Synthesis and structural characterization of iron–sulfur complexes with hydrophilic nitrogen–phosphorus ligands

Reaction of the parent complex (μ-PDT)Fe₂-(CO)₆ (A) (PDT = 1,3-SCH₂CH₂CH₂S^2?) with the bidentate N/P ligand [(Ph₂P)₂N(C₆H₄Cl-p)] in the presence of Me₃NO as decarbonylating agent produced an unexpected iron–sulfur complex [(μ-PDT)Fe₂(CO)₅{PPh₂(NHC₆H₄Cl-1,4)}] (1). Extending this chemistry further, two similar complexes [(μ-PDT)Fe₂(CO)₅{PPh₂(NHC₆H₄NO₂-1,4)}] (2) and [(μ-PDT)Fe₂(CO)₅{PPh₂(NHC₆H₄CO₂Et-1,4)}] (3) could be prepared from the simple substitution reactions of the precursor A with the monodentate N/P ligands Ph₂P(NHC₆H₄NO₂-1,4) and Ph₂P(NHC₆H₄CO₂Et-1,4), respectively. These new complexes, which can be considered as active site models of [FeFe] hydrogenases, have been characterized by elemental analysis, FTIR, and NMR (¹H, ¹³C, ³¹P) spectroscopies, as well as by X-ray crystallography for complex 1.     

Synthesis and characterization of half-sandwich ruthenium(II) complexes with N-alkyl pyridyl-imine ligands and their application in transfer hydrogenation of ketones

A series of new arene ruthenium(II) complexes were prepared by reaction of ruthenium(II) precursors of the general formula [(η⁶-arene)Ru(μ-Cl)Cl]₂ with N,N′-bidentate pyridyl-imine ligands to form complexes of the type [(η⁶-arene)RuCl(C₅H₄N-2-CH=N-R)]PF₆, with arene = C₆H₆, R = iso-propyl (1a), tert-butyl (1b), cyclohexyl (1c), cyclopentyl (1d) and n-butyl (1e); arene = p-cymene, R = iso-propyl (2a), tert-butyl (2b). The complexes were fully characterized by ¹H NMR and ¹³C NMR, UV–Vis and IR spectroscopies, elemental analyses, and the single-crystal X-ray structures of 2a and 2b have been determined. The single-crystal molecular structure revealed both compounds with a pseudo-octahedral geometry around the Ru(II) center, normally referred to as a piano stool conformation, with the pyridyl-imine as a bidentate N,N ligand. The activity of all complexes in the transfer hydrogenation of cyclohexanone in the presence of NaOH and iso-propanol is reported, the compounds showing turnover numbers of close to 1990 and high conversions. Complex 2b was also shown to be very effective for a range of aliphatic and cyclic ketones, giving conversions of up to 100 %.     

Directed assembly of cobalt(II) 1-H-indazole-3-carboxylic acid coordination networks by bipyridine and its derivatives: structural versatility,electrochemical properties,and antifungal activity

This paper describes the hydrothermal synthesis, full characterization, and architectural diversity of three intriguingly bioactive cobalt–organic frameworks, namely, 3D [Co(HL ^? )₂(BPY)] _n ·4nH₂O (1), 2D [Co(HL ^? )₂(BPE)] _n (2), and 2D [Co(HL ^? )₂(DPP)] _n (3) coordination polymers, synthesized through a mixed ligand strategy using H ₂ L (1-H-indazole-3-carboxylic acid) as a main structural block and the flexible bipyridine and its derivatives (BPY = 4,4′-bipydine, BPE = 1,2-bis(4-pyridyl)ethane, DPP = 1,3-bis(4-pyridyl)propane) as auxiliary ligand sources. Complexes 1–3 were isolated as air stable and slightly soluble crystalline solids and characterized using elemental analysis, FT-IR, electrochemical technique, thermogravimetric analysis, powder X-ray diffractometer, and single-crystal X-ray crystallography. The bipyridine derivatives played key roles in defining the structural space group and dimensionality feature of the obtained networks. The abundant H-bonding and π–π stacking interactions in complexes 1–3 gave rise to their intricate metal–organic structures of 3D (1), 2D (2), and 2D (3). In addition, the solutions of complexes 1–3 showed profound antifungal activities against the selected strain of Colletotrichum musae compared with the controlled group using benomyl as a traditional agrochemical fungicide.     

