Effects of tributyltin(IV) chloride on the gametes and fertilization of Ascidia malaca (Ascidiacea: Tunicata)

Ascidia malaca gametes before fertilization incubated in 10^?5 or 10^?7 M solutions of tributyltin(IV) chloride, TBTCl, for 3 h appear highly damaged under transmission electron microscopy observation. Also, the fertilization process is affected by the compound: the damaged spermatozoa are present in the vitelline coat and the egg does not cleave. An increase of microbodies, structurally similar to peroxisomes, have been detected in the egg peripheral cytoplasm, probably in relation to their role in alleviating damage to some cellular components. The results have shown that the reproduction of ascidians under unfavourable environmental conditions is prevented. Copyright © 2003 John Wiley & Sons, Ltd.     

Aquachlorobis(4,4′,4′′‐tri‐tert‐butyl‐2,2′;6′,2′′‐terpyridine‐κ3N)terbium(III) diperchlorate ethanol disolvate

In the title compound, [TbCl(C₂₇H₃₅N₃)₂(H₂O)](ClO₄)₂·2C₂H₆O, the Tb^III ion has a coordination number of eight, composed of two tridentate substituted‐ter­pyridine ligands, a water mol­ecule and a bound Cl^? anion. The first coordination shell can be described as a distorted bicapped trigonal prism. The dihedral angles between pyridine rings belonging to the same tpy ligand range from 5.2 (5) to 16.8 (5)°.     

The binding ability of iron bonded to porphodimethene: structural, magnetic, and electronic relationship to iron porphyrin complexes

The availability of the parent compound, meso-hexaethylporphodimetheneiron(II), [(Et6N4)Fe] (2), of this report results from a novel synthetic methodology that makes [Et6N4Li2] (1) easily available. The major focus is on how the axial positions, which are the key reactive sites in metalloporphyrins, and the electronic configuration of the metal can be affected by the breakdown of the aromaticity of the porphyrin skeleton and by the nonplanar conformation of the ligand. DFT calculations indicate a 3B1(dz2)1(dyz)1 ground state for 2 versus the 3A2(dxz)1(dyz)1 ground state in the porphyrin analogue. The intermediate-spin state (S = 1) of 2 changed drastically upon addition of one or two axial ligands, as hexacoordination is preferred by iron(II). The hexacoordinate complexes [(Et6N4)Fe(L)(L')] (L = L' = THF, 3; L = L' = Py, 4; L = PhNO, L' = Py, 14) have been isolated and structurally characterized. Strong-field ligands lead to a low-spin diamagnetic state for iron(II), namely for complexes 4-7, 9, and 14, whereas 3 is a typical d6 high-spin complex, as is the pentacoordinate [(Et6N4)Fe(CN)]Bu4N (8). The structural analysis showed common features for 6, 7, 9, and 14: i) a small displacement of the metal from the N4 plane, and ii) an N4 cavity, larger than that in the corresponding porphyrins, affecting the Fe-N bond lengths. The 1H NMR spectrum is quite diagnostic of the two-fold symmetry in the diamagnetic hexacoordinate complexes, revealing either a D2h or a C2v symmetry. The CO stretching frequency (1951 cm(-1)) in complex 6 probes the good electron density at the metal. The one-electron oxidation of 2 led to pentacoordinate iron(III) derivatives [(Et6N4)Fe(Cl)] (10), [(Et6N4)2Fe2(mu-O)] (11), and [(Et6N4)2Fe2(mu-p-OC6H4-O)] (12). Complex 10 is a typical high-spin iron(III) (5.85muB at 298 K), while 11 and 12 behave as antiferromagnetic coupled iron(III) (J = -9.4cm(-1), 12, and J = -115cm(-1), 11). In complexes 10, 11, and 12 iron is sitting in a quite distorted square pyramidal geometry, in which the ligand displays a very distorted roof conformation with different degrees of ruffling. Distinctive structural and magnetic features have been found for the nitrosyl derivative [(Et6N4)Fe-NO], which has a low-spin state (S = 1/2) and the following structural parameters: Fe-N-O, 147.3(2) degrees; Fe-N, 1.708(2) A; N-O, 1.172(3) A. A comparative structural, magnetic, and theoretical analysis of the compounds listed above has been made with the analogous porphyrin derivatives. The detailed structural investigation has been mapped through the X-ray analysis of 2, 7, 8, 9, 11, 13, and 14.     

