Coordinating properties of C2-symmetric chiral bis(oxazolinylpyridinyl)dioxolane ligands

Metal complexes of general formula M(L)X₂ and M(L)X₃ [L = (4S,5S)-2,2-dimethyl-4,5-bis{6-[(4,5-dihydro-4-(S)-(1-methylethyl)oxazol-2-yl)pyridin-2-yl]}-1,3-dioxolane] were obtained by reacting, respectively, Co^II, Cu^II, Ni^II, and Zn^II nitrate salts and the Rh^III chloride salt, with a chiral C₂-symmetric bis(oxazolinylpyridinyl)dioxolane (L) ligand, in MeOH/CHCl₃ solution. A single crystal X-ray analysis was carried out on [Ni(L)(OH₂)₂](NO₃)₂ · 2H₂O and the molecular structure of L was also determined. In the free ligand the two symmetric arms are essentially planar and oriented nearly perpendicular to the dioxolane average plane. In the Ni complex one seven-membered and two five-membered chelation rings are formed. The metal atom also lies on the C₂ axis, and two symmetry-related water molecules complete the octahedral coordination environment. Both compounds crystallize in chiral space groups; the ligand crystallizes in orthorhombic system, space group C 2 2 2₁, Z = 4; the nickel complex crystallizes in tetragonal system, space group P 4₃ 2₁ 2, Z = 4.     

Electrophilic cyclization of o-acetoxy- and o-benzyloxyalkynylpyridines: an easy entry into 2,3-disubstituted furopyridines

[reaction: see text] 2,3-Disubstituted furo[3,2-b]pyridines, 2,3-disubstituted furo[2,3-b]pyridines, and 2,3-disubstituted furo[2,3-c]pyridines are readily prepared under mild conditions via the palladium-catalyzed cross-coupling of 1-alkynes with o-iodoacetoxy- or o-iodobenzyloxypyridines, followed by electrophilic cyclization by I(2) or by PdCl(2) under a balloon of carbon monoxide.     

Enthalpies of solvation for N-alkylamides in water and in carbon tetrachloride at 25°C

Molar enthalpies of solution at infinite dilution have been determined at 25°C for several N-alkyl and N,N-dialkylamides in water and in carbon tetrachloride, using a Calvet-type rotating calorimeter, and solution concentrations below 5×10^–2 molal. Relevant enthalpies of transfer between the two solvents also have been derived. Molar enthalpies of solvation have been obtained by adding enthalpies of vaporization to solution values. Results are compared with those of other laboratories on other substituted amides, and their dependence on the number of carbon atoms in the chain is discussed. A possible computation of solvation enthalpies of functional groups is suggested and results for hydration of peptide or similar groups present in the compounds examined are discussed in terms of current models of their hydration and hydrogen bond formation.Presented at the sixth Italian meeting on Calorimetry and Thermal Analysis (AICAT) held in Naples, December 4–7, 1984.     

Binuclear wirelike dimers based on ruthenium(II)-bipyridine units linked by ethynylene-oligothiophene-ethynylene bridges

The syntheses, structural characteristics, electrochemical behavior, ground-state spectra, photophysical properties, and transient absorption (TA) spectra in CH(3)CN solvent are reported for binuclear [(bpy)(2)Ru(bpy-E(T)(n)()E-bpy)Ru(bpy)(2)](4+) complexes, Ru(bpyT(n)bpy)Ru, where the Ru-based units are connected by alternating 3,4-dibutylthiophene (DBT')/thiophene (T') fragments linked via ethynyl groups (E) to bpy ligands at the 5-position (bpy is 2,2'-bipyridine). The ligand bpyT(3)bpy represents a module containing DBT'/T'/DBT' subunits, and bpyT(5)bpy accounts for a DBT'/T'/DBT'/T'/DBT' pattern. The syntheses and electrochemical and spectroscopic (emission and TA) properties in CH(2)Cl(2) solvent of the bpyT(n)()bpy ligands are likewise reported. The behavior of the Ru(bpyT(n)bpy)Ru dimers has been compared to that of the bpyT(n)bpy ligands and to that of a related mononuclear complex, [(bpy)(2)Ru(bpy-E-DBT')](2+), Ru(bpyDBT'). For the dimeric complexes, the electrochemical results show that the first reduction step takes place at the bpy ligand(s) bearing an ethynylene group, the first oxidation step is thiophene-centered, and further oxidation involves the metal centers, which are only weakly interacting. The photophysical and TA results for the Ru(bpyT(n)bpy)Ru dimers account for the presence of low-lying oligothiophene-centered (3)pi,pi levels, while higher-lying metal-ligand charge transfer ((3)MLCT) levels are thermally accessible only for the case of Ru(bpyT(3)bpy)Ru; the possible role of charge separation (CS) levels (from oxidation at the thiophene bridge and reduction at one of the coordinated bpy's) is also discussed.     

