Luminescent rhenium(I)-gold(I) hetero organometallics linked by ethynylphenanthrolines

The first luminescent rhenium(I)-gold(I) hetero organometallics, Re{phenAu(PPh₃)}(CO)₃Cl (3) and Re{(PPh₃)AuphenAu(PPh₃)}(CO)₃Cl (4), have been prepared using the gold(I) complex AuCl(PPh₃) (PPh₃ = triphenylphosphine) and the novel rhenium(I) complexes Re(phenH)(CO)₃Cl (5) (phenH = 3-ethynyl-1,10-phenanthroline) or Re(HphenH)(CO)₃Cl (6) (HphenH = 3,8-bis(ethynyl)-1,10-phenanthroline). All the present rhenium(I) complexes 3-6 were revealed to possess a facial configuration (fac-isomer) with respect to the three carbonyl ligands. The main frameworks for these new gold(I) organometallics were constructed by the Au-C σ-bonding (with the η¹-type coordination) between the ethynylphenanthrolines and the Au(I) phosphine unit. Re(I)-Au(I) heterometallics 3 and 4 have shown single phosphorescence from the ³MLCT excited state and this observation can be interpreted in terms of the efficient intramolecular energy transfer from the Au(I) unit to the Re(I) unit.     

Oxidatively induced reactions of a diimine platinum(IV) tetramethyl complex

The oxidation of the Pt(IV) tetramethyl complex [ArNCHCHNAr]PtMe₄ (Ar = 2,6-Me₂C₆H₃) has been investigated in acetonitrile and dichloromethane. Cyclic voltammetry demonstrates that the irreversible oxidation of [ArNCHCHNAr]PtMe₄ occurs at a slightly less positive oxidation potential than the irreversible oxidation of the analogous Pt(II) species [ArNCHCHNAr]PtMe₂. The product distribution arising from the oxidation depends strongly on the reaction conditions and includes cationic Pt(IV) species (acetonitrile, dichloromethane solvents) and Pt(II) species (dichloromethane only). Evidence is presented that suggests that homolytic cleavage of a weakened PtC bond in is involved in the oxidatively induced reactions.     

Synthesis and characterization of phenylacetylene-terminated poly(silyleneethynylene-4,4′-phenylethereneethynylene)s

Two kinds of phenylacetylene-terminated poly(silyleneethynylene-4,4′-phenylethereneethynylene)s, {C₆H₅CC[Si(R)₂CCC₆H₄OC₆H₄CC]_nC₆H₅} wherein R represents methyl or phenyl, were synthesized by condensation reaction between dichlorosilanes and 4,4′-diethynyldiphenyl ether using organomagnesium reagents. The polymers were characterized by NMR, IR, gel permeation chromatography, thermogravimetric analysis, and differential scattering calorimetry.     

Reactivity of [CpRh(η-C6H3NH2-2,6-i-Pr2)](OTf)2 toward phosphines and alkynes

The cationic aniline complex [Cp^∗Rh(η⁶-2,6-(Me₂CH)₂C₆H₃NH₂)](OTf)₂ (1) was prepared from either [Cp^∗Rh(η²-NO₃)(η¹-OTf)] or [Cp^∗Rh(OH₂)₃](OTf)₂ and 2,6-diisopropylaniline. Complex 1 underwent substitution with phosphines or phosphites, indicating the labile character of the η⁶-aniline ligand. Complex 1 mediated cycloaddition reactions of several alkynes in refluxing ethanol: the [2 + 2] dimerization for PhCCPh and the [2 + 2 + 1] trimerization for PhCCH and CH₃C₆H₄CCH. The unexpected cyclobutadiene complex [Cp^∗Rh(η⁴-C₄(C(O)CH₃)₂H(SiMe₃))] was obtained from complex 1 and Me₃SiCCCCSiMe₃ and structurally characterized by X-ray diffraction.     

