Gabriele Bocelli

Synthesis, characterisation and X-ray crystal structure of copper(II) complexes with unsymmetrical tetradentate Schiff base ligands: first evidence of Cu(II) catalysed rearrangement of unsymmetrical to symmetrical complex

Abstract The mononuclear copper(II) complexes, [CuL1](ClO4) (1), and [CuL2](ClO4) (2) with unsymmetrical quadridentate Schiff base ligands derived from the 1:1:1 condensation of 2,4-pentanedione, pyridine-2-carboxaldehyde and 1,2-ethanediamine (HL1) or 1,3-propanediamine (HL2) have been prepared and characterised. Complex 2 undergoes Cu(II)/H+ catalysed rearrangement to [CuL3](ClO4)2 (3) where L3 is a symmetrical tetradentate Schiff base involving 1,3-propanediamine and pyridine-2-carboxaldehyde. Structures of all the three compounds have been verified by single crystal X-ray analysis. The geometry around Cu(II) is square-planar in 1 and 2 whereas that in 3 is distorted octahedral with two axially coordinated perchlorate ions.

Regioselective ring opening of a palladium(IV) alkylaromatic metallacycle by benzyl group migration from palladium to the aromatic carbon and X-ray structure of the resulting palladium(II) complex

Abstract The stereochemical course of a PdII → PdIV → PdII transformation is described for the first time through isolation of organometallic species containing the entire carbon skeleton.

Preparation, characterization and activity of palladium(II) halide complexes with diethyl 8-quinolylmethylphosphonate (8-dqmp). X-ray crystal structure of [8-dqmpH]2[PdCl4]·2H2O and [8-dqmpH]2[Pd2Br6]

Abstract The synthesis, spectroscopic and biological properties of the novel palladium(II) halide complexes with diethyl 8-quinolylmethylphosphonate (8-dqmp) have been reported. It was shown that the square planar complexes trans-[Pd(8-dqmp)2X2] were obtained by reaction of 8-dqmp with PdX42− (XCl, Br) in the neutral ethanolic/aqueous solution. In the HX acidic medium the quinolinium salt complexes [8-dqmp H]2[PdX4] were isolated. They were converted by heating in methanol into the corresponding hexahalodipalladium salt complexes [8-dqmpH]2[Pd2X6]. The new complexes were characterized on the basis of elemental and thermogravimetric analysis, magnetic and conductance measurements, by the IR and 1H NMR spectra and some X-ray crystal structure determinations. The complexes were tested for their cytostatic activity on KB and L1210 cell lines. The coordination behaviour of 8-dqmp as well as the spectral and biological properties of its complexes were compared with the results reported for the diethyl ester of 2-quinolylmethylphosphonic acid (2-dqmp) and its palladium(II) halide complexes. The molecular structures of the complexes [8-dqmpH]2[PdCl4]·2H2O (3) and [8-dqmpH]2[Pd2Br6] (6) have been fully characterized by X-ray diffraction studies. The crystals of both complexes are triclinic, space group P1, Z=2, with lattice parameters for 3: a=9.438(2), b=9.481(2), c=11.082(2) A, α=83,4(1), β=107.5(1), γ=77.0(1)°, the final R factors are R=0.0481 and R′=0.0551 for 3208 observed diffractometer collected reflections; and for 6: a=11.943(2), b=10.644(2), c=8.873(2) A, α=102.08(2), β=85.56(2), γ=69.54(2)°, the final R factors are R=0.0725 and R′=0.0804 for 2584 observed diffractometer collected reflections. The structure of 3 is composed of the square planar PdCl42− anion lying in a centre of symmetry (average PdCl=2.330 A), of two quinotinium phosphonate cations and two water molecules. The structure of 6 consists of two quinolinium moieties as a cationic part separated by the Pd2Br6 centrosymmetric dianionic dimer.

Oxidative coupling of dichloroaluminium phenolates: Highly selective synthesis of hydroxylated Bi- and tetraaryls

Abstract Dichloroaluminium phenolates 4 undergo highly selective FeCl3-promoted oxidative coupling. Variously substituted symmetric 2,2′-dihydroxy biaryls 2 are obtained in good yields and excellent selectivities. The chelation control in the final reaction products 7 promotes the chemoselectivity of the process.

Supramolecular organisation via hydrogen bonding in trimethoprim sulfonate salts

The present study deals with the crystal structures of four organic salts, namely, trimethoprim benzene sulfonate monohydrate 1, trimethoprim sulfanilate monohydrate 2, trimethoprim p-toluene sulfonate 3 and trimethoprim 3-carboxy-4-hydroxybenzene sulfonate dihydrate 4. Trimethoprim (TMP) is protonated at one of the ring nitrogens of the pyrimidine ring. Generally, in the TMP carboxylate complexes, the protonated pyrimidine ring is hydrogen-bonded to the carboxylate group forming a cyclic fork-like hydrogen-bonded bimolecular motif. In structures 1–3, the sulfonate group plays the role of the carboxylate anion. In compounds 1 and 2, there is no pairing of the pyrimidine rings because the pairing sites are blocked by water molecules donating hydrogen to the unprotonated ring nitrogen. Two of the cyclic motifs are bridged by the water molecule donating two hydrogen atoms, leading to a hydrogen-bonded supramolecular chain. This chain pairs with another chain running in the opposite direction. These two chains are cross-linked by O–H⋯O hydrogen bonds. In compound 2, two of the hydrogen atoms of the amino group of the sulfanilate bridge two methoxy oxygen of the two TMP cations via N–H⋯O hydrogen bonds resulting in a supramolecular zig-zag chain. In compound 3, two inversion related cyclic motifs are paired through a pair of N–H⋯N hydrogen bonds involving the 4-amino group and the N3 atom of the pyrimidine ring. In addition to the pairing, one of the sulfonate oxygen atoms bridges the 2-amino and 4-amino groups on either side of the paired bases, resulting in a self-complementary DADA (D represents the hydrogen bond donor and A represents hydrogen bond acceptor) array of quadruple hydrogen bonding patterns. In compound 4, one of the water molecules forms a hydrogen-bonded dimer with the inversion-related water molecule. The 3-carboxy-4-hydroxybenzene sulfonate moiety self-assembles into a supramolecular chain along the c axis through O–H⋯O hydrogen bonds. Two such oppositely running supramolecular chains are connected by dimeric and monomeric water molecules. The variation of supramolecular organization via hydrogen bonding in the four different trimethoprim sulfonate salts has been discussed.

Electron density distribution studies on ZnS4N2 chromophore in solution and solid phases: XPS and cyclic voltammetric studies on 1,10-phenanthroline and 2,2′-bipyridine adducts of bis(piperidinecarbodithioato-S,S′)zinc(II). Single crystal X-ray structure of (2,2′-bipyridine)bis-(piperidinecarbodithioato-S,S′)zinc(II)

Abstract (1,10-phenanthroline)bis(piperidinecarbodithioato-S,S′)zinc(II), [Zn(pipdtc)2(1,10-phen)] (1) and (2,2′-bipyridine)bis(piperidinecarbodithioatao-S,S′)zinc(II), [Zn(pipdtc)2(bipy)] (2) adducts were prepared and the crystal structure of 2 is reported. The Zn–S distances in 2 are longer than those in Zn(dtc)2 complexes. The presence of an additional neutral ligand causes an increase of the Zn–S bond lengths. S2p binding energies show a significant reduction in value compared to the parent dithiocarbmate [Zn(pipdtc)2](3), indicating the weakening of the Zn–S bond on adduct formation. The observed reduction in binding energy is due to the increased electron density on the metal in the adducts. The cyclic voltammetric study on the complexes also show an increase of electron density on zinc in the adducts compared to Zn(pipdtc)2. The S–Zn–S angle in the adduct shows a reduction due to increased coordination around zinc. The thioureide C–N distance of 1.343(13) A in compound 2 is in line with the νC–N observed at 1469 cm−1.

Preparation, characterization and activity of palladium(II) halide complexes with diethyl 2-quinolylmethylphosphonate (2-dqmp). X-Ray crystal structures of trans-[Pd(2-dqmp)2X2](X = Cl or Br)

