De-Cai Fang

A Highly Selective Fluorescent Chemosensor for AlIII Ion and Fluorescent Species Formed in the Solution

A chemosensor for the Al(3+) ion, 1-[(3-hydroxypyridin-2-ylamino)methylene]naphthalen-2(1H)-one (H2L), based on inhibited excited-state intramolecular proton transfer was synthesized. The experimental and theoretical calculations at B3LYP+PCM/6-31G(d) revealed that Al(3+) and H2L form a 1:1 complex, [AlL(OH)(H2O)]2, in dimethyl sulfoxide that exhibits two remarkably enhanced fluorescent emissions at 523 and 553 nm. It is confirmed that H2L could be used to detect Al(3+) ions in cells by bioimaging.

Thorium Oxo and Sulfido Metallocenes: Synthesis, Structure, Reactivity, and Computational Studies

The synthesis, structure, and reactivity of thorium oxo and sulfido metallocenes have been comprehensively studied. Heating of an equimolar mixture of the dimethyl metallocene [η(5)-1,2,4-(Me(3)C)(3)C(5)H(2)](2)ThMe(2) (2) and the bis-amide metallocene [η(5)-1,2,4-(Me(3)C)(3)C(5)H(2)](2)Th(NH-p-tolyl)(2) (3) in refluxing toluene results in the base-free imido thorium metallocene, [η(5)-1,2,4-(Me(3)C)(3)C(5)H(2)](2)Th═N(p-tolyl) (4), which is a useful precursor for the preparation of oxo and sulfido thorium metallocenes [η(5)-1,2,4-(Me(3)C)(3)C(5)H(2)](2)Th═E (E = O (5) and S (15)) by cycloaddition-elimination reaction with Ph(2)C═E (E = O, S) or CS(2). The oxo metallocene 5 acts as a nucleophile toward alkylsilyl halides, while sulfido metallocene 15 does not. The oxo metallocene 5 and sulfido metallocene 15 undergo a [2 + 2] cycloaddition reaction with Ph(2)CO, CS(2), or Ph(2)CS, but they show no reactivity with alkynes. Density functional theory (DFT) studies provide insights into the subtle interplay between steric and electronic effects and rationalize the experimentally observed reactivity patterns. A comparison between Th, U, and group 4 elements shows that Th(4+) behaves more like an actinide than a transition metal.

A Highly Selective Chemosensor for Al(III) and Zn(II) and Its Coordination with Metal Ions

This paper reports a fluorescence chemosensor, N-(benzimidazol-2-yl)salicylaldimine (H2L), for Zn(II) and Al(III) ions. H2L has high selectivity for Al(III) in dimethyl sulfoxide (DMSO) and for Zn(II) in N,N-dimethylformamide (DMF). In methanol, Zn(II) and Al(III) could also be distinguished by H2L with different excitation wavelengths. The fluorescent species [Zn(HL)(H2O)(CH3OH)](+), [Zn(HL)(H2O)(DMF)](+), [Al(HL)2(OH)(H2O)], and [Al(HL)(OH)2(H2O)(DMSO)] formed in solution were established by a combination of experimental and theoretical methods, including Jobs plot, (1)H NMR titration, electrospray inonization mass spectrometry (ESI-MS), and B3LYP-SCRF/6-31(d) and TD-B3LYP-SCRF/6-31G* density functional theory methods. The results show that Zn(II) and Al(III) are all coordinated to the imine nitrogen atom and the hydroxyl oxygen atom from H2L, which is the same as the M(2+) ions in the obtained mononuclear complexes [M(HL)2(CH3OH)2] (where M = Cd, Ni, Co, and Mg). The detection limits of H2L for Zn(II) were 5.98 μM in methanol and 5.76 μM in DMF, while the detection limits of H2L for Al(III) were 3.3 μM in methanol and 5.25 μM in DMSO. Furthermore, it is also confirmed that H2L has low toxicity for HeLa cells and could be used to detect Zn(II) and Al(III) ions in living cells by bioimaging.

