The importance of a single methyl group in determining the reaction chemistry of pentamethylcyclopentadienyl cyclooctatetraenyl uranium metallocenes

The steric factors that allow trivalent [(C(5)Me(5))(3)U] (1) to function as a three-electron reductant with C(8)H(8) to form tetravalent [{(C(5)Me(5))(C(8)H(8))U}(2)(μ-C(8)H(8))] (2) have been explored by examining the synthesis and reactivity of the intermediate, "[(C(5)Me(5))(2)(C(8)H(8))U]" (3), and the slightly less crowded analogues, [(C(5)Me(5))(C(5)Me(4)H)(C(8)H(8))U] and [(C(5)Me(4)H)(2)(C(8)H(8))U], that have, successively one less methyl group. The reaction of [{(C(5)Me(5))(C(8)H(8))U(μ-OTf)}(2)] (4; OTf=OSO(2) CF(3)) with two equivalents of KC(5)Me(5) in THF gave ring-opening to "[(C(5)Me(5))(C(8)H(8))U{O(CH(2))(4)(C(5) Me(5))}]" consistent with in situ formation of 3. Reaction of 4 with two and four equivalents of KC(5)Me(4)H generates two equivalents of [(C(5)Me(5))(C(5)Me(4)H)(C(8)H(8))U] (5) and [(C(5)Me(4)H)(2)(C(8)H(8))U] (6), respectively, which in contrast to 3 were isolable. Tetravalent 5 reduces phenazine and PhEEPh (E=S, Se, and Te) to form the tetravalent uranium reduction products, [{(C(5)Me(5))(C(8)H(8))U}(2)(μ-C(12)H(8)N(2))] (7), [{(C(5)Me(5))(C(8)H(8))U}(2)(μ-SPh)(2)] (8), [{(C(5)Me(5))(C(8)H(8))U}(2)(μ-SePh)(2)] (9), and [{(C(5)Me(5))(C(8)H(8))U}(2)(μ-TePh)(2)] (10), consistent with sterically induced reduction. In contrast, the less sterically crowded 6 does not react with these substrates.     

Traceability along the production chain of Italian tomato products on the basis of stable isotopes and mineral composition

The paper shows the variability of stable isotope ratios and mineral composition in tomato and derivatives along the production chain (juice, passata and paste) in order to evaluate the possibility of tracing their geographical origin. The ratios (13)C/(12)C, (15)N/(14)N, (18)O/(16)O, D/H, (34)S/(32)S and the content of Li, Be, B, Na, Mg, Al, P, K, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Rb, Sr, Y, Mo, Ag, Cd, Sn, Sb, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Tm, Yb, Ir, Tl, Pb, U and of nitrates, chlorides, sulphates and phosphates were measured by Isotope Ratio Mass Spectrometry, Inductively Coupled Plasma Mass Spectrometry and Ion Chromatography, respectively. The tomato products were from three Italian regions - Piedmont, Emilia Romagna, and Apulia. By applying linear discriminant analysis on 17 of these parameters (Gd, La, Tl, Eu, Cs, Ni, Cr, Co, δ(34)S, δ(15)N, Cd, K, Mg, δ(13)C, Mo, Rb and U) excellent discrimination among products from the three regions was achieved. Irrespective of the processing technology, over 95% of the samples were correctly reclassified in cross-validation into the production site. The use of these parameters will allow the development of analytical control procedures that can be used to check the geographical provenance of Italian tomatoes and products derived from them.     

Coordination and reductive chemistry of tetraphenylborate complexes of trivalent rare earth metallocene cations, [(C5Me5)2Ln][(μ-Ph)2BPh2

The reactivity of the tetraphenylborate salts of the rare earth metallocene cations [(C(5)Me(5))(2)Ln][(μ-Ph)(2)BPh(2)] (Ln = Y, 1; Sm, 2) has been investigated with substrates that undergo reduction with f element complexes to probe metal-substