Bidentate Chelating Coordination Research Articles

Binding of ligands containing carbonyl and phenol groups to iron(iii): new Fe6, Fe10 and Fe12 coordination clusters.

The initial use of ligands 2'-hydroxyacetophenone (HL1), 2-hydroxybenzophenone (HL2) and 2,2'-dihydroxybenzophenone (H2L3) in iron(iii) chemistry is described. The syntheses and crystal structures are reported for five iron(iii) clusters: [Fe10O4(OMe)14(L1)6(MeOH)2](NO3)2·3MeOH (1·3MeOH), [Fe12O4(OH)(OMe)17(L1)8](ClO4)2·2H2O (2·2H2O), [Fe10O4(OMe)14Cl4(L2)4(MeOH)2] (3), [Fe10O4(OMe)14(L2)6(py)2](ClO4)2·MeOH (4·MeOH), where py = pyridine, and [Fe6O2(OEt)6(O2CMe)2(L3)2(HL3)2] (5). The molecular structures of the decanuclear clusters 1, 3 and 4 are organized around a {Fe10(μ4-O)4(μ3-OMe)2(μ-OMe)12}8+ core consisting of ten {Fe3O4} face-sharing defective cubane units. The core of 2 consists of a {Fe12(μ4-O)4(μ3-OMe)4(μ-OH)(μ-OMe)13}10+ unit composed of twelve {Fe3O4} face-sharing defective cubanes. The ligands (L1)- and (L2)- in 1-4 adopt the O,O'-bidentate chelating coordination mode and their roles are to terminate the further aggregation of the FeIII/O2-/RO- cores. Complex 5 contains the {Fe6(μ4-O)2(μ-OEt)6(μ-Ocarbonyl)2}4+ core, where the μ-Ocarbonyl atoms are the bridging carbonyl oxygens of the two η1:η2:η1:μ (L3)2- ligands; the (HL3)- groups behave as Ophenolate, Ocarbonyl-bidentate chelating ligands with the neutral hydroxyl group being unbound to the FeIII atoms. The core is composed of four {Fe3O4} face-sharing defective cubanes. The FeIII atoms in 1-5 are all six-coordinate with distorted octahedral geometries. The IR spectra of the complexes are discussed in terms of the known coordination modes of the ligands and the ionic character of nitrates and perchlorates. Variable-temperature magnetic susceptibility and variable-field magnetization measurements establish that 2, 3 and 5 have S = 3, 0 and 5 ground states, respectively. The susceptibility data for 5 were fitted using a 3-J model indicating the simultaneous presence of both antiferromagnetic and ferromagnetic FeIIIFeIII exchange interactions. Known magnetostructural correlations in oxido-bridged iron(iii) systems have been applied to rationalise the magnetic behaviour of the three clusters. The results of the present study demonstrate the utility of HL1, HL2 and H2L3 in the stabilisation of robust iron(iii)/oxido/alkoxido clusters.

A highly stable and luminescent mononuclear Cu(I) bis-{5-tert-butyl-3-(6-methyl-2-pyridyl)-1H-1,2,4-triazole} complex

A new emissive mononuclear homoleptic Cu(I) complex of 5-tert-butyl-3-(6-methyl-2-pyridyl)-1H-1,2,4-triazole (bmptzH), [Cu(bmptzH)2](ClO4) (1), has been synthesized by treatment of [Cu(PPh3)2(CH3CN)2](ClO4) or [Cu(CH3CN)4](ClO4) with the bmptzH ligand. It is revealed that complex 1 displays a distorted N4 tetrahedral arrangement formed by two bmptzH chelates, in which bmptzH adopts a neutral bidentate chelating coordination mode using the N atom of the pyridyl ring and the 4-N not 2-N atom of the 1,2,4-triazolyl ring. It is shown that complex 1 is highly stable and exhibits good luminescence properties in solution and solid states at room temperature due to the introduction of a methyl group at the ortho-position of the pyridyl ring.

