Formation of a macrocycle from dichlorodimethylsilane and a pyridoxalimine Schiff base ligand

The reaction of dichlorodimethylsilane with a polydentate Schiff base ligand derived from pyridoxal and 2-ethanolamine yielded the macrocyclic silicon compound (8E,22E)-4,4,12,18,18,26-hexamethyl-3,5,17,19-tetraoxa-8,13,22,27-tetraaza-4,18-disilatricyclo[22.4.0.010,15]octacosa-1(24),8,10,12,14,22,25,27-octaene-11,25-diol, C24H36N4O6Si2. The asymmetric unit contains the half macrocycle with an intramolecular O—H...N hydrogen bond between the imine nitrogen atom and a neighbouring oxygen atom. The crystal structure is dominated by C—H...O and C—H...π interactions, which form a high ordered molecular network.

Rationale on the High Radical Scavenging Capacity of Betalains

Betalains are water-soluble natural pigments of increasing importance as antioxidants for pharmaceutical use. Although non-phenolic betalains have lower capacity to scavenge radicals compared to their phenolic analogues, both classes perform well as antioxidants and anti-inflammatory agents in vivo. Here we show that meta-hydroxyphenyl betalain (m-OH-pBeet) and phenylbetalain (pBeet) show higher radical scavenging capacity compared to their N-methyl iminium analogues, in which proton-coupled electron transfer (PCET) from the imine nitrogen atom is precluded. The 1,7-diazaheptamethinium system was found to be essential for the high radical scavenging capacity of betalains and concerted PCET is the most thermodynamically favorable pathway for their one-electron oxidation. The results provide useful insights for the design of nature-derived redox mediators based on the betalain scaffold.

New Molybdenum(II) Complexes with α-Diimine Ligands: Synthesis, Structure, and Catalytic Activity in Olefin Epoxidation

Three new complexes [Mo(η3-C3H5)Br(CO)2{iPrN=C(R)C5H4N}], where R = H (IMP = N-isopropyl 2-iminomethylpyridine), Me, and Ph, were synthesized and characterized, and were fluxional in solution. The most interesting feature was the presence, in the crystal structure of the IMP derivative, of the two main isomers (allyl and carbonyls exo), namely the equatorial isomer with the Br trans to the allyl and the equatorial with the Br trans to one carbonyl, the position trans to the allyl being occupied by the imine nitrogen atom. For the R = Me complex, the less common axial isomer was observed in the crystal. These complexes were immobilized in MCM-41 (MCM), following functionalization of the diimine ligands with Si(OEt)3, in order to study the catalytic activity in olefin epoxidation of similar complexes as homogeneous and heterogeneous catalysts. FTIR, 13C- and 29Si-NMR, elemental analysis, and adsorption isotherms showed that the complexes were covalently bound to the MCM walls. The epoxidation activity was very good in both catalysts for the cis-cyclooctene and cis-hex-3-en-1-ol, but modest for the other substrates tested, and no relevant differences were found between the complexes and the Mo-containing materials as catalysts.

Electronic versus steric control in palladium complexes of carboranyl phosphine-iminophosphorane ligands

Subtle changes in the electronic properties of C- and B3-carboranyl phosphineiminophosphoranes allows a fine control of the donor ability of the imine nitrogen atom, which results in Pd complexes with the ligands providing (P,N)-chelating or P-terminal coordination.

{1-[1-(2-Hydroxyphenyl)ethylidene]-2-(pyridin-2-yl-κN)hydrazine-κ2 N′,O}{1-[1-(2-oxidophenyl)ethylidene]-2-(pyridin-2-yl-κN)hydrazine-κ2 N′,O}nickelate(II) nitrate hemihydrate

The 2-hydrazinopyridine precursor has been widely used to prepare ligands of various kinds by condensation with carbonyl compounds. These types of ligands are suitable for synthesizing novel transition metal (II) complexes with interesting magnetic properties. In this context we have synthesized the ligand 1-(2-hydroxyphenyl-2-ethylidene)-2-(pyridin-2-yl)hydrazine (HL) which was used in the preparation of the mononuclear title complex, [Ni(C13H12N3O)(C13H13N3O)]NO3·0.5H2O. As a result of the presence of HL and L in the [{Ni(HL)(L)}]+ unit, the complex appears to be a supramolecular dimer composed of the Δ(−) and Λ(−) optical isomers, which are linked by strong hydrogen-bonds. As well as the dimer generated by two mononuclear [{Ni(HL)(L)}]+ cations, the asymmetric unit also contains two nitrate anions and one water molecule. Each Ni atom is coordinated to two ligand molecules by a nitrogen atom of the pyridine ring, an imine nitrogen atom and a phenolic oxygen atom of one of the ligand molecules and a phenolate oxygen atom of the other organic molecules. The environment around the cation is a distorted octahedron. The basal planes are defined by the two nitrogen atoms of the pyridine rings and the two phenolic oxygen atoms of the ligand, the apical positions being occupied by the azomethine atoms. The O atoms of one of the nitrate ions are disordered over two sets of sites in a 0.745 (9):0.255 (9) ratio. In the crystal, the dimers are linked by numerous hydrogen bonds, forming a three-dimensional framework.

