Amino-closo-dodecaborate--a new ligand in coordination chemistry

The synthesis and characterization of three ruthenium complexes [Bu(3)MeN][Ru(PPh(3))(2)(NH(2)-B(12)H(11))Cl], [Bu(4)N][Ru(dppb)(NH(2)-B(12)H(11))Cl] and [RuCO(PPh(3))(2)(NH(2)-B(12)H(11))] with amino-closo-dodecaborate as the coordinating ligand are described.     

Scaffolding a cage-like 3D framework by coordination and constitutional dynamic chemistry

By exploiting the supramolecular assistance of a sterically encumbered phenanthroline-Cu(+) motif, we report on the self-assembly of a trigonal nanoprism, its post-self-assembly functionalization, and transformation into a cage-like 3D framework with distinct compartments.     

"Clickphine": a novel and highly versatile P,N ligand class via click chemistry

[Structure: see text] A novel P,N-type ligand family (ClickPhine) is disclosed that is easily accessible using the Cu(I)-catalyzed azide-alkyne "click" cycloaddition. A diverse set of ligands was made in just three steps from readily available starting materials to give several homogeneous and a heterogeneous catalyst. Preliminary experiments show the efficacy of these ligands in the Pd-catalyzed allylic alkylation reaction.     

Synthesis and coordination chemistry of a photoswitchable bis(phosphine) ligand

A 1,2-dithienylethene compound bearing bis(phosphine) groups (1o) represents a new class of photoresponsive ligands where there are steric and electronic differences between two photogenerated isomers. The coordination chemistry of this ligand class is demonstrated by preparing a gold(I) complex (2o) and a phosphine selenide (3o).     

Spectroscopy and coordination chemistry of a new bisnaphthalene-bisphenanthroline ligand displaying a sensing ability for metal cations

A new fluorescent macrocyclic structure (L1) bearing two naphthalene units at both ends of a cyclic polyaminic chain containing two phenanthroline units was investigated with potentiometric and fluorescence (steady-state and time-resolved) techniques. The fluorescence emission spectra show the simultaneous presence of three bands: a short wavelength emission band (naphthalene monomer), a middle emission band (phenanthroline emission), and a long-wavelength band. All three bands were found to be dependent on the protonation state of the macrocyclic unit (including the polyaminic and phenanthroline structures). The existence of the long-wavelength emission band is discussed and is shown to imply that a bending movement involving the two phenanthroline units leads to excimer formation. This is determined by comparison with the excimer emission formed by intermolecular association of 1,10-phenanthroline. With ligand L1, excimer formation occurs only at pH values above 4. At very acidic pH values, the protonation of the polyamine bridges is extensive leading to a rigidity of the system that precludes the bending movement. The interaction with metal cations Zn(II) and Cu(II) was also investigated. Excimer formation is, in these situations, increased with Zn(II) and decreased with Cu(II). The long-emission band is shown to present a different wavelength maximum, depending on the metal, which can be considered as a characteristic to validate the use of ligand L1 as a sensor for a given metal.     

Synthesis, characterization and coordination chemistry of a macrocyclic ligand containing arsenic donors

The preparation and characterization of the macrocyclic diamido-diarsine ligand [As2N2]Li2(1,4-dioxane) (1) (where As2N2 = PhAs(CH2SiMe2NSiMe2CH2)2AsPh) and a series of early transition metal complexes are presented. The complexes [As2N2]MCl2 (M = Zr, 2; Ti, 4) and the complex ([As2N2]Y)2(mu-Cl)2 (5) can be prepared by reaction of 1 with the corresponding THF adduct of the metal halide. The iodide derivative of 2, [As2N2]ZrI2 (3) can be prepared by reaction with iodotrimethylsilane. The lithium complex 1 displays a very long lithium-arsenic bond distance of 3.162(10) A, and the yttrium complex 5 is the first known complex containing a yttrium-arsenic bond. Reduction of 2, 3 or 4 using C8K or activated magnesium decomposed the complexes in such a manner that the ligand was separated from the metal centre. Indirect evidence suggests this may be due to reduction of arsenic in the ligand in preference to the metal.     

Synthesis and studies on metal coordination with a novel carboxyamide ligand

Novel complexes of Co(II), Ni(II), Cu(II) and Pd(II) with the new ligand [N,N'-bis(2-carboxy-1-oxo-phenelenyl)ethylenediamine] (H2L) have been synthesized and characterized on the basis of elemental analyses, magnetic susceptibility, thermal, infrared, electronic, 1H NMR and EPR spectral studies. Infrared and 1H NMR spectra show that H2L acts as a binegative tetradentate ligand. Coordination occurs through deprotonated carboxylate oxygens and nondeprotonated amido nitrogens in all the complexes. Electronic spectral studies and magnetic moment values suggest N2O2 coordination around each metal centre with strong field square planar chromophores. The probable structures of the complexes have been assigned on the basis of spectral studies. The complex formation between M(II) [M(II) = Mn(II), Co(II), Ni(II), Cu(II) and Zn(II)] and (L2-) has also been studied potentiometrically in 75% aqueous DMF at 25 degrees C in 0.1 M NaClO4. The stability constants were found to follow the order: Mn(II) < Co(II) < Ni(II) < Cu(II) > Zn(II).     