A Base‐Free Thorium–Terminal‐Imido Metallocene: Synthesis, Structure, and Reactivity

The synthesis, structure, and reactivity of a base-free thorium terminal-imido metallocene have been comprehensively studied. Treatment of thorium metallocenes [{η(5)-1,2,4-(Me(3)C)(3)C(5)H(2)}(2)ThMe(2)] and [{η(5)-1,3-(Me(3)C)(2)C(5)H(3)}(2)ThMe(2)] with RNH(2) gives diamides [{η(5)-1,2,4-(Me(3)C)(3)C(5)H(2)}(2)Th(NHR)(2)] (R=Me (7), p-tolyl (8)) and [{η(5)-1,3-(Me(3)C)(2)C(5)H(3)}(2)Th(NH-p-tolyl)(2)] (9), respectively. Diamides 7 and 9 do not eliminate methylamine or p-toluidine, but sublime without decomposition at 150 °C under vacuum (0.01 mmHg), whereas diamide 8 is converted at 140 °C/0.01 mmHg into the primary amine p-tolyl-NH(2) and [{η(5)-1,2,4-(Me(3)C)(3)C(5)H(2)}(2)Th=N(p-tolyl)] (10), which may be isolated in pure form. Imido metallocene 10 does not react with electrophiles such as alkylsilyl halides; however, it reacts with electron-rich or unsaturated reagents. For example, reaction of 10 with sulfur affords the metallacycle [{η(5)-1,2,4-(Me(3)C)(3)C(5)H(2)}(2)Th{N(p-tolyl)S-S}]. Imido 10 is an important intermediate in the catalytic hydroamination of internal alkynes, and an efficient catalyst for the trimerization of PhCN. Density functional theory (DFT) studies provide a detailed understanding of the experimentally observed reactivity patterns.

Hydrothermal Reaction of Cu(II)/Pyrazine-2,3,5-tricarboxylic acid and Characterization of the Copper(II) Complexes

Four copper(II) complexes [Cu3(PZHD)2(2,2-bpy)2(H2O)2].3H2O (1), [Cu3(DHPZA)2(2,2-bpy)2] (2), [Cu(C2O4)phen(H2O)].H2O (3), and [Cu3(PZTC)2(2,2-bpy)2].2H2O (4) were synthesized by hydrothermal reactions, in which the complexes 1-3 were obtained by the in situ Cu(II)/H3PZTC reactions (PZHD3- = 2-hydroxypyrazine-3,5-dicarboxylate, 2,2-bpy = 2,2-bipyridine, DHPZA3- = 2,3-dihydroxypyrazine-5-carboxylate, C2O42- = oxalate, phen = 1,10-phenanthroline, and H3PZTC = pyrazine-2,3,5-tricarboxylic acid). The Cu(II)/H3PZTC hydrothermal reaction with 2,2-bpy, without addition of NaOH, results in the formation of complex 4. The complexes 1-4 and transformations from H3PZTC to PZHD3-, DHPZA3-, and C2O4(2-) were characterized by single-crystal X-ray diffraction and theoretical calculations. In the complexes 1, 2, and 4, the ligands PZHD3-, DPHZA3-, and PZTC3- all show pentadentate coordination to Cu(II) ion forming three different trinuclear units. The trinuclear units in 1 are assembled by hydrogen-bonding and pi-pi stacking to form a 3D supramolecular network. The trinuclear units in 2 acting as building blocks are connected by the carboxylate oxygen atoms forming a 2D metal-organic framework (MOF) with (4,4) topology. While the trinuclear units in 4 are linked together by the carboxylate oxygen atoms to form a novel 2D MOF containing right- and left-handed helical chains. The theoretical characterization testifies that electron transfer between OH- and Cu2+ and redox of Cu 2+ and Cu+ are the most important processes involved in the in situ copper Cu(II)/H3PZTC reactions, forming complexes of 1-3.

Hydrothermal in situ synthesis and characterization of Cu(II) complexes.

The hydrothermal in situ Cu(II)/2,3-pyrazine dicarboxylic acid reactions at 100 and 140 degrees C result in Cu(II) 3-hydroxy-2-pyrazinecarboxylate and oxalate complexes, respectively. This is the first example of a combination of experimental and theoretical study on in situ metal/ligand reactions under hydro- and solvothermal conditions.

An Actinide Metallacyclopropene Complex: Synthesis, Structure, Reactivity, and Computational Studies

The synthesis, structure, and reactivity of an actinide metallacyclopropene were comprehensively studied. The reduction of [η(5)-1,2,4-(Me3C)3C5H2]2ThCl2 (1) with potassium graphite (KC8) in the presence of diphenylacetylene (PhC≡CPh) yields the first stable actinide metallacyclopropene [η(5)-1,2,4-(Me3C)3C5H2]2Th(η(2)-C2Ph2) (2). The magnetic susceptibility data show that 2 is indeed a diamagnetic Th(IV) complex, and density functional theory (DFT) studies suggest that the 5f orbitals contribute to the bonding of the metallacyclopropene Th-(η(2)-C═C) moiety. Complex 2 shows no reactivity toward alkynes, but it reacts with a variety of heterounsaturated molecules such as aldehyde, ketone, carbodiimide, nitrile, organic azide, and diazoalkane derivatives. DFT studies complement the experimental observations and provide additional insights. Furthermore, a comparison between Th and group 4 metals reveals that Th(4+) shows unique reactivity patterns.