Iron(II) and iron(III) complexes containing ethynyl thiophene fragments

The synthesis of the new complexes Cp*(dppe)FeCC2,5-C₄H₂SR (Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl; dppe = 1,2-bis(diphenylphosphino)ethane; 2a, R = CCH; 2b, R = CCSi(CH₃)₃; 2c, R = CCSi(CH(CH₃)₂)₃; 3a, R = CC2,5-C₄H₂SCCH; 3c, R = CC2,5-C₄H₂SCCSi(CH(CH₃)₂)₃) is described. The ¹³C NMR and FTIR spectroscopic data indicate that the π-back donation from the metal to the carbon rich ligand increases with the size of the organic π-electron systems. The new complexes were also analyzed by CV and the chemical oxidation of 2a and 3c was carried out using 1 equiv of [Cp₂Fe][PF₆]. The corresponding complexes 2a[PF₆] and 3c[PF₆] are thermally stable, but 2a[PF₆] was too reactive to be isolated as a pure compound. The spectroscopic data revealed that the coordination of large organic π-electron systems to the iron nucleus produces only a weak increase of the carbon character of the SOMO for these new organoiron(III) derivatives.     

Selective anodic fluorination of electrophilic alkenes

Anodic fluorination of some electrophilic alkenes (conjugated with electron-withdrawn groups), ethyl cinnamates, RC₆H₄CHCHCO₂Et (R = H, CH₃, CH₃O, F and CF₃), cinnamonitrile, C₆H₄CHCHCN, phenyl stryryl ketone, and t-butyl styryl ketone using ammonium fluorides as the fluorine source and supporting electrolyte, in CH₂Cl₂ as electrolytic solvent yields the expected vicinal difluoro compounds, as mixture of erythro and threo isomers. The anodic fluorination of phenyl 3,5-di-t-butyl-4-hydroxystyryl ketone yields two monofluoro compounds. A possible reaction mechanism is discussed.     

P-Modular bis(phosphines) based on the 1,2-trans-disubstituted cyclopentane framework in synthesis, coordination chemistry, and catalysis

The review describes a class of versatile bidentate phosphines having a homochiral 1,2-disubstituted cyclopentane backbone, the use of such ligands in coordination chemistry, and their application in transition metal-catalyzed synthesis, including CH activation, CC coupling, CC hydrogenation, and hydroformylation. In particular, the synthetic potential of the multi-purpose PH and PCl reagents (R,R)- and (S,S)-C₅H₈(PX₂)₂ (X = H, Cl) is highlighted, since these open up the possibility to incorporate virtually any other PO-, PN- or PC-bonded residue (“module”) into the homochiral bis(phosphine) framework. The resulting chelate ligands allow access to transition metal catalysts with stereodiscriminating properties determined by parameters such as (i) the presence of P-substituents that are equal or pairwise different in steric demand, (ii) the spatial orientation of such substituents with respect to the coordination plane of the catalyst complex, and (iii) the combination of C- and P-chirogenic stereoelements in matched (or mismatched) fashion. A comparative discussion of the crystal structures that are currently available for the free ligands and their transition metal complexes is also presented.     

Ionic polymers and oligomers with expanded π-conjugation system derived from through-space interaction in piperazinium ring

Reactions of N-(2,4-dinitrophenyl)-4-arylpyridinium chlorides (aryl (Ar) = phenyl and 4-pyridyl) with piperazines caused the ring opening of the pyridinium ring and yielded polymers that consisted of 5-piperazinium-3-aryl-penta-2,4-dienylideneammonium chloride units [N(CH(R)CH₂)₂N⁺(Cl⁻)CHCHC(Ar)CHCH, RH, Me, and phenyl]. However, the same reactions occurring in the presence of piperidine yielded oligomers that consisted of 5-piperazinium-3-aryl-penta-2,4-dienylideneammonium chloride units having piperidine and/or piperazine rings at both ends. ¹H NMR spectra suggested that π-electrons of the penta-2,4-dienylideneammonium group of the polymers and the oligomers were delocalized. UV-vis measurements revealed that the π-conjugation system expanded along the polymer and oligomer chains due to the orbital interaction between electrons on the two nitrogen atoms of the piperazinium ring. Conversion of the piperazinium ring from the boat form to the chair form caused decrease in the π-conjugation length. The rate constants of the conversion of the oligomers depended on their chain lengths. The surface of pellets that were molded from the polymers and oligomers exhibited metallic luster. These polymers and oligomers underwent electrochemical oxidation in solution.     