Synthesis, crystal structures, and magnetic properties of three new iron(II) complexes with pyrrolyl-substituted triaryltriazoles

Three pyrrolyl-substituted triaryltriazoles, 3-(N-methyl-2-pyrrolyl)-4-(p-R-phenyl)-5-(2-pyridyl)-1,2,4-triazole (L1: R = MeO; L2: R = Cl; L3: R = Br), and their mononuclear iron(II) complexes, trans-[Fe(L1–3)2(NCS)2]∙2MeOH (1: L1; 2: L2; 3: L3), have been synthesized and characterized by elemental analysis, FT-IR, ESI-MS, and single-crystal X-ray crystallography. Crystallographic studies revealed that 1–3 are isomorphous and crystallize in the triclinic space group P-1. All the complexes have a similar octahedral [FeN6] core with two trans-NCS− ions. Each ligand adopts a chelating bidentate coordination mode via the pyridyl N and one N of the triazole. Intermolecular O–H⋯O hydrogen bonding and C–H⋯π interactions link the molecules of 1–3 to form a 1-D chain or 2-D framework. Variable-temperature magnetic susceptibility measurements indicated that all the complexes remained in a high-spin state from 1.8 to 300 K and had a weak antiferromagnetic interaction.

Two coordination polymers containing the dicyanamide ligand: Synthesis, crystal structures, and HFEPR studies

Two new compounds [Ni(dca)2(dmdpy)] (1) and [Zn(dca)2(dmdpy)] (2), (dca=dicyanamide and dmdpy=5,5′-dimethyl-2,2′-dipyridine) were synthesized and characterized by single crystal X-ray diffraction, FTIR and thermal analysis. In both compounds, the dmdpy ligand adopts a bidentate chelating coordination mode while dca anions act in a μ1,5 bridging fashion. In 1, the NiII centers lie on a distorted octahedral geometry, whereas in 2 the ZnII geometry is distorted square pyramidal. In compounds 1 and 2, dca ligands connect the metal sites giving rise to 2D and 1D coordination polymers, respectively. The magnetic properties of 1 were studied by magnetic susceptibility and high field/frequency electron paramagnetic resonance (HFEPR) measurements.

Complexes of some tervalent metals with N-alkyl(benzyl)nitrozohydroxylamine derivatives

Twenty two new complexes of some tervalent metals (aluminum, chromium, iron, and lanthanides) with nitrozohydroxylamine N-alkyl(benzyl) derivatives ML 3 m · nH2O, (m = 1‒5) were synthesized and isolated in a crystalline state. The crystal and molecular structures of the iron(III) complex with N-(2-fluorobenzyl)-N-nitrozohydroxylamine were determined by X-ray diffraction. An octahedral coordination of the central ion and a bidentate chelating coordination of the organic ligand were established. The spectral criteria of coordination of nitrozohydroxylamine alkyl(benzyl) derivatives were determined, and the complexation processes in solutions were studied.

Chain Length and Thermal Sensitivity of the Infrared Spectra of a Homologous Series of Anhydrous Silver(I)n-Alkanoates

The thermal and chain length sensitivity of the infrared spectra of some solid state anhydrous silver(I) salts (n-octanoate ton-eicosanoate, inclusive) are discussed. At ambient temperature, the tilted alkyl chains, anchored to the metal planes via chelating bidentate coordination to the silver ions, are crystallized in the fully extendedall-transconformation. Interestingly, though all compounds are crystallized in a monoclinic crystal system, their lateral chain packing,van der Waalseffects, and hence vibrational features are chain length-dependent. This is a direct result of electrostatic effects of the COO group in addition to vibrational coupling between CH2, CH3, and COO modes, an effect which varies significantly with chain length. Variable temperature infrared measurements indicate significant irreversible changes in the metal-carboxyl coordination sphere, most likely due to bond fission. For long chain adducts (nc>12), thermally induced crystal system switching, monoclinic to triclinic, indicates greater thermal sensitivity of their alkyl chains. During heating, the regions of the hydrocarbon chains, furthest from the COO, become increasingly molten and mobile as the stepwise melt advances towards the solid COO moieties. This solid-liquid melting behaviour is responsible for mesophase formation in metal carboxylate systems.