Nitrile-functionalized pyridinium ionic liquids: synthesis, characterization, and their application in carbon-carbon coupling reactions

A series of relatively low-cost ionic liquids, based on the N-butyronitrile pyridinium cation [C(3)CNpy](+), designed to improve catalyst retention, have been prepared and evaluated in Suzuki and Stille coupling reactions. Depending on the nature of the anion, these salts react with palladium chloride to form [C(3)CNpy](2)[PdCl(4)] when the anion is Cl(-) and complexes of the formula [PdCl(2)(C(3)CNpy)(2)][anion](2) when the anion is PF(6)(-), BF(4)(-), or N(SO(2)CF(3))(2)(-). The solid-state structures of [C(3)CNpy]Cl and [C(3)CNpy](2)[PdCl(4)] have been established by single-crystal X-ray diffraction. The catalytic activity of these palladium complexes following immobilization in both N-butylpyridinium and nitrile-functionalized ionic liquids has been evaluated in Suzuki and Stille coupling reactions. All of the palladium complexes show good catalytic activity, but recycling and reuse is considerably superior in the nitrile-functionalized ionic liquid. Inductive coupled plasma spectroscopy reveals that the presence of the coordinating nitrile moiety in the ionic liquid leads to a significant decrease in palladium leaching relative to simple N-alkylpyridinium ionic liquids. Palladium nanoparticles have been identified as the active catalyst in the Stille reaction and were characterized using transmission electron microscopy.     

Single metal four-electron reduction by U(ii) and masked “U(ii)” compounds

The redox chemistry of uranium is dominated by single electron transfer reactions while single metal four-electron transfers remain unknown in f-element chemistry. Here we show that the oxo bridged diuranium(iii) complex [K(2.2.2-cryptand)]₂[{((Me₃Si)₂N)₃U}₂(μ-O)], 1, effects the two-electron reduction of diphenylacetylene and the four-electron reduction of azobenzene through a masked U(ii) intermediate affording a stable metallacyclopropene complex of uranium(iv), [K(2.2.2-cryptand)][U(η²-C₂Ph₂){N(SiMe₃)₂}₃], 3, and a bis(imido)uranium(vi) complex [K(2.2.2-cryptand)][U(NPh)₂{N(SiMe₃)₂}₃], 4, respectively. The same reactivity is observed for the previously reported U(ii) complex [K(2.2.2-cryptand)][U{N(SiMe₃)₂}₃], 2. Computational studies indicate that the four-electron reduction of azobenzene occurs at a single U(ii) centre via two consecutive two-electron transfers and involves the formation of a U(iv) hydrazide intermediate. The isolation of the cis-hydrazide intermediate [K(2.2.2-cryptand)][U(N₂Ph₂){N(SiMe₃)₂}₃], 5, corroborated the mechanism proposed for the formation of the U(vi) bis(imido) complex. The reduction of azobenzene by U(ii) provided the first example of a “clear-cut” single metal four-electron transfer in f-element chemistry.

Both a masked and the actual complex [U(ii){N(SiMe₃)₂}₃]⁺ effect the reduction of azobenzene to yield a U(vi) bis-imido species providing the first example of a “clear-cut” metal centred four-electron reduction in f-element chemistry.     

A Mesoionic Diselenolene Anion and the Corresponding Radical Dianion

Dichalcogenolenes are archetypal redox non-innocent ligands with numerous applications. Herein, a diselenolene ligand with fundamentally different electronic properties is described. A mesoionic diselenolene was prepared by selenation of a C2-protected imidazolium salt. This ligand is diamagnetic, which is in contrast to the paramagnetic nature of standard dichalcogenolene monoanions. The new ligand is also redox-active, as demonstrated by isolation of a stable diselenolene radical dianion. The unique electronic properties of the new ligand give rise to unusual coordination chemistry. Thus, preparation of a hexacoordinate aluminum tris(diselenolene) complex and a Lewis acidic aluminate complex with two ligand-centered unpaired electrons was achieved.     

Alcohol‐Induced C−N Bond Cleavage of Cyclometalated N‐Heterocyclic Carbene Ligands with a Methylene‐Linked Pendant Imidazolium Ring

Reaction of the pentamethylcyclopentadienyl rhodium iodide dimer [Cp*RhI₂]₂ with 1,1′‐diphenyl‐3,3′‐methylenediimidazolium diiodide in non‐alcohol solvents, in the presence of base, led to the formation of bis‐carbene complex [Cp*Rh(bis‐NHC)I]I (bis‐NHC=1,1′‐diphenyl‐4,4′‐methylenediimidazoline‐5,5′‐diylidene). In contrast, when employing alcohols as the solvent in the same reaction, cleavage of a methylene C?N bond is observed, affording ether‐functionalized (cyclometalated) carbene ligands coordinated to the metal center and the concomitant formation of complexes with a coordinated imidazole ligand. Studies employing other 1,1′‐diimidazolium salts indicate that the cyclometalation step is a prerequisite for the activation/scission of the C?N bond and, based on additional experimental data, a S_N2 mechanism for the reaction is tentatively proposed.     

