Electron-Poor Thiophene 1,1-Dioxides: Synthesis, Characterization, and Application as Electron Relays in Photocatalytic Hydrogen Generation.

The synthesis and characterization of electron-poor thiophene 1,1-dioxides bearing cyanated phenyl groups are reported. The electron-accepting nature of these compounds was evaluated by cyclic voltammetry, and highly reversible and facile reductions were observed for several derivatives. Moreover, some of the reduced thiophene dioxides form colorful anions, which were investigated spectroelectrochemically. Photoluminescence spectra of the electron-deficient sulfones were measured in CH2 Cl2, and they emit in the blue-green region with significant variation in the quantum yield depending on the aryl substituents. By expanding the degree of substitution on the phenyl rings, quantum yields up to 34 % were obtained. X-ray diffraction data are reported for two of the thiophene 1,1-dioxides, and the electronic structure was probed for all synthesized derivatives through DFT calculations. The dioxides were also examined as electron relays in a photocatalytic water reduction reaction, and they showed potential to boost the efficiency.

Properties and ATRP activity of copper complexes with substituted tris(2-pyridylmethyl)amine-based ligands.

Synthesis, characterization, electrochemical studies, and ATRP activity of a series of novel copper(I and II) complexes with TPMA-based ligands containing 4-methoxy-3,5-dimethyl-substituted pyridine arms were reported. In the solid state, Cu(I)(TPMA*(1))Br, Cu(I)(TPMA*(2))Br, and Cu(I)(TPMA*(3))Br complexes were found to be distorted tetrahedral in geometry and contained coordinated bromide anions. Pseudo-coordination of the aliphatic nitrogen atom to the copper(I) center was observed in Cu(I)(TPMA*(2))Br and Cu(I)(TPMA*(3))Br complexes, whereas pyridine arm dissociation occurred in Cu(I)(TPMA*(1))Br. All copper(I) complexes with substituted TPMA ligands exhibited a high degree of fluxionality in solution. At low temperature, Cu(I)(TPMA*(1))Br was found to be symmetrical and monomeric, while dissociation of either unsubstituted pyridine and/or 4-methoxy-3,5-dimethyl-substituted pyridine arms was observed in Cu(I)(TPMA*(2))Br and Cu(I)(TPMA*(3))Br. On the other hand, the geometry of the copper(II) complexes in the solid state deviated from ideal trigonal bipyramidal, as confirmed by a decrease in τ values ([Cu(II)(TPMA*(1))Br][Br] (τ = 0.92) > [Cu(II)(TPMA*(3))Br][Br] (τ = 0.77) > [Cu(II)(TPMA*(2))Br][Br] (τ = 0.72)). Furthermore, cyclic voltammetry studies indicated a nearly stepwise decrease (ΔE ≈ 60 mV) of E1/2 values relative to SCE (TPMA (-240 mV) > TPMA*(1) (-310 mV) > TPMA*(2) (-360 mV) > TPMA*(3) (-420 mV)) on going from [Cu(II)(TPMA)Br][Br] to [Cu(II)(TPMA*(3))Br][Br], confirming that the presence of electron-donating groups in the 4 (-OMe) and 3,5 (-Me) positions of the pyridine rings in TPMA increases the reducing ability of the corresponding copper(I) complexes. This increase was mostly the result of a stronger influence of substituted TPMA ligands toward stabilization of the copper(II) oxidation state (log ß(I) = 13.4 ± 0.2, log ß(II) = 19.3 (TPMA*(1)), 20.5 (TPMA*(2)), and 21.5 (TPMA*(3))). Lastly, ARGET ATRP kinetic studies show that with more reducing catalysts an induction period is observed. This was attributed to slow regeneration of Cu(I) species from the corresponding Cu(II).

Tuning thiophene with phosphorus: synthesis and electronic properties of benzobisthiaphospholes.

