Benzophenone Ketyl Radical Research Articles

Reactions of Ru3(CO)12 with 1,5-bis(diphenylphosphino)pentane: Synthesis, characterization, crystal structure, Hirshfeld surface and QTAIM Analysis of Ru3(CO)10(µ-dpppe)

Reactions of Ru3(CO)12 with 1,5-bis(diphenylphosphino)pentane (dpppe) in THF induced by sodium benzophenone ketyl radical anion, resulted in the expected metal cluster [Ru3(CO)11]2(µ-dpppe) (1) and Ru3(CO)10(µ-dpppe) (2) as the main products. Clusters 1 and 2 were characterized by spectroscopic methods, including Fourier-transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (1H and 31P{1H} NMR).The structural features were determined using single crystal X-ray diffraction analysis. In cluster 1 and 2, the (dpppe) links two trinuclear cluster units via phosphine moieties and bridges to Ru–Ru bond, respectively. Both clusters were stabilized by the presence of C–H⋯O interactions and were further analyzed by Hirshfeld surface analysis. The bonding interactions within cluster 2 were studied using the Quantum Theory of Atoms in Molecules (QTAIM). Various local and integral topological properties of the electron density were calculated, along with the source function (SF) calculations and electron localization function (ELF) analysis.

Thermolysis of Ru3(CO)10(µ-dppp): A new Ru4- cluster derived from 1,3-bis(diphenylphosphino)propane

The reaction of Ru3(CO)12 and dppp [dppp = 1,3-bis(diphenylphosphino)propane/Ph2P(CH2)3PPh2] in the presence of benzophenone ketyl radical anion afforded [Ru3(CO)11]2(µ-dppp) (1) Ru3(CO)10(µ-dppp) (2), Ru3(CO)9(µ-dppp)(ƞ1-dppp) (3) and Ru3(CO)8(µ-dppp)2 (4). Refluxing 2 in octane yields new triruthenium clusters Ru3(CO)9(μ3-PPh(CH2)3PPh(C6H4)) (5) and Ru4(CO)9(µ-CO){µ4-η2-P(CH2)3PPh2}(µ4-η4-C6H4) (6), as a result of CH and CP bond activation involving the Ph2P(CH2)3PPh2 ligand. Compounds 2 and 6 have been structurally determined by the single crystal X-ray diffraction. As expected, the Ph2PCH2CH2CH2PPh2 ligand in 2 is equatorially bonded to Ru–Ru bond in µ2-η2 mode. In contrast, the X-ray structure of 6 shows an µ4-η2-PCH2CH2CH2PPh2 and a benzyne group coordinated to a square of Ru atoms. A rotation of benzyne group on a square of Ru atoms was supported by variable temperature NMR studies. The topological analysis was performed on 6 to further elucidate their chemical bond properties.

Time-resolved electron paramagnetic resonance spectrometer based on ultrawide single-sideband phase-sensitive detection.

A time-resolved electron paramagnetic resonance (TREPR) method with 40ns time resolution and a high sensitivity suitable for the detection of short-lived radicals under thermal equilibrium is developed. The key is the introduction of a new detection technique named ultrawide single sideband phase sensitive detection (U-PSD) to the conventional continuous-wave EPR, which remarkably enhanced the sensitivity for the detection of broadband transient signals compared with the direct detection protocol. By repeatedly triggering a transient kinetic event f(t) (e.g., by laser flash photolysis) under a 100kHz magnetic field modulation with precise phase control, this technique can build an ultrawide single sideband modulated signal. After single sideband demodulation, the flicker noise-suppressed signal f(t) with wide bandwidth is recovered. A U-PSD TREPR spectrometer prototype has been built, which integrated timing sequence control, laser flash excitation, data acquisition systems, and the U-PSD algorithm with a conventional continuous-wave EPR. It exhibited excellent performance in monitoring a model transient radical system, laser flash photolysis of benzophenone in isopropanol. Both the intense chemically induced dynamic electron polarization signals and the much weaker thermal equilibrium EPR signals of the generated acetone ketyl radical and benzophenone ketyl radical were clearly observed within a wide timescale ranging from sub-microsecond to milliseconds. This prototype validated the feasibility of the U-PSD technique and demonstrated its superior performance in studying complex photochemical systems containing various transient radicals, which complements the established TREPR techniques and provides a powerful tool for deep mechanistic understandings, such as in photoredox catalysis and artificial photosynthesis.