Synthesis,crystal structures and photocatalytic properties of four silver(I) coordination polymers based on semirigid bis(pyrazole) and carboxylic acid co-ligands

Four Ag(I) coordination polymers, formulated as [Ag(L1)(tpa)_0.5] _n (1), {[Ag(L2)(ndc)_0.5]·0.5H₂ndc} _n (2), [Ag(L3)_0.5(ndc)_0.5] _n (3) and {[Ag(L3)]·H₃bptc} _n (4) (L1 = 4,4′-bis(pyrazole-1-ylmethyl)-biphenyl, L2 = 4,4′-bis(3,5-dimethylpyrazol-1-ylmethyl)-biphenyl, L3 = 1,4-bis(3,5-dimethylpyrazol-1-ylmethyl)benzene, H₂tpa = terephthalic acid, H₂ndc = 2,6-naphthalenedicarboxylic acid, H₄bptc = 3,3′,4,4′-biphenyltetracarboxylic acid), have been hydrothermally synthesized and structurally characterized. Complex 1 features the rare binodal (4,4)-connected 2D 4,4L10 topological network with a point symbol of {3²·4.6²·7}₂{3²·6²·7²}. Complex 2 has a folded ladder-like chain structure, which is further extended into a 3D supramolecular network via O–H···O hydrogen bonding and π···π stacking interactions. Complexes 3 and 4 both possess 1D zigzag chain structures. Complex 3 is further extended into a binodal (3,4)-connected network with the point symbol of {4.8⁴·10}{6²·8²}₂ by Ag···O weak interactions, while complex 4 is further connected through O–H···O hydrogen bonding and π···π interactions to afford a 2D supramolecular structure. The photoluminescence spectra and photocatalytic properties of these complexes for degradation of methylene blue and methyl orange are reported.     

Synthesis,characterization, and crystal structures of 2D cobalt(II) and nickel(II) coordination polymers containing flexible bis(benzimidazole) ligands

Three coordination polymers, namely {[Ni(L1)(nip)(H₂O)]·2H₂O} _n (1), [Co(L2)(tbip)] _n (2), and {[Co₂(L3)₂(bptc)]·3H₂O} _n (3) (L1 = 1,4-bis(5,6-dimethylbenzimidazole)butane, L2 = 1,4-bis(5,6-dimethylbenzimidazole)-2-butylene, L3 = 1,3-bis(5,6-dimethylbenzimidazole)propane, H₂nip = 5-nitro-isophthalic acid, H₂tbip = 5-tert-butyl-isophthalic acid, H₄bptc = biphenyl-3,3′,4,4′-tetracarboxylic acid), have been synthesized under hydrothermal conditions and characterized by physicochemical and spectroscopic methods as well as by single-crystal X-ray diffraction analysis. Complexes 1 and 2 both feature a two-dimensional (4,4) layer with (4⁴ × 6²) topology. Complex 3 possesses a uninodal 4-connected 2D htb network. The fluorescence spectra and catalytic properties of the complexes for the degradation of methyl orange by sodium persulfate in a Fenton-like process are reported.     