1,4-Dimercapto-2,5-diphosphinobenzene and 3,6-bis(hexyloxy)-1,4-dimercapto-2,5-diphosphinobenzene were synthesized and combined with various acid chlorides to obtain a series of benzobisthiaphospholes. Electrochemical and photophysical properties of the substituted benzobisthiaphospholes have been evaluated, and the observed reductions are more facile than the related benzothiaphospholes and 2,6-diphenylbenzobisthiazole. A benzobisthiaphosphole with C6H4-p-CN substituents was reduced at E(1/2)=-1.08 V (vs. saturated calomel electrode (SCE)). X-ray diffraction data for several of these phosphorus heterocycles has been obtained, and DFT calculations at the B3LYP level have been performed.

[Ir(N

The relatively unexplored luminophore architecture [Ir(N^N^N)(C^N)L](+) (N^N^N = tridentate polypyridyl ligand, C^N = 2-phenylpyridine derivative, and L = monodentate anionic ligand) offers the stability of tridentate polypyridyl coordination along with the tunability of three independently variable ligands. Here, a new family of these luminophores has been prepared based on the previously reported compound [Ir(tpy)(ppy)Cl](+) (tpy = 2,2':6',2″-terpyridine and ppy = 2-phenylpyridine). Complexes are obtained as single stereoisomers, and ligand geometry is unambiguously assigned via X-ray crystallography. Electrochemical analysis of the materials reveals facile HOMO modulation through ppy functionalization and alteration of the monodentate ligand's field strength. Emission reflects similar modulation shifting from orange to greenish-blue upon replacement of chloride with cyanide. Many of the new compounds exhibit impressive room temperature phosphorescence with lifetimes near 3 µs and quantum yields reaching 28.6%. Application of the new luminophores as photosensitizers for photocatalytic hydrogen generation reveals that their photostability in coordinating solvent is enhanced as compared to popular [Ir(ppy)2(bpy)](+) (bpy = 2,2'-bipyridine) photosensitizers. Yet, the binding of their monodentate ligand emerges as a source of instability during the redox processes of cyclic voltammetry and mass spectrometry. DFT modeling of electronic structure is provided for all compounds to elucidate experimental properties.

Kinetic and mechanistic aspects of atom transfer radical addition (ATRA) catalyzed by copper complexes with tris(2-pyridylmethyl)amine.

Kinetic and mechanistic studies of atom transfer radical addition (ATRA) catalyzed by copper complexes with tris(2-pyridylmethyl)amine (TPMA) ligand were reported. In solution, the halide anions were found to strongly coordinate to [Cu(I)(TPMA)](+) cations, as confirmed by kinetic, cyclic voltammetry, and conductivity measurements. The equilibrium constant for atom transfer (K(ATRA) = k(a)/k(d)) utilizing benzyl thiocyanate was determined to be approximately 6 times larger for Cu(I)(TPMA)BPh(4) ((1.6 ± 0.2) × 10(-7)) than Cu(I)(TPMA)Cl ((2.8 ± 0.2) × 10(-8)) complex. This difference in reactivity between Cu(I)(TPMA)Cl and Cu(I)(TPMA)BPh(4) was reflected in the activation rate constants ((3.4 ± 0.4) × 10(-4) M(-1) s(-1) and (2.2 ± 0.2) × 10(-3) M(-1) s(-1), respectively). The fluxionality of Cu(I)(TPMA)X (X = Cl or Br) in solution was mainly the result of TPMA ligand exchange, which for the bromide complex was found to be very fast at ambient temperature (ΔH(‡) = 29.7 kJ mol(-1), ΔS(‡) = -60.0 J K(-1) mol(-1), ΔG(‡)(298) = 47.6 kJ mol(-1), and k(obs,298) = 2.9 × 10(4) s(-1)). Relatively strong coordination of halide anions in Cu(I)(TPMA)X prompted the possibility of activation in ATRA through partial TPMA dissociation. Indeed, no visible differences in the ATRA activity of Cu(I)(TPMA)BPh(4) were observed in the presence of as many as 5 equiv of strongly coordinating triphenylphosphine. The possibility for arm dissociation in Cu(I)(TPMA)X was further confirmed by synthesizing tris(2-(dimethylamino)phenyl)amine (TDAPA), a ligand that was structurally similar to currently most active TPMA and Me(6)TREN (tris(2-dimethylaminoethyl)amine), but had limited arm mobility due to the rigid backbone. Indeed, Cu(I)(TDAPA)Cl complex was found to be inactive in ATRA, and the activity increased only by opening the coordination site around the copper(I) center by replacing chloride anion with less coordinating counterions such as BF(4)(-) and BPh(4)(-). The results presented in this Article are significant from the mechanistic point of view because they indicate that coordinatively saturated Cu(I)(TPMA)X complexes catalyze the homolytic cleavage of carbon-halogen bond during the activation step in ATRA by prior dissociation of either halide anion or TPMA arm.