Study on the Translational Diffusion of Transient Species in 1-Alkyl-3-methylimidazolium-Based Ionic Liquids by Transient Grating Spectroscopy

Abstract Translational diffusion coefficients of two transient species in 1-alkyl-3-methylimidazolium-based ionic liquids (Cnmim+) with different alkyl chain lengths (n = 4, 8, 12) and the bis(trifluoromethanesulfonyl)imide anion were measured by transient grating spectroscopy. The systems of interest are the benzophenone ketyl radical (BPK) produced by the hydrogen-abstraction reaction of benzophenone (BP) and the zwitterionic merocyanine dye (MC) produced by the photoisomerization of 1,3,3-trimethylindolino-6′-nitrobenzopyrylospiran (SP). The diffusion coefficients of BPK and MC closely obey the Stokes-Einstein (SE) relation in the ionic liquids regardless of the alkyl chain lengths of the cations, whereas the diffusion coefficients of BP are larger than those predicted by the SE equation. The temperature dependences of the translational diffusion coefficients of BP, BPK, and MC reveal that the diffusional activation energies of BPK and MC are larger than those of BP in all solvents. The origin of this difference is discussed in terms of intermolecular interactions within the ionic-liquid solvents.

Water-Triggered Photoinduced Electron Transfer in Acetonitrile-Water Binary Solvent. Solvent Microstructure-Tuned Reactivity of Hydrophobic Solutes.

The solvent-composition dependence of quenching triplet states of benzophenone (3BP) by anisole in acetonitrile–water (ACN–H2O) mixtures was investigated by laser flash photolysis over the water mole fraction (xw) increasing from 0 to 0.92. Single exponential decay of 3BP was observed over the whole composition range. The quenching rate constant consistently increased with the water content but increased far more rapidly with xw > 0.7. The water-triggered electron-transfer (ET) mechanism was confirmed by a steeply growing quantum yield of the benzophenone ketyl radical anion, escaping back-ET when the partial water volume exceeded the acetonitrile one. The water-content influence on the 3BP quenching rate was described by a kinetic model accounting for the microheterogeneous structure of the ACN–H2O mixtures and the very different solubility of the reactants in the solvent components. According to the model, the ET mechanism occurs at a rate constant of 1.46 × 109 M–1 s–1 and is presumably assisted by the ACN–H2O hydrogen-bonding interaction.

Opening up the Valence Shell: A T-Shaped Iron(I) Metalloradical and Its Potential for Atom Abstraction.

A thermally stable, T‐shaped, d7 high‐spin iron(I) complex was obtained by reduction of a PNP‐supported ferrous chloride. Paramagnetic NMR spectroscopy combined with DFT modeling was used to analyze the electronic structure of the coordinatively highly unsaturated complex. The metalloradical character of the compound was demonstrated by the formation of a benzophenone ketyl radical complex upon addition of benzophenone. Furthermore, the compound displays a rich chemistry as an oxygen‐atom abstractor from epoxides, yielding a dinuclear, diferrous [Fe2O] complex.

Dual Benzophenone/Copper-Photocatalyzed Giese-Type Alkylation of C(sp3 )-H Bonds.

Photocatalyzed Giese-type alkylations of C(sp3 )-H bonds are very attractive reactions in the context of atom-economy in C-C bond formation. The main limitation of such reactions is that when using highly polymerizable olefin acceptors, such as unsubstituted acrylates, acrylonitrile, or methyl vinyl ketone, radical polymerization often becomes the dominant or exclusive reaction pathway. Herein, we report that the polymerization of such olefins is strongly limited or suppressed when combining the photocatalytic activity of benzophenone (BP) with a catalytic amount of Cu(OAc)2 . Under mild and operationally simple conditions, the Giese adducts resulting from the C(sp3 )-H functionalization of amines, alcohols, ethers, and cycloalkanes could be synthesized. Preliminary mechanistic studies have revealed that the reaction does not proceed through a radical chain, but through a dual BP/Cu photocatalytic process, in which both CuII and low-valent CuI/0 species, generated in situ by reduction by the BP ketyl radical, may react with α-keto or α-cyano intermediate radicals, thus preventing polymerization.