Study on the behavior of sulfur in hydrolysis process of titanyl sulfate solution

The existing forms of sulfur in hydrolysis process of titanyl sulfate solution were studied. Also the effects of sulfur on crystal structure, crystallite size and crystal phase transition of the hydrated titanium dioxide(TiO2·H2O) and titanium dioxide (TiO2) were conducted. The analysis and methods of thermogravimetric-differential scanning calorimet (TG-DSC), energy dispersive spectrometer (EDS), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), UV–Vis diffuse reflectance spectra and Raman spectroscopy were employed to characterize. The results indicated that the sulfur was present in the form of SO42− ions in the hydrolysate of titanyl sulfate solution, and a portion of SO42− ions were combined on the surface of hydrated titanium dioxide by chemical adsorption in the forms of inorganic chelating bidentate coordination and covalent sulfate coordination, the residual SO42− ions were adsorbed on the surface of hydrated titanium dioxide by physical adsorption. The chemical adsorption of SO42− ions were conducive to the formation and stabilization of anatase, which changed the crystal structure, and hindered the transformation of the anatase into rutile. The results of Raman spectroscopy showed that the sulfur was dissociated in the forms of SO42− and HSO4− ions during the hydrolysis of titanyl sulfate solution. The characteristic peak at 1004 cm−1 corresponding to a new complex has been observed, which was composed of SO42− and hydrated titanium complex ions through the bonding on the surface. In basis of the above experimental results, the hydrolysis process of titanyl sulfate solution was illustrated from the microstructure with 3D atlas.

Fabrication of TiO2-modified polytetrafluoroethylene ultrafiltration membranes via plasma-enhanced surface graft pretreatment

Surface hydrophilic modification of polymer ultrafiltration membrane using metal oxide represents an effective yet highly challenging solution to improve water flux and antifouling performance. Via plasma-enhanced graft of poly acryl acid (PAA) prior to coating TiO2, we successfully fixed TiO2 functional thin layer on super hydrophobic polytetrafluoroethylene (PTFE) ultrafiltration (UF) membranes. The characterization results evidenced TiO2 attached on the PTFE-based UF membranes through the chelating bidentate coordination between surface-grafted carboxyl group and Ti4+. The TiO2 surface modification may greatly reduce the water contact angle from 115.8° of the PTFE membrane to 35.0° without degradation in 30-day continuous filtration operations. The novel TiO2/PAA/PTFE membranes also exhibited excellent antifouling and self-cleaning performance due to the intrinsic hydrophilicity and photocatalysis properties of TiO2, which was further confirmed by the photo-degradation of MB under Xe lamp irradiation.

Synthesis and structural analysis of formamidinate-supported Mg complexes

Reactions of 2-mesitylmagnesium bromide with N,N′-diarylformamidines afforded five Mg compounds [(DPhF)Mg(THF)2]2(μ-Br)2 (1), [D(3,5-Xyl)F]2Mg(THF)2 (2), [D(2,6-Xyl)F]2Mg(THF) (3), [D(2-iPrPh)F]MgBr(THF)3 (4), and [D(2-tBuPh)F]2Mg(THF) (5). Complexes 1, 2 and 4 displayed monomeric octahedral metal centers supported by formamidinates, bromide counter anions, and coordinating THF solvent molecules, while the metal cores in 3 and 5 were five-coordinated and in distorted square-pyramidal geometries. Detailed structural analysis indicated that only dimagnesium or mononuclear complexes were obtained through the use of formamidinate ligands. Ligands of increased steric demands resulted in the formation of monomeric complexes. Solvent molecules and counter anions that can coordinate to the metal cores further regulated the product conformation. Monoanionic formamidinates in the complexes, mostly featuring two nearly identical N–C bonds on the N–C–N backbone upon complexation, exhibited a symmetric bidentate chelating (η2) coordination mode.

Six new metal(II) complexes with 3D network structures based on carboxylate and hexamethylenetetramine: Syntheses and structures

Hexamethylenetetramine (hmt) reacted with Cd(II), Ag(I) and Zn(II) salts of carboxylic acids and resulted in the formation of six novel coordination architectures, [Cd(hmt)2(L1)2H2O] (1) (L1=1,3-benzodioxole-5-carboxylate), [Cd(hmt)2(L2)2(H2O)2] (2) (L2=2-methyl-2-phenoxypropionate), [Ag(hmt)(L3)]·H2O (3) (L3=2-hydroxy-5-(phenyldiazenyl)benzoate), [Cd(hmt)2(L4)2(H2O)] (4) (L4=3-(4-methoxyphenyl)acrylate), [Cd(hmt)(L5)2(H2O)2]·2H2O 5 (L5=3,5-dinitrobenzoate) and [Zn(hmt)(L6)2)]2 (6) (L6=o-chlorobenzoate). All the complexes have been structurally characterized by elemental analysis, IR, TG and X-ray diffraction analysis. The different coordination modes of the carboxylate anions and the hmt molecules lead to a wide range of different coordination structures. All these complexes display 3-D framework structures as a result of a number of non-conventional weak interactions. The carboxylate groups adopt monodentate and bidentate chelating coordination modes. The μ1-hmt, μ2-hmt and μ3-hmt modes were found for the tetradentate hmt ligand. The central metal ions are coordinated in N2O5, N2O4, NO4 and N3O fashions, depending on the center metals and the ancillary ligands. In addition, the frameworks of the six compounds are thermally stable up to 200°C.