A Series of Dimeric Selenidogermanates with Lanthanide Complexes of Multidentate Chelating Amines

A series of lanthanide selenidogermanates (H₃O)[Tm(teta)₂][Ge₂Se₆] (1, teta = triethylenetetramine) and [Ln(teta)(tren)Cl]₂[Ge₂Se₆](en) {en = ethylenediamine, tren = N,N,N- tris(2-aminoethyl)amine, Ln = Pr (2a), Nd (2b), Sm (2c), Eu (2d), Gd (2e), Tb (2f)}were prepared under mild solvothermal conditions and structurally characterized. 1 contains isolated [Tm(teta)₂]³⁺ ions, protonated H₃O⁺ ions and dimeric [Ge₂Se₆]^4? anions, while 2a–f are composed of [Ln(teta)(tren)Cl]³⁺ ions, dimeric [Ge₂Se₆]^4? anions and free en molecules. The lighter lanthanide ions (Pr–Tb) adopt a distorted tricapped trigonal prism with the nine-coordinated number, and the heavier Tm³⁺ ion adopts a distorted bicapped trigonal prism with the eight-coordinated number. Their band gaps in the range of 1.52–1.86 eV are derived from optical absorption spectra.     

Hexa(isothiocyanato)chromates(III) of Some Yttrium Group Lanthanide(III) and Europium Complexes with Nicotinic Acid: Synthesis and Crystal Structures

Double ionic complexes [M(C₅H₅NCOO)₃(H₂O)₂][Cr(NCS)₆] · nH₂O, where M = Eu (I), n = 1.15; Dy (II), Er (III), n = 1.5; M = Yb (IV), n = 2, have been synthesized by the reaction between M(NO₃)₃, M = Eu, Dy, Er, Yb, K₃[Cr(NCS)₆], and nicotinic acid (C₅H₅NCOO) in an aqueous solution and studied by chemical analysis, IR spectroscopy, and X-ray diffraction. Crystals of complexes I–IV are monoclinic, space group P2₁/n, Z = 4; a = 9.5358(2) Å, b = 25.4871(5) Å, c = 15.4303(4) Å, β = 105.513(1)°, V = 3613.6(1) ų, ρ_calcd = 1.799 g/cm³ for I, a = 9.5901(5) Å, b = 25.8599(15) Å, c = 15.6316(9) Å, β = 106.829(2)°, V = 3710.6(4) ų, ρ_calcd = 1.782 g/cm³ for II, a = 9.5640(3) Å, b = 25.8936(11) Å, c = 15.6498(7) Å, β = 106.895(2)°, V = 3708.3(3) ų, ρ_calcd = 1.791 g/cm³ for III, and a = 9.5049(2) Å, b = 25.6378(4) Å, c = 15.5120(3) Å, β = 106.934(1)°, V = 3616.1(1) ų, ρ_calcd = 1.864 g/cm³ for IV.     

A New Three-Dimensional Framework Based on K<Subscript>2</Subscript>Zr<Subscript>3</Subscript>-Substituted Sandwich-Type Polyoxometalate Clusters and K–O Chains

A new Zr-substituted sandwich-type polyoxometalate, H₈K₃[Zr₃K₂(μ₃-O)₂(μ₂-OH)(H₂O)₂(A-α-PW₉O₃₄)₂]·2Cl^?·7H₂O (1), has been made under hydrothermal conditions. 1 was characterized by IR spectrum, thermogravimetric analysis, powder X-ray diffraction and single-crystal X-ray diffraction, respectively. Crystal data for 1: tetragonal space group P4₂2₁2, a = 24.0096(3), b = 24.0096(3), c = 14.7416(3) Å, V = 8498.0(2) Å³ and Z = 4. Single crystal X-ray structure analysis reveals that 1 exhibits a three-dimensional framework structure based on Zr₃K₂-substituted sandwich-type polyanions [Zr₃K₂(μ₃-O)₂(μ₂-OH)(H₂O)₂(PW₉O₃₄)₂]^9? linked by K–O chains. UV–Vis spectrum indicates that 1 is a wide-gap semiconductor. In addition, the SHG of 1 was also investigated.     