Crystal structures of Au2 complex and Au25 nanocluster and mechanistic insight into the conversion of polydisperse nanoparticles into monodisperse Au25 nanoclusters.

We previously reported a size-focusing conversion of polydisperse gold nanoparticles capped by phosphine into monodisperse [Au(25)(PPh(3))(10)(SC(2)H(4)Ph)(5)Cl(2)](2+) nanoclusters in the presence of phenylethylthiol. Herein, we have determined the crystal structure of [Au(25)(PPh(3))(10)(SC(2)H(4)Ph)(5)Cl(2)](2+) nanoclusters and also identified an important side-product-a Au(I) complex formed in the size focusing process. The [Au(25)(PPh(3))(10)(SC(2)H(4)Ph)(5)Cl(2)](2+) cluster features a vertex-sharing bi-icosahedral core, resembling a rod. The formula of the Au(I) complex is determined to be [Au(2)(PPh(3))(2)(SC(2)H(4)Ph)](+) by electrospray ionization (ESI) mass spectrometry, and its crystal structure (with SbF(6)(-) counterion) reveals Au-Au bridged by -SC(2)H(4)Ph and with terminal bonds to two PPh(3) ligands. Unlike previously reported [Au(2)(PR(3))(2)(SC(2)H(4)Ph)](+) complexes in the solid state, which exist as tetranuclear complexes (i.e., dimers of [Au(2)(PR(3))(2)(SC(2)H(4)Ph)](+) units) through a Au···Au aurophilic interaction, in our case we found that the [Au(2)(PPh(3))(2)(SC(2)H(4)Ph)](+) complex exists as a single entity, rather than being dimerized to form a tetranuclear complex. The observation of this Au(I) complex allows us to gain insight into the intriguing conversion process from polydisperse Au nanoparticles to monodisperse Au(25) nanoclusters.

Total structure determination of thiolate-protected Au38 nanoparticles.

We report the total structure of Au(38)(SC(2)H(4)Ph)(24) nanoparticles determined by single crystal X-ray crystallography. This nanoparticle is based upon a face-fused Au(23) biicosahedral core, which is further capped by three monomeric Au(SR)(2) staples at the waist of the Au(23) rod and six dimeric staples with three on the top icosahedron and other three on the bottom icosahedron. The six Au(2)(SR)(3) staples are arranged in a staggered configuration, and the Au(38)S(24) framework has a C(3) rotation axis.

Structural comparison of copper(I) and copper(II) complexes with tris(2-pyridylmethyl)amine ligand.

Copper(I) complexes with the tris(2-pyridylmethyl)amine (TPMA) ligand were synthesized and characterized to examine the effect of counteranions (Br(-), ClO(4)(-), and BPh(4)(-)), as well as auxiliary ligands (CH(3)CN, 4,4'-dipyridyl, and PPh(3)) on the molecular structures in both solid state and solution. Partial dissociation of one of the pyridyl arms in TPMA was not observed when small auxiliary ligands such as CH(3)CN or Br(-) were coordinated to copper(I), but was found to occur with larger ones such as PPh(3) or 4,4'-dipyridyl. All complexes were found to adopt a distorted tetrahedral geometry, with the exception of [Cu(I)(TPMA)][BPh(4)], which was found to be trigonal pyramidal because of stabilization via a long cuprophilic interaction with a bond length of 2.8323(12) Å. Copper(II) complexes with the general formula [Cu(II)(TPMA)X][Y] (X = Cl(-), Br(-) and Y = ClO(4)(-), BPh(4)(-)) were also synthesized to examine the effect of different counterions on the geometry of [Cu(II)(TPMA)X](+) cation, and were found to be isostructural with previously reported [Cu(II)(TPMA)X][X] (X = Cl(-) or Br(-)) complexes.