Syntheses, Structures and Fluorescent Properties of Lead(II) Complexes Based on 5,6-Substituted 1,10-Phenanthroline Derivatives and Benzene Dicarboxylic Acids

Three new coordination polymers, [Pb(1,3-bdc)(MOPIP)2]n·nH2O (1), [Pb(1,4-bdc)(MOPIP)]n (2) and [Pb2(1,4-bdc)2(MEDPQ)2]n·nH2O (3) (MOPIP = 2-(4-methoxyphenyl)-1H-imidazo[4,5-f] [1, 10] phenanthroline, MEDPQ = 2-methyldipyrido [3,2-f:2′,3′-h]quinoxaline, 1,3-H2bdc = benzene-1,3-dicarboxylic acid, 1,4-H2bdc = benzene-1,4-dicarboxylic acid), have been prepared through hydrothermal reactions. The transformation of coordination modes of organic carboxylate ligands and 5,6-substituted 1,10-phen derivatives has a crucial influence on the structures of these series. In compound 1, 1,3-bdc anion adopts a chelating bidentate and bridging monodentate coordination mode, which results in a hepta-coordinated environment of Pb(II) center. However, in complex 2, 1,4-bdc anion acts in the chelating bidentate mode, which results in a hexa-coordinated environment of Pb(II) center. Complex 3 shows face-to-face π···π interactions between MEDPQ and benzene rings, which are different to that of the complexes 1 and 2. The fluorescence property and thermal stability were also investigated.

Two Zn(II) coordination complexes assembled by trithiocyanuric acid and two different N-donor auxiliary ligands.

The dipyridyl-type building blocks 4-amino-3,5-bis(pyridin-3-yl)-1,2,4-triazole (3-bpt) and 4,4'-bipyridine (bpy) have been used to assemble with Zn(II) in the presence of trithiocyanuric acid (ttcH3) to afford two coordination compounds, namely bis[4-amino-3,5-bis(pyridin-3-yl)-1,2,4-triazole-κN(3)]bis(trithiocyanurato-κ(2)N,S)zinc(II), [Zn(C3H2N3S3)2(C12H10N6)2]·2H2O, (1), and catena-poly[[[bis(trithiocyanurato-κ(2)N,S)zinc(II)]-μ-4,4'-bipyridine-κ(2)N:N'] 4,4'-bipyridine monosolvate], {[Zn2(C3H2N3S3)4(C10H8N2)3]·C10H8N2}n, (2). Single-crystal X-ray analysis indicates that complex (1) is a mononuclear structure, while complex (2) presents a one-dimensional chain coordination motif. In both complexes, the central Zn(II) cation adopts an octahedral geometry, coordinated by four N- and two S-donor atoms. Notably, trithiocyanurate (ttcH2(-)) adopts the same bidentate chelating coordination mode in each complex and exists in the thione tautomeric form. The 3-bpt co-ligand in (1) adopts a monodentate coordination mode and serves as a terminal pendant ligand, whereas the 4,4'-bipyridine (bpy) ligand in (2) adopts a bidentate-bridging coordination mode. The different coordination characters of the different N-donor auxiliary ligands lead to structural diversity for complexes (1) and (2). Further analysis indicates that the resultant three-dimensional supramolecular networks for (1) and (2) arise through intermolecular N-H...S and N-H...N hydrogen bonds. Both complexes have been further characterized by FT-IR spectroscopy and elemental analyses.

