Phenyltellurenyl halide complexes of ruthenium and rhenium (CO)2RuBr2(PhTeBr)2 and (CO)3Re(PhTeI)3(μ3-I): Synthesis and crystal and molecular structures

Reactions of Ru₃(CO)₁₂ with PhTeBr₃ and of Re(CO)₅Cl with PhTeI in benzene give the stable complexes (CO)₂RuBr₂(PhTeBr)₂ (I) and (CO)₃Re(PhTeI)₃(μ³-I) (II) containing two and three ligands PhTeX (X = Br or I), respectively. The bonds between these ligands and the central metal atom are fairly shortened (on average, Ru-Te, 2.608 ?; Re-Te, 2.7554(12)-2.7634(13) ?). The Te-X bonds in the ligands PhTeBr (2.5163(5) ?) and PhTeI (2.7893(15) ?) are not lengthened appreciably. In complex II, the iodide anion is not coordinated by rhenium, yet being attached through weak secondary bonds to three Te atoms of the three ligands PhTeI.     

Synthesis and dynamics of atropisomeric (S)-N-(α-phenylethyl)benzamides

The synthesis of atropisomeric 2-substituted benzamides 2a-e, 3a-e, and 4a-e, and characterization by X-ray structure analysis of 2d, 2e, 3c, 3e, 4c, and 4e are reported. Dynamic ¹H NMR spectroscopic studies of benzamides 2b-d, 3b-d, and 4b-d indicate that only two of the four possible rotamers are present in solution, with population ratios ranging between 1.5:1 and 4.1:1. The measured free energy of activation to interconversion of the rotamers ranged from 12.4 to 18.9 kcal mol⁻¹. Benzamides ArCON[(S)-phenethyl]₂ (2e, 3e, and 4e), exhibited atropisomer ratios between 1.7:1 and 1:1, and free energies of interconversion of the rotamers ranged from 11.5 to 17.6 kcal mol⁻¹. The highest rotation barriers were observed for the ortho-nitro derivatives 2a-e. Molecular calculations at the semiempirical level (PM3MM) gave free energies of activation for benzamides 2e and 3e of 23.6 and 12.4 kcal mol⁻¹, respectively, which are comparable to the experimental values.     

Synthesis and X-ray investigation of novel Fe and Mn phenyltellurenyl-halide complexes: (CO)3FeBr2(PhTeBr), (η-C5H5)Fe(CO)2(PhTeI2) and CpMn(CO)2(PhTeI)

New complexes of transition metals with organotellurium halide ligands are reported. Iodination of [CpMn(CO)₂]₂(μ-Ph₂Te₂) leads to the Te-Te bond cleavage and formation of CpMn(CO)₂(PhTeI). Oxidative addition of PhTeBr₃ to Fe(CO)₅ gives the monomeric complex (CO)₃FeBr₂(PhTeBr) which is isostructural with the recently reported (CO)₃FeI₂(PhTeI). Insertion of phenyltellurenyl iodide (PhTeI) into the Fe-I bond of CpFe(CO)₂I forms CpFe(CO)₂(TeI₂Ph). Molecular structures of the reported complexes were determined by single-crystal X-ray diffraction analysis (XRD). A considerable shortening of metal-tellurium distances is observed.     

Thiolate-bridged heterometallic complexes of manganese and platinum: Synthesis and molecular structures of (CO)4Mn(μ-SPh)Pt(PPh3)2, (CO)3(PPh3)Mn(μ-SPh)Pt(PPh3)(CO), and (CO)3Mn(μ-SPh)Pt(PPh3)(Dppm)

A reaction of the dimer [Mn(CO)₄(SPh)]₂ with (PPh₃)₂Pt(C₂Ph₂) gave the heterometallic complex (CO)₄Mn(μ-SPh)Pt(PPh₃)₂ (I) and its isomer (CO)₃(PPh₃)Mn(μ-SPh)Pt(PPh₃)(CO) (II). A reaction of complex I with a diphosphine ligand (Dppm) yielded the heterometallic complex (CO)₃Mn(μ-SPh)Pt(PPh₃)(Dppm) (III). Complexes I–III were characterized by X-ray diffraction. In complex I, the single Mn-Pt bond (2.6946(3) ?) is supplemented with a thiolate bridge with the shortened Pt-S and Mn-S bonds (2.3129(5) and 2.2900(6) ?, respectively). Unlike complex I, in complex II, one phosphine group at the Pt atom is exchanged for one CO group at the Mn atom. The Mn-Pt bond (2.633(1) ?) and the thiolate bridge (Pt-S, 2.332(2) ?; Mn-S, 2.291(2) ?) are retained. In complex III, the Mn-Pt bond (2.623(1) ?) is supplemented with thiolate (Pt-S, 2.341(2) ?; Mn-S, 2.292(2) 0?) and Dppm bridges (Pt-P, 2.240(1)?; Mn-P, 2.245(2) ?). Apparently, the Pt atom in complexes I–III is attached to the formally double bond , as in Pt complexes with olefins.     