Preparation of soluble functional polymers by modification of nanosized polyacetylene

The reaction of electrophilic reagents such as halogens, nitric and sulfuric acids, and sulfur dioxide with nanosized stereoregular polyacetylene was studied. Polymers with chlorine content as much as 65% were obtained and the MW properties of the polymers were found to depend on the structure of pristine polyacetylene prepared under various conditions. The reaction between nitric acid and stereoregular polyacetylene occurred to give first [CH(NO₂)CHCHCH(OH)]_n while the totally nitrated product [CH(NO₂)CH(ONO₂)]_n was obtained with nitrogen content of 18.3% after complete nitration. GPC, NMR- and IR-spectroscopy were used for structural and MWD analysis of the original polyacetylene and obtained products. The mechanism of the reaction between electrophilic reagents and polyacetylene is discussed on the basis of the experimental and literature data.     

2π + 2π cycloaddition kinetics of some fluoro olefins and fluoro vinyl ethers

The second order 2π + 2π homo- and co-dimerization between various classes of fluorinated olefins has been investigated. The fluorinated olefins examined in this study were: (1) R_fOCFCF₂ (perfluorinated vinyl ethers); (2) R_fCFCF₂ (perfluorinated terminal olefins); (3) RCH₂CFCF₂; (4) PhOCFCF₂ (aryl perfluorinated vinyl ethers).Homo-dimerizations between vinyl ethers have an E_a between 20 and 24 kcal mol⁻¹ while homo-dimerizations between terminal olefins have an average E_a between 35 and 40 kcal mol⁻¹; vinyl groups have a second order cyclodimerization rate constant of formation between 1 × 10⁻⁷ and 1 × 10⁻⁴ M⁻¹ S⁻¹ while vinyl ethers have a second order cyclodimerization rate constant of formation = 1 × 10⁻¹ M⁻¹ s⁻¹. If there is a CH₂ group α to the terminal olefin, the E_a of cyclodimerization is about 7 kcal mol⁻¹) lower with respect to those olefins with a CF₂ α to the instauration. At 270 °C co-dimerizations have an average ΔS^≠ = −45 cal K⁻¹ mol⁻¹ and a second order rate constant of cyclodimerization ranging between 0.1 × 10⁻⁴ M⁻¹ S⁻¹ and 16 × 10⁻⁴ M⁻¹ S⁻¹ while homo-dimerizations have an average ΔS^≠ = −17 cal K⁻¹ mol⁻¹ and a second order rate constant which can span from 7 × 10⁻⁷ M⁻¹ S⁻¹ to as much as 1 × 10⁻¹ M⁻¹ S⁻¹ depending on the electronic nature of the perfluorinated terminal olefin.A good correlation between the electronegativity χ and the activation energy E_a demonstrates that “polarizing” groups, O, PhO, α to the olefin play an important role in the formation and stabilization of the cyclodimerization biradical intermediate.     

