Bromo Complexes Research Articles

Synthesis and Reactivity of Dipalladated Derivatives of Terephthalaldehyde.

The polynuclear complex [{μ-C1,C4,N,N″-C6H2{C(H)=N(nBu)}2-2,5}{Pd(μ-OAc)}]2 (I) reacts with tbbpy (4,4'-di-tert-butyl-2,2'-bipyridine) and TlOTf to form the dinuclear complex [{μ-C1,C4,N,N″-C6H2{C(H)=N(nBu)}2-2,5}{Pd(tbbpy)}2] (1). The hydrolysis of I with acetic acid in a 5:1 acetone/water mixture, in the presence of two equivalents of tbbpy and excess NaX (X = Br, I), yields the dipalladated terephthalaldehyde complexes [C6H2{PdX(tbbpy)}2-1,4-(CHO)2-2,5] [X = Br (2a), X = I (2b)], which are the first fully characterized complexes of this type. The reaction of 2a,b with CO results in the insertion of CO into both aryl-Pd bonds, forming [C6H2{C(O){PdX(tbbpy)}}2-1,4-(CHO)2-2,5] [X = Br (3a), X = I (3b)], which are the first examples of complexes with CO inserted into two separate aryl-metal bonds involving the same ligand. The bromo complex 2a reacts with excess XylNC in acetone, causing the precipitation of the dinuclear complex 2,3,6,7-tetrahydrobenzo[1,2-c:4,5-c']dipyrrole-1,5-dione-2,6-dixylyl-3,7-bis{=C(NHXyl)-C(=NXyl)-[PdBr(CNXyl)2]} (4), which is the result of the insertion of three molecules of the isocyanide into each aryl-Pd bond and the nucleophilic attack of one of them at each formyl group. When complex 4 reacts with TlOTf and residual water in 1,2-dichloroethane at 70 °C, depalladation occurs, and the organic compound 2,3,6,7-tetrahydrobenzo[1,2-c:4,5-c']dipyrrole-1,5-dione-2,6-dixylyl-3,7-bis{=C(NHXyl)-C(O)NHXyl} (5) can be isolated. The crystal structures of 1·4CHCl3, 4·2CH2Cl2·3hexane, and 5·2CDCl3 have been determined by X-ray crystallography.

Reactions of Cadmium(II) Halides and Di-2-Pyridyl Ketone Oxime: One-Dimensional Coordination Polymers.

The coordination chemistry of 2-pyridyl ketoximes continues to attract the interest of many inorganic chemistry groups around the world for a variety of reasons. Cadmium(II) complexes of such ligands have provided models of solvent extraction of this toxic metal ion from aqueous environments using 2-pyridyl ketoxime extractants. Di-2-pyridyl ketone oxime (dpkoxH) is a unique member of this family of ligands because its substituent on the oxime carbon bears another potential donor site, i.e., a second 2-pyridyl group. The goal of this study was to investigate the reactions of cadmium(II) halides and dpkoxH in order to assess the structural role (if any) of the halogeno ligand and compare the products with their zinc(II) analogs. The synthetic studies provided access to complexes {[CdCl2(dpkoxH)∙2H2O]}n (1∙2H2O), {[CdBr2(dpkoxH)]}n (2) and {[CdI2(dpkoxH)]}n (3) in 50-60% yields. The structures of the complexes were determined by single-crystal X-ray crystallography. The compounds consist of structurally similar 1D zigzag chains, but only 2 and 3 are strictly isomorphous. Neighboring CdII atoms are alternately doubly bridged by halogeno and dpkoxH ligands, the latter adopting the η1:η1:η1:μ (or 2.0111 using Harris notation) coordination mode. A terminal halogeno group completes distorted octahedral coordination at each metal ion, and the coordination sphere of the CdII atoms is {CdII(η1 - X)(μ - X)2(Npyridyl)2(Noxime)} (X = Cl, Br, I). The trans-donor-atom pairs in 1∙2H2O are Clterminal/Noxime and two Clbridging/Npyridyl; on the contrary, these donor-atom pairs are Xterminal/Npyridyl, Xbridging/Noxime, and Xbridging/Npyridyl (X = Br, I). There are intrachain H-bonding interactions in the structures. The packing of the chains in 1∙2H2O is achieved via π-π stacking interactions, while the 3D architecture of the isomorphous 2 and 3 is built via C-H∙∙∙Cg (Cg is the centroid of one pyridyl ring) and π-π overlaps. The molecular structures of 1∙2H2O and 2 are different compared with their [ZnX2(dpkoxH)] (X = Cl, Br) analogs. The polymeric compounds were characterized by IR and Raman spectroscopies in the solid state, and the data were interpreted in terms of the known molecular structures. The solid-state structures of the complexes are not retained in DMSO, as proven via NMR (1H, 13C, and 113Cd NMR) spectroscopy and molar conductivity data. The complexes completely release the coordinated dpkoxH molecule, and the dominant species in solution seem to be [Cd(DMSO)6]2+ in the case of the chloro and bromo complexes and [CdI2(DMSO)4].