Diverse topologies of three cobalt(II) coordination polymers constructed from flexible bis(benzimidazole) and dicarboxylate ligands

Three cobalt(II) coordination polymers {[Co(L1)(nda)(H₂O)₂]·2H₂O} _n (1), [Co(L2)(tbi)(H₂O)] _n (2) and [Co(L2)(bpdc)(H₂O)] _n (3) (L1 = 1,3-bis(5,6-dimethylbenzimidazol-1-yl)-2-propanol, L2 = 1,3-bis(benzimidazol-1-yl)-2-propanol, H₂nda = 2,6-naphthalenedicarboxylic acid, H₂tbi = 5-tert-butyl isophthalic acid and H₂bpdc = 4,4′-biphenyldicarboxylic acid) were synthesized and characterized by physicochemical and spectroscopic methods. Complex 1 exhibits a 1D loop-like structure, which is further extended into a 3D 3,3,4T31 network through two O–H···O hydrogen bonding interactions. Complex 2 displays a 1D ladder-like chain, arranged into a 2D supramolecular network with 3,3,4L34 topology via classical O–H···O hydrogen bonding interactions, whereas complex 3 features a 2D 3,4L13 layer structure and further assembles into a 3D framework with a twofold interpenetrating sqc65 topology through O–H···O hydrogen bonding interactions. The fluorescence and catalytic properties of these complexes for the degradation of Congo red in a Fenton-like process have been investigated.     

Lanthanide contraction effect on the crystal structures of 2D lanthanide coordination polymers based on 2-(trifluoromethyl)-1<Emphasis Type="Italic">H</Emphasis>-imidazole-4,5-dicarboxylic acid

A series of new two-dimensional (2D) lanthanide(III) coordination polymers, namely {[Ln₂(μ ₂-HTFMIDC)₃(DMA)₄] · 2H₂O} _n [Ln = Pr (1); Nd (2); Sm (3); Eu (4); H₃TFMIDC = 2-(trifluoromethyl)-1H-imidazole-4,5-dicarboxylic acid, DMA = N,N′-dimethylacetamide] for type I and {[Ln₂(μ ₂-HTFMIDC)₃(DMA)₂(H₂O)₂] · DMA} _n [Ln = Eu (5); Gd (6)] for type II, have been successfully prepared under solvothermal conditions and structurally characterized for the first time. Both two types of structures exhibit similar 2D honeycomb-like networks, which are constructed by the linkages of μ ₂-HTFMIDC^2? bis-(bidentate) bridging ligands and Ln(III) metal centers. However, slightly different ABAB stacking fashions of the 2D layers and distinctly different hydrogen bonding interactions between the neighboring 2D layers are observed in crystal structures of type I and type II, which may be attributed to the lanthanide contraction effect. Meanwhile, the solid-state luminescent properties of 4 and 5 have been also investigated.     

Hydrostable coordination polymers of a methyl-functionalized 4,4′-bipyridine ligand: structure,stability, magnetic and luminescent properties

The reactions of aromatic dicarboxylic acids and methyl-functionalized 4,4′-bipyridine ligands with metal salts under hydrothermal conditions generated four structurally diverse cobalt(II), zinc(II) and cadmium(II) coordination polymers, [Co(CH₃-BDC)(dmbpy)_0.5] _n (1), [Cd(OH-HBDC)₂(dmbpy)] _n (2), [Zn(NDC)(dmbpy)] _n , (3) and {[Cd(DBA)(dmbpy)_0.5]·2H₂O} _n (4) (CH₃–H₂BDC = 5-methylisophthalic acid, OH–H₂BDC = 5-hydroxyisophthalic acid, H₂NDC = 1,4-naphthalenedicarboxylic acid, H₂DBA = 4,4′-methylenedibenzoic acid, dmbpy = 2,2′-dimethyl-4,4′-bipyridine). All four complexes have been structurally characterized by X-ray crystallography. Complex 1 shows a 3D jsm topology structure with two 1D channels parallel to the a and b axes. Complex 2 has a zigzag chain in which the OH-HBDC ligands point alternately up and down. Complexes 3 and 4 show 2D (4,4) networks when the dinuclear metal centers and their ligands are regarded as nodes and linkers, respectively. Complex 3 also shows twofold interpenetration with 1D channels along the b axis. Two nets of complex 4 interlock in parallel, giving rise to a polycatenated layer (2D → 2D). Thermogravimetric and chemical stabilities, magnetic and luminescent properties of these complexes were investigated.     

