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We report the synthesis of a heterogenous silver catalyst stabilized by bidentate N-heterocyclic carbene ligands. The heterogeneous nature of the catalyst is inherently derived from the unprecedented internal structural features observed for the catalyst. X-ray studies show that the silver complex forms a two-dimensional cross-linked system, where one dimension of the network is formed by inorganic polymer strings and the second direction is formed by the interconnection of these inorganic strings with NHC bidentate ligands. This organized internal arrangement renders the complex insoluble in many common organic solvents and enables its utilization as a reusable heterogeneous catalyst in multicomponent A3 coupling reactions. Notably, propargylic amines were obtained with yields of up to 97%, and the catalyst demonstrated reusability for six cycles. These results can facilitate the further development of heterogeneous NHC catalysts. [ABSTRACT FROM AUTHOR]

This study reports the synthesis and characterization of new molybdenum compounds bearing benz[e]indenyl and benz[f]indenyl ligands. The capability of the ligands to undergo η5-to-η3 haptotropic rearrangement was evidenced on reactions with tris(pyrazolyl)methane. Appearance of the η3-coordination mode was determined by NMR spectroscopy and X-ray structure analysis on a single crystal. [ABSTRACT FROM AUTHOR]

Orthoplatinated complexes [Pt(C^C*)(acac)] (1R), in which C^C* is orthoplatinated 3-R-1-phenyl-1H-benzo[d]imidazol-2-ylidene and R = Me and Ph, reacted with 1′-(diphenylphosphino)ferrocene-1-carboxylic acid (Hdpf) under protonation of the acetylacetonate ligand (acac) to produce the corresponding phosphinocarboxylate bischelate complexes [Pt(C^C*)(dpf-κ2O,P)] (2R) as single isomers with trans-P,C(carbene) geometry. The compounds were fully characterized by elemental analysis, spectroscopic methods, single-crystal X-ray diffraction analysis, and cyclic voltammetry. In addition, DFT calculations were used to determine differences in energy and the bonding situation between 2R and the hypothetical geometric isomers 3R with a trans-P,C(phenyl) arrangement. The experimental and theoretical results are consistent with the antisymbiosis effect observed in complexes of soft metal ions, namely with weakening of Pt–C bonds by strongly trans-influencing ligands. [ABSTRACT FROM AUTHOR]

Novel hybrid ligands based on [1,2,3]-diazaphosphole (dap) were prepared and their coordination behaviour toward selected transition metals has been studied. The syntheses and spectroscopic properties of polydentate bis(5-t-butyl-[1,2,3]-diazaphosphol-2-yl)-dimethylsilane (BdapsH,tBu) and bis(4-methyl-5-ethyl-[1,2,3]-diazaphosphol-2-yl)-dimethylsilane (BdapsMe,Et) are reported. In zerovalent compounds of the type [M(CO)4(κ2-P,P′-BdapsR1,R2)] (R1 = Me, R2 = Et, M = Cr, Mo and W; R1 = H, R2 = t-Bu, M = W) and [Ni(κ2-P,P′- BdapsH,tBu)2] the ligand serves as a P,P′-donor, giving rigid six-membered chelate rings. BdapsMe,Et is also capable of behaving as an N,N′-chelator as confirmed by isolation of high-spin chelate complex [CoBr2(κ2-N,N′-BdapsMe,Et)]. The reaction of parent 2H-4-methyl-5-ethyl-[1,2,3]-diazaphosphole with NiBr2·DME yielded paramagnetic compound [NiBr2(κ-N-dap)2], where the dap heterocycle bonds with the nickel(II) centre via a 1-nitrogen donor atom in a distorted tetrahedral environment. All the studied complexes showing different coordination modes of the new ligands were fully characterized, including single-crystal X-ray diffraction analysis. [ABSTRACT FROM AUTHOR]

