Homogeneous oxidative coupling catalysts: stoichiometry and characterization of the first stable oxotetranuclear solids [(Pip)nCuX]4O2 (n=1 or 2, Pip=piperidine, X=Cl, Br, I)

Copper(I) halides react quantitatively with piperidine (Pip) in dioxygen-free methylene chloride or nitrobenzene to form tetranuclear copper(I) complexes [(Pip)_nCuX]₄; n=1 or 2, X=Cl, Br or I. These complexes are very soluble and completely reduce dioxygen to dioxo bridging ligand, with stoichiometry, Δ[Cu(I)]/Δ[O₂]=4.0. The stable oxo solids [(Pip)_nCuX]₄O₂ mimic tyrosinase copper protein. They act as a homogeneous oxidative coupling catalysts for phenols. Electronic transition spectra in the near infrared with high molecular absorptivity are diagnostic for tetranuclear “Cu₄X₄” core structure. The electronic transitions are more likely due to charge transfer between a minimum of three halo ligands and copper(II) center. The room temperature EPR spectra of [(Pip)_nCuX]₄O₂ in methylene chloride are isotropic with four hyperfine lines. The room temperature solid-state EPR spectra of [PipCuX]₄O₂ show an axial spectra with d_x²−y² ground state, suggesting square pyramidal arrangement of the five coordinated ligands around copper(II) centers. Cyclic voltammetry measurements show that they are more likely irreversible in character and show slight quasi-reversability when X=Br or I. Constant potential electrolysis indicate that the number of electrons consumed are equal to four electrons which will be due to the reduction of four copper(II) to copper(I).     

Metal-metal bonding and charge localisation in [Ru2X9], X=Cl or Br; n=1, 2, 3, 4. A spectroelectrochemical study

A spectroelectrochemical study of [Ru₂X₉]ⁿ⁻, X=Cl, Br; n=1, 2, 3, 4 has been undertaken. Stable solutions of n=4, 2, 1 can be formed by electrolysis at low temperatures. Analysis of the Vis-NIR spectra of the complexes indicate that the Ru^II---R^III dimers (n=4) have delocalised mixed valence and that the Ru^III---R^III (n=3) dimers have a strong Ru---Ru bond. The more oxidised materials do not form a Ru---Ru bond; the spectroscopic data indicates the Ru^III---R^IV dimers have localised valency.     

Co-ordination compounds derived from dimethylhydrazones of cyclohexane-1,2-dione, 2-acetyl- and 2-benzoylpyridines and 4-bezoylpyridine

The 1,1-dimethylhydrazones of cyclohexane-1,2-dione (CDDMH), 2-acetylpyridine (APDMH) and 2-benzoylpyridine (2BPDMH) from tetrahedral complexes MX₂L (M = Co(II), Zn(II); X = Cl, Br) in which the ligand is chelating through the methylene nitrogen atoms (CDDMH) or one methylene and one pyridine nitrogen atom (APDMH, 2BPMDH). Octahedral complexes CoX₂L₂ (X = Cl, NCS; L = APDMH, 2BPDMH) have also been isolated but no tris-ligand complexes. The ligand 4-benzoylpyridine-dimethylhydrazone (4BPDMH) does not chelate but forms tetrahedral complexes MX₂(4BPDMH)₂ in which the unidentate ligand co-ordinates through the pyridine nitrogen atom.     

Tellurium tetrahalides in rubber chemistry: Some new tellurium(IV) complexes with an S2X4 (X = halogen) ligand environment

The reaction of tellurium tetrahalides with natural rubber parallels closely reactions with model compounds such as cyclohexene and 2-methyl- pent-2-ene carried out under similar conditions. In both cases an α-elimination reaction of an ‘organic halide’ with deposition of elemental tellurium is a dominant process, but some evidence for cross- linking of natural rubber is obtained. If methyl cyanide is the solvent for cyclohexene, or if a nitrile rubber is used, elimination of tellurium is inhibited.Tellurium tetrachloride enhances the rate and density of cross-link formation when added to tetramethylthiuram disulphide (TMTD) based natural rubber vulcanisates, but this effect is negated in the presence of triphenylphosphine. TeCl₄ reacts with TMTD to eliminate an atom of sulphur and to form a complex of tetramethylthiuram monosulphide (TMTM) viz. [Te(TMTM)Cl₄]. Corresponding bromo- and iodo-complexes have been prepared, the iodo- complex is a 1:1 electrolyte. ¹²⁵Te Mössbauer data for the complexes are briefly discussed.Further reactions of the complexes are described which lead to the formation of: [Te(TMTM)Cl₂(O)(pyridine)], [Te(TMTM)X₂(O)] (X=Br, I), and [Cu(TMTM)₂] [TeCl₅]₂. Organyltellurium(IV) trihalides also react with TMTD to release sulphur and give complexes of TMTM, i.e. [(p-EtO·C₆H₄)Te- X₃]₂(TMTM) (X=Cl, Br, I).     