Synthesis,crystal structures,and antibacterial studies of silver(I) complexes with reduced Schiff base amino acid ligands

Three Ag(I) complexes of reduced Schiff base amino acid ligands, [Ag₂(Hshis)₂]·3H₂O (1), Ag(Hcgly) (2), and Ag(cala) (3) (H₂shis = N-(2-hydroxybenzyl)-l-histidine, H₂cgly = N-(2-hydroxy-5-chlorobenzyl)-glycine, Hcala = N-(4-chlorobenzyl)-d,l-alanine), have been synthesized and characterized by X-ray crystallography. Complex 1 shows a dimeric structure, while complex 2 shows one-dimensional zigzag chains, which are extended into a two-dimensional supramolecular sheet by hydrogen bonds. Complex 3 exhibits a 2D sheet structure with dangling arms. The antimicrobial activities of the complexes have been investigated.     

Supramolecular structure,spectroscopic, thermal studies and antimicrobial activities of Schiff base complexes

Metal(II) complexes of 4-(((2-hydroxynaphthalen-1-yl)methylene)amino)-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one (HL) were prepared, and their compositions and physicochemical properties were characterized on the basis of elemental analysis, with¹HNMR, UV–Vis, IR, mass spectroscopy and thermogravimetric analysis. All results confirm that the novel complexes have a 1:1 (M:HL) stoichiometric formulae [M(HL)Cl₂] (M = Cu(II)(1), Cd(II)(5)), [Cu(L)(O₂NO)(OH₂)₂](2), [Cu(HL)(OSO₃)(OH₂)₃]2H₂O(3), [Co(HL)Cl₂(OH₂)₂]3H₂O(4), and the ligand behaves as a neutral/monobasic bidentate/tridentate forming a five/six-membered chelating ring towards the metal ions, bonding through azomethine nitrogen, exocyclic carbonyl oxygen, and/or deprotonated phenolic oxygen atoms. The XRD studies show that both the ligand and Cu(II) complex (1) show polycrystalline with monoclinic crystal structure. The molar conductivities show that all the complexes are non-electrolytes. On the basis of electronic spectral data and magnetic susceptibility measurements, a suitable geometry has been proposed. The trend in g values (g _ll > g _⊥ > 2.0023) suggest that the unpaired electron on copper has a \(d_{{x^{2} - y^{2} }}\) character, and the complex (1) has a square planar, while complexes (2) and (3) have a tetragonal distorted octahedral geometry. The molecular and electronic structures of the ligand (HL) and its complexes (1–5) have been discussed. Molecular docking was used to predict the binding between HL ligand and the receptors of the crystal structure of Escherichia coli (E. coli) (3t88) and the crystal structure of Staphylococcus aureus (S. aureus) (3q8u). The activation thermodynamic parameters, such as activation energy (E _a), enthalpy (ΔH), entropy (ΔS), and Gibbs free energy change of the decomposition (ΔG) are calculated using Coats–Redfern and Horowitz–Metzger methods. The ligand and its metal complexes (1–5) showed antimicrobial activity against bacterial species such as Gram positive bacteria (Bacillus cereus and S. aureus), Gram negative bacteria (E. coli and Klebsiella pneumoniae) and fungi (Aspergillus niger and Alternaria alternata); the complexes exhibited higher activity than the ligand.     

X-ray study of rhodium(III) sulfates

Compounds with compositions [Rh(H₂O)₆]₂(SO₄)₃·4H₂O (I), (H₃O)[Rh(H₂O)₆](SO₄)₂ (II), [Rh(H₂O)₅OH](SO₄)·0.5H₂O (III), and [Rh(H₂O)₆]₂(SO₄)·(H₂SO₄) _x ·5H₂O (IV) have been studied. The crystal structures of II, III, and IV were determined. All compounds crystallized in the monoclinic crystal system. Crystal data for II: a = 7.279(2) Å, b = 10.512(7) Å, c = 15.806(3) Å, β = 96.71(3)°, space group P2₁/n, Z = 2, d _calc = 2.334 g/cm³; III: a = 20.433(4) Å, b = 7.820(2) c = 11.215(2) Å, β = 114.14(1)°, space group C2/c, Z = 8, d _calc = 2.559 g/cm³; IV: a = 6.2250(4 Å), b = 27.0270(12) Å, c = 7.2674(5) Å, β = 97.04(3)°, space group P2₁/c, Z = 4, d _calc = 2.143 g/cm³. The compounds were studied by IR spectroscopy and powder X-ray diffraction. All of the isolated crystalline phases are sparingly soluble in ethanol and well soluble in water.     