Interferometrically stable, enclosed, spinning sample cell for spectroscopic experiments on air-sensitive samples.

In experiments with high photon flux, it is necessary to rapidly remove the sample from the beam and to delay re-excitation until the sample has returned to equilibrium. Rapid and complete sample exchange has been a challenge for air-sensitive samples and for vibration-sensitive experiments. Here, a compact spinning sample cell for air and moisture sensitive liquid and thin film samples is described. The principal parts of the cell are a copper gasket sealed enclosure, a 2.5 in. hard disk drive motor, and a reusable, chemically inert glass sandwich cell. The enclosure provides an oxygen and water free environment at the 1 ppm level, as demonstrated by multi-day tests with sodium benzophenone ketyl radical. Inside the enclosure, the glass sandwich cell spins at ≈70 Hz to generate tangential speeds of 7-12 m/s that enable complete sample exchange at 100 kHz repetition rates. The spinning cell is acoustically silent and compatible with a ±1 nm rms displacement stability interferometer. In order to enable the use of the spinning cell, we discuss centrifugation and how to prevent it, introduce the cycle-averaged resampling rate to characterize repetitive excitation, and develop a figure of merit for a long-lived photoproduct buildup.

Time-Resolved Detection of Magnetic Field Effects on Radical Pairs in Micelles: Two-Step Two-Laser Fluorescence Spectroscopy of Transient Radicals

A two-step two-laser fluorescence spectroscopy method was employed to enable time-resolved detection of magnetic field effects (MFEs) on radical pairs (RPs). In the photoinduced hydrogen abstraction reaction of benzophenone (BP) in sodium dodecyl sulfate (SDS) micellar solution, fluorescence from the BP ketyl radical (BPH•) was observed under various magnetic fields; BPH• forms RPs with hydrogen-abstracted SDS radicals (•SDS) in the micelles. Kinetic parameters of the RP dynamics such as the spin relaxation rate, the generation rate, and the escape rate were determined from the simple analysis. The MFEs on BPH• observed from the fluorescence measurements were explained by the spin relaxation mechanism proposed by Hayashi and Nagakura. In this study, we demonstrate that two-step two-laser fluorescence spectroscopy in combination with a magnetic field provides valuable information about photochemical reactions in which RPs play important roles.

Raft-like osmium- and ruthenium-antimony carbonyl clusters

The higher nuclearity raft-like cluster Os6(CO)20(μ-SbPh2)2, 5-Os, was isolated from the base hydrolysis of Os3(CO)11(SbPh2Cl), 1-Os. The ruthenium analogue, viz., Ru6(CO)20(μ-SbPh2)2, 5-Ru, was obtained from the reduction of Ru3(CO)12, 7-Ru, with the benzophenone ketyl radical followed by treatment with SbPh2Cl. These clusters undergo facile ligand substitution reactions with two-electron donors to afford the mono- and disubstituted derivatives M6(CO)20-n(μ-SbPh2)2(L)n, (M = Ru or Os; n = 1 (8) or 2 (9); L = PMe3 (a), PPh3 (b), or tBuNC (c)).

Sulfonated polyetheretherketone/polypropylene polymer blends for the production of photoactive materials

ABSTRACTSulfonated polyetheretherketone (SPEEK) was synthesized via a mono‐substitution reaction of PEEK in concentrated sulphuric acid and was blended with polypropylene (PP) in 2–10%w/w concentration to be used for the production of photoactive thermoplastic products. SPEEK and SPEEK/PP blends were characterized using FTIR, DSC, TGA, NMR, rheology, SEM, and EPR. Under UV‐Vis irradiation, stable benzophenone ketyl (BPK) radicals were generated by hydrogen extraction from PP. By increasing the amount of SPEEK in the polymer blend a linear increase in the BPK radicals was achieved according to the EPR data. DSC and TGA tests indicated weaknesses in the thermal stability of SPEEK but according to the rheological tests this should not have a major effect on processabililty. The optimal amount of SPEEK in the blend was obtained at 5%w/w. This concentration provided a good compromise between radical concentration, material processability, and cost. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41509.