The Preparation and Structure of [(2,4-Dimethyl-8-ethyl-5,8-diazadec-4-ene-2-amine)chlorocopper(II)] Perchlorate

Copper(II) chloride and perchlorate, N,N-diethylethane-1,2-diamine, react in (m)ethanol with acetone and ammonia to form [(2,4-dimethyl-8-ethyl-5,8-diazadec-4-ene-2-amine)chlorocopper(II)] perchlorate, C12H27Cl2CuN3O4, , monoclinic, C2/c, (Hall-C2/c); a, 26.418(1), b, 9.7385(4); c, 14.0993(5) Å; β, 91.134(3)°. This has copper(II) in tetrahedrally distorted square-planar coordination by one primary, one tertiary, and one imine nitrogen atom and the chloride ion.

Synthesis and crystal structures of a poliaza receptor macrigiland: 1,3-BTS(2-Nitrobenzyldenamino)Propan-2-0L

The asymmetric unit of the title compound C11H16N,05 , contains one molecule of the compound (L3) (1,3-bis(2-nitrobenzylideneamino )propan-2-ol). The molecule shows a chiral C atom but the absolute structure was not possible to be determined by X-ray diffraction. The molecule shows intermolecular hydrogen bonding involving the hydroxy group and an imine nitrogen atom of a symmetry related molecule. The molecular distribution shows weak interactions between oxygen atoms of the nitro groups and two different C-H groups of benzene rings. The extended weak H bond formation, using the N02 groups, probably gives a more stable crystal structure. The molecule represents a precursor of a polyaza macrocylic ligands.

Synthesis and Properties of 2-(Dimesitylboryl)benzylideneamines

Lithiation of 2-(2-bromophenyl)-dioxolane (1) followed by reaction with dimesitylboron fluoride afforded 2-(2-dimesitylborylphenyl)-dioxolane (2) which was deprotected to afford 2- dimesitylboryl-benzaldehyde (3). Compound 3 reacts with aliphatic amines such as n-butylamine and ethanolamine to afford the corresponding imines 2-(dimesitylboryl)benzylidenebutylamine (4) and 2-(dimesitylboryl)benzylideneethanolamine (5), respectively. Structural studies indicate coordination of the imine-nitrogen atom to the boron center. Imines 4 and 5 emit a green fluorescence near 510 nm with quantum yields approaching 10%. TD-DFT calculations suggest that this emission arises from an intramolecular charge-transfer excited state

Complexes of Pd(II) and Pt(II) with 9-Aminoacridine: Reactions with DNA and Study of Their Antiproliferative Activity

Four new metal complexes {M = Pd(II) or Pt(II)} containing the ligand 9-aminoacridine (9AA) were prepared. The compounds were characterized by FT-IR andH,C, andPtNMR spectroscopies. Crystal structure of the palladium complex of formulae[Pd(9AA)(μ-Cl)]2·2DMF was determined by X-ray diffraction. Two 9-acridine molecules in the imine form bind symmetrically to the metal ions in a bidentate fashion through the imine nitrogen atom and the C(1) atom of the aminoacridine closing a new five-membered ring. By reaction with phosphine or pyridine, the Cl bridges broke and compounds with general formulae [Pd(9AA)Cl(L)] (whereL=PPh3or py) were formed. A mononuclear complex of platinum of formulae [Pt(9AA)Cl(DMSO)] was also obtained by direct reaction of 9-aminoacridine and the complex [PtCl2(DMSO)2]. The capacity of the compounds to modify the secondary and tertiary structures of DNA was evaluated by means of circular dichroism and electrophoretic mobility. Both palladium and platinum compounds proved active in the modification of both the secondary and tertiary DNA structures. AFM images showed noticeable modifications of the morphology of the plasmid pBR322 DNA by the compounds probably due to the intercalation of the complexes between base pairs of the DNA molecule. Finally, the palladium complex was tested for antiproliferative activity against three different human tumor cell lines. The results suggest that the palladium complex of formula[Pd(9AA)(μ-Cl)]2has significant antiproliferative activity, although it is less active than cisplatin.