are supposed to involve high valent Ni(III)-OCl or Ni(III)-O· intermediates. 3 is the best epoxidation catalyst among the three complexes with 99% conversion and very high turnover number (TON, 396).

The modulated structure of Bi2Sr3−xCaxCu2O8: A commensurate model from single crystal X-ray diffraction data

Abstract The modulated structure of Bi 2 Sr 3− x Ca x Cu 2 O 8 is analyzed in the conventional three-dimensional space group Pnm utilizing single crystal X-ray diffraction data collected from a crystal showing a commensurate modulation period p =5 a . The correlations of the parameters of related ions were large but a reliable model ( R =0.0.082, R w =0.071) is obtained. On the basis of the obtained results the structural modulation seems to be produced mainly by the mismatch between the perovskite block and the sterochemical requirements of Bi in the BiO layers. Differently from what was suggested in recent works, no clear evidence of extra oxygen in the BiO layer was found; a charge modulation on the Bi atoms seems indeed to play a role in determining the superconducting properties of this place.

Near-infrared-emitting phthalocyanines. A combined experimental and density functional theory study of the structural, optical, and photophysical properties of Pd(II) and Pt(II) α-butoxyphthalocyanines.

The structural, optical, and photophysical properties of 1,4,8,11,15,18,22,25-octabutoxyphthalocyaninato-palladium(II), PdPc(OBu)(8), and the newly synthesized platinum analogue PtPc(OBu)(8) are investigated combining X-ray crystallography, static and transient absorption spectroscopy, and relativistic zeroth-order regular approximation (ZORA) Density Functional Theory (DFT)/Time Dependent DFT (TDDFT) calculations where spin-orbit coupling (SOC) effects are explicitly considered. The results are compared to those previously reported for NiPc(OBu)(8) (J. Phys. Chem. A 2005, 109, 2078) in an effort to highlight the effect of the central metal on the structural and photophysical properties of the group 10 transition metal octabutoxyphthalocyanines. Different from the nickel analogue, PdPc(OBu)(8) and PtPc(OBu)(8) show a modest and irregular saddling distortion of the macrocycle, but share with the first member of the group similar UV-vis spectra, with the deep red and intense Q-band absorption experiencing a blue shift down the group, as observed in virtually all tetrapyrrolic complexes of this triad. The blue shift of the Q-band along the MPc(OBu)(8) (M = Ni, Pd, Pt) series is interpreted on the basis of the metal-induced electronic structure changes. Besides the intense deep red absorption, the title complexes exhibit a distinct near-infrared (NIR) absorption due to a transition to the double-group 1E (π,π*) state, which is dominated by the lowest single-group (3)E (π,π*) state. Unlike NiPc(OBu)(8), which is nonluminescent, PdPc(OBu)(8) and PtPc(OBu)(8) show both deep red fluorescence emission and NIR phosphorescence emission. Transient absorption experiments and relativistic spin-orbit TDDFT calculations consistently indicate that fluorescence and phosphorescence emissions occur from the S(1)(π,π*) and T(1)(π,π*) states, respectively, the latter being directly populated from the former, and the triplet state decays directly to the S(0) surface (the triplet lifetime in deaerated benzene solution was 3.04 μs for Pd and 0.55 μs for Pt). Owing to their triplet properties, PdPc(OBu)(8) and PtPc(OBu)(8) have potential for use in photodynamic therapy (PDT) and are potential candidates for NIR light emitting diodes or NIR emitting probes.

Two phthalocyanine units ‘stapled’ by carbon–carbon σ bonds in a new sandwich-type molecule: {5,5′;19,19′-bi[phthalocyaninato (2–)]}titanium(IV). Synthesis, X-ray crystal structure, and properties

{5,5′;19,19′-Bi[phthalocyaninato(2–)]}titanium(IV)–1-chloronaphthalene(1/1 ), [TiL]·C10H7Cl, is obtained by the reaction of [Ti(pc)Cl2](pc = phthalocyaninato dianion, [C32H16N8]2–) with Na2(pc) in 1-chloronaphthalene at 190 °C, An X-ray single-crystal structure (monoclinic, space group C/2c, a= 16.327(3), b= 18.568(4), c= 19.022(4)A; β= 94.50(1)°, Z= 4) indicates for this complex a sandwich-type structure with the titanium atom in the centre of the molecule and the two phthalocyaninato units ‘stapled’ by two inter-ring C–C σ bonds [C(11)–C(11′) 1.556(6) and C(31)–C(31′) 1.575(6)A]. Due to the staggered orientations of the two macrocyclic rings (relative rotation 45°) the planes of the two inner N4 systems (each of which is slightly distorted from planarity) form a square-antiprism, with an average interplane distance of 2.32 A(much shorter than that found in similar ‘unstapled’ complexes), and Ti–N bond distances in the range 2.17–2.26 A. The complex shows high thermal stability and can be oxidized by nitric acid to give the species [TiL]NO3. The complexes [TiL] and [TiL]NO3 show differing solid-state electrical conductivity properties.

Tantalum–Carbon Functionalities Bonded to a Calix[4]arene-Oxo Matrix: The Chemistry of Mono-, Dialkyl, and Butadiene Derivatives of Tantalum(V)

Tantalum–carbon functionalities bonded over an oxo matrix (here calix[4]arene anions) undergo a variety of multiple migratory insertion reactions which lead to the metal-assisted formation of C–C and CC bonds.

Molecular Batteries Based on Carbon–Carbon Bond Formation and Cleavage in Titanium and Vanadium Schiff Base Complexes

A novel mode of storing and releasing electrons, based on the reversible formation and cleavage of C−C bonds, has been created. The C−C bonds formed by the reductive coupling of imino groups across two [M(salophen)] complexes (see structure) function as shuttle for two electrons, permitting long-range electron transfer to a variety of substrates (e.g. quinone, dioxygen, and azides). This electron transfer is mediated by the metal, which becomes the reactive site, while the C–C functionality is never directly involved.

Porphyrazines with Annulated Diazepine Rings, 1 Synthesis and Characterization of Tetrakis‐2,3‐(5,7‐diphenyl‐6H‐1,4‐diazepino)porphyrazine and Its MgII, CuII, and ZnII Complexes – X‐ray Crystal Structure of 2,3‐Dicyano‐5,7‐diphenyl‐6H‐1,4‐diazepine

A new class of porphyrazine macrocycles carrying peripheral diazepine rings, i.e. tetrakis-2,3-(5,7-diphenyl-6H-1,4-diazepino)porphyrazine [Ph2DzPzH2](H2O)4, and its metal derivatives of formula [Ph2DzPzM](H2O)x=2–7 [M = MgII(H2O), CuII, ZnII] have been prepared and characterized. Single crystal X-ray work on the monomeric precursor 5,7-diphenyl-2,3-dicyano-6H-1,4-diazepine, Ph2(CN)2Dz, and NMR spectra (CDCl3, (CD3)2SO) and UV/Vis spectra in solution of different media (basic, neutral, acid) of the monomer and its macrocyclic derivatives have provided information on the conformational flexibility of the diazepine ring as well as on the structural and electronic features of the entire porphyrazine skeleton.