New Reactions of Cyclopentadienylnickel Chelates with Secondary Phosphane Tethers

AbstractIn continuation of our research in cyclopentadienylalkylphosphane nickel chelates with secondary phosphane tethers the first cationic representatives of this class of compounds are reported. These were obtained by reaction of the respective bromo complex with tris(4‐trifluoromethylphenyl)phosphane as well as with a number of alkyl and aryl isonitriles in the presence of indium tribromide. This Lewis acid is crucial for the success of the reactions leading to the respective tetrabromoindate salts. The compounds were characterized spectroscopically, including rare 14N,13C couplings being observed. Finally, deprotonation experiments are reported, which provide some evidence for deprotonation taking place, although the expected phosphinidene chelates could not be isolated due to rapid decomposition.

Synthesis, spectroscopic, thermal decomposition, DFT studies and antibacterial activity of uracil cobalt(III)dimethylglyoximato complexes

ABSTRACT Three new mixed-ligand complexes of the type [Co(Hdmg)2(Ura)X], where Hdmg = dimethylglyoximato anion, Ura = uracil, and X = Cl, Br, or I, were synthesized and characterized using elemental analyses, molar conductance, IR and UV–visible spectroscopies. The molar conductance values indicate that the compounds are not electrolytes. The thermal decomposition was studied using TG and DSC techniques. It is shown that the decomposition process of all complexes occurs in three steps. The IR spectra of the complexes show that the four nitrogen atoms of oxime functions of the two Hdmg mono-anions are linked to the central atom, the whole moiety forming an equatorial plane. Uracil (-N) and halogen occupy the apical sites in the trans position in an octahedral arrangement. The absorption bands observed in the UV-visible spectra are due either to intra-ligand transitions, ligand-metal charge transfer transitions or d -d transitions. Density Functional Theory (DFT) calculations have been successfully used to investigate the nature of the bonding in the complexes. The antibacterial activities of the complexes and their combinations were tested against Escherichia coli, pseudomonas aeruginosa, klebsiella pneumonia, proteus mirabilis, staphylococcus aureus, and bacillus cereus. The combination of iodo and bromo complexes showed a strong inhibitory power compared to the other combinations and to the free complexes.

Unsymmetrical nickel (PCN) pincer complexes with a benzothiazole side-arm: Synthesis, characterization and electrochemical properties

The newly prepared unsymmetrical pincer ligand with a benzothiazole side-arm 2-(3-((di-tert-butylphosphino)methyl)phenoxy)benzo[d]thiazole [BzTz(H)PCN] has been reacted with anhydrous NiBr2 to get the corresponding NiII square planar bromo complex (BzTzPCN)NiBr (1) after HBr elimination and CH activation on the pincer central phenyl ring. Starting from 1, reaction with AgF in toluene or with AgBF4 in THF led to bromide abstraction and formation of the fluoro complex (BzTzPCN)NiF (2) and the ionic aquo species [(BzTzPCN)Ni(H2O)]BF4 (3), respectively. All species have been characterized in solution (multinuclear 1H, 13C{1H}, 31P{1H} and 11B NMR spectroscopy) and in the solid state (single-crystal X-ray diffraction analysis). Finally, comparative electrochemical measurements (CV and in situ EPR-spectroelectrochemistry) carried out on the halide complexes 1 and 2 revealed that the anodic oxidation process leads to the formation of stable NiIII species bearing a coordinated bromide ligand in case of 1 and a fluoride-free complex in case of 2.