Chalcogen- and halogen-bonds involving SX<Subscript>2</Subscript> (X = F,Cl, and Br) with formaldehyde

The capacity of SX₂ (X = F, Cl, and Br) to engage in different kinds of noncovalent bonds was investigated by ab initio calculations. SCl₂ (SBr₂) has two σ-holes upon extension of Cl (Br)?S bonds, and two σ-holes upon extension of S?Cl (Br) bonds. SF₂ contains only two σ-holes upon extension of the F?S bond. Consequently, SCl₂ and SBr₂ form chalcogen and halogen bonds with the electron donor H₂CO while SF₂ forms only a chalcogen bond, i.e., no F···O halogen bond was found in the SF₂:H₂CO complex. The S···O chalcogen bond between SF₂ and H₂CO is the strongest, while the strongest halogen bond is Br···O between SBr₂ and H₂CO. The nature of these two types of noncovalent interaction was probed by a variety of methods, including molecular electrostatic potentials, QTAIM, energy decomposition, and electron density shift maps. Termolecular complexes X₂S···H₂CO···SX′₂ (X = F, Cl, Br, and X′ = Cl, Br) were constructed to study the interplay between chalcogen bonds and halogen bonds. All these complexes contained S···O and Cl (Br)···O bonds, with longer intermolecular distances, smaller values of electron density, and more positive three-body interaction energies, indicating negative cooperativity between the chalcogen bond and the halogen bond. In addition, for all complexes studied, interactions involving chalcogen bonds were more favorable than those involving halogen bonds.

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Graphical Abstract Molecular electrostatic potential and contour map of the Laplacian of the electron density in Cl₂S···H₂CO···SCl₂ complex

     

Synthesis and characterization of [Fe2OX6]2tau; (X = Cl,Br, I) complexes. Crystal and molecular structure of (BzPh3P)2 [Fe2OCl6]

Improved and simple methods for the preparation of [Fe₂OX₆]^2tau; (X = Cl Br I) complexes are described. The complexes were obtained in high and purified yields as the BzPh₃P⁺ or R₄N⁺ salts. An X-ray crystallographic study of (BzPh₃P)₂ [Fe₂OCl₆] revealed a structure for the complex anion in which the two iron atoms are linked by gdot; -oxo bridge and the terminal coordination sites are occupied by the chloride ligands. Mcolon; ssbauer and infrared spectra for the complexes are reported.     

Synthesis and reactions of [M(CO)4(Ph2PSiMe3)X] complexes (M = Mn,Re; X = Halogen)