Reactions of ligands from BT(B)P family with solvated electrons and benzophenone ketyl radicals in 1-octanol solutions. Pulse radiolysis study

Pulse radiolysis involving reactions of solvated electrons and benzophenone ketyl radicals in 1-octanol with selected compounds from bis-triazinyl pyridines and bis-triazinyl bipyridines, BT(B)P family, developed for extraction of trivalent actinides have been studied. The designated ligands were: 2,6-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-benzo-[1,2,4]triazin-3-yl)pyridine, 6,6′-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-benzo-[1,2,4-]triazin-3-yl)-[2,2′]bipyridine, 6,6′-bis(5,6-diethyl-[1,2,4]triazin-3-yl)-[2,2′]bipyridine and 6,6′-bis(5,6-dipentyl-[1,2,4]triazin-3-yl)-[2,2′]bipyridine. Reactions of the ligands with solvated electrons in 1-octanol are fast. The rate constants were determined as equal to: $$ k_{{{\text{CyMe}}_{4} {\text{BTP}}}} . $$ = (2.4 ± 0.2) × 109 dm3 mol−1 s−1, $$ k_{{{\text{CyMe}}_{ 4} {\text{BTBP}}}} $$ = (1.7 ± 0.3) × 109 dm3 mol−1 s−1, $$ k_{{{\text{C}}_{ 2} {\text{BTBP}}}} $$ = (1.3 ± 0.3) × 109 dm3 mol−1 s−1 and $$ k_{{{\text{C}}_{ 5} {\text{BTBP}}}} $$ = (1.7 ± 0.3) × 109 dm3 mol−1 s−1. Reactions of the ligands with benzophenone ketyl radicals are much slower and the measured rate constants were as follows: $$ k_{{{\text{CyMe}}_{ 4} {\text{BTP}}}} $$ = 6.7 × 107 dm3 mol−1 s−1 and $$ k_{{{\text{CyMe}}_{ 4} {\text{BTBP}}}} $$ = 3.2 × 107 dm3 mol−1 s−1.

Cage lifetimes of ionic liquids as studied by the magnetic field effect probe

Magnetic field effects (MFEs) on the photoinduced hydrogen abstraction reaction of benzophenone with phenol were investigated in ionic liquids (ILs) with a short alkyl chain (N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)amide (TMPA TFSA)) and long alkyl chains ((N,N,N-trimethyl-N-octylammonium bis(trifluoromethanesulfonyl)amide (TMOA TFSA) and N-decyl-N,N,N-trimethylammonium bis(trifluoromethanesulfonyl)amide (DTMA TFSA)) by a nanosecond laser flash photolysis technique. In each ionic liquid, escaped radical yield of a benzophenone ketyl radical rapidly increased with increasing magnetic field strength (B) of 0 T < B≤ 0.01 T. At 0.01 T < B≤ 0.4 T, the escaped radical yield almost saturated in TMPA TFSA or gradually increased in TMOA TFSA and DTMA TFSA. At much higher fields of 0.4 T < B≤ 30 T, the yield gradually decreased, resulting in 10-15% decrease at 30 T. The observed MFEs can be explained by the hyperfine coupling and Δg mechanisms together with the relaxation mechanism. On the time profiles of the transient absorption observed for the benzophenone ketyl radical, MFEs were generated in the time range of 0 < t < 0.6 μs. The cage lifetimes of TMOA TFSA and DTMA TFSA were estimated to be at least 120 ns.