Syntheses and X-ray structure characterization of dimeric copper(I) halo(X)complexes (X = Br, I) of (diisopropylamino)(morpholino)(phenyl)phosphine

On continuing the investigation with the reaction between aminophosphines and Cu(I) halides, the reaction of aminophosphine, viz (Diisopropylamino)(morpholino)(phenyl)phosphine with CuX (X = Br, I) was studied in acetonitrile solvent. Dimeric bromo and iodo Cu(I) complexes were obtained at room temperature. In bromo and iodo complexes, copper(I) was found to be tri-coordinate and tetra-coordinate, respectively. In iodo complex solvent, acetonitrile coordinates to copper through nitrogen atom. The Cu–P bond distances in bromo complex was ∼2.19 Å. Cu–P bond distance for iodo complex was slightly longer, 2.249(4) Å. 31P NMR coordination chemical shifts of the complexes were negative.

Structural, Non-Covalent Interaction, and Natural Bond Orbital Studies on Bromido-Tricarbonyl Rhenium(I) Complexes Bearing Alkyl-Substituted 1,4-Diazabutadiene (DAB) Ligands

The synthesis, characterization, structural and computational studies of Re(I) tricarbonyl bromo complexes bearing alkyl-substituted 1,4-diazabutadiene ligands, [Re(CO)3(1,4-DAB)Br], where 1,4-DAB = N,N-bis(2,4-dimethylbenzene)-1,4-diazabutadiene, 2,4-Me2DAB (1); N,N-bis(2,4-dimethylbenzene)-2,3-dimethyl-1,4-diazabutadiene, 2,4-Me2DABMe (2); N,N-bis(2,4,6-trimethylbenzene)-1,4-diazabutadiene, 2,4,6-Me3DAB (3); and N,N-bis(2,6-diisopropylbenzene)-1,4-diazabutadiene, 2,6-ipr2DAB (4) are reported. The complexes were characterized by different spectroscopic methods such as FT-IR, 1H-NMR, 13C-NMR, and elemental analyses and their solid-state structures were confirmed by X-ray diffraction. In each complex, the Re(I) centre shows a distorted octahedral shape with a facial geometry of carbonyl groups. The gas phase geometry of the complexes was identified by density functional theory. Interesting intermolecular n…π* interactions of complexes 1 and 3 were investigated by non-covalent interaction index (NCI), and natural bond orbital (NBO) analyses. The intramolecular n…σ*, σ…π*, π…σ* interactions were also studied in complexes 3 and 4.

Do Gold(III) Complexes Form Hydrogen Bonds? An Exploration of AuIII Dicarboranyl Chemistry.

The reaction of 1,1'-Li2 [(2,2'-C2 B10 H10 )2 ] with the cyclometallated gold(III) complex (C^N)AuCl2 afforded the first examples of gold(III) dicarboranyl complexes. The reactivity of these complexes is subject to the trans-influence exerted by the dicarboranyl ligand, which is substantially weaker than that of non-carboranyl anionic C-ligands. In line with this, displacement of coordinated pyridine by chloride is only possible under forcing conditions. While treatment of (C^N)Au{(2,2'-C2 B10 H10 )2 } (2) with triflic acid leads to Au-C rather than Au-N bond protonolysis, aqueous HBr cleaves the Au-N bond to give the pyridinium bromo complex 7. The trans-influence of a series of ligands including dicarboranyl and bis(dicarboranyl) was assessed by means of DFT calculations. The analysis demonstrated that it was not sufficient to rely exclusively on geometric descriptors (calculated or experimental) when attempting to rank ligands for their trans influence. Complex (C^N)Au(C2 B10 H11 )2 containing two non-chelating dicarboranyl ligands was prepared similar to 2. Its reaction with trifluoroacetic acid also leads to Au-N cleavage to give trans-(Hpy^C)Au(OAcF )(C2 B10 H11 )2 (8). In crystals of 8 the pyridinium N-H bond points towards the metal centre, while in 7 it is bent away. The possible contribution of gold(III)⋅⋅⋅H-N hydrogen bonding in these complexes was investigated by DFT calculations. The results show that, unlike the situation for platinum(II), there is no evidence for an energetically significant contribution by hydrogen bonding in the case of gold(III).