Richness of isomerism in labile octahedral Werner-type cobalt(II) complexes demonstrated by 19F NMR spectroscopy: structure and stability

The cobalt(II) complexes [CoL2(R2-Py)2] (1-4) where HLA = 1,1,1-trifluoro-5,5-dimethyl-2,4-hexanedione, R2-Py = 4-methylpyridine (1), HLB = 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione, R2-Py = 4-methylpyridine (2), 4-phenylpyridine (3) and S-(-)-1-(4-pyridyl)ethanol (4) were prepared by two-step reactions. X-ray structure analysis of [CoLA2(CH3-Py)2] revealed the {trans(N)-trans(CF3)-trans} configuration for the complex obtained by crystallization from ethanol. A dynamic equilibrium between the five possible stereoisomers was observed for each complex 1-4 in solution by 19F NMR spectroscopy. The criteria used for full NMR assignment (180-265 K) include comparison of integral ratios, cis(N) and trans(N) differentiation in presence of the chiral amine [S-(-)-1-(4-pyridyl)ethanol], effect of solvent polarity on the relative stabilities of the five isomers and observation of trans influences in a mixture of complexes. Thermodynamic parameters for the equilibria between the isomers of 2 in CD2Cl2 (DeltaHi,j, DeltaSi,j and Ki,j) were obtained from signal integrals. The two trans(N) isomers are slightly more stable than the three cis(N) isomers at low temperature [DeltaGdegreesi,j (max) = 2.8 kJ mol(-1) at 179.8 K], but this stability difference almost vanishes with increasing temperature [DeltaGdegreesi,j (max) = 1.0 kJ mol(-1) at 265.0 K]. The values found for DeltaHdegreesi,j are relatively small and largely entropy compensated.     

The pi complexation of alkali and alkaline earth ions by the use of meso-octaalkylporphyrinogen and aromatic hydrocarbons

The full metallation of meso-octaalkylporphyrinogens [R8N4H4] (R=Et, 1; nBu, 2; CH2Ph, 3; (CH2)4, 4) with heavy alkali metals (M = K, Rb, Cs) leads to the porphyrinogen-M4 compounds, in which the solvation of the alkali cations is largely assured by the intra- and intermolecular phi-interactions with the pyrrolyl anions. Such a mode of complexation results in a structural diversity as a function of the meso substituents, the size of the metal ion, and the solvent. The structure of the unsolvated polymers [R8N4M4]n (R= Et, M=K, 5; M=Rb, 6; M=Cs, 7; R= (CH2)4, M = Rb, 8; M = Cs, 9) have been clarified through the X-ray analysis of 7 recrystallized from diglyme. The structure shows that the tetraanion binds two Cs ions inside the cavity, which display in one case eta1:eta1:eta1:eta1 and in the other eta5:eta5:eta5:eta5 interaction modes. Bidimensional polymerization is assured by four Cs ions, which each bind at the eta5 position on the exo face of each pyrrole. With bulkier meso substituents, different polymeric forms are obtained (R = nBu, M = K, 10; M = Rb, 11; M = Cs, 12), and their structures were clarified through the X-ray analysis of 10, which was recrystallized from dimethoxyethane. The polymeric units are made up by the monomeric units [Bu8N4K2]2-, in which one potassium is eta1:eta1:eta1:eta5 and the other eta5:eta1:eta5:eta1 bonded inside the porphyrinogen cavity. In the case of R=CH2Ph, the monomeric anion [(PhCH2)8N4K2]2- (13) has been structurally identified. The metallation of 1 and 2 with active forms of alkaline earth metals (M' = Ca, Sr, Ba) led to dinuclear compounds [R,N4M'2] (R = Et, M' = Ca, 14; M'=Sr, 15; M'=Ba, 16; R=nBu. M'=Ba, 18), in which both metals inside the cavity are eta1:eta3:eta1:eta3 (Ca) and eta1:eta5:eta1:eta5 (Sr and Ba) bonded to the porphyrinogen tetraanion. The coordination sphere of each metal ion is completed by two THF molecules, which, in the case of Ba, are easily replaced by an arene ring [Bu8N4Ba2(eta6-arene)2] (arene=durene, 22; naphthalene, 23; toluene, 24; benzene, 25). The X-ray structures of 14, 15, 18, 22, and 23 are described in detail. We have tried to establish a relationship between the solid-state and solution structures by analyzing the 1H NMR spectra of the porphyrinogen complexes.