Synthesis and studies of complex compounds of carboxyl-derivatives of methylphloroglucinol with metals

Ten new complexes of 2,4,6–trihydroxy-3-methyl benzoic acid (methylphloroglucinol, L1) and 2,4,6–trihydroxy benzoic acid (phloroglucinol, L2) are isolated in the solid state, and their formulae were detected.The spectroscopic methods indicate that the coordination of L1 and L2 to the metallic ions occurs through one of the O-atom of the deprotonated carboxylic group and an O atom of the non-deprotonated neighboring hydroxy-group (bidentate chelating coordination). The schemes of the structure of complexes are proposed.The complex formation in solution is studied, and formation constants are calculated. It is shown that for the metal complexes of the 1st transitional series, the formation constants for the complexes are arranged as Mn(II) < Co(II) < Ni(II) < Cu(II) > Zn(II). The obtained results correlate with the Irving-Williams Series.

Benign synthesis of the unsymmetrical ligand N-(8-quinolyl)quinoline-2-carboxamide (Hqcq) and the varied crystal chemistry of its Cu(II), Zn(II), and Cd(II) complexes bearing acetato and aqua co-ligands

A new benign and highly efficient procedure, with the ionic liquid tetrabutylammonium bromide as reaction medium, has been used for synthesis of the unsymmetrical ligand N-(8-quinolyl)quinoline-2-carboxamide. Three new complexes [Cu(qcq)(OAc)(H2O)], [Zn(qcq)(OAc)(H2O)], and [Cd(qcq)(OAc)(H2O)] were synthesized and characterized by elemental analysis, IR, UV–visible and 1H NMR spectroscopy, and X-ray crystallography. The mono-anionic qcq– is a tridentate unsymmetrical ligand furnishing an N3 set, such that two N atoms of the two quinoline rings and one amido N atom occupy three meridional positions. In [Cd(qcq)(OAc)(H2O)] the acetate anion has a chelating bidentate coordination mode, whereas in [Cu(qcq)(OAc)(H2O)] and [Zn(qcq)(OAc)(H2O)] it acts as a terminal monodentate ligand. The coordination geometry around the M(II) ion is distorted square pyramid in the Cu complex, distorted trigonal bipyramid in the Zn complex, and distorted octahedron in the Cd complex. The discrete molecular units of these complexes are linked by hydrogen bonds and face-to-face π–π stacking interactions. The spectroscopic and electrochemical properties of these complexes are reported and discussed. .

Synthesis, crystal structures, and magnetic properties of three iron(II) complexes with 3-(p-bromophenyl)-4-phenyl-5-(2-pyridyl)-1,2,4-triazole

Three iron(II) complexes with 3-(p-bromophenyl)-4-phenyl-5-(2-pyridyl)-1,2,4-triazole (L), trans-[FeL2(NCS)2] (1), trans-[FeL2(NCS)2]·2MeOH (1·2MeOH), and trans-[FeL2(NCSe)2] (2), have been synthesized and characterized by elemental analysis, FT-IR, ESI-MS, and single crystal X-ray crystallography. Crystallographic studies reveal that all the complexes contain a distorted octahedral [FeN6] core with two trans NCS(Se)− ions. Each L adopts a chelating bidentate coordination via one N of pyridyl and one N of triazole. Magnetic susceptibility measurement indicated that both 1 and 1·2MeOH are in a high-spin state from 2 to 300 K.

Synthesis, Crystal Structure, and Antibacterial and Antioxidant Properties of a New Ag(I) Coordination Polymer Based on 3-Chloro-6-(1H-1,2,4-triazol-1-yl) Pyridazine

A new Ag(I) complex [AgL2(NO3)] (1) (L = 3-chloro-6-(1H-1,2,4-triazol-1-yl) pyridazine) was synthesized and characterized by IR spectra and X-ray single-crystal diffraction. The structure reveals that each nitrate ion adopts not only bidentate chelating coordination, but also the bridging mode to connect surrounding Ag(I) atoms. Each ligand L binds three Ag(I) ions and each Ag(I) ion links three L to form a 1D chain structure. All 1D chains further construct a 3D supramolecular framework by hydrogen bonds (C-H…O) and π…π interactions (offset stacking) in the solid state. The antibacterial activity and antioxidant activity of L and 1 were also studied.

