Bu 4N Research Articles

Selectivity of Thiolate Ligand and Preference of Substrate in Model Reactions of Dissimilatory Nitrate Reductase

Complexes analogous to the active site of dissimilatory nitrate reductase from Desulfovibrio desulfuricans are synthesized. The hexacoordinated complexes [PPh 4][Mo (IV)(PPh 3)(SR)(mnt) 2] (R = -CH 2CH 3 ( 1), -CH 2Ph ( 2)) released PPh 3 in solution to generate the active model cofactor, {Mo (IV)(SR)(mnt) 2} (1-), ready with a site for nitrate binding. Kinetics for nitrate reduction by the complexes 1 and 2 followed Michaelis-Menten saturation kinetics with a faster rate in the case of 1 ( V Max = 3.2 x 10 (-2) s (-1), K M = 2.3 x 10 (-4) M) than that reported earlier ( V Max = 4.2 x 10 (-3) s (-1), K M = 4.3 x 10 (-4) M) ( Majumdar, A. ; Pal, K. ; Sarkar, S. J. Am. Chem. Soc. 2006, 128, 4196- 4197 ). The oxidized molybdenum species may be reduced back by PPh 3 to the starting complex, and a catalytic cycle involving [Bu 4N][NO 3] and PPh 3 as the oxidizing and reducing substrates, respectively, is established with the complexes 1 and 2. Isostructural complexes, [Et 4N][Mo (IV)(PPh 3)(X)(mnt) 2] (X = -Br ( 3), -I ( 4)) did not show any reductive activity toward nitrate. The selectivity of the thiolate ligand for the functional activity and the cessation of such activity in isostructural halo complexes demonstrate the necessity of thiolate coordination. Electrochemical data of all these complexes correlate the ability of the thiolated species for such oxotransfer activity. Compounds 1 and 2 are capable of reducing substrates like TMANO or DMSO, but after the initial 15-20% conversion, the product trimethylamine or dimethylsulfide formed interacts with the active parent complexes 1 and 2 thereby slowing down further oxo-transfer reaction similar to feedback type reactions. From the functional nitrate reduction, the molybdenum species finally reacts with the nitrite formed leading to nitrosylation similar to the NO evolution reaction by periplasmic nitrate reductase from Pseudomonas dentrificans. All these complexes ( 1- 4) are characterized structurally by X-ray, elemental analysis, electrochemistry, electronic, FT-IR, mass and (31)P NMR spectroscopic measurements.

Two novel mono-organoimido functionalized polyoxometalate clusters: Convenient synthesis, crystal structure and bioactivity of [( n-C 4H 9) 4N] 2[Mo 6O 18(NAr)] (Ar = o-CF 3C 6H 4, p-OCF 3C 6H 4)

The hexamolybdate cluster has been functionalized with fluorine-containing aromatic amine by the DCC ( N, N′-dicyclohexylcarbodiimide) dehydrating protocol and two novel mono-functionalized arylimido derivatives of hexamolybdates bearing the electron-withdrawing trifluoromethyl group and trifluoromethoxy group, (Bu 4N) 2[Mo 6O 18(≡NAr)] (Ar = o-CF 3C 6H 4) 1 and (Bu 4N) 2[Mo 6O 18(≡NAr)] (Ar = p-OCF 3C 6H 4) 2 have been synthesized by improved method. Complete assignments were achieved for the title compounds by elemental analysis, IR, 1H NMR, UV/visible and single-crystal X-ray diffraction analyses. The preliminary herbicidal activity test indicated that they have some herbicidal activities.

Practical synthesis of 1,4-dioxane derivative of the closo-dodecaborate anion and its ring opening with acetylenic alkoxides

Practical method of synthesis of the 1,4-dioxane derivative of the closo-dodecaborate anion was developed. The cleavage of the dioxonium ring in [B 12H 11O(CH 2CH 2) 2O] − with acetylenic alcohols gave rise to the preparation of closo-dodecaborate derivatives with terminal acetylene group. These compounds can be introduced into click reactions with phenylazide leading to the corresponding triazoles. The structures of (Bu 4N)[B 12H 11O(CH 2CH 2) 2O] and (Bu 4N) 2[B 12H 11(OCH 2CH 2) 2OCH 2C CH] · 0.5HOCH 2C CH were determined by single-crystal X-ray diffraction.