Substitution of aqua ligands from <Emphasis Type="Italic">cis</Emphasis>-platinum(II) complexes bearing 2-(phenylthiomethyl)pyridine spectator ligands

Cis-Pt(II) complexes, namely [Pt{2-(phenylthiomethyl)pyridine}(H₂O)₂](CF₃SO₃)₂ Pt(pyS ^Ph ), [Pt{2-(4-tert-butylphenylthiomethyl)pyridine}(H₂O)₂](CF₃SO₃)₂ Pt(pyS ^{Ph( t -But)} ) and [Pt{2-(4-fluorophenylthiomethyl)pyridine}(H₂O)₂](CF₃SO₃)₂ Pt(pyS ^PhF ), were synthesised and characterised. The pK _a1 and pK _a2 values of the complexes were determined titrimetrically. Substitution of the aqua ligands from these complexes by thiourea nucleophiles was studied at a pH of 2 and ionic strength of 0.1 M under pseudo-first-order conditions using stopped-flow and UV–visible spectrophotometric techniques. Substitution of the aqua ligands depends on both the nature and concentration of the incoming ligand, with low enthalpy and negative entropy of activation values. Substitution of the first and second aqua ligands occurs sequentially and fits the rate laws: k _{obs (1/2)} = k _(1/2) [Nu]. The second-order rate constant, k ₁, relates to the substitution trans to sulphur, while k ₂ is the second-order rate constant for the subsequent substitution of the aqua ligand trans to pyridine. The rate of substitution of the first aqua ligand decreases in the order: Pt(pyS ^{Ph( t -But)} ) > Pt(pyS ^PhF ) > Pt(pyS ^Ph ), while that of the second decreases in the order: Pt(pyS ^{Ph( t -But)} ) > Pt(pyS ^Ph ) > Pt(pyS ^PhF ), reflecting the influence of the substituents on the spectator ligands. ¹⁹⁵Pt NMR spectra of aged solutions of complexes with the thiourea nucleophile suggest a subsequent but rapid concentration-independent ring opening of the N,S-bidentate ligand to form a PtS ₄ species. The crystal structure of Pt(pyS ^PhF )Cl ₂ was elucidated by X-ray diffraction analysis.     

Three cobalt(II) coordination polymers constructed from flexible bis(thiabendazole) and dicarboxylate linkers: crystal structures,fluorescence, and photocatalytic properties

Three Co(II) coordination polymers, namely, {Co(btbb)_0.5(ndc)(H₂O)}_n (1), {[Co(btbb)(bpdc)]·1.5H₂O}_n (2), and {[Co(btbp)₂(3-npa)]·2H₂O}_n (3) (btbb = 1,4-bis(thiabendazole)butane, btbp = 1,3-bis(thiabendazole)propane, H₂ndc = 2,6-naphthalenedicarboxylic acid, H₂bpdc = 4,4′-biphenyldicarboxylic acid and 3-H₂npa = 3-nitro phthalic acid) were synthesized under hydrothermal conditions. Their X-ray crystal structures show that complexes 1 and 2 both have 2D uninodal 3-connected hcb (honeycomb) structures. Complex 1 is further extended into a threefold interpenetrating 3D 4,4-connected mog (moganite) supramolecular architecture with the point symbol of {4.6⁴.8}₂{4².6².8²} by O–H···O hydrogen bonding interactions. Complex 2 shows a 3D supramolecular framework involving π···π stacking interactions. Complex 3 features a uninuclear structure, which is further assembled into an ordered 2D hydrogen-bonded-driven pattern with O–H···O and O–H···N hydrogen bonding interactions. The fluorescence spectra and photocatalytic properties of complexes 1–3 for degradation of methyl orange were investigated.     