Kinetic studies of the initiation step in copper catalyzed atom transfer radical addition (ATRA) in the presence of free radical diazo initiators as reducing agents.

Kinetic parameters for the reduction of copper(II) complexes in atom transfer radical addition (ATRA) in the presence of free-radical diazo initiator (AIBN) were determined using both experimental and kinetic modeling techniques. The rate constant of decomposition of AIBN (k(dc)) in various solvents was determined at 60 degrees C using UV-vis spectroscopy. Rate constants of deactivation (k(d,AIBN)) of [Cu(II)(TPMA)Cl][Cl] (TPMA = tris(2-pyridylmethyl)amine), [Cu(II)(Me(6)TREN)Cl][Cl] (Me(6)TREN = tris[2-(N,N-dimethylamino)ethyl]amine), [Cu(II)(PMDETA)Cl(2)] (PMDETA = N,N,N',N'',N''-pentamethyldiethylenetriamine), and [Cu(II)(bpy)(2)Cl][Cl] (bpy = 2,2'-bipyridine) complexes by radicals generated from the decomposition of AIBN were measured using the TEMPO-trapping method in a competitive clock reaction. Activation rate constants (k(a,AIBN)) were finally estimated from kinetic modeling utilizing the experimentally determined rate constants of decomposition of AIBN and deactivation. The effect of k(a,AIBN), k(d,AIBN), k(dc) and initial AIBN concentration on the overall copper(I) and copper(II) concentrations in the initiation step of the ATRA process was also evaluated through kinetic modeling.

Copper catalyzed atom transfer radical cascade reactions in the presence of free-radical diazo initiators as reducing agents.

Exceptional activity of [Cu(II)(TPMA)Cl][Cl] (TPMA = tris(2-pyridylmethyl)amine) complex in atom transfer radical addition (ATRA) of CCl(4) to 1,6-dienes followed by sequential atom transfer radical cyclization (ATRC) in the presence of free-radical diazo initiators as reducing agents is reported.

Persistent radical effect in action: kinetic studies of copper-catalyzed atom transfer radical addition in the presence of free-radical diazo initiators as reducing agents.

Kinetic features of the atom transfer radical addition (ATRA) of CCl(4) to 1-octene, styrene, and methyl acrylate catalyzed by [Cu(II)(TPMA)Cl][Cl] (TPMA = tris(2-pyridylmethyl)amine) in the presence of free-radical diazo initiator (AIBN) as a reducing agent were investigated. For 1-octene, the catalyst concentration was found to affect the alkene conversion and the yield of monoadduct for [1-octene](0)/[Cu(II)](0) ratios above 10,000:1. A more pronounced effect of the catalyst loading was observed in the case of methyl acrylate and styrene, due to the formation of AIBN-initiated oligomeric/polymeric side products. For all three alkenes, the optimum reaction conditions were achieved using 5 mol % AIBN relative to alkene. It was also found that excess alkyl halide (CCl(4)) was not necessary in ATRA reactions that utilize AIBN as a reducing agent. Kinetic studies of the ATRA process revealed that the rate of alkene consumption was dependent on the concentration and rate of decomposition of the radical initiator, but independent of the concentration of the copper catalyst. However, selectivity of the desired monoadduct ultimately depended on the nature of the catalyst.

Strong coordination of tetraphenylborate anion to copper(I) bipyridine and phenanthroline-based complexes and its effect on catalytic activity in the cyclopropanation of styrene.

The synthesis, characterization, and cyclopropanation activity of tetrahedral copper(I) complexes with bipyridine- and phenanthroline-based ligands containing strongly coordinated tetraphenylborate anions are reported. Cu(I)(bpy)(BPh(4)), Cu(I)(phen)(BPh(4)), and Cu(I)(3,4,7,8-Me(4)phen)(BPh(4)) complexes are the first examples in which the BPh(4)(-) counterion chelates a transition metal center in bidentate fashion through eta(2) pi interactions with two of its phenyl rings.