Synthesis, structure and cytotoxicity of a zinc(II) bromide complex with caffeine

The synthesis and structure of a zinc(II) bromide complex with caffeine (caf), [Zn(caf)(H2O)Br2], are described in comparison with [Zn(caf)(H2O)X2] (X = Cl, I) complexes. Data on the cytotoxicity of [Zn(caf)(H2O)X2] (X = Cl, Br, I) towards human tumor cell lines are presented. The bromo complex has some advantages over chloro and iodo complexes for cytotoxicity on MCF-7 breast cancer cell line, and it is comparable to the chloro complex in cytotoxicity for Jurkat human T cell leukemia.

Nickel(II) Complexes with Electron-Rich, Sterically Hindered PNP Pincer Ligands Enable Uncommon Modes of Ligand Dearomatization

We report the reactivity and characterization of hydride, methyl, and bromo NiII complexes with a new class of electron-rich and sterically hindered PNP pincer ligands, Me4PNPR (R = iPr, tBu), in which a classical metal–ligand cooperative mode of reactivity via CH2 arm deprotonation is blocked by methylation. This enables new, uncommon modes of PNP ligand dearomatization that involve reactivity in the para position of the pyridine ring. In particular, the reduction of [(Me4PNPiPr)NiIIMe]B(ArF)4 with KC8 leads to the formation of a new C–C bond via dimerization of two complexes through the para position. This reactivity stands in sharp contrast to the previously reported bromo or chloro complexes, where stable NiI halogen moieties are formed. Computational analysis showed a greater propensity for ligand-centered radical formation for the presumed intermediate one-electron-reduced species. UV-induced homolysis of the NiII–Me bond in [(Me4PNPiPr)NiIIMe]B(ArF)4 leads to the formation of a Me radical detected by radical traps and NiI intermediates that can be trapped in the presence of halide ions to give previously characterized, stable NiI halogen complexes. In addition, treatment of the bromo complexes [(Me4PNPR)NiIIBr]BPh4 with a powerful hydride source, LiBEt3H, leads to the reduction of the pyridine ring and the formation of NiII complexes with an anionic amide donor reduced pincer ligand, although aromatic NiII hydride complexes could also be obtained with a weaker hydride source. We have observed that steric bulk at the phosphine donors controls the reactivity of the resulting NiIIH complexes. While t-Bu-substituted [(Me4PNPtBu)NiIIH]Y (Y = BPh4, B(ArF)4) does not react with O2, the less sterically hindered iPr-substituted [(Me4PNPiPr)NiIIH]Y reacts instantaneously to give an unstable superoxide adduct that can be observed by EPR.

An On-Line Flow-Injection Sorbent Extraction System Coupled with Flame Atomic Absorption Spectrometry for Thallium Determination Using a PTFE Turning-Packed Column

A novel time-based flow-injection–solid-phase extraction system (FI–SPE) coupled with flame atomic absorption spectrometry (FAAS) for automatic on-line preconcentration and determination of thallium was developed. The efficiency of poly-tetrafluoroethylene (PTFE) turnings packed into a column as sorbent material was investigated for thallium extraction. Total thallium was determined by oxidizing thallium(I) to thallium(III), adding bromine in acidic solution. The formed [TlBr4]− anionic bromo complex was retained onto the PTFE turnings by on-line mixing with sodium diethyl dithiocarbamate (DDTC). The preconcentrated Tl(III)-DDTC complex was then effectively eluted with methyl isobutyl ketone (MIBK) and introduced into the flame atomizer for measurement and quantification. The column proved to be effective, stable, and reproducible, with a long lifetime. The enrichment factor was 105 for 60 s preconcentration time, and the sampling frequency 40 h−1. The detection limit was 1.93 μg L−1, and the relative standard deviation (RSD) was 3.2% at 50.0 μg L−1 concentration. The accuracy of the proposed method was estimated by analyzing certified reference materials and environmental and biological samples.