A series of new palladium(II) halide complexes with diethyl 2-quinolylmethylphosphonate (2-dqmp) were prepared and studied. Two types of square-planar palladium dihalide complexes, trans-[Pd(2-dqmp)2X2] with the N-bonded monodentate ligand and cis-[Pd(2-dqmp)X2] where dqmp acts as a bidentate N,O-bonded chelate ligand, could be obtained by reaction of 2-dqmp with [PdX4]2–(X = Cl or Br) in neutral methanolic-aqueous solution. The ion-pair salt complexes, [2-Hdqmp]2[PdX4], containing the protonated quinoline ligand as cation and the square-planar tetrahalogenopalladate complex as anion, were isolated upon treatement of the ethanolic–aqueous solution with HX. The new complexes were identified and characterized by elemental and thermogravimetric analysis, magnetic and conductometric measurements, and by infrared and 1H NMR spectral studies. All were tested for cytostatic activity on KB and L1210 cell lines, but only [Pd(2-dqmp)2Br2]2 displayed a significant anti-tumour effect in both systems. The molecular structures of the complexes [Pd(2-dqmp)2X2](X = Cl, 1; Br, 2) were determined by single-crystal X-ray analysis. The crystals are triclinic, space group P, Z= 2, with other parameters: 1, a= 10.209(3), b= 9.812(3), c= 8.949(2)A, α= 78.36(2), β= 94.82(2), γ= 111.60(2)°, R= 0.0598, and R′= 0.0648 for 2982 observed reflections; 2, a= 10.502(3), b= 9.405(3), c= 9.009(3)A, α= 72.00(2), β= 103.96(2), γ= 100.63(2)°, R= 0.0574, and R′= 0.0614 for 2033 observed reflections. Each complex has a trans square-planar structure, the palladium being co-ordinated by two halogen and two nitrogen atoms and lying at a centre of symmetry.

Stereochemistry of cercosporin

Abstract The absolute configuration of the asymmetric carbons and the axial chirality of the natural mold metabolite cercosporin (from Cercospora sp .) have been established on the basis of X-ray analysis and chemical reactions. The results confirm the inherent dissymmetry of the perylenequinone ring, the twisting of which gives rise to the diastereoisomer isocercosporin. The energy barrier for the conversion of cercosporin into isocercosporin has been evaluated.

Synthesis, crystal structure and thermochromism of benzimidazolium tetrachlorocuprate: (C7H7N2)2[CuCl4]

The synthesis and crystal structure of thermochromic, yellow benzimidazolium tetrachlorocuprate(II), (C7H7N2)2CuCl4 (1), have been reported. The compound crystallizes in the C 2/c space group and contains discrete tetrahedral CuCl4 2� species. It absorbs one molecule of water from humid atmosphere at room temperature to produce a hydrated green form, (C7H7N2)2CuCl4/H2O, which upon heating loses the water molecule in two steps to form the anhydrous yellow compound 1. The role of the water molecule on the solid state, yellow v/green thermochromic transformation is discussed. # 2002 Elsevier Science Ltd. All rights reserved.

Synthesis, spectral and cyclic voltammetric studies on (4,4′-bipyridyl)bis(di(2-hydroxyethyl)dithiocarbamato)zinc(II) and (4,4′-bipyridyl)bis(bis(N-methyl, N-ethanoldithiocarbamato)zinc(II) and their X-ray crystal structures

Abstract Synthesis, spectral and cyclic voltammetric characterization of [Zn2(deadtc)4(4,4′-bipy)] (1) (deadtc=di(2-hydroxyethyl)dithiocarbamate anion) and [Zn2(nmedtc)4(4,4′-bipy)] (2) (nmedtc=N-methyl, N-ethanoldithiocarbamate anion) are reported. The single crystal X-ray structures of the adducts have also been determined. IR spectra of complexes 1 and 2 show the thioureide ν(CN) bands at 1480 and 1489 cm−1, respectively which are lower than the values observed for the parent dithiocarbamates. A reduction in the thioureide stretching frequency is due to the increase in coordination around the zinc ion and the resultant increase in electron density. The charge transfer transitions are observed in the region 260–320 nm. The X-ray crystal structures show that the two adducts are dimeric in nature. The zinc ions are five coordinated with the ZnS4N coordination environment in both complexes. Both adducts have two short ZnS bonds which are close to those observed in the respective parent dithiocarbamate. The asymmetry introduced in ZnS bond lengths in both adducts is due to the coordination of nitrogen from the 4,4′-bipyridine moiety. The ZnN distances are 2.072(4) and 2.054(8) A for compounds 1 and 2, respectively. In complex 1, two sets of thioureide CN distances are observed; one set averages to 1.328(5) A and the other which is longer, averages to 1.346(6) A. In complex 2 the thioureide CN distance (mean of C(6)N(7) and C(12)N(13)) is 1.339(48) A) indicates the partial double bond nature. However, a longer CN distance (C(6)N(7)′:1.374(75) A) is also observed due to the disorder associated with the aliphatic chain of the ethanolic group on dithiocarbamate. All the CS distances are symmetric in both complexes. Two of the CS distances, namely S(3)C(6) (1.702(5) A) in complex 1 and S(2)C(6) (1.706(11) A) in 2, are different. The cyclic voltammetric studies show clearly the presence of excess electron density on the zinc ions in both adducts compared to the parent dithiocarbamates.