Synthesis and Reactions of <i>cis</i>-Silyl(boryl)platinum(II) Complexes

Four kinds of silyl(boryl)platinum(II) complexes, 2a−2d, have been prepared by oxidative addition of silylboranes to platinum(0) complexes, in situ generated from Pt(cod)2 and 2 molar quantity of tertiary phosphine ligands (L) in Et2O:  cis-Pt(SiMe2Ph)(BX2)L2 (X2 = −OCMe2CMe2O− (pin), L = PMe3 (2a), PMe2Ph (2b), PEt3 (2c); X2 = −NMeCH2CH2NMe− (dmeda), L = PMe3 (2d)). Complexes 2a−2c undergo selective insertion of phenylacetylene into the Pt−B bond at room temperature in CD2Cl2, giving cis-Pt{C(Ph)CH(Bpin)}(SiMe2Ph)L2 (L = PMe3 (3a), PMe2Ph (3c), PEt3 (3c)), respectively, while 2d is inactive toward insertion. The X-ray structure of 3b has been determined. Kinetic study using 2a indicates the mechanism involving prior dissociation of L, followed by insertion of phenylacetylene into the Pt−B bond. The insertion complexes 3a−3c undergo C−Si reductive elimination to give (Z)-α-silyl-β-borylstyrene. The reactivity decreases in the order 3c ≫ 3b > 3a

Insertion of Phenylacetylene into Pt(SnMe₃)₂(PMe₂Ph)₂

Oxidative addition of Me3SnSnMe3 to a platinum(0) complex, in situ generated from Pt(nbe)3 (nbe = norbornene) and PMe2Ph in Et2O, gives a 72:28 mixture of cis and trans isomers of Pt(SnMe3)2(PMe2Ph)2 (1), which are rapidly interconverted with each other in solution in the presence of PMe2Ph. The trans isomer is further converted to a five-coordinate species Pt(SnMe3)2(PMe2Ph)3 (2) by the coordination of PMe2Ph. Treatment of an equilibrium mixture of 1 and 2 with phenylacetylene in CD2Cl2 forms two regioisomers of insertion complexes, cis-Pt{C(Ph)CH(SnMe3)3}(SnMe3)(PMe2Ph)2 (5) and cis-Pt{CHC(Ph)(SnMe3)}(SnMe3)(PMe2Ph)2 (6). The product ratio varies with the amount of PMe2Ph added to the system. Thus 6 is favorably formed in the absence of PMe2Ph, whereas 5 is predominantly formed in the presence of PMe2Ph. The formation processes of 5 and 6 are discussed

Self-Assembled Fibrillar Networks through Highly Oriented Aggregates of Porphyrin and Pyrene Substituted by Dialkyl l-Glutamine in Organic Media^†

Microfibrous self-aggregation of chromophoric groups of porphyrin and/or pyrene substituted by didodecyl l-glutamic acid in organic media is confirmed by transmission electron microscopic (TEM) observation. Chromophoric probes of porphyrin and pyrene moieties enable evaluation of their assembling behavior photophysically through UV−vis, circular dichroism (CD), and fluorescence spectroscopic characterization. This spectroscopic characterization was able to compensate the lack of TEM observation for the aggregation even at a low concentration below the critical gel concentration. The temperature affects the salient features of the photophysics of porphyrin or pyrene in the microfibrous assemblies. Highly oriented network structures were formed at low temperature since the CD intensities of the porphyrin and pyrene systems increased with lowering the temperature. Fluorescence spectroscopic characterization confirmed the monomer excitation of porphyrin itself, and efficient excimer formation for the pyrene−pyrene charge transfer was detected at low temperature. In particular, we also obtained the preliminary results of fluorescence spectroscopic measurement on singlet−singlet energy migration from pyrene to porphyrin in the mixed assemblies for mimicry of the efficient energy transfer process of the photosynthetic antenna complex

Tunable Light Emission from Lignin: Various Photoluminescence Properties Controlled by the Lignocellulosic Species, Extraction Method, Solvent, and Polymer