Synthesis,spectral and thermal studies on dicarboxylate-bridged palladium(II) coordination polymers. Part II

The synthesis and thermal behavior of the new [Pd(fum)(bipy)] _n ·2nH₂O (1), [Pd(fum)(bpe)] _n ·nH₂O (2) and [Pd(fum)(pz)] _n ·3nH₂O (3) {bipy = 4,4′-bipyridine, bpe = 1,2-bis(4-pyridyl)ethene and pz = pyrazine} fumarate complexes are described in this work as well their characterization by IR and ¹³C CPMAS NMR spectroscopies. TG curves showed that the compounds released organic ligands and lattice water molecules in the temperature range of 46–491 °C. In all the cases, metallic palladium was identified as the final residue.     

A series of 3d metal complexes prepared by in situ reactions of a flexible diacylhydrazine ligand: synthesis,structures and magnetic properties

The coordination reactions of 3d metal salts with malonic acid N,N′-bis(salicyloyl) bishydrazide (H₆mbshz) afforded three complexes, namely [Cu₂(H₂bshz)(Py)₄Cl₂]·Py (1) (Py = pyridine), [Fe₂(bshz)(Py)₂] (2) and the known complex [Ni₄(aehba)₂(DMF)₂(H₂O)₂]·2DMF (3), where bshz = N,N′-bis(salicyloyl)hydrazine anion and aehba^4? = azo-enolic-2-hydroxybenzamide anion. The X-ray crystal structures of all three complexes have been obtained. Complexes 1 and 2 are composed of N–N-bridged binuclear units, while complex 3 displays a planar tetranuclear structure in which four Ni(II) centers are linked together by N–N and N=N bonds. The bshz anions in 1 and 2 and aehba^4? anions in 3 were all generated in situ from H₆mbshz. A mechanism for these reactions is proposed, involving tandem C–N cleavage and C–N/N–N coupling processes via free radical intermediates. Magnetic investigations revealed dominant antiferromagnetic interactions between the metallic centers of each complex.     

Palladacycles incorporating a carboxylate-functionalized phosphine ligand: syntheses,characterization and their catalytic applications toward Suzuki couplings in water

A series of acetato-bridged [C^X]-type (C = aryl carbanion, X = N, P) palladacycles (1–5) of the general formula [Pd(μ-CH₃COO)(C^X)]₂ were synthesized as metal precursors via slightly modified procedures. However, in the case of complex 5 with Dpbp (Dpbp = 2′-(diphenylphosphino-κP)[1,1′-biphenyl]-2-yl-κC) as the supporting C^P ligand, an unexpected dinuclear complex [Pd(μ-CO₂)(Dpbp)]₂ (6) was obtained as a by-product and structurally determined by X-ray crystallography. The reactions of complexes 1–4 with 2-(diphenylphosphino)benzoic acid conveniently afforded four carboxylate-functionalized phosphine complexes [Pd(C^N)(Dpb)] (Dbp = 2-(diphenylphosphino-κP)benzoato-κO, 7–10), two of which (9/10) are newly synthesized in the present work and have been fully characterized. A comparative catalytic study revealed that complex [Pd(Ppy)(Dpb)] (7) (Ppy = 2-(2-pyridinyl-κN)phenyl-κC) is the best performer in Suzuki cross-couplings in H₂O. In addition, complex 7 exhibits much better catalytic activity compared to the non-functionalized phosphine equivalent [Pd(OAc)(PPh₃)(Ppy)] (11), which clearly indicates the superiority of incorporating a carboxylate-functionalized phosphine ligand into the palladacycles. A preliminary mechanistic study uncovered a different precatalyst initiation pathway compared to other known analogues of catalyst precursors.