Organic–inorganic hybrid material as zwitterion: Synthesis and structure of terminal ammonium ions-containing organosilyl species supported on mono-lacunary Dawson polyoxometalate

The title compound 1 with a formula of (Bu 4N) 4[α 2-P 2W 17O 61{Me 3N +(CH 2) 3Si} 2O] · CH 3CN was obtained in 77.1% (4.21 g scale) yield by a 1:2 molar-ratio reaction of the mono-lacunary Dawson polyoxometalate (POM) [P 2W 17O 61] 10− with N-trimethoxysilylpropyl- N, N, N-trimethylammonium chloride ([Me 3N(CH 2) 3Si(OMe) 3]Cl) in mixed water/acetonitrile solution under acidic conditions and unequivocally characterized with complete elemental analysis, thermogravimetric and differential thermal analyses (TG/DTA), FTIR, solution ( 31P, 1H, 13C and 29Si) NMR and X-ray crystallography. Compound 1 contained two types of the ammonium cations, i.e., the counterions Bu 4N + (free cations) and the terminal quaternary ammonium ions (bound cations) which are connected to the POM through the organosilyl groups.

Synthesis, spectroscopic characterization and vulcanization activity of a new compound containing the anion bis(4-methylphenylsulfonyldithiocarbimato)zincate(II)

A new compound of the formula: (Bu 4N) 2[Zn(4-CH 3C 6H 4SO 2N CS 2) 2] (Bu 4N = tetrabutylammonium cation) was obtained by the reaction of CH 3C 6H 4SO 2N CS 2K 2 · 2H 2O with zinc(II) acetate dihydrate and tetrabutylammonium bromide in dimethylformamide. The elemental analyses of C, H, N and Zn are consistent with the proposed formula. The IR data point to the formation of a zinc(II)–bis(dithiocarbimato) complex. The 1H NMR and 13C NMR spectra showed the expected signals for the tetrabutylammonium cation and the dithiocarbimato moiety. This compound was evaluated as for the vulcanization activity and compared to the commercial accelerators CBS, MBTS and TMTD. These studies showed that the zinc(II)–ditiocarbimates are a new class of rubber vulcanization accelerators, worth of further investigation.

Electrochemical synthesis of a crystalline film of tetrabutylammonium bromide

An anodic oxidation of aqueous Br − ions on platinum substrate in the presence of tetrabutylammonium (Bu 4N +) ions leads to the formation of Br 3 −. This accompanies the self-assembly of Bu 4N + cations to the electrogenerated Br 3 − anions being accumulated near the electrode surface. The deposited Br 3 − anions can be replaced with Br − in solution by ion exchange, resulting in a thin film of Bu 4NBr salt with high crystallinity and low electrical conductivity.

Compressibility studies of tetraalkylammonium salts in binary mixtures of dimethysulfoxide and acetone

Present work reports the results of ultrasonic velocity studies of tetrabutylammoniumtetraphenyl boride Bu 4NBPh 4, tetrapropylammonium iodide Pr 4NI, tetrabutylammonium iodide Bu 4NI, tetrapentylammonium iodide Pen 4NI and sodium tetraphenyl boride NaBPh 4 in binary mixtures of DMSO and Ac. Adiabatic compressibility coefficient, β and corresponding limiting molar adiabatic compressibility, ϕ κ o(s) of R 4NI salts are noted to decrease with the decrease in the size of hydrophobic group. This observation is suggested to be of relevance to the reorganizing of solvent molecules at the hydrocarbon–solvent interface, and not to direct solute–solvent interaction. The variation in ϕ κ o(s) with solvent composition, although reflects the contribution due to intermolecular interaction, insensitivity of solvent composition dependence of limiting ionic molar compressibility ϕ κ o(i) and its sign for Pen 4N +, Bu 4N +, Pr 4N +and Ph 4B − indicate their poor solvation behaviour. ϕ κ o(i) < 0 for Na + and I − on the contrary, is suggested to support the solvation effect of these ions.

Aerobic oxidations of α-pinene over cobalt-substituted polyoxometalate supported on amino-modified mesoporous silicates

Co-containing polyoxometalate [Bu 4N] 4H[PW 11Co(H 2O)O 39] (Co-POM) was supported on various NH 2-modified mesoporous silicate matrixes (SBA-15, MCF, and SiO 2-xerogel). The catalysts were characterized by elemental analysis, N 2 adsorption, DRS–UV, and FTIR spectroscopy. α-Pinene autoxidation and its co-oxidation with isobutyraldehyde (IBA) over the supported Co-POM catalysts have been studied and compared with the corresponding processes in the presence of the homogeneous Co-POM. The autoxidation process affords allylic oxidation products, the selectivity to verbenol/verbenone decreases with alkene conversion and attains 70% at 20% conversion and 40% at 46% conversion. The catalysts can be used repeatedly without loss of the activity and selectivity during several catalytic cycles. Co-oxidation of α-pinene and IBA produces selectively α-pinene epoxide with up to 94% selectivity at 96% alkene conversion. The catalysts can be regenerated by evacuation.

Two new bromo-functionalized organoimido derivatives of hexamolybdate: Synthesis, crystal structure, spectroscopic and electrochemical studies

Two organic–inorganic hybrid compounds, (Bu 4N) 2[Mo 6O 18(NAr)] (Ar = 2-CH 3-4-BrC 6H 3 ( 1) or 2,6-CH 3-4-BrC 6H 2 ( 2)) have been synthesized via the DCC dehydrating protocol of the reaction of [α-Mo 8O 26] 4− with 2-methyl-4-bromoaniline hydrochloride or 2,6-dimethyl-4-bromoaniline hydrochloride in anhydrous acetonitrile, which have been characterized by UV–Vis spectra, 1H NMR, IR, cyclic voltammetry and X-ray single-crystal diffraction study. Both compounds crystallize in the monoclinic space group P 1 ¯ , which are featured in a terminal phenylimido group linked to a Mo atom of a hexamolybdate cluster by a Mo–N triple bond. Interestingly, there are two conformational isomers of the cluster anions of 1 and 2 in the crystals. By cyclic voltammetry study, their special redox properties were also found in the end.

Synthesis, isolation and spectroscopic characterization of Dawson polyoxotungstate-supported, organometallic complex, [{(C 6H 6)Ru}P 2W 15V 3O 62] 7−: The two positional isomers

The Dawson polyoxotungstate (POM)-based, organometallic ruthenium(II) complex, [{(C 6H 6)Ru}P 2W 15V 3O 62] 7−, was synthesized as two materials, i.e. 1 · 2Bu 4NCl and 1 · 1Bu 4NCl ( 1 = (Bu 4N) 7[{(C 6H 6)Ru}P 2W 15V 3O 62]), which contained two positional isomers a and b as major or minor species. In isomer a with the overall C s symmetry, the (C 6H 6)Ru 2+ group was supported on one vanadium(V) octahedral site (two V–O–V bridging oxygens and one O V terminal oxygen) of the three edge-shared vanadium(V) octahedra (V 3 site, B-site) in the Dawson POM-support [1,2,3-P 2W 15V 3O 62] 9−, whereas in the other isomer b with the overall C 3 v symmetry, the (C 6H 6)Ru 2+ group was supported on the center of the V 3 site in the Dawson POM-support. Material 1 · 2Bu 4NCl was prepared by a stoichiometric reaction in CH 2Cl 2 at ambient temperature of the Dawson POM-support (Bu 4N) 9[1,2,3-P 2W 15V 3O 62] with the precursor [(C 6H 6)RuCl 2] 2, whereas material 1 · 1Bu 4NCl was prepared by a stoichiometric reaction in CH 3CN under refluxing conditions. The temperature-varied 31P NMR spectra revealed that b was thermodynamically more stable than a.

Synthesis, structure and magnetic properties of 2-D and 3-D [cation]{M[Au(CN) 2] 3} (M = Ni, Co) coordination polymers

In order to study the templating effect of the cation and the resulting impact on the magnetic properties, reactions of M(II) salts with [cation][Au(CN) 2] were conducted, yielding a series of coordination polymers of the form [cation]{M[Au(CN) 2] 3} (cation = n Bu 4N +, PPN + (bis(triphenylphosphoranylidene)ammonium); M = Ni(II) and Co(II)). The structures of n Bu 4N{M[Au(CN) 2] 3} and PPN{M[Au(CN) 2] 3} (M = Ni and Co) contain two distinct 3-D anionic frameworks of {M[Au(CN) 2] 3} −, hence the framework was sensitive to the cation, but not to the identity of the metal center. In n Bu 4N{M[Au(CN) 2] 3}, the metal centers are connected by [Au(CN) 2] units to form six 2-D (4, 4) rectangular grids that are fused through the M centers to yield a complex three-dimensional framework which accommodates the n Bu 4N + cations. In PPN{M[Au(CN) 2] 3}, the framework adopts a simpler non-interpenetrated Prussian-blue-type pseudo-cubic array, with the PPN + cations occupying each cavity; no reduction in dimensionality occurs despite the large cation size. In the presence of water, {Co(H 2O) 2[Au(CN) 2] 2} · n Bu 4N[Au(CN) 2] was obtained, a 2-D layered polymer that contains neutral sheets of {Co(H 2O) 2[Au(CN) 2] 2} which are separated by n Bu 4N[Au(CN) 2] layers; aurophilic interactions of 3.4250(13) Å and hydrogen-bonding connect the layers. The magnetic properties of all compounds were investigated by SQUID magnetometry. The Ni(II) polymers have similar magnetic behaviour, which are dominated by zero-field splitting with very weak antiferromagnetic interactions at low temperature ( D ∼ 2–3 cm −1, zJ < 1 cm −1). The magnetic behaviour of all of the Co(II) polymers were found to be very similar, and dominated by single-ion effects (i.e. a large first-order orbital contribution). No significant magnetic coupling is observed in any of these coordination polymers, suggesting that the [Au(CN) 2] bridging unit behaves as a poor mediator of magnetic exchange in these high-dimensionality systems.

A convenient method for the conversion of [Sn 3S 4] 2− to [Sn 3S 3(μ 3-OH)] −: Syntheses, structures and characterizations of (Bu 4N)[Sn 3(μ 3-OH)S 3(edt) 3] · DMF and (Bu 4N)[Sn 3(μ 3-OH)S 3(edt) 3] · H 2O (edt = 1,2-ethanedithiolate)

Two new trinuclear tin(IV) oxy-sulfide complexes, (Bu 4N)[Sn 3(μ 3-OH)S 3(edt) 3] · DMF ( 1) and (Bu 4N)[Sn 3(μ 3-OH)S 3(edt) 3] · H 2O ( 2), which are the same salt with different solvates, were unexpectedly obtained by the reaction of (Bu 4N) 2[Sn 3S 4(edt) 3] with CuCl 2 (or KCuI 2) and Zn(phen)(SCN) 2 (or Cd(phen)(SCN) 2), respectively. The two complexes have been characterized by X-ray single crystal diffraction, IR, far-IR, Raman, 1H NMR, ES-MS and element analysis. X-ray structure determinations reveal that complexes 1 and 2 possess the same incomplete cubane-like anion cluster of [Sn 3(μ 3-OH)S 3(edt) 3] −.

Spin density distribution in oxamato-type transition metal complexes

The spin density distribution of the paramagnetic [ n Bu 4N] 2[Cu(dana)] dana = N, N′-(naphthalene-2,3-diyl)-bis(oxamato) has been derived from angular dependent electron paramagnetic resonance measurements at room temperature. The results indicate a noticeable spin density transfer from the central metal to the coordinated N and O atoms. Quantum chemical studies using density functional theory reinforce the results.