Crystal structure of ammonium bis-[(pyridin-2-yl)meth-yl]ammonium dichloride.

In the title molecular salt, C12H14N3 (+)·NH4 (+)·2Cl(-), the central, secondary-amine, N atom is protonated. The bis-[(pyridin-2-yl)meth-yl]ammonium and ammonium cations both lie across a twofold rotation axis. The dihedral angles between the planes of the pyridine rings is 68.43 (8)°. In the crystal, N-H⋯N and N-H⋯Cl hydrogen bonds link the components of the structure, forming a two-dimensional network parallel to (010). In addition, weak C-H⋯Cl hydrogen bonds exist within the two-dimensional network.

Crystal structure of ortho-rhom-bic {bis-[(pyridin-2-yl)meth-yl](3,5,5,5-tetra-chloro-pent-yl)amine-κ(3) N,N',N''}chlorido-copper(II) perchlorate.

In the title compound, [CuCl(C17H19Cl4N3)]ClO4, the Cu(II) ion adopts a distorted square-planar geometry defined by one chloride ligand and the three nitro-gen atoms from the bis-[(pyridin-2-yl)meth-yl](3,5,5,5-tetra-chloro-pent-yl)amine ligand. The perchlorate counter-ion is disordered over three sets of sites with refined occupancies 0.0634 (17), 0.221 (16) and 0.145 (7). In addition, the hetero-scorpionate arm of the bis-[(pyridin-2-yl)meth-yl](3,5,5,5-tetra-chloro-pent-yl)amine ligand is disordered over two sets of sites with refined occupancies 0.839 (2) and 0.161 (2). In the crystal, weak Cu⋯Cl inter-actions between symmetry-related mol-ecules create a dimerization with a chloride occupying the apical position of the square-pyramidal geometry typical of many copper(II) chloride hetero-scorpionate complexes.

Structural studies of (prop-2-en-1-yl)bis[(pyridin-2-yl)methylidene]amine hetero-scorpionate copper complexes.

The structures of five compounds consisting of (prop-2-en-1-yl)bis[(pyridin-2-yl)methylidene]amine complexed with copper in both the Cu(I) and Cu(II) oxidation states are presented, namely chlorido{(prop-2-en-1-yl)bis[(pyridin-2-yl)methylidene]amine-κ(3)N,N',N''}copper(I) 0.18-hydrate, [CuCl(C15H17N3)]·0.18H2O, (1), catena-poly[[copper(I)-µ2-(prop-2-en-1-yl)bis[(pyridin-2-yl)methylidene]amine-κ(5)N,N',N'':C(2),C(3)] perchlorate acetonitrile monosolvate], {[Cu(C15H17N3)]ClO4·CH3CN}n, (2), dichlorido{(prop-2-en-1-yl)bis[(pyridin-2-yl)methylidene]amine-κ(3)N,N',N''}copper(II) dichloromethane monosolvate, [CuCl2(C15H17N3)]·CH2Cl2, (3), chlorido{(prop-2-en-1-yl)bis[(pyridin-2-yl)methylidene]amine-κ(3)N,N',N''}copper(II) perchlorate, [CuCl(C15H17N3)]ClO4, (4), and di-µ-chlorido-bis({(prop-2-en-1-yl)bis[(pyridin-2-yl)methylidene]amine-κ(3)N,N',N''}copper(II)) bis(tetraphenylborate), [Cu2Cl2(C15H17N3)2][(C6H5)4B]2, (5). Systematic variation of the anion from a coordinating chloride to a noncoordinating perchlorate for two Cu(I) complexes results in either a discrete molecular species, as in (1), or a one-dimensional chain structure, as in (2). In complex (1), there are two crystallographically independent molecules in the asymmetric unit. Complex (2) consists of the Cu(I) atom coordinated by the amine and pyridyl N atoms of one ligand and by the vinyl moiety of another unit related by the crystallographic screw axis, yielding a one-dimensional chain parallel to the crystallographic b axis. Three complexes with Cu(II) show that varying the anion composition from two chlorides, to a chloride and a perchlorate to a chloride and a tetraphenylborate results in discrete molecular species, as in (3) and (4), or a bridged bis-µ-chlorido complex, as in (5). Complex (3) shows two strongly bound Cl atoms, while complex (4) has one strongly bound Cl atom and a weaker coordination by one perchlorate O atom. The large noncoordinating tetraphenylborate anion in complex (5) results in the core-bridged Cu2Cl2 moiety.