Photocatalysis: a promising route for 21st century organic chemistry

One of the main goals of 21st century chemistry is to replace environmentally hazardous processes with energy efficient routes allowing to totally avoid the use and production of harmful chemicals and to maximise the quantity of raw material that ends up in the final product. Selective photocatalytic conversions will play a major role in this evolution and this account shows how photocatalysis is offering an alternative green route for the production of organics.     

Unprecedented eta3-M3 coordination mode in a terpyridine ligand

The gold(I) complex [Au3(C6F5)3(eta3-Fcterpy)](Fcterpy = 4'-ferrocenyl-2,2'ratio6',2'-terpyridine) represents the first example of a terpyridine ligand bonded to three different metals. The aurophilic interactions present in the molecule may contribute to the overall stability of the system, as was shown by DFT calculations. The positive Mayer indices (0.152 and 0.138), as well as the magnitude of the binding interaction between terpy and the Au(I)L fragments, support this interpretation.     

The coordination chemistry of group 15 element ligand complexes--a developing area

A survey of the contemporary challenges of the field of unsubstituted group 15 element ligand complexes (excluding N) is given. The focus of the article is on the coordination chemistry behaviour of such E(n) ligand complexes. This field is subdivided into two areas of reactivity: E(n) ligand complexes with (i) noncoordinated Lewis-acidic cations and (ii) Lewis-acidic coordination compounds containing at least one permanently coordinating ligand. In the latter case, insoluble 1D and 2D polymers respectively are obtained; however, under special conditions soluble, spherical, fullerene-like giant molecules are formed. These nano-sized molecules are up to 2.4 nm in diameter and are able to encapsulate small molecules in their holes. In contrast, the first-mentioned field uses weakly coordinating anions to obtain readily soluble di- and polycationic products. These show depolymerisation tendencies in solution under the formation of oligomer-monomer equilibria and thus reveal dynamic supramolecular aggregation processes.     

Rigidity extremes in coordination chemistry: a fine energetic balance in the isolation of a trapped ligand inversion intermediate

An unusual copper(ii) complex of a highly rigid and bulky ligand (a macrocycle-glyoxal condensate) has been synthesized and investigated via DFT calculations and structural characterisation.     

Syntheses, structures, and coordination chemistry of phosphole-containing hybrid calixphyrins: promising macrocyclic P,N2,X-mixed donor ligands for designing reactive transition-metal complexes

The syntheses, structures, and coordination chemistry of phosphole-containing hybrid calixphyrins (P,N2,X-hybrid calixphyrins) and the catalytic activities of their transition-metal complexes are reported. The 5,10-porphodimethene type 14pi-P,(NH)2,X- and 16pi-P,N2,X-hybrid calixphyrins (X = O, S, NH) are prepared via acid-promoted dehydrative condensation between a sigma4-phosphatripyrrane and the corresponding 2,5-bis[hydroxy(phenyl)methyl]heteroles followed by DDQ oxidation. Both spectroscopic and crystallographic data of the hybrid calixphyrins have revealed that the conformation and size of the macrocyclic platforms as well as the oxidation state of the -conjugated pyrrole-heterole-pyrrole (N-X-N) units vary considerably depending on the combination of heteroles. The sigma3-P,(NH)2,S- and sigma3-P,N2,S-hybrids react with Pd(OAc)2 and Pd(dba)2, respectively, to afford the same Pd(II)-P,N2,S-hybrid complex, in which the calixphyrin platform is regarded as a dianionic ligand. In the complexation with [RhCl(CO)2]2 in dichloromethane, the sigma3-P,N2,S-hybrid behaves as a neutral ligand to afford an ionic Rh(I)-P,N2,S-hybrid complex, whereas the sigma3-P,N2,NH-hybrid behaves as an anionic ligand to produce Rh(III)-P,N3-hybrid complexes. In the latter reaction, it is likely that a neutral Rh(I)-P,N3-hybrid complex, generated as a highly nucleophilic intermediate, undergoes C-Cl bond activation of the solvent. The complexation of AuCl(SMe2) with the sigma3-P,N2,X-hybrids (X = S, NH) leads to the formation of the corresponding Au(I)-monophosphine complexes. The spectral data and crystal structures of these metal complexes exhibit the hemilabile nature of the phosphole-containing hybrid calixphyrin platforms derived from the flexible phosphole unit and the redox active N-X-N units. The hybrid calixphyrin-palladium and -rhodium complexes catalyze the Heck reaction and hydrosilylations, respectively, implying that the metal center in the core is capable of activating the substrates under appropriate reaction conditions. The present results demonstrate the potential utility of the phosphole-containing hybrid calixphyrins as a new class of macrocyclic P,N2,X-mixed donor ligands for designing highly reactive transition-metal complexes.     