The inverse sandwich complex [(K(18-crown-6))2Cp][CpFe(CO)2] – unpredictable redox reactions of [CpFe(CO)2]I with the silanides Na[SiRtBu2] (R = Me, tBu) and the isoelectronic phosphanyl borohydride K[PtBu2BH3

The dimeric iron carbonyl [CpFe(CO)(2)](2) and the iodosilanes tBu(2)RSiI were obtained from the reaction of [CpFe(CO)(2)]I with the silanides Na[SiRtBu(2)] (R = Me, tBu) in THF. By the reactions of [CpFe(CO)(2)]I and Na[SiRtBu(2)] (R = Me, tBu) the disilanes tBu(2)RSiSiRtBu(2) (R = Me, tBu) were additionally formed using more than one equivalent of the silanide. In this context it should be noted that reduction of [CpFe(CO)(2)](2) with Na[SitBu(3)] gives the disilanes tBu(3)SiSitBu(3) along with the sodium ferrate [(Na(18-crown-6))(2)Cp][CpFe(CO)(2)]. The potassium analogue [(K(18-crown-6))(2)Cp][CpFe(CO)(2)] (orthorhombic, space group Pmc2(1)), however, could be isolated as a minor product from the reaction of [CpFe(CO)(2)]I with [K(18-crown-6)][PtBu(2)BH(3)]. The reaction of [CpFe(CO)(2)](2) with the potassium benzophenone ketyl radical and subsequent treatment with 18-crown-6 yielded the ferrate [K(18-crown-6)][CpFe(CO)(2)] in THF at room temperature. The crown ether complex [K(18-crown-6)][CpFe(CO)(2)] was analyzed using X-ray crystallography (orthorhombic, space group Pna2(1)) and its thermal behaviour was investigated.

Magnetic Field Effects on Photochemical Reactions in Ionic Liquids with Short Alkyl Chains

Magnetic field effects (MFEs) on the photoinduced hydrogen abstraction reactions of benzophenone and thiobenzophenone from thiophenol were investigated in several ionic liquids with short alkyl chains by a nanosecond laser flash photolysis technique. In each ionic liquid, escaped radical yields of benzophenone and thiobenzophenone ketyl radicals gradually decreased with increasing magnetic field strength. The observed results were analyzed by using the stochastic Liouville equation (SLE), employing a solvent separated radical pair (SSRP) model where the SSRP with a specific radical–radical distance is stable and has a long lifetime. The SLE analysis revealed that the lifetime of the SSRP and the radical rotation in the SSRP states are strongly correlated with the macroviscosity of the ionic liquids.

Photochemical Generation of Nanometer-Sized Cu Particles in Octane

Irradiation with 350 nm photons of anhydrous, air-free octane or toluene solutions of copper(II) oleate containing benzophenone as a photosensitizer and oleoylsarcosine as a stabilizer resulted in metallic Cu particles with nanometer dimensions. Evidence is presented that implicates the hydrocarbon as the predominant H-atom donor in the generation of reductive benzophenone ketyl radicals and a kinetic model is constructed to rationalize the rate dependencies with respect to the Cu2+/Cu+ step. Rates of both Cu2+ consumption and Cu formation vary linearly with light intensity and exhibit a first-order dependence on benzophenone concentration but the latter step shows little dependence otherwise. The initial rate of reactant consumption decreases with increasing concentration of cupric ions or sarcosine. Quenching of the excited state of benzophenone by the stabilizer occurs with a rate constant of k4 = 1.6 × 105 M–1 s–1 and is explained by the formation of a contact ion pair between the reduced chromophore ...

Nanoscale Structure of Ionic Liquid and Diffusion Process as Studied by the MFE Probe

Magnetic field effects (MFEs) observed for photoinduced hydrogen abstract reaction between benzophenone and thiophenol, generating phenylthiyl and benzophenone ketyl radicals, in an ionic liquid of N,N,N,-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)amide (TMPA TFSA) were analyzed by using the stochastic Liouville equation (SLE) with the cage model and the solvent separated radical pair model, respectively. The MFEs observed on the yield of escaped benzophenone ketyl radical in the range of 0 < B ≤ 2.0 T were explained by the transverse spin relaxation in the radical pair caused by the large anisotropy of the g-value and the slow rotation of phenylthiyl radical in the IL. The calculated MFE was dependent on a rotational correlation time of the radical as well as the mutual diffusion coefficient for the translational diffusion of the radicals. The SLE analysis revealed that the IL has at least two different viscosity regions, causing the nanoscale cage effect on the radical diffusion in the IL.