Crystal structure of {(but-3-en-1-yl)bis-[(pyridin-2-yl)meth-yl]amine-κ(3) N,N',N''}di-chlorido-copper(II) diethyl ether hemisolvate.

The five-coordinate Cu(II) atom in the title complex [CuCl2(C16H19N3)]·0.5C4H10O, adopts a near-ideal square-pyramidal geometry (τ-5 = 0.01). The apical Cu-Cl distance is 0.2626 (6) Šlonger than the basal Cu-Cl distance. Weak C-H⋯Cl interactions between pyridine rings and the Cl atoms of adjacent complex molecules are present. The solvent molecule, located on a twofold rotation axis, is situated in the voids of this arrangement. Copper atoms coordinated by tridentate nitro-gen-containing ligands have been found to be excellent promoters of Atom Transfer Radical Addition (ATRA) reactions.

Atom transfer radical addition (ATRA) catalyzed by copper complexes with tris[2-(dimethylamino)ethyl]amine (Me6TREN) ligand in the presence of free-radical diazo initiator AIBN.

In this article, we focus on the evaluation of tris[2-(dimethylamino)ethyl]amine (Me(6)TREN) ligand in copper catalyzed ATRA in the presence of free-radical diazo initiator AIBN (2,2'-azobis(2-methylpropionitrile)). The addition of carbon tetrachloride to 1-hexene, 1-octene and cis-cyclooctene proceeded efficiently to yield 89, 85 and 85% of monoadduct, respectively, using the catalyst to alkene ratio of 1 : 2500. For alkenes that readily undergo free radical polymerization, such as methyl acrylate, catalyst loadings as high as 0.4 mol-% were required. Furthermore, modest yields of the monoadduct were obtained with less active alkyl halides (chloroform and bromoform) using 250 : 1 and 500 : 1 ratios of alkene to copper(II). Interestingly, the addition of carbon tetrachloride to cis-cyclooctene produced only 1-chloro-4-(trichloromethyl)-cyclooctene, while carbon tetrabromide yielded 1,2 and 1,4-regioisomers in 75 : 25 ratio. The activity of [Cu(II)(Me(6)TREN)X][X] (X = Br(-) and Cl(-)) complexes in ATRA in the presence of AIBN was additionally probed by adding excess free ligand, source of halide anions and triphenylphosphine. The results indicated that disproportionation is a likely cause for lower activity of Me(6)TREN as compared to TPMA (tris(2-pyridylmethyl)amine).

Photoinitiated ambient temperature copper-catalyzed atom transfer radical addition (ATRA) and cyclization (ATRC) reactions in the presence of free-radical diazo initiator (AIBN).

The use of UV light in copper-catalyzed atom transfer radical addition (ATRA) and cyclization (ATRC) reactions of various (poly)halogenated compounds to highly active alkenes in the presence of AIBN is reported. Radicals generated from photodecomposition of AIBN efficiently regenerated the copper(I) complex at ambient temperature enabling ATRA of CCl(4) and CBr(4) with catalyst loadings as low as 0.05 mol-%. The desired monoadduct was obtained in lower yields in the ATRA of less active halogenated compounds, which was mostly due to incomplete alkene conversions. Ambient temperature ATRA of CCl(4) to various 1,6-dienes followed by sequential ATRC was also performed in the presence of UV light using [Cu(II)(TPMA)Cl][Cl] complex and AIBN. High yields of the 5-exo-trig cyclic product were obtained for all dienes with preferential formation of the cis isomer.