The silylphosphine ligand Ph₂PSiMe₃ reacts readily with a slurry of [Re(CO)₅X] (X  Cl, Br) in polar and in non-polar solvents to yield soluble cis-[Re(CO)₄- (Ph₂PSiMe₃)X] (Ia, X  Cl;Ib, X  Br) via CO substitution. Compound I is readily hydrolyzed by water or silica gel to cis-[Re(CO)₄(Ph₂PH)X]. Compound Ib reacts with [Re(CO)₅Br] to yield [Re₂(CO)₈(μ-PPh₂)- (μ-Br)] (II), and with [Mn(CO)₅Br] to yield [MnRe- (CO)₈(μ-PPh₂)(μ-Br)] (III).The reaction of Ph₂PSiMe₃ with [Mn(CO)₅X] (X=Cl,Br,I) is highly dependent upon reaction conditions.In polar and in non-polar solvents, an excess of ligand gives mainly cis-[Mn(CO)₄(Ph₂PSiMe₃)X] (IVa, X  Cl;IVb, X  Br;IVc, X I). With ligand: [Mn(CO)₅X] reacting ratios in the range 0.5–1.0:1, the products from the three respective halomanganese complexes in THF were: (a) mainly [Mn₂(CO)₈(μ- PPh₂)(μ-Cl) (Va); (b) both [Mn(CO)₄(Ph₂PSiMe₃)Br] and [Mn₂(CO)₈(μ-PPh₂)(μ-Br)] (Vb); and (c) exclusively [Mn(CO)₄(Ph₂PSiMe₃)I]. The compounds IVa-c are stable in solution at ambient temperatures and are readily hydrolyzed by water or methanol to [Mn(CO)₄(Ph₂PH)X]. Compound IVb reacts at room temperature with [Mn(CO)₅Cl] to yield only [Mn₂- (CO)₈(μ-PPh₂)(μ-Br)] (Vb); compound IVc reacts in hot toluene with [Mn(CO)₅Cl] to yield mainly [Mn₂(CO)₈(μ-PPh₂)(μ-I)] (Vc), together with a small amount of the chloro-bridged analog.The dinuclear species II, III and Va-c appear to be formed mainly via an intermolecular elimination of Me₃SiX from the appropriate [M(CO)₄(Ph₂PSiMe₃)X] and metalpentacarbonylhalide (chloride or bromide) complexes.     

Cobaltocene reductions of multiply bonded dirhenium complexes. II. The isolation of the paramagnetic species [(η5-C5H5)2Co][Re2(hp)4X2] (hp = anion of 2-hydroxypyridine; X = Cl,Br, or I)

Reaction of the quadruply bonded dirhenium(III) complexes (n-Bu₄N)₂Re₂X₈ (X = Cl, Br, or I) with 2-hydroxypyridine (Hhp) in refluxing n-pentanol gives Re₂(hp)₄X₂ in high yield (>;90%). These complexes are reduced by cobaltocene to yield the paramagnetic salts [(η⁵-C₅H₅)₂Co][Re₂(hp)₄X₂]. The spectroscopic (electronic absorption and infrared) and electrochemical properties of these sets of complexes are in accord with them possessing σ²π⁴δ²(Re₂⁶⁺) or σ²π⁴δ²δ*¹(Re₂⁵⁺ ground state electronic configurations.     

Metal complexes of 1-methyl-3,4-diphenylpyrazole,a ligand formed by the reaction between benzil and N,N,-dimethylhydrazine

New complexes of the general formulae MnX₂L₂ (X = Cl,Br), MnBr₂L₃, CoX₂L₂ (X = Cl, Br, I, NCS, NO₃), NiX₂L₂ (X = Cl, NO₃), NiBr₂L₃·H₂O, NiL₂L₄·H₂O, CuCl₂L, CuBr₂L₂·H₂O, Cu(NO₃)₂L₂, ZnX₂L₂ (X = Cl, Br, NO₃, Zn(NCS)₂L₂·H₂O, CdX₂L₂ (X = I, NO₃) and HgCl₂L, where L is 1-methyl-3,4-diphenylpyrazole, have been prepared and characterized by elemental analysis, conductivity measurements, magnetic moments and spectral (¹H-NMR, IR and electronic) studies. The ligands is formed by the reaction between benzil and N,N-dimethylhydrazine. The nitrogen of the >CN bond is the donor atom to the metal ions. The bis-ligand halide complexes are pseudotetrahedral, while the nitrate complexes contain octahedrally coordinated metal ions. The IR spectra of MCl₂L (M = Cu, Hg) are indicative of the presence of both terminal and bridging metal-halogen bonds supporting polymeric structures. The stereochemistry and the nature of the nickel(II) complexes are markedly dependent upon the anions; the chloride complex is pseudotetrahedral, the iodide square planar, the nitrate polymeric octahedral, while the proposed structural formula for NiBr₂L₃·H₂O comprises Nickel(II) atoms present in both square planar and octahedral coordination environments.     