This report describes the tunable light emission from lignin, which was achieved by carefully selecting the lignocellulosic species, extraction method, solvent, and polymer. Lignins comprising various taxonomic species with distinct primary structures exhibited diverse photoluminescence (PL) intensities and spectral patterns. Investigations probing how the solvent affects the PL properties revealed that the PL quenching phenomenon originated from the decreasing distance between aromatic moieties (luminophores). Therefore, polymers can play key roles as media to modulate the distance between luminophores, and the PL intensity can be enhanced by employing a relatively stiff polymer. In terms of the emission color, the PL spectral pattern can be tuned by changing the lignin primary structures or by deprotonating the phenolic hydroxyl groups. By modulating these influencing factors, various light emissions were obtained from lignins in solutions and transparent solid materials

Electrospun Ag-TiO₂ Nanofibers for Photocatalytic Glucose Conversion to High-Value Chemicals

TiO2 nanofibers were fabricated by combination of sol–gel and electrospinning techniques. Ag-doped TiO2 nanofibers with different Ag contents were prepared by two different methods (in situ electrospinning or wetness impregnation of Ag on TiO2 nanofibers) and heat treated at 500 °C for 2 h under an air or N2 atmosphere. The obtained catalysts were characterized by field emission scanning electron microscopy, X-ray diffraction, photoluminescence, and N2 adsorption analyzed by the Brunauer–Emmett–Teller (BET) method. Photocatalytic glucose conversions with electrospun TiO2 and Ag-doped TiO2 nanofibers for production of high-value products were carried out. From different doping methods, the results indicated that 1 wt % Ag-TiO2 nanofibers prepared by an in situ method with calcination under N2 achieved the highest glucose conversion (85.49%). From several Ag loading contents (i.e., 0, 1, 2, and 4 wt %) in Ag-doped TiO2 nanofibers, the nanofibers exhibited different glucose conversions [in order of 2 wt % (99.65%) > 1 wt % (85.49%) > 4 wt % (77.72%) > 0 wt % (29.64%)]. Arabinose, xylitol, gluconic acid, and formic acid were found as the high-value chemicals with the photocatalytic reaction of TiO2 and Ag-doped TiO2 nanofibers under UVA irradiation. Product yields of each converted chemicals from different photocatalysts from different Ag loading contents showed relatively same trends with the glucose conversion. From all results, it can be concluded that the good characteristics of 2 wt % Ag-TiO2 nanofibers such as the smallest anatase crystallite size (8.25 nm) and the highest specific surface area (SBET = 53.69 m2/g) promoted the highest photocatalytic activity. Additionally, TiO2 and Ag-doped TiO2 nanofibers exhibited higher photocatalytic performance for glucose conversion than commercial TiO2 (P25) and synthesized TiO2 nanoparticles. Finally, Ag-doped TiO2 nanofibers showed recycling ability with high photocatalytic glucose conversion after four-time use

Photocatalytic Activity for Hydrogen Evolution of Electrospun TiO₂ Nanofibers

We report herein a simple procedure for the fabrication of TiO2 nanofibers by the combination of electrospinning and sol−gel techniques by using poly(vinylpyrrolidone) (PVP), titanium(IV) butoxide, and acetylacetone in methanol as a spinning solution. TiO2 nanofibers (260−355 nm in diameter), with a bundle of nanofibrils (20−25 nm in diameters) aligned in the fiber direction, or particle-linked structures were obtained from the calcination of as-spun TiO2/PVP composite fibers at temperatures ranging from 300 to 700 °C. These nanofibers were utilized as photocatalysts for hydrogen evolution. The nanofiber photocatalyst calcined at 450 °C showed the highest activity among the TiO2 nanofibers tested such as ones prepared by the hydrothermal method and anatase nanoparticles (Ishihara ST-01). These results indicate that one-dimensional electrospun nanofibers with highly aligned bundled nanofibrils are beneficial for enhancement of the crystallinity, large surface area, and higher photocatalytic activity

Surface Modification of ZnO Nanorods with Small Organic Molecular Dyes for Polymer–Inorganic Hybrid Solar Cells

ZnO nanorod arrays modified with dye molecules demonstrate specific light-harvesting and charge-collecting properties which are promising for the enhancement of the characteristic performance of hybrid solar cells based on ZnO/poly(3-hexylthiophene). The properties of dyes commonly used for dye-sensitized solar cells were investigated in relation to the performance of polymer–inorganic hybrid photovoltaic devices. The use of indoline dye D205, which has dipole moments directing away from the ZnO surface, was found to suppress the reverse saturation dark current density and charge recombination and to consequently lead to higher open-circuit voltage and improved power conversion efficiency (PCE) from 0.22% to 0.71%. Derivatized squaraine molecules were synthesized and were found to improve device performance by extending the light-harvesting range to the near-infrared region, leading to increased short-circuit current density and the highest PCE of 1.02%