Scanning tunneling microscopy (STM) and tunneling spectroscopy (TS) studies of polyoxometalates (POMs) of the Wells–Dawson structural class

Presented in this work is an extensive scanning tunneling microscopy (STM) study of self-assembled monolayers of polyoxometalates (POMs) belonging to the Wells–Dawson structural class. The effects of cation and framework atom substitutions in these POMs and their salts have been examined. The Wells–Dawson POMs and their salts formed self-assembled and well-ordered arrays on graphite surfaces. Tunneling spectroscopy (TS) measurements revealed that these POMs exhibited negative differential resistance (NDR) behavior in their tunneling spectra. The arrays of vanadium-substituted POMs, H 6+ x [P 2Mo 18− x V x O 62] ( x = 1, 2, 3), showed periodicities of ca. 11 Å × 14 Å. The shapes and periodicities of the corrugations in the STM images are consistent with the structure and the characteristic dimensions of the Wells–Dawson polyanion, [P 2Mo 18O 62] 6−, as determined from X-ray crystallography studies. Moreover, the STM results indicated that framework substitutions and increases in the number of charge-compensating protons had negligible effects on the array periodicities. Various salts of trisubstituted Wells–Dawson POMs, Q[P 2W 15Nb 3O 62] (Q = Na 9, Cs 9, (Bu 4N) 9, (Bu 4N) 5Na 3(Re(CO) 3)), also formed two-dimensional monolayer arrays with various periodicities. For this class of POM salts, the periodicities were greater than the anion dimensions, reflecting the size of the counter cation (Q). TS measurements revealed the positions of the counter cations in the POM salt arrays, and the positions were consistent with the cation positions found in the bulk crystal structures. For each class of Wells–Dawson anions, it was shown that the packing of the polyanions in the monolayers was not identical to, but resembled that found in bulk cleavage planes of the corresponding POM. A correlation between NDR peak voltage and reduction potential established for both POM series revealed that more reducible POMs showed NDR peaks at less negative applied voltage. In other words, a less negative NDR peak voltage corresponded to a higher reduction potential. This trend is consistent with those previously elucidated for POM catalysts with the Keggin structure.

Synthesis and structure of the tetradeca-iron(III) oxide–alkoxide cluster [Bu 4N] 2[Fe 14O 8(OCH 2CH 3) 20Cl 8

The iron(III) oxide–alkoxide cluster, di-tetra- n-butylammonium octachloro-tetra(μ 3-oxo)-tetra(μ 4-oxo)- icosa(μ 2-ethoxo)-tetradeca-iron(III), has been isolated and its X-ray crystal structure determined.

Synthesis and structural characterization of several dirhenium(III) compounds

Reaction between Re 2(OAc) 4Cl 2 and N, N′-dicyclohexylbenzamidine (HDCyBA) under molten conditions yielded Re 2(DCyBA) 2Cl 4 ( 1); reaction of [Bu 4N] 2[Re 2Cl 8] with N, N′-di(3-methoxyphenyl)formamidine (HDmAniF) resulted in Re 2(DmAniF) 2Cl 4 ( 2); reaction of cis-Re 2(OAc) 2Cl 4 with HDmAniF under reflux conditions resulted in cis-Re 2(OAc) 2(DmAniF) 2Cl 2 ( 3). Reaction between Re 2(OAc) 4Cl 2 and α,α,α′,α′-tetramethyl-1,3-benzenedipropionic acid (H 2esp) under reflux conditions led to Re 2(esp) 2Cl 2 ( 4). Crystallographic studies of compounds 1– 4 revealed Re–Re bond lengths of 2.1679(6), 2.1804(5), 2.2468(7), and 2.2304(6) Å, respectively, which are consistent with the presence of Re–Re quadruple bond. Also reported are electrochemical properties of compounds 1– 4.