Copper(II) halide coordination complexes with 2-(3,5-diphenyl-1-pyrazolyl)-2-thiazoline (DPhPyTn): Synthesis, characterization and crystal structures

Reactions between CuX2 (X=Cl, Br) and 2-(3,5-diphenyl-1-pyrazolyl)-2-thiazoline (DPhPyTn) yield the complexes [{CuCl(DPhPyTn)}2(μ-Cl)2] (1), [CuBr(DPhPyTn)2]Br (2) and [{CuBr(DPhPyTn)}2(μ-Br)2] (3). Copper(II) complexes have been characterized by elemental analysis, IR, electronic spectra, single crystal X-ray diffraction and magnetic susceptibility measurements. Likewise, the crystal structure of DPhPyTn has been determined. Complexes 1 and 3 are dimeric molecules in which copper ions are bridged by two halide anions whereas 2 is a monomeric unit. The geometry around the copper(II) center in the dimeric units is a distorted squared pyramid, while in the monomeric compound is a distorted trigonal bipyramid. The magnetic susceptibility data of dimeric compounds were followed by the Bleaney–Bowers dimer equation with J=−1.17 and −2.36cm−1 for the chloro and bromo complexes respectively, indicating that there are weak antiferromagnetic interactions between the copper(II) ions in the solid state.

Fluoro and Trifluoromethyl Derivatives of POCOP-Type Pincer Complexes of Nickel: Preparation and Reactivities in SN2 Fluorination and Direct Benzylation of Unactivated Arenes

This report describes the synthesis, characterization, and reactivities of the pincer-type complexes κP,κC,κP-(R-POCOP)NiX (R-POCOP = 2,6-(i-Pr2PO)2,4-R-C6H3; R = H, X = F (2a), CF3 (3a); R = OMe, X = F (2b), X = CF3 (3b)). These complexes were prepared by treating their Ni–Br analogues with excess AgF at rt (2a and 2b) or excess AgF and Me3SiCF3 (3a and 3b) at 45 °C. The Ni–F derivative 2a was shown to be an intermediate for the formation of the Ni–CF3 derivative 3a. Complexes 2a, 3a, and 3b were fully characterized by multinuclear NMR spectroscopy, cyclic voltammetry, and X-ray diffraction analysis. Variable temperature, multinuclear NMR analysis of 2a helped elucidate interaction of the fluoride ligand with hydrofluoric acid present in the reaction medium. The bromo complexes 1a or 1b catalyzed fluorination of benzyl halides at 90 °C in the presence of excess AgF, whereas the Ni–CF3 complexes 3 failed to promote trifluoromethylation of benzyl bromide, leading instead to a direct benzylation of the aromatic reaction solvent (benzene, toluene, xylene, or bromobenzene). Possible mechanisms for this benzylation reaction have been probed and discussed.

The binding of platinum hexahalides (Cl, Br and I) to hen egg-white lysozyme and the chemical transformation of the PtI6 octahedral complex to a PtI3 moiety bound to His15.

This study examines the binding and chemical stability of the platinum hexahalides K2PtCl6, K2PtBr6 and K2PtI6 when soaked into pre-grown hen egg-white lysozyme (HEWL) crystals as the protein host. Direct comparison of the iodo complex with the chloro and bromo complexes shows that the iodo complex is partly chemically transformed to a square-planar PtI3 complex bound to the N(δ) atom of His15, a chemical behaviour that is not exhibited by the chloro or bromo complexes. Each complex does, however, bind to HEWL in its octahedral form either at one site (PtI6) or at two sites (PtBr6 and PtCl6). As heavy-atom derivatives of a protein, the octahedral shape of the hexahalides could be helpful in cases of difficult-to-interpret electron-density maps as they would be recognisable 'objects'.

Synthesis and characterisation of new PCsp3P-supported nickel complexes

The coordination behaviour of the aliphatic pincer ligand cis-1,3-bis-((di-tert-butylphosphino)methyl)cyclohexane with NiCl2 and NiBr2 was studied. Reflux in toluene afforded cyclometalated, tridentate PCsp3P pincer complexes, that were characterised by elemental analysis and NMR spectroscopy; the solid state structures were determined by X-ray diffraction showing an unusually long Ni–Br bond in the bromo complex. A preliminary account of their reactivity is reported and they were found to be unreactive towards base and hydride sources and to be poor catalysts in Kumada coupling reactions.