Open-shell localized Hartree-Fock method based on the generalized adiabatic connection Kohn-Sham formalism for a self-consistent treatment of excited states

An effective exact-exchange Kohn-Sham approach for the treatment of excited electronic states, the generalized adiabatic connection open-shell localized Hartree-Fock (GAC-OSLHF) method is presented. The GAC-OSLHF method is based on the generalized adiabatic connection Kohn-Sham formalism and therefore capable of treating excited electronic states, which are not the energetically lowest of their symmetry. The method is self-interaction free and allows for a fully self-consistent computation of excited valence as well as Rydberg states. Results for atoms and small- and medium-size molecules are presented and compared to restricted open-shell Hartree-Fock (ROHF) and time-dependent density-functional results as well as to experimental data. While GAC-OSLHF and ROHF results are quite close to each other, the GAC-OSLHF method shows a much better convergence behavior. Moreover, the GAC-OSLHF method as a Kohn-Sham method, in contrast to the ROHF approach, represents a framework which allows also for a treatment of correlation besides an exchange by appropriate functionals. In contrast to the common time-dependent density-functional methods, the GAC-OSLHF approach is capable of treating doubly or multiply excited states and can be easily applied to molecules with an open-shell ground state. On the nodal planes of the energetically highest occupied orbital, the local multiplicative GAC-OSLHF exchange potential asymptotically approaches a different, i.e., nonzero, value than in other regions, an asymptotic behavior which is known from exact Kohn-Sham exchange potentials of ground states of molecules.     

Structure and conformations of N-(fluoroformyl)imidosulfurous dichloride,FC(O)N=SCl2

The IR (gas) and Raman (liquid) spectra of FC(O)NSCl(2) demonstrate the presence of a conformational mixture in both phases. According to a gas electron diffraction study, the main conformer (94(8)%) possesses a syn-syn structure (C(O)F group synperiplanar with respect to the SCl(2) bisector and the C=O bond synperiplanar to the N=S bond). Quantum chemical calculations (HF, B3LYP and MP2 with 6-31G basis set, and MP2/6-311(2df)) predict a syn-anti structure for the second conformer. Analysis of the IR (gas) spectrum results in a contribution of 5(1)% of the minor form, corresponding to a Gibbs free energy difference DeltaG degrees = G degrees (syn-anti) - G degrees (syn-syn) = 1.75(15) kcal/mol. This value is reproduced very well by quantum chemical calculations, which include electron correlation effects (DeltaG degrees = 1.28-1.56 kcal/mol). The HF approximation overestimates this energy difference (DeltaG degrees = 3.24 kcal/mol).     

Trifluoroacetylsulfenyl trifluoroacetate,CF(3)C(O)-S-O-C(O)CF(3), a novel compound with a symmetrically substituted S-O bond: synthesis,spectroscopic characterization,and quantum chemical calculations

The new compound trifluoroacetylsulfenyl trifluoroacetate, CF(3)C(O)SOC(O)CF(3), which possesses two identical carbonyl substituents attached to the S-O bond, has been synthesized. The IR and UV spectra of the gas phase as well as the (13)C NMR spectrum of the solution in CDCl(3) were recorded and assigned. Quantum chemical calculations were performed with the ab initio methods HF and MP2 and the density functional approach B3LYP. The 6-31G basis set was chosen in all calculations. The molecule possesses a skew structure, and according to all computational methods, the syn-syn structure (C=O bonds of both C(O)CF(3) groups synperiplanar to S-O bond) represents the most stable conformer. In agreement with the quantum chemical calculations, the presence of small amounts (< or =5%) of a second conformer (anti-syn) cannot be excluded on the basis of the IR spectrum. The calculated values for the torsional angle around the S-O bond (delta(C-S-O-C)) of the syn-syn form are smaller than 80 degrees (72-78 degrees). Comparison with theoretical results for the corresponding disulfide CF(3)C(O)SSC(O)CF(3) and peroxide CF(3)C(O)OOC(O)CF(3) indicates that the structural properties of sulfenyl compounds are more similar to those of disulfides than to those of peroxides.     

Novel selenium-containing non-natural diamino acids

The general synthesis of a new class of non-natural diamino acids, 2-amino-3-[(2′-aminoalkyl)seleno]propanoic acids, or Se-(aminoalkyl)selenocysteines, is reported. Under the conditions devised, enantiopure N-Boc-protected β-l-iodoamines, which are readily generated from proteinogenic α-amino acids, were treated with the selenolate anion obtained from NaBH₄ splitting of the Se-Se bond in commercial l-selenocystine. The Se-alkylation products were enantiomerically pure and the reaction is high yielding (92-98%), without any detectable traces of accompanying by-products.     

α-Hydroxyalkylation of heteroaromatic bases by alcohols and hydroxylamine-O-sulphonic acid

The homolytic decomposition of hydroxylamine-O-sulphonic acid in alcoholic solvents was investigated in the presence or absence of protonated heteroaromatic bases and Fe(II) salt. The addition of the α-hydroxyalkyl radicals to the base and their oxidation by Fe(III) salt to the corresponding alkyl cyanide were competitive processes. A redox chain process involving the amino radical cation, NH₃^t., is suggested and the factors affecting the yields of the homolytic substitution are discussed.     

Synthesis, Structure, and Antimicrobial Activity of Complexes of Pt(II), Pd(II), and Ni(II) with the Condensation Product of 2-(Diphenylphosphino)benzaldehyde and Semioxamazide

Complexes of Pt(II), Pd(II), and Ni(II) with the condensation derivative of 2-(diphenylphosphino)benzaldehyde and semioxamazide were synthesized, characterized, and their antimicrobial activity was evaluated. The ligand and the complexes were characterized by spectroscopic methods with the particular accent on NMR spectral analysis. For the palladium(II) complex, the crystal structure was determined by X-ray analysis. In all the complexes the ligand is coordinated as a tridentate via a P, N, O donor set. The Pd(II) and Pt(II) complexes have a square planar geometry, whereas the geometry of the Ni(II) complex is tetrahedral. The ligand showed antibacterial and antifungal activity, which was enhanced upon complexation.