A kinetic investigation of the oxidative addition reactions of the dimeric Bu 4N[Ir 2(μ-Dcbp)(cod) 2] complex with iodomethane

The kinetic results of the oxidative addition of iodomethane to Bu 4N[Ir 2(μ-Dcbp)(cod) 2] (Dcbp = 3,5-dicarboxylatepyrazolate anion) show that oxidative addition can occur via a direct equilibrium pathway ( K 1 = 88(22) acetone, 51(3) 1,2-dichloroethane, 55(4) dichloromethane, 52(12) acetonitrile and 43(5) M −1 chloroform) or a solvent-assisted pathway ( k 2, k 3). Oxidative addition occurs mainly along the direct pathway, which is a factor 10–40 faster than the solvent-assisted pathway. The observed solvent effect cannot be attributed to the donosity or polarity of the solvents. The fairly negative Δ S ≠ value (−110(7) J K −1 mol −1) and the positive Δ H ≠ value (+47(2) kJ mol −1) for the oxidative addition step are indicative of an associative process.

Base-free efficient palladium catalyst of Heck reaction in molten tetrabutylammonium bromide

Phosphine-free palladium precursors (PdCl 2, PdCl 2(PhCN) 2 and Pd(OAc) 2) in molten [ n Bu 4N]Br as the reaction medium and without addition of base were used as components for efficient catalytic systems for Heck coupling of bromobenzene with butyl acrylate. In all the systems under studies the yield of product, butyl cinnamate 1, strongly depends on the concentration of palladium. The maximum yield of 1 was obtained for PdCl 2(PhCN) 2 at 0.09 mol% and for PdCl 2 and Pd(OAc) 2 at ca. 0.4 mol%. Lower yields were obtained below and over that concentration. Addition of bases (NaHCO 3, NaHCO 2, Et 3N or Bu 3N) caused an increase of acrylate conversion and formation of butyl β-phenyl cinnamate 2. During recycling experiments the change of selectivity was observed with increase of 1/ 2 products ratio.

Kinetic investigations of the mechanism of dihydrogen driven catalytic reduction of methylene blue, safranine O, methyl viologen and ferricyanide using platinum carbonyl cluster anions (Chini-clusters) as catalyst

[Bu 4N] 2[Pt 12(CO) 24] ( 1) catalyses the selective reduction of electron acceptors ( S), methylene blue (MB +), safranine O (Saf +), methyl viologen (MV 2+) and ferricyanide by dihydrogen. Macroscopic rate investigations for the cationic substrates in DMF, and for ferricyanide in DMSO have been carried out. In all cases, k obs is given by k 1 [ S] + k 2, indicating that there are two catalytic cycles. In one of them, the formation of a complex between S and [Pt 12(CO) 24] 2− in the rate determining step (rate constant k 1) is followed by electron transfer and/or other fast steps. In the other catalytic cycle, the rate determining step (rate constant k 2) involves formation of the solvated cluster anion [Pt 12(CO) 24] 2−. The solvated cluster then undergoes fast reduction by dihydrogen and other reactions. The relative contributions of these two cycles depend on the substrate, and for MB +, Saf +, MV 2+ and [Fe(CN) 6] 3− the contribution of the second cycle is about 99%, 55%, 77% and 97%, respectively. Both k 1 and k 2 of ferricyanide are about three orders of magnitude smaller than those of the cationic electron acceptors. The rates of reduction of MB + and Saf + have also been studied in the presence of added water. Rates increase as the presence of water provides an additional pathway for the reduction of [Pt 12(CO) 24] 2− to [Pt 9(CO) 18] 2−.

Synthesis and characteristic of a new arylimido derivative of hexamolybdate with remote strong electro-donating group (Bu 4N) 2[Mo 6O 18NC 6H 4N(CH 3) 2− p

A new monofunctionized arylimido derivative of hexamolybdate, (Bu 4N) 2[Mo 6O 18NC 6H 4N(CH 3) 2− p], is synthesized by α-octamolybdate and hydrochloride salt of N, N-dimethyl-1,4-dianiline with DCC as a dehydrating agent. The derivative’s crystal data has been obtained and the IR, UV–Vis, 1H NMR spectra and cyclic voltammetry properties have also been studied.