Calculated linear free energy relationships in the course of the Suzuki–Miyaura coupling reaction

Concerning the Suzuki–Miyaura coupling reaction, we report detailed theoretical study of thermodynamic data (at the B3PW91/LANL2DZ level with polarization functions added and including dispersion force corrections) concerning each step of the catalytic cycle. In each case, we have observed a Hammett plotting of δE or δG versus σp of substituent of various reagents, which accounts for multiple-substituent effects. Therefore, these calculations predict the influence of the electron-donor/electron-acceptor character of each substituents on the thermodynamic requirements for reaction. Our major conclusion is that the transmetalation between a palladium hydroxo complex and an arylboronic acid is preferable to the transmetalation with a palladium bromo complex. Moreover, the alkaline hydrolysis of palladium bromo complex appears as a strong exothermic reaction. Concerning the reductive elimination step alternative processes have been investigated.The overall process giving rise to biphenyls appears as a very strong exothermic reaction (∼−110 kcal/mol in ideal gas; ∼−95 kcal/mol using water as solvent).

Five new mononuclear zinc(II) complexes with a tetradentate N-donor Schiff base: Syntheses, structures and influence of anionic coligands on the luminescence behaviour and supramolecular interactions

The present report describes the syntheses, structures and luminescence properties of five mononuclear complexes, [Zn(L)Cl]ClO4 (1), [Zn(L)Br]ClO4 (2), [Zn(L)I]ClO4 (3), [Zn(L)N3]ClO4 (4), and [Zn(L)(NCS)](SCN) (5), derived from the tetradentate ligand L, N,N′-bis(2-pyridylmethylene)-1,3-propanediamine. The geometry around the Zn2+ centre is best described as square pyramidal, although significant distortion towards the trigonal pyramidal geometry is noticed, especially for the halide complexes, of the later, the chloro (1) and bromo (2) complexes are isostructural and isomorphous. The stabilization of the crystal lattices is maintained by interesting, relatively strong hydrogen bonds and π⋯π interactions which lead to various supramolecular architectures. All the five complexes show photoluminescence properties and their trend can be correlated with the position of the apical anionic coligands in the spectrochemical series of ligands.

Photo- and Vapor-Controlled Luminescence of Rhombic Dicopper(I) Complexes Containing Dimethyl Sulfoxide

Halide-bridged rhombic dicopper(I) complexes, [Cu2(μ-X)2(DMSO)2(PPh3)2] (X = I(-), Br(-); DMSO = dimethyl sulfoxide; PPh3 = triphenylphosphine), were synthesized, the iodide complex of which exhibited interesting photochromic luminescence driven by photoirradiation and by exposure to DMSO vapor in the solid state. Single-crystal X-ray diffraction measurements revealed that the iodo and bromo complexes (abbreviated Cu2I2-[O,O] and Cu2Br2-[O,O]) were isomorphous, and that the two DMSO ligands were coordinated to the Cu(I) ion via the O atom in both complexes. Both complexes exhibited bright blue phosphorescence at room temperature (λ(em) = 435 nm, Φ(em) = 0.19 and 0.14 for Cu2I2-[O,O] and Cu2Br2-[O,O], respectively) with a relatively long emission lifetime (τ(em) ~ 200 μs at 77 K) derived from the mixed halide-to-ligand and metal-to-ligand charge transfer ((3)XLCT and (3)MLCT) excited state. Under UV irradiation, the blue phosphorescence of Cu2Br2-[O,O] disappeared uneventfully and no new emission band appeared, whereas the blue phosphorescence of Cu2I2-[O,O] rapidly disappeared with simultaneous appearance of a new green emission band (λ(em) = 500 nm). On further irradiation, the green emission of the iodide complex gradually changed to bright yellowish-green (λ(em) = 540 nm); however, this change could be completely suppressed by lowering the temperature to 263 K or in the presence of saturated DMSO vapor. The initial blue phosphorescence of Cu2I2-[O,O] was recovered by exposure to DMSO vapor at 90 °C for a few hours. IR spectroscopy and theoretical calculations suggest that the DMSO ligand underwent linkage isomerization from O-coordination to S-coordination, and both the occurrence of linkage isomerization and the removal of DMSO result in contraction of the rhombic Cu2(μ-I)2 core to make the Cu···Cu interaction more effective. In the contracted core, the triplet cluster-centered ((3)CC) emissive state is easily generated by thermal excitation of the (3)XLCT and (3)MLCT mixed transition state, resulting in the green to yellowish-green emission. In contrast, the Cu···Cu distance in Cu2Br2-[O,O] is considerably longer than that of Cu2I2-[O,O], which destabilizes the (3)CC emissive state, resulting in the nonemissive character.