Insight into the lithium/hydrogen bonding in (CH<Subscript>2</Subscript>)<Subscript>2</Subscript>X...LiY/HY (X: C=CH<Subscript>2</Subscript>, O,S; Y=F,Cl, Br) complexes

The nature of the lithium/hydrogen bonding between (CH₂)₂X(X: C=CH₂, O, S) and LiY/HY(Y=F, Cl, Br) have been theoretically investigated at MP2/6-311++G (d, p) level, using Bader’s “atoms in molecules (AIM)” theory and Weinhold’s “natural bond orbital (NBO)” methodology. The molecule formation density differences (MFDD) of the titled complexes are analyzed. Two kinds of geometries of the lithium/hydrogen bonded complexes are compared. As a whole, the nature of lithium bond and hydrogen bond are different. For the same electron donor and the same acceptor, lithium bond is stronger than hydrogen bond. For the same electron acceptor and different kind of donors, the interaction energies follows the n-type> π-type > pseudo-π-type order. For the same (CH₂)₂X, the interaction energy increases in the sequence of Y=F, Cl and Br for lithium bond systems while it decreases for hydrogen bond systems. Electron transfer plays an important role in the formation of lithium bond systems while it is less important in the hydrogen bond systems.     

N-(2-Pyridyl)acetamide complexes of palladium(II), cobalt(II), nickel(II), and copper(II)

N-(2-Pyridyl)acetamide (aapH) complexes of palladium(II), cobalt(II), nickel(II), and copper(II) have been studied by means of magnetic susceptibilities, and infrared, electronic, and PMR spectra. In the octahedral complexes M(aapH)₂X₂(M = Co, Ni, Cu; X = Cl, Br, NCS, NO₃), bidentate aapH is chelated through the pyridine-N and amid-O atomes, whereas in the square-planar Pd(aapH)₂X₂ (X = Cl, Br) unidentate aapH is coordinated through the pyridine-N atom alone. Under alkaline conditions aapH is deprotonated in the presence of palladium(II) to form Pd(aap)₂·4H₂O, aap being an anionic bidentate ligand and chelating through the pyridine-N and amide-O atoms.     

Computational characterisation of the charge-transfer and T-shaped molecular complexes of N-methyl imidazoline-2-thione and N-methyl imidazolidine-2-thione with the dihalogens Br2 and I2

The computational characterisation of the molecular complexes of N-methyl imidazoline-2-thione (methimazole) and the related saturated analogue N-methyl imidazolidine-2-thione with Br₂ and I₂ is carried out using quantum mechanical electronic structure methods. Two kinds of molecular connectivity have been examined. The first displays a collinear S–X–X geometry (X = Br, I) and leads to charge-transfer (CT) type adducts, possible in two stereoisomeric conformations depending on the direction of the X₂-axis, either planar or perpendicular to the NCS plane. The second kind corresponds to T-shaped hypervalent complexes in which sulphur is connected to both the X atoms forming the linear X–S–X arrangement. The structural changes, the spectroscopic findings, the natural bond orbital analysis and the examination of the molecular orbital second-order perturbation energies give interesting information about the nature of the halogen bonding interaction between the electron-donor organic species and the electron-acceptor dihalogen molecule. Similar trends are followed by the energy and relative stability results including basis set superposition error corrections, which show the larger stabilisation of the planar CT conformers of both dihalogens vs. the perpendicular configurations. They also indicate the higher stability of the T-shaped bromine complexes relative to the CT species, opposite to the energy order of the corresponding diiodine adducts. A critical comparison is carried out with literature results on similar systems.     

The coordination chemistry of N-(2-pyridyl)pyridine-2′-carboxamide; A potentially tridentate ligand containing one secondary amide and two 2-pyridyl donor groups