Theoretical study on homoleptic mononuclear and binuclear ruthenium carbonyls Ru(CO)n (n= 3–5) and Ru2(CO)n (n = 8, 9)

Homoleptic mononuclear and binuclear ruthenium carbonyls Ru(CO) _n (n = 3–5) and Ru₂(CO) _n (n = 8,9) have been investigated using density functional theory. Sixteen isomers are obtained. For Ru(CO)₅, the lowest-energy structure is the singlet D _3h trigonal bipyramid. Similar to Os(CO)₅, the distorted square pyramid isomer with C _2v symmetry lies ∼7 kJ·mol⁻¹ higher in energy. For the unsaturated mononuclear ruthenium carbonyls Ru(CO)₄ and Ru(CO)₃, a singlet structure with C _2v symmetry and a C _s bent T-shaped structure are the lowest-energy structures, respectively. The global minimum for the Ru₂(CO)₉ is a singly bridged (CO)₄Ru(μ-CO)Ru(CO)₄ structure. A triply bridged Ru₂(CO)₆(μ-CO)₃ structure analogous to the known Fe₂(CO)₉ structure is predicted to lie very close in energy to the global minimum. For Ru₂(CO)₈, the doubly bridged C ₂ structure is predicted to be the global minimum. For the lowest-energy structures of M₂(CO) _n (M = Fe, Ru, Os, n = 9,8), it is found that both iron and ruthenium are favored to form structures containing more bridging carbonyl groups, while osmium prefers to have structures with less bridging carbonyl groups. The study of dissociation energy shows that the dissociation of Ru₂(CO)₉ into the mononuclear fragments Ru(CO)₅ + Ru(CO)₄ is a less energetically demanding process than the dissociation of one carbonyl group from Ru₂(CO)₉ to give Ru₂(CO)₈.     

Synthesis of (E)- and (Z)-α,β-difluorourocanic acid

Horner-Emmons fluoroolefination of an aryl aldehyde followed by introduction of a second fluorine via “FBr” addition provides an original approach to the preparation of 1-alkyl-2-aryl-1,2-difluoroethenes. The utility of this procedure is demonstrated by the preparation of (E and Z)-α,β-difluorourocanic acid.     

The first asymmetric total synthesis of (R)-tuberolactone, (S)-jasmine lactone and (R)-δ-decalactone

A general synthetic approach has been developed for the first asymmetric total synthesis of tuberolactone 1, jasmine lactone 2 and δ-decalactone 3. The key step is the selective hydrogenation of triple and endocyclic double bonds in the key intermediate 4.     

Complexation and eutectic crystallization in poly(2-vinyl pyridine)-block-poly(ε-caprolactone) and pentadecylphenol mixtures

Crystallization behavior via hydrogen bonding interaction in amphiphilic block copolymer/surfactant mixtures consisting of poly(2-vinyl pyridine)-block-poly(ε-caprolactone) (P2VP-PCL) and 3-pentadecylphenol (PDP) were investigated by differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy. The P2VP-PCL/PDP mixtures exhibit eutectic crystallization behavior; the eutectic composition is approximately at 70 wt.% PDP. Scanning probe microscopy (SPM) observation revealed the microphase structure in the P2VP-PCL/PDP mixtures and the unique eutectic morphology at the eutectic composition, which was further confirmed by small angle X-ray scattering (SAXS) results. To our knowledge, this is the first example of eutectic crystallization observed in amphiphilic block copolymer/surfactant systems. The FTIR study proved that there are competitive hydrogen bonding interactions between P2VP block/PDP and PCL block/PDP pairs in the P2VP-PCL/PDP mixtures. On the basis of the SPM results and FTIR study, a model describing the microstructure of the P2VP-PCL/PDP eutectic mixtures is proposed. The amorphous P2VP blocks are expelled from the ordered eutectic lamellae formed by the crystalline PCL blocks and PDP, which deviates remarkably from the existing structural model proposed by other authors for poly(vinyl pyridine)/PDP and poly(styrene-block-4-vinyl pyridine)/PDP mixtures.     