Spectrophotometric determination of the formation constants of the cupric halogen complexes with 1,3-propanediamine and 1,4-butanediamine in methanol solution and their activity on the oxidative coupling of the 2,6-di-tert-butylphenol

In order to understand the effect that diamine ligands induce in the cupric complexes used as catalyst in the oxidative coupling of 2,6-di-tert-butylphenol, a spectrophotometric study of the speciation of copper(II) with 1,3-propanediamine and 1,4-butanediamine both with Cl− or Br− in methanol solution, was carried out at 303K. The formation constants and the individual calculated electronic spectra of each species in methanol solution were obtained. The obtained formation constants for the copper(II)–1,3-propanediamine system are: log β110=6.70±0.06, log β120=11.59±0.09, while for the ternary-chloro or -bromo complexes are log β111=10.23±0.06 and log β111=10.39±0.02, respectively. On the other hand, for the copper(II)–1,4-butanediamine system are log β110=7.44±0.04, log β210=11.07±0.04, log β120=11.86±0.05, log β230=22.53±0.09, though for the ternary systems copper(II)–1,4-butanediamine–chloro or –bromo, the formation constants cannot be determined.A comparative study of the kinetics for the oxidation reaction of 2,6-di-tert-butylphenol, catalyzed using the different cupric complexes with 1,3-propanediamine or 1,4-butanediamine and –chloro or –bromo, has been carried out. The catalytic activity of each complex on the oxidation of 2,6-di-tert-butylphenol was monitored in methanol solution, following the corresponding quinone formation, at 418nm (ε=3.95×104Lmol−1cm−1 at 303K). These kinetic studies indicate that all the copper(II)–1,4-butanediamine complexes, show a remarkable high activity, while the complexes with 1,3-propanediamine are less active although much more active than 1,2-ethylenediamine complexes.

C–Br Activation of Aryl Bromides at Ni0(NHC)2: Stoichiometric Reactions, Catalytic Application in Suzuki–Miyaura Cross-Coupling, and Catalyst Degradation

Complex [Ni2(iPr2Im)4(COD)] (1) (iPr2Im = 1,3-diisopropylimidazolin-2-ylidene) is a very efficient catalyst for the Suzuki–Miyaura cross-coupling reaction of 4-bromotoluene with phenylboronic acid and also mediates the Ullmann-type homo-cross-coupling reaction of bromobenzene with a moderate efficiency. Stoichiometric reactions of complex 1 with aryl bromides (ArBr) at room temperature lead to mixtures of aryl bromo complexes of the type trans-[Ni(iPr2Im)2(Br)(Ar)] and the bis(bromo) complex trans-[Ni(iPr2Im)2(Br)2] 2. The complexes trans-[Ni(iPr2Im)2(Br)(Ar)] (for Ar = Ph 3, 4-MeC6H44, 4-Me(O)CC6H45, 4-MeOC6H46, 4-MeSC6H47, 4-Me2NC6H48, 2-C5NH49) can be selectively synthesized by working at low temperatures and using a high dilution of the starting materials. A major deactivation pathway for trans-[Ni(iPr2Im)2(Br)(Ar)] was identified in the presence of aryl bromides. This deactivation process includes (i) the formation of trans-[Ni(iPr2Im)2(Br)2] from trans-[Ni(iPr2Im)2(Br)(Ar)] (2) and ArBr and (ii) the formation of an imidazolium salt of the type 2[iPr2Im-Ar]+[NiBr4]2– from trans-[Ni(iPr2Im)2(Br)2] (2) and ArBr. The reactions of complex 2 with a series of aryl halides at higher temperatures lead to the decomposition of the bis(carbene) nickel moiety with formation of the imidazolium salts 2[iPr2Im-Ar]+[NiBr2X2]2– (for X = I, Ar = Ph 10 and X = Br, Ar = Ph 11, 4-MeC6H412, 4-FC6H413, 4-OSi(CH3)3-C6H414) in high yields.