New complexes of the general compositions M(LH)X₂ (M = Co, Zn; X = Cl, Br, I), Zn(LH)(NCS)₂, Zn(LH)(NO₃)₂ ·H₂O, Cu(LH)X₂ (X = Cl, Br, ONO₂), Ni(LH)Cl₂·H₂O, Co(LH)₂X₂ (X = NCS, ONO ₂), Ni(LH)₂X₂ (X = Cl, Br, NCS, ONO₂), Pt(LH)₂Cl₂ and MLCl·nH₂O (M = Ni, Cu, Pd; n = 2, 3), where LH = N-(2-pyridyl)pyridine-2′-carboxamide, have been isolated. The complexes were characterized by elemental analyses, conductivity measurements, X-ray powder patterns, thermal methods, magnetic susceptibilities and spectroscopic (IR, ligand field, ¹H NMR) studies. Pseudotetrahedral, square planar, square pyramidal and distorted octahedral stereochemistries are tentatively assigned in the solid state. Most complexes appear to be monomeric, while polymeric structural types are attributed for Ni(LH)Cl₂·H₂O and CuLCl·2H₂O. The neutral amide group of LH is coordinated to Co(II), Ni(II), Cu(II) and Zn(II) through oxygen, while N-coordination is observed for PdLCl·2H₂O. The amide group of L⁻ is bound to different Cu(II) atoms in CuLCl·2H₂O through both its nitrogen and oxygen. The rare O-coordination of the deprotonated amide bound is proposed for NiLCl· 3H₂O. The N(1) atom is not involved in coordination except in the complexes Ni(LH)Cl₂·H₂O, NiLCl· 3H₂O and CuLCl·2H₂O, where both pyridine residues are coordinated. The variation in structural types observed is believed to be a consequence of the stereochemical adaptability of the ligand to the electronic demands of the metal ions.     

CO-loss and geometric isomerization in the frozen matrix photochemistry of cis-Fe(CO)4X2, where X = Br and I, cis-[Et4N][Mn(CO)4Br2], cis-Mn(CO)4(PBu3)Br, and Mn(CO)3(PBu3)2Br

Photolysis of cis-Fe(CO)₄X₂, where X = Br and I, results in low energy, facile rearrangement to the trans isomer with no evidence of CO-loss. In contrast, the isoelectronic cis-Mn(CO)₄Br₂ anion exhibits CO-loss upon photolysis with only weak evidence for the trans isomer. The photolysis of Mn(CO)₅Br, Mn(CO)₄Br(PBu₃) and Mn(CO)₃Br(PBu₃)₂ have also been examined in frozen matrices.     

Preparation and characterisation of Ni(II), Pd(II) and Pt(II) complexes of 1-diphenylphosphino-2-bis (m -trifluoromethylphenyl)phosphinoethane,(m -CF3 P-P)

A series of four-coordinate, square-planar, dia- magnetic 1-diphenylphosphino-2-bis(_m-trifluoro- methylphenyl)phosphinoethane complexes of type cis-[MX₂(_m-CF₃P-P)] (M = Ni, Pd, Pt; X = Cl, Br, I or NCS) have been prepared. These complexes have been characterized by ³¹P {₁H} NMR, ¹H NMR, IR and UV spectroscopy, elemental analyses and magnetic susceptibility measurements. The effects of various substituents on the phenyl groups of the ditertiary phosphines on the solubility characteristics of the metal complexes are discussed.     

The coordination chemistry of N-(2-aminophenyl)- and N-(3-aminophenyl)quinoline-2′-carboxamide; two potentially tridentate ligands containing secondary amide and N-donor groups

New complexes of the general formulae Co(o-LH)₂X₂ (XCl, NCS), Co(o-LH)₂Br₂·EtOH (EtOHethanol), M(o-LH)(NO₃)₂ (MCo, Ni), Ni(o-LH)₂X₂ (XCl, Br, NCS), Cu(o-L)X (XCl, Br), Zn(o-LH)X₂ (XCl, Br), Pd(o-L)Cl, Pt(o-LH)₂Cl₂·H₂O, M(m-LH)Cl₂·nH₂O (MCo, Ni, Pd; n=0, 0.5, 1), Cu(m-LH)Cl₂·EtOH, M(m-LH)₂Cl₂·nH₂O (MCo, Zn, Pt; n=0, 1), M(m-LH)Br₂ (MCu, Zn), M(m-LH)₂Br₂ (MCo, Ni), Co(m-LH)(NCS)₂ and Co(m-LH)₂(NCS)₂, where o-LH=N-(2-aminophenyl)quinoline-2′-carboxamide and m-LH=N-(3-aminophenyl)quinoline-2′-carboxamide, have been prepared. The complexes were characterised by elemental analyses, conductivity measurements, X-ray powder patterns, thermogravimetric analyses, magnetic moments and spectral (¹H NMR, IR, and electronic) studies. Copper(II) and palladium(II) promote amide deprotonation at nearly acidic pH on coordination with o-LH. A variety of stereochemistries is assigned for the complexes prepared. The deprotonated copper(II) and the nickel(II) and palladium(II) complexes of m-LH appear to be polymeric. The neutral amide group of the ligands is coordinated to the metal ions through oxygen, while N(amide)-coordination is observed for the deprotonated complexes. Coordination of the secondary amide group is not observed for Zn(m-LH)₂Cl₂, Pd(m-LH)Cl₂·0.5H₂O and platinum(II) complexes. The neutral ligand o-LH shows bidentate N(ring), O-behaviour, while the anion o-L⁻ exhibits tridentate N,N,N-coordination. m-LH acts as a monodentate, bidentate and tridentate ligand depending on the metal ion, the anion and the preparative conditions.     