Theoretical and experimental study of fullerenol molecules and ions C60(OH)24 ? n(OL)n and C60(OH)24 ? n(OL)nL+ successively substituted by Alkali Metal atoms L (n = 1?24)

The equilibrium geometric parameters and the energetic characteristics of fullerenol molecules and ions C₆₀(OH)_{24 − n} (OL) _n and C₆₀(OH)_{24 − n} (OL) _n L⁺ successively substituted by alkali metal atoms L with the number of substitutions n = 1–24 have been calculated by the density functional theory B3LYP/6-31G* method. For all compounds, the structure of the covalent [C₆₀O₂₄] cage in which the oxygen atoms are bound to the C atoms of the six-membered [C₆] rings of the fullerene cage, six O atoms per [C₆] ring. The lithium derivatives have been considered in most detail. Computations have shown that the first four single substitutions of Li for H in the OH groups attached to the same C₆ ring require very low energy inputs, no more than 1 kcal/mol, and can spontaneously occur under common conditions. The further fifth and sixth single substitutions in the same C₆ ring are endothermic, but the required energy inputs are also modest (on the order of few kcal/mol). The first and second cooperative substitutions of Li for H simultaneously in all four hydroxylated C₆ rings require energy inputs of ∼3 and 11.6 kcal/mol, respectively; in the third and fourth fourfold substitutions, the energies increase by ∼15–16 kcal/mol. The mean partial energy per single substitution of Li for H in this series (n = 1−6) is ∼2 kcal/mol. Calculations have predicted that all C₆₀(OH)_{24 − n} (OLi) _n molecules with intermediated degrees of substitution (n = 1−16) can be obtained under the conditions of relatively low energy inputs (for example, under the conditions of the MALDI experiment) and can exist in the isolated state. For the sodium- and potassium-substituted analogues, the qualitative pattern persists, but the H/Na and H/K substitutions are somewhat more endothermic. The computational results are compared with the MALDI mass spectrum of the [C₆₀(OH) _x (ONa) _y -CH₃COONa) system.     

Crystal Structures and Characterizations of Bis(pyrrolidinedithiocarbamato) Cu(II) and Zn(II) Complexes

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Phenyl(acyloxy)fluorosilanes C6H5Si(OCOR)nF3?n (n = 1, 2) and phenyl(acyloxy)fluorochlorosilanes C6H5Si(OCOR)FCl

The method of synthesis of the hitherto unknown class of organosilicon compounds, phenyl(acyloxy)fluorosilanes C₆H₅Si(OCOR) _n F_3−n (n = 1, 2) and phenyl(acyloxy)fluorochlorosilanes C₆H₅Si(OCOR) FCl in up to 91% yield has been developed based on the reaction of phenyl(fluoro)chlorosilanes C₆H₅SiCl _n F_3−n (n = 1, 2) with trimethylsilyl esters of carboxylic acids Me₃SiOC(O)R [R = H, CH₃, CF₃, CCl₃, ClCH₂, BrCH₂, CH₂=CHCH₃, CH₂=CHPh, CH(CH₃)=CH₂, Ph].     

Solvatochromism and piezochromism of pentacyanoferrates(II) and of mixed valence iron(II)—iron(III) and ruthenium(II)—ruthenium(III) species

Pressure effects on the MLCT bands of the pyrazine- and 4-cyanopyridine-pentacyanoferrate(II) anions have been established. The relation of these piezochromic effects to the solvatochromism of each complex is put into the correlation between these parameters developed for other d⁶ ternary complexes. The conformance of piezochromic and solvatochromic efrects on MMCT bands for diiron and diruthenium mixed valence complexes to this correlation is examined.     

Two novel Mo(V) and Mo(V)/Mo(VI) barium phosphates with a tunnel structure: β-Ba(MoO)2(P2O7)2, and Ba(MoO)2O(P2O7)PO4

Two new Mo(V) and Mo(V)/Mo(VI) phosphates, β-Ba(MoO)₂(P₂O₇)₂ and Ba(MoO)₂O(P₂O₇)PO₄, with original tunnel structures have been synthesized. The first one crystallizes in the space group P2₁/n with , , , β=91.67°, and the second one in the space group Cc with , , , β=99.50°. β-Ba(MoO)₂(P₂O₇)₂ shows close relationships with the α-form, i.e., it consists of similar MoP₂O₁₁ units sharing their apices and forming [MoP₂O₁₀]_∞ chains. It differs from the latter by the configuration of the chains, so that one chain is linked to four other identical chains, instead of six chains in the α-form. Like the α-form, the β-form exhibits intersecting tunnels running along [010] and [011] direction where the Ba²⁺ cations sit. The 3D-framework of the second phosphate Ba(MoO)₂O(P₂O₇)PO₄, is built up of MoO₆ octahedra, P₂O₇ groups, and PO₄ tetrahedra, can be described by the assemblage of zig-zag [Mo₂P₂O₁₄]_∞ chains through PO₄ tetrahedra, forming large tunnels running along , occupied by Ba²⁺ cations. In this framework one observes that adjacent tunnels communicate through large six-sided windows, showing the opened character of this structure. The magnetic behaviour of these phosphates is discussed with respect to the results previously obtained by Canadell et al. [Chem. Mater. 9 (1997) 68].     