Imino sulfinamidines: synthesis and coordination chemistry of a novel class of chiral bidentate ligands

The new imino sulfinamidine ligand PhS(NHt-Bu)=NC(Me)=N(C6H3-2,6-iPr2), LH (11) was synthesized from N-(2,6-diisopropylphenyl)acetamidine (9) and N-tert-butyl phenylsulfinimidoyl chloride (10). Reaction of LH (11) with ZnEt2 or AlMe3 gave the complexes LZnEt (12) and LAlMe2 (13), respectively. The structures of 12 and 13 were determined by X-ray diffraction and were shown to contain L as a kappa2-N1,N5 bidentate ligand in a six-membered chelate. Formation of the magnesium complex (LMgN(TMS)2 x L2Mg) (14) from 11, MgI2, and KN(SiMe3)2 highlighted a secondary coordination mode of L, binding through the sulfinamidine nitrogens in a four-membered chelate.     

Helical and network coordination polymers based on a novel C2-symmetric ligand : SHG enhancement through specific metal coordination

Cu(I) and Ag(I) coordination polymers of an axially chiral "push-pull" ligand possess respectively 2-D network and helical structures and the coordination mode strongly influences the solid state SHG reduction/enhancement with respect to the free ligand.     

Novel 3D coordination palladium-network complex: a recyclable catalyst for Suzuki-Miyaura reaction

A novel solid-phase 3D metal-organic coordination network catalyst was prepared via self-assembly from PdCl2(CH3CN)2 and a trisphosphine hub with three flexible alkyl-chain linkers. This insoluble network complex efficiently catalyzed the Suzuki-Miyaura reaction under atmospheric conditions in water. This catalyst was reused without loss of catalytic activity.     

Unusual ligand coordination for cesium

When complexed by tetrabenzo-24-crown-8, the cesium ion can accommodate unprecedented ligation. The structures of the following complexes are presented. [Cs(tetrabenzo-24-crown-8)(eta 1-NCMe)2(eta 2-NCMe)][NO3] (1): triclinic P1, a = 12.0119(14) A, b = 13.3680(15) A, c = 13.7859(12) A, alpha = 89.124(8) degrees, beta = 66.928(9) degrees, gamma = 71.536(10) degrees, V = 1916.7(4) A3, Z = 2. [Cs(tetrabenzo-24-crown-8)(eta 1-NCMe)2(eta 2-CH2Cl2)][NO3] (2): triclinic, P1, a = 12.295(3) A, b = 13.295(3) A, c = 13.782(3) A, alpha = 89.105(17) degrees, beta = 66.096(18) degrees, gamma = 71.980(19) degrees, V = 1929.5(8) A3, Z = 2. These structures are the first reported examples of linear eta 2-acetonitrile coordination to any metal ion and the first structures illustrating eta 2-acetonitrile and dichloromethane ligation to an alkali metal ion. Possible steric and electronic origins of these unusual metal-ligand interactions are discussed.     

Synthesis and coordination chemistry of the first C2-chiral bisoxazine ligand

The ligand 2,5-bis(oxazinyl)-3,4-diethylpyrrole (4) was obtained in three reaction steps from the known pyrrole derivative 3,4-diethylpyrrole-2,5-dicarboxylic acid (1) which was first coupled with 2 molar equiv of (S)-1-benzoxy-3-butylamine to give the corresponding diamide 2 using dicyclohexylcarbodiimide and 1-hydroxybenzitriazole as coupling reagents. Subsequent hydrogenolysis of the benzyl ether functions yielded the dialcohol 3 which was cyclized in high yield after methylsulfonation and treatment with an excess of NaOH giving the target compound 2,5-bis[2-((S)-5-methyloxazinyl)]-3,4-diethylpyrrole (4). Lithiation of 4 by reaction with 1 molar equivalent of nBuLi at -78 degrees C and addition of [PdCl(2)(COD)] to the lithium pyrrolide cleanly gave the palladium complex 5 which was fully characterized. Complex 5 is unstable in solution and dimerizes to give a mixture of two diastereomeric helical dinuclear complexes, 6a and 6b, which cocrystallized in a 1:1 ratio to give X-ray quality single crystals. Both isomers possess virtual molecular 2-fold symmetry (though no crystallographic rotational symmetry), the molecular C(2)-axis being orthogonal to the Pd...Pd vector.