Selectivity and rate of complex formation with metal radionuclides are crucial parameters for the utilization of ligating systems in nuclear medicine. One of the very suitable metals used in these applications is copper, which has a number of radioisotopes with useful properties. The thermodynamic and kinetic properties of Cu(ii) complexes with 10 macrocyclic 1,4,8-trimethylcyclam-based ligands having one coordinating acid pendant arm (Me3cyclam–R) were investigated in solution, allowing a direct comparison of the influence of the particular pendant arm on the properties of the complexes. They include the derivative with R = CH2CO2H (HL1) and a family containing various phosphorus acids R = CH2P(O)(OH)–X, where X = OEt (HL2); X = OH (H2L3); X = H (HL4); X = CH2CH2CO2H (H2L5); X = CH2P(O)(H)OH (H2L6); X = CH2P(O)(OH)2 (H3L7); X = CH2N(CH2C6H5)2 (HL8); X = CH2NH2 (HL9) and X = CH2N(CH2CO2H)2 (H3L10). For comparison, 1,4,8,11-tetramethylcyclam (TMC: R = Me) was used. The formation kinetics showed that ligands endowed with a coordinating pendant arm bind Cu(ii) ions much faster when compared to TMC. At pH ＜ 4, the fastest complexation was observed for acetate derivative HL1. At higher pH and, especially, at pH relevant for living and biocompatible systems (pH ≈ 6–7), the ligands with methylene(phosphonatomethyl)phosphinate and methylenephosphonate pendant arms (H3L7 and H2L3) showed the fastest complexation. Acid-assisted dissociation of Cu(ii) complexes with the ligands endowed with a coordinating pendant arm is similar for all studied systems (τ1/2 = 7–35 min, 1 M HClO4, 25 °C). In contrast, the inertness of the Cu(ii)–TMC complex is much lower (τ1/2 = 22 s under the same conditions). Potentiometric study of the selected ligands has confirmed a high thermodynamic selectivity of the studied ligands for Cu(ii) binding over complexation of Ni(ii) and Zn(ii) (the differences between the stability constants reach 6–7 orders of magnitude). Fast complexation of Cu(ii) at radio-level concentrations was observed, showing that the best ligands for potential in vivo use are those containing phosphonate or mixed geminal phosphinate–phosphonate pendant groups. One of the ligands (H2L3) and three Cu(ii) complexes (of H2L5, H3L7 and H3L10) were structurally characterized by means of X-ray diffraction study. The predicted conformation I of the macrocycle was confirmed in all three complexes. [ABSTRACT FROM AUTHOR]

A novel method enabling the synthesis of receptors based on the calix[4]arenes immobilized in the partial cone conformation is reported. The application of a protection/deprotection strategy using nosyl groups enables the regioselective introduction of functional groups (NO2 and NH2) into the upper rim of calix[4]arenes, leading finally to the substitution pattern so far inaccessible to calixarene chemistry. The introduction of two ureido functions at the para positions of the partial cone conformer yields a novel type of receptor which can bind anions even in a highly competitive solvent (DMSO). This revealed that the partial cone conformation, so far rather ignored in supramolecular chemistry, can be also very useful in design of novel anion receptors. [ABSTRACT FROM AUTHOR]

Amide FcCONHC(CH2OH)3 (1; Fc = ferrocenyl), prepared from fluorocarbonylferrocene and tris(hydroxymethyl)methylamine, reacts with (Bu4N)3[H3V10O28] in N,N-dimethylacetamide to afford a salt containing a bis(triolato) capped hexavanadate anion bearing two ferrocenylgroups at its periphery, (Bu4N)2[{FcC(O)NHC(CH2O)3}2V6O13] (2). Compounds 1 and 2 were characterised by elemental analysis, spectroscopic methods (IR, NMR, and MS) and by cyclic voltammetry; the crystal structures of 1·1/2CH3CO2Et and (Bu4N)2[{FcC(O)NHC(CH2O)3}2V6O13]·2Me2NCHO were determined by X-ray diffraction analysis. Single-point DFT calculations performed for the isolated hexavanadate anion revealed the presence of 3-centre 4-electron (3c4e) O–V–O bonds on the hexavanadate cage, which are responsible for the high energy of the occupied frontier orbitals. The upper eleven occupied molecular orbitals including the HOMO are all delocalized over the hexavanadate cage and, therefore, any electrochemical oxidation can be expected to occur preferentially at the hexavanadate anion without affecting the pendant ferrocene moieties. [ABSTRACT FROM AUTHOR]