Pd(OAc)2-catalyzed C-H activation/C-O cyclization: mechanism, role of oxidant-probed by density functional theory.

A series of density functional theory determinations have been carried out to characterize Pd(OAc)2-catalyzed C-H activation and subsequent intramolecular C-O bond-coupling of phenyl-tert-butanol in perfluorobenzene (C6F6) solvent. Full, nontruncated models of the real chemical transformations were studied, with structures in agreement with recent X-ray determinations. Conformational analyses have provided thermodynamic validity of the geometric structures used. The B3LYP/DZVP and B3LYP/BS1 methods (BS1 = TZVP(H,C,O) + SDD(Pd,I)) were comparatively employed, with C6F6 solvent contributions accounted for by the IDSCRF method; key transition states were confirmed by intrinsic reaction coordinate determinations. The novel reaction mechanism proposed was divided into the following four steps: C-H activation, oxidation, reductive elimination, catalyst recovery. Two competing reaction routes were quantitatively compared, differing in the oxidation state of Pd (+2 vs +4). Results reveal the pathway involving Pd(IV) intermediates to be more spontaneous and, therefore, more probable than the Pd(II) path, the latter hindered by a kinetically inaccessible reductive elimination step, with total energy and free energy barriers of 41.0 and 38.6 kcal·mol(-1), respectively. The roles played by the oxidant and Pd(IV) species have also been addressed through Baders atoms-in-molecules wave function analyses, providing a quantitative electronic metric for C-H activation chemistry.

Experimental and Computational Studies on the Reactivity of a Terminal Thorium Imidometallocene towards Organic Azides and Diazoalkanes

The reaction of the base-free terminal thorium imido complex [{η(5)-1,2,4-(Me3C)3C5H2}2Th=N(p-tolyl)] (1) with p-azidotoluene yielded irreversibly the tetraazametallacyclopentene [{η(5)-1,2,4-(Me3C)3C5H2}2Th{N(p-tolyl)N=N-N(p-tolyl)}] (2), whereas the bridging imido complex [{[η(5)-1,2,4-(Me3C)3C5H2]Th(N3)2}2{μ-N(p-tolyl)}2][(n-C4H9)4N]2 (3) was isolated from the reaction of 1 with [(n-C4H9)4N]N3. Unexpectedly, upon the treatment of 1 with 9-diazofluorene, the NN bond was cleaved, an Nu2005atom was transferred, and the η(2)-diazenido iminato complex [{η(5)-1,2,4-(Me3C)3C5H2}2Th{η(2)-[N=N(p-tolyl)]}{N=(9-C13H8)}] (4) was formed. In contrast, the reaction of 1 with Me3SiCHN2 gave the nitrilimido complex [{η(5)-1,2,4-(Me3C)3C5H2}2Th{NH(p-tolyl)}{N2CSiMe3}] (5), which slowly converted into [{η(5)-1,2,4-(Me3C)3C5H2}{η(5):κ-N-1,2-(Me3C)2-4-CMe2(CH2NN=CHSiMe3)C5H2}Th{NH(p-tolyl)}] (6) by intramolecular C-H bond activation. The experimental results are complemented by density functional theory (DFT) studies.

A highly selective and sensitive Zn(II) complex-based chemosensor for sequential recognition of Cu(II) and cyanide

Two new Schiff base complexes, [ZnL(Ac)]2 (1) and [CuLCl]·H2O (2) (HL = 2-(2-hydroxynaphthylmethylene)aminophenylbenzimidazole, Ac = acetate) were synthesized by a one-pot reaction and characterized by elemental analyses, IR and single-crystal X-ray diffraction. Fluorescence of complex 1 showed on-off-on switching when Cu(2+) and cyanide were sequentially detected. This phenomenon was investigated by UV-Vis absorption, fluorescence and ESI-MS spectra, and theoretical calculations to explain the response. Complex 1 can selectively respond to Cu(2+) with the fluorescence turn-off owing to the formation of complex 2 in the solution. Interestingly, the quenched fluorescence of complex 1 by Cu(2+) ions could be turned on after the addition of cyanide owing to the displacement of L(-) by CN(-) to form [Cu(CN)x](n-), making complex 1 a selective CN(-) probe. In addition, the results of the MTT assay experiment indicate that complex 1 has a low toxicity to cells and can be used to detect intracellular Cu(2+) ion by live cell imaging.