Supramolecular Photochemistry in β-Cyclodextrin Hosts: A TREPR, NMR, and CIDNP Investigation

A systematic investigation of the photochemistry and ensuing radical chemistry of three guest ketones encapsulated in randomly methylated beta-cyclodextrin (beta-CD) hosts is reported. Dibenzyl ketone (DBK), deoxybenzoin (DOB), and benzophenone (BP) triplet states are rapidly formed after photolysis at 308 nm. Time-resolved electron paramagnetic resonance (TREPR) spectroscopy, steady-state NMR spectroscopy, and time-resolved chemically induced nuclear polarization (TR-CIDNP) experiments were performed on the ketone/CD complexes and on the ketones in free solution for comparison. The major reactivity pathways available from these excited states are either Norrish I alpha-cleavage or H-atom abstraction from the interior of the CD capsule or the solvent. The DOB triplet state undergoes both reactions, whereas the DBK triplet shows exclusively alpha-cleavage and the BP triplet shows exclusively H-atom abstraction. Radical pairs are observed in beta-CDs by TREPR, consisting of either DOB or BP ketyl radicals with sugar radicals from the CD interior. The TREPR spectra acquired in CDs are substantially broadened due to strong spin exchange. The electron spin polarization mechanism is mostly due to S-T(0) radical pair mechanism (RPM) in solution but changes to S-T(-) RPM in the CDs due to the large exchange interaction. The TR-CIDNP results confirm the reactivity patterns of all three ketones, and DOB shows strong nuclear spin polarization from a novel rearrangement product resulting from the alpha-cleavage reaction.

Reactions of excited-state benzophenone ketyl radical in a room-temperature ionic liquid

The photochemistry of the benzophenone ketyl radical in D(1) excited state, BPH(D(1)), was studied by means of two-color dual-pulse laser flash photolysis (355 and 532 nm) in a room-temperature ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide (Bmim-TFSA), and in methanol. Upon excitation with the 532 nm pulse, BPH(D(1)) emitted strong fluorescence. The transient absorption and fluorescence spectra of BPH(D(1)) were measured with nanosecond and sub-nanosecond time resolution, respectively. The observed Stokes shift was 1700 cm(-1) in Bmim-TFSA, and this shift was close to that in acetonitrile. The fluorescence lifetime of BPH(D(1)) was determined to be 5 ns in Bmim-TFSA, and again the value was close to that in acetonitrile. The rate constant of the reaction of BPH(D(1)) with CCl(4) in Bmim-TFSA was determined to be (2.1 +/- 0.4) x 10(9) M(-1) s(-1), which was 10 times the rate constant calculated on the basis of the bulk viscosity of Bmim-TFSA. The results are discussed in terms of the effective microscopic viscosity of the ionic liquid that was recently reported for the cage effect.

A peculiar quenching concentration dependence of photoinduced fragmentation in dithiane–carbonyl adducts: A mechanistic experimental and theoretical study

Photoinduced fragmentation in methyldithiane–benzaldehyde adduct, which is externally sensitized by electron transfer sensitizers such as benzophenone, shows a peculiar Stern–Volmer quenching dependence when quenched by diethyl sulfide or DABCO. At lower diethyl sulfide concentration not only negative curvature but also negative slope is observed. At higher concentration the slope of the plot is conventionally positive. This atypical behavior is rationalized in terms of co-sensitization by the quencher at low concentrations. Ab initio and DFT computations were carried out to support the suggested mechanistic rationale. Also the partitioning of the dithianyl radical and benzophenone ketyl radical between the productive disproportionation channel and the recombination channel is determined to be 1:1 at low conversion. These findings provide critical experimental and theoretical insights into the mechanism of this photoinduced fragmentation.