Synthesis,thermal and spectral studies of oxoperoxo and dioxo complexes of vanadium(V), molybdenum(VI) and tungsten(VI) with 2-(α-hydroxyalkyl/aryl)benzimidazole

Reaction of 2-(-hydroxymethyl)benzimidazole or 2-(-hydroxyethyl)benzimidazole (LH) with the peroxovanadium(V) species, generated in situ by stirring V₂O₅, KOH and 30% aqueous H₂O₂, gives the corresponding complexes of formula K[VO(O₂)L₂]. Similar peroxo species of molybdenum and tungsten generated by stirring MoO₃ or WO₃·H₂O with an excess of 30% aqueous H₂O₂ readily react with 2-(-hydroxyethyl) benzimidazole in aqueous EtOH to give the peroxo complexes [MO(O₂)L₂] (M=Mo or W). The dioxo complexes of general formula [MO₂L₂] have also been isolated by the reaction of [MoO₂(acac)₂] or [WO₂- (acac)₂] (acacH=acetylacetone) with the above ligands and with 2-(-hydroxybenzyl)benzimidazole. The dioxo complexes are white, whereas peroxo complexes are light yellow to orange. The peroxo complexes generally decompose in two steps: (i) the decomposition of the peroxo group and (ii) the decomposition of the alkyl/aryl group followed by decomposition of the complete ligand. On the other hand, decomposition of the dioxo complexes follows only in a later step. All the peroxo complexes exhibit three i.r. active vibrational modes at ca. 860cm^–1, 760cm^–1 and 600cm^–1, characteristic of the ²-coordinated peroxo group. The dioxo complexes are dominated by the presence of two sharp bands in the 900cm^–1 region due to _sym(O=M=O) and _asym(O=M=O) modes. The (C=N) (ring) and (OH) shifts have also been measured in order to locate the coordination sites of the ligands. A broad band at ca. 400nm in the peroxovanadium(V) complexes, while the absorption at ca. 350nm in the peroxomolybdenum(VI) and tungsten(VI) complexes is assigned to the peroxo-metal charge transfer band.     

Synthesis and Properties of D-Thymidylyl (3'→5')L-Thymidine (D/L-TpT)

Inrecentyearsmuchefforthasbeenspenttodevelopoligonucleotideanalogsashighlyselectivepharmaceuticalagentstoblockexpressionofdisease-associatedproteins'-'.andtheseefT'ortshaveresultedilltheapprovaloffomiversensodium(vitravene',"),thefirstantisensedrug,byFDAinAugust1998fortreatmentofAIDSpatientswithcytomegalovirus(CMV)-inducedretinitis6.However,thegreatpotentialofantisenseoligonucleotidesasantiviralandanticanceragentsiscompromisedbytheirnucleasesusceptibilityandlowcellmembranepermeability.L-D…     

Electrochemistry and UV/visible spectroscopy of phosphino-substituted bis(η-indenyl)iron(II) complexes

Six phosphino-functionalized diindenyl ferrocenes have been characterized by UV/vis spectroscopy and cyclic voltammetry in dichloromethane. The complexes contain the following ligands: 1-diphenylphosphino- (1), 1-diphenylphosphino-2-methyl- (2), 1-diphenylphosphino-3-methyl- (3), 1-diphenylphosphino-3-trimethylsilyl- (4), 1-diphenylphosphino-2,3-dimethyl- (5), and 1-diphenylphosphino-4,7-dimethyl-indenide (6). The cyclic voltammetry shows an approximately additive relationship between oxidation potential and the type of substituent and its ring position, but with increasing substitution leading to lower than otherwise expected oxidation potentials. The UV/vis spectra show two absorptions with the low energy band moving to lower energy with increasing substitution on the C₅ ring.     

Visible-light photoresponsive heterojunctions of (Nb–Ti–Si) and (Bi/Bi-O) nanoparticles

The increasing motivation to seek alternative sources of clean and sustainable energy has intensified, due to a growing awareness that fossil fuels are finite in quantity, and that the combustion products of such fuels contribute to global warming. Solar energy is considered one of the most readily available alternatives, but materials which are able to harness this form of energy need to be developed. This study details the development of a novel composite material, of the form of Bi/Bi-O nanoparticles supported on a (Nb–Ti–Si) oxide. Characterized using electrochemical and other methods, this material generates a photocurrent, and is capable of photo-oxidizing airborne-styrene in a fluidized-bed photoreactor when exposed to visible-light.     