Synthesis of novel highly heat-resistant fluorinated silane coupling agents

Novel fluorinated silane coupling agents with a biphenyl structure, C_nF_2n+1(C₆H₄)₂CH₂CH₂Si(OCH₃)₃ (n = 4, 6, and 8), were synthesized with the aim to improve the heat-resistance, oxidation-resistance, and acid-resistance of the surface modified with a common fluorinated silane coupling agent. Alcohols, Rf(C₆H₄)₂CH(OH)CH₃, were obtained by reducing the intermediates, Rf(C₆H₄)₂COCH₃, the products of the reaction of 4-acetyl-4′-bromobiphenyl with perfluoroalkyl iodides in the presence of copper powder. The reaction of the alcohols with phosphorus tribromide gave olefins, Rf(C₆H₄)₂CHCH₂, which were then allowed to react with tetramethoxysilane in the presence of hexachloroplatinate(IV) catalyst to yield novel fluorinated silane coupling agents with a biphenyl structure. The coupling agents with four and six carbon atoms in their fluorocarbon chains were obtained as a colorless liquid while that with 8 carbon atoms was a white gel. Evaluations were made of the coupling agents using surfaces modified with them in terms of water contact angles, heat-resistance, oxidation-resistance, and acid-resistance. The agents behaved similarly to the conventional fluorinated silane coupling agents with respect to water contact angles, oxidation-resistance, and acid-resistance, whereas the former showed an extremely higher heat-resistance (up to 350 °C). In addition, C₆H₅C₆H₄CH₂CH₂Si(OCH₃)₃ and CH₃(C₆H₄)₂CH₂CH₂Si(OCH₃)₃ with no fluoroalkyl group were synthesized and the heat-resistance of glass surfaces modified with these compounds was examined.     

Solvent and phosphine dependency in the reaction of cis-RuCl2(P-P)2 (P-P = dppm or dppe) with terminal alkynes

Reaction of cis-[RuCl₂(dppm)₂] (dppm = 1,2-bis(diphenylphosphino)methane) with PhCCH and NaPF₆ utilising methanol as solvent results in the formation of the η³-butenynyl complex [Ru(η³-PhCCCCHPh)(dppm)₂][PF₆] in good yield. Similar reactions with Bu^tCCH and PrⁿCCH resulted in the corresponding alkyl-substituted complexes and all three of these compounds have been characterised by NMR spectroscopy and X-ray crystallography. The mechanism of this reaction has been probed by employing labelling experiments with both PhCCD and PhC¹³CH allowing the identity of possible intermediates in the reaction to be determined. Furthermore, [Ru(η³-PhCCCCHPh)(dppm)₂][PF₆] has been shown to be an effective regio- and stereo-selective catalyst for the dimerisation of PhCCH to Z-PhCCCHCHPh in the absence of solvent. In contrast, no evidence for the formation of alkyne coupling was obtained from the reaction of cis-[RuCl₂(dppe)₂] (dppe = 1,2-bis(diphenylphosphino)ethane) with PhCCH and NaPF₆.     

Synthesis and properties of conjugated bimetallic ruthenium complexes with σ,σ-bridging azobenzene chains

A versatile synthetic route to conjugated bimetallic ruthenium complexes with σ,σ-bridging azobenzene chains was developed, and new ruthenium complexes with various ligands were synthesized and characterized. These bimetallic complexes showed a remarkable absorption in the visible region (λ_max: 452-483 nm), and undergo trans-to-cis isomerization under UV light irradiation for short time. Electrochemical study showed that the metal centers in bimetallic complexes containing the CHCHC₆H₄NNC₆H₄CHCH bridge interact with each other.     

Ab initio and DFT investigation of fluorinated methyl hydroperoxides: Structures, rotational barriers, and thermochemical properties

Ab initio and density functional theory (DFT) calculations have been performed on CH₂FOOH, CHF₂OOH, CF₃OOH, CF₂ClOOH, and CFCl₂OOH. Geometries of stable conformers are optimized at the MP2(FULL)/6-31G(d,p) and B3LYP/6-31G(d,p) levels of theory. The enthalpies of formation () and the ROOH, ROOH, and ROOH bond dissociation enthalpies (BDEs) are estimated for each of the studied hydroperoxides using the calculated reaction enthalpies () of the adopted isodesmic reactions. The results show that the progressive fluorine substitution of hydrogen atoms in methyl group results in an increase in each of BDE(OH), BDE(OO), and BDE(CO). This has been explained in terms of the stabilizing influence of fluorine-substituted methyl groups. However, the replacement of F by Cl when going from CF₃OOH to CFCl₂OOH leads to a decrease in both BDE(OO) and BDE(CO). Potential energy barriers for internal rotation about CO and OO are calculated at the B3LYP/6-31G(d,p) level for each of the studied hydroperoxides.