Quantum chemical topological analysis of hydrogen bonding in HX…HX and CH3X…HX dimers (X = Br,Cl, F)

We present a systematic investigation of the nature and strength of the hydrogen bonding in HX···HX and CH₃X…HX (X = Br, Cl and F) dimers using ab initio MP2/aug-cc-pVTZ calculations in the framework of the quantum theory of atoms in molecules (QTAIM) and electron localisation functions (ELFs) methods. The electron density of the complexes has been characterised, and the hydrogen bonding energy, as well as the QTAIM and ELF parameters, is consistent, providing deep insight into the origin of the hydrogen bonding in these complexes. It was found that in both linear and angular HX…HX and CH₃X…HX dimers, F atoms form stronger HB than Br and Cl, but they need short (～2 Å) X…HX contacts.     

The multidentate chemistry of manganese(II). III. Complexes of linear quadridentate nitrogenous ligands

Linear quadridentate nitrogenous ligands have been shown to yield three different types of Manganese(II) compound. Simple octahedral compounds of formulation Mn(quad)X₂*(where X = Cl, Br, ClO₄ or BPh₄) are obtained with most ligands. However, with sterically rigid ligands, compounds of the type [Mn(quad)₂]X₂ (X = ClO₄ or BPh₄, possibly 8-coordinate) can also be prepared, while on the other hand with less rigid ligands, bridged dimers of the type [Mn₂(quad)₃]X₄ (X = ClO₄ or BPh₄) are also obtained.     

Suppressing X‐Migrations and Enhancing the Phase Stability of Cubic FAPbX3 (X = Br,I)

Chemical bonding of formamidinium (FA) with the inorganic perovskite skeleton of FAPbX₃ (X = Br, I) is studied with emphasis on the differences to methylammonium: stronger hydrogen bonding, the presence of π‐anion bonding, and more sterically hindered motion inside the perovskite inorganic cage. Organic cation dopants fitting in the perovskite cubic cell and being capable of hydrogen and halogen bonding with overall doubled bonding strength as compared to FA are proposed. They are shown to suppress not only X‐migrations but also the undesirable α–δ phase transition of FAPbI₃. In addition, a possible atomistic explanation of the champion solar cell efficiency achieved experimentally is developed.     

M2X (M= Li,Na; X= F,Cl): the smallest superalkali clusters with significant NLO responses and electride characteristics

Hypervalent M₂X (M = Li, Na; X = F, Cl) clusters are prototype species possessing lower ionisation potentials than Li, therefore classified as superalkalis. This study reveals some interesting properties of these small clusters using ab initio MP2/aug-cc-pVTZ and QCISD/aug-cc-pVTZ methods. These clusters are shown as an ionic species, composed of positively charged cage of alkali metals (M₂⁺) and halogen anion (X^?). Therefore, the stability of M₂X is governed by both ionic and covalent interactions. We show that the excess valence electron of (M₂⁺) is pushed out by anionic X^?, which allows M₂X clusters to possess ‘electride’ characteristics. It is also due to this excess electron that M₂X clusters exhibit significant non-linear optical (NLO) properties. The dipole moment, mean polarisability and hyperpolarisability suggest their significant NLO responses, which are explained on the basis of electronic transitions in crucial excited states using TD-B3LYP/aug-cc-pVTZ method. The first static hyperpolarisabilities of Li₂F and Na₂F take the values of order of 10⁴ a.u. due to their lower transition energies. This study should provide new insights into the design of novel materials with significant NLO responses useful for electro-optical applications.