Synthesis and properties of ms- and β-substituted Pt(II) and Pt(IV) tetraphenylporphyrinates

The interaction of 5,10,15,20-tetraphenylporphyrin, 5,10,15,20-tetra-(4-chlorophenyl)porphyrin, 2-bromo-5,10,15,20-tetraphenylporphyrin, and 2,3,12,13-tetrabromo-5,10,15,20-tetraphenylporphyrin with platinum(II) chloride in boiling phenol has been studied. The corresponding platinum(II) porphyrinates have been synthesized; their subsequent treatment with bromine in chloroform resulted in platinum(IV) porphyrinates. The Pt(II) and Pt(IV)(Br)₂ porphyrinates have been identified by elemental analysis, electron absorption, IR, and ¹H NMR spectroscopy.     

Complexes of technetium(I) (Tc, Tc) pentacarbonyl core with π-acceptor ligands (tert-butyl isocyanide and triphenylphosphine): Crystal structures of [Tc(CO)5(PPh3)]OTf and [Tc(CO)5(CNC(CH3)3)]ClO4

A procedure was developed for preparing [^99mTcX(CO)₅] (X = Cl, Br, I) in a reasonable yield by high-pressure carbonylation with CO of ^99mTcO₄⁻ in aqueous solutions. In the synthesis, the substantial part of the target product is accumulated in the gas phase and can be transferred from the autoclave into various solvents when relieving the pressure. Compounds [^99mTcX(CO)₅] (X = Cl⁻, Br⁻, I⁻) are stable in solutions for several hours, but in the course of longer storage they gradually decompose to give the tricarbonyl species. Substitution of the halide ligands in [⁹⁹TcX(CO)₅] and [^99mTcX(CO)₅] with tert-butyl isocyanide and triphenylphosphine was studied. The structures of the complexes [Tc(CO)₅(PPh₃)]OTf and [Tc(CO)₅(CNC(CH₃)₃)]ClO₄ are presented.     

Structural variations of nickel complexes in NiS4 and NiS2PN coordination environments: spectral and single-crystal X-ray structural studies on bis(4-methylpiperidinecarbodithioato-S,S′)nickel(II) and (4-methylpiperidinecarbodithioato-S,S′)(thiocyanato-N)(triphenylphosphine)nickel(II)

Abstract  

[Ni(4-mpipdtc)₂] and [Ni(4-mpipdtc)(PPh₃)(NCS)] (4-mpipdtc = 4-methylpiperidinecarbodithioate anion) have been characterized by electronic, IR, and NMR spectroscopy, single crystal X-ray analysis, and cyclic voltammetry. IR spectra of the complexes show the contribution of the thioureide form to the structures. ¹H NMR spectra show the deshielding of α-CH₂ protons on complexation. ¹³C NMR spectra shows interesting differences between the N¹³CS₂ carbon signals of the parent complex [Ni(4-mpipdtc)₂] and the mixed ligand complex [Ni(4-mpipdtc)(PPh₃)(NCS)]. The N¹³CS₂ carbon signal for [Ni(4-mpipdtc)(PPh₃)(NCS)] is observed at 204.85 ppm with an upfield shift of about 3.8 ppm compared with that found in [Ni(4-mpipdtc)₂] (201.06 ppm). The observed shielding in [Ni(4-mpipdtc)(PPh₃)(NCS)] indicates the effect of PPh₃ on the mesomeric drift of electron density toward nickel through the thioureide C–N bond. Single crystal X-ray analysis of [Ni(4-mpipdtc)₂] and [Ni(4-mpipdtc)(PPh₃)(NCS)] confirms the presence of four-coordinated nickel in a distorted square-planar arrangement with the NiS₄ and NiS₂PN chromophores, respectively. The C–N (thioureide) bond lengths of [Ni(4-mpipdtc)(PPh₃)(NCS)] are shorter than those found in [Ni(4-mpipdtc)₂], because of the presence of the π-acid (triphenylphosphine) in [Ni(4-mpipdtc)(PPh₃)(NCS)]. Significant asymmetry in Ni–S bond distances was observed in Ni(4-mpipdtc)(PPh₃)(NCS)] (2.162(2) and 2.211(2) ?). This observation clearly supports the less effective trans effect of SCN^– over PPh₃. The piperidine ring in the dithiocarbamate fragment is in the normal chair conformation.