Alkyne Insertion into <i>cis</i>-Silyl(stannyl)platinum(II) Complexes

A series of cis-silyl(stannyl)platinum(II) complexes have been prepared by oxidative addition of silylstannanes to Pt(cod)2 in toluene in the presence of tertiary phosphine ligands:  cis-Pt(SiR3)(SnMe3)L2 [L = PMe2Ph, SiR3 = SiMe3 (1a), SiMe2Ph (1b), SiMePh2 (1c), SiPh3 (1d); SiR3 = SiMe2Ph, L = PMe3 (1e), PEt3 (1f), PMePh2 (1g)]. These complexes undergo competitive insertion of alkynes (R‘C⋮CH) into the Pt−Sn and Pt−Si bonds under kinetic conditions to give the insertion complexes cis-Pt{C(R‘)CHSnMe3}(SiR3)L2 (2) and cis-Pt(SnMe3){C(R‘)CHSiR3}L2 (3), respectively. Furthermore, once 2 is formed in the reaction systems, it is converted to 3 under thermodynamic conditions. The kinetic ratio of 2 to 3 is significantly affected by the silyl and phosphine ligands as well as the alkynes employed. Thus, in the insertion of phenylacetylene, the kinetic ratio changes depending on the silyl and phosphine ligands attached to the complexes as follows:  2/3 = 0/100 (1a), 30/70 (1b), 59/41 (1c), 93/7 (1d), 36/64 (1e), 25/75 (1f), 25/75 (1g). On the other hand, in the reactions of 1b, the kinetic ratio varies with alkynes as follows:  2/3 = 12/88 (p-H2NC6H4C⋮CH), 28/72 (p-MeC6H4C⋮CH), 30/70 (PhC⋮CH), 46/54 (p-OHCC6H4C⋮CH), 100/0 (MeO2CC⋮CCO2Me). Reasons for the variations are discussed on the basis of the insertion mechanism elucidated by kinetic investigations

Mechanisms of C−Si and C−H Bond Formation on the Reactions of Alkenylruthenium(II) Complexes with Hydrosilanes

Reactions of the four alkenylruthenium(II) complexes Ru[C(R1)CH(R2)]Cl(CO)(PPh3)2 (R1 = H, R2 = Ph (1b); R1 = H, R2 = t-Bu (1c); R1 = Ph, R2 = Ph (1d); R1 = CHCH(SiMe3), R2 = SiMe2Ph (1e)) with HSiMe2Ph, which constitute the product-forming step of ruthenium-catalyzed hydrosilylation of alkynes, have been examined. Two reaction courses are operative:  one provides the C−Si coupling product PhMe2SiC(R1)CH(R2) and RuHCl(CO)(PPh3)3 (path A), and the other forms the C−H coupling product HC(R1)CH(R2) and Ru(SiMe2Ph)Cl(CO)(PPh3)2 (path B). The ratio of the two courses significantly varies with substituents on the alkenyl ligands, particularly with the α-substituent (R1). Thus, 1b and 1c, without an α-substituent, react mainly by path A. In contrast, 1d and 1e, bearing an α-substituent, exclusively undergo path B. Kinetic studies using 1b and its para-substituted styryl ligand derivatives have revealed that path A proceeds by direct interaction of the five-coordinated complexes with hydrosilane, without dissociation of the PPh3 ligand. On the other hand, path B involves dissociation of PPh3 prior to the reaction of 1d or 1e with hydrosilane. Mechanisms of the C−Si and C−H bond formation are discussed with kinetic data in detail

Control of Self Organization in Conjugated Polymer Fibers

We propose new strategy to facilitate the fabrication of conjugated polymer fiber with higher oriented structures, which focused on electrospinning of a blend solution of regioregular poly(3-hexylthiophene) (rr-P3HT) and poly(vinyl pyrrolidone) (PVP). SEM observation revealed that the blend system forms homogeneous composite nanofibers. This system exhibits the specific feature of strong interchain contribution of P3HT from UV−vis absorption, fluorescence spectroscopic, XRD, and photoelectron spectrometric (for HOMO levels) investigations. We also demonstrate the removal of the PVP component from the P3HT/PVP composite fibers through the selective extraction and such strong interchain stacking of pristine P3HT fiber mat can be remarkably maintained