Synthesis and Crystal Structures of Two New Supramolecular Complexes: [Cu(tmbpm)(ox)(H2O)]·4H2O and [Zn(tmbpm)2(H2O)]·(ClO4)2·5H2O

Two new 3D supramolecular complexes, [Cu(tmbpm) (ox)(H2O)]·4H2O (1) and [Zn(tmbpm)2(H2O)]·(ClO4)2·5H2O (2) (tmbpm = 4,4′,6,6′-tetramethyl-2,2′-bipyrimidine, ox = C2O4 2–), have been synthesized and structurally characterized by elemental analysis, IR spectra, and single-crystal X-ray diffraction. Compound 1 is monoclinic, C2/c, a = 22.429(4) Å, b = 7.6501(14) Å, c = 25.866(6) Å, β = 114.630(2)°; and compound 2 is monoclinic, C2, a = 18.854(3) Å, b = 7.7273(14) Å, c = 12.200(2) Å, β = 93.793(2)°. Both compounds 1 and 2 have a mononuclear structure in which the tmbpm ligand adopts bidentate chelating coordination mode. Two 3D supramolecular structures containing 1D water chains are formed via intermolecular O−H···O and O−H···N hydrogen bonds. Supplementary materials are available for this article. Go to the publisher's online edition of Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry to view the supplemental file.

Synthesis, crystal structure, Hirshfeld surfaces, and spectral properties of Cu(II) and Co(II) complexes with 3-phenoxymethyl-4-phenyl-5-(2-pyridyl)-1,2,4-triazole

A new asymmetrical substituted triazole, 3-phenoxymethyl-4-phenyl-5-(2-pyridyl)-1,2,4-triazole (L) and its complexes, cis-[Cu2 L 2Cl4]·2CH3CN (1) and trans-[CoL 2Cl2]·2H2O·2CH3CN (2), have been synthesized and characterized by IR, single-crystal X-ray diffraction, thermogravimetric analyses and Hirshfeld surfaces. In the structure, two L are mainly stabilized by an intermolecular C–H⋯N hydrogen bond. In 1 (or 2), each L involves a doubly-bidentate (or chelating bidentate) coordination mode through one pyridine and two nitrogens (or one) of triazole, respectively. Complex 1 has a distorted trigonal bipyramidal [CuN3Cl2] core with two cis Cl− while 2 shows a distorted octahedron [CoN4Cl2] with two trans Cl−. We also prepared molecular Hirshfeld surface and fingerprint plot for L, 1 and 2, which revealed the influence of different metals on coordinate of L.

Syntheses, crystal structures, and spectral characterization of an asymmetrically substituted 1,2,4-triazole and its iron(II) complex

One new asymmetrically substituted 1,2,4-triazole, 4-amino-3-(p-bromophenyl)-5-(2-pyridyl)-1,2,4-triazole (L), and its iron(II) complex, trans-[FeL2(NCS)2] (1), have been synthesized and characterized by elemental analyses, FT-IR, 1H NMR, ESI mass spectra, and single-crystal X-ray crystallography. Crystallographic studies revealed that 1 contains a distorted octahedral [FeN6] core with two trans NCS−. Each L adopts a chelating bidentate coordination via N of pyridyl and one N of the triazole ring. Magnetic susceptibility measurements indicated that 1 remained in a high-spin state between 1.8 and 300 K.

Pd(II) and Pt(II) complexes of cyclic bidentate (S)PNP(S) ligands: Synthesis, structure and catalytic activity in the Suzuki reaction

The synthetic approach to the novel cyclic (S)PNP(S) ligands ▪ (5a–c, R=EtO, Me, Ph), i.e. 1-thiophosphoryl-2-thioxo-1,2-azaphospholanes having different surrounding at the exocyclic phosphorus atom, has been developed. Compounds bearing two asymmetric phosphorus atoms were obtained as individual (R∗,R∗)- and (R∗,S∗)-diastereomers. Reacting with (PhCN)2MCl2 (M=Pd, Pt) in MeCN under ambient conditions the ligands readily form complexes MLCl2 [6a–c (M=Pd), 7b (M=Pt)] via bidentate chelating coordination mode. The structures and stereochemistry both of the ligands and their complexes were confirmed by IR, multinuclear NMR and X-ray diffraction study. The palladium complexes demonstrated high activity as precatalysts for the Suzuki cross-coupling reaction, which was found to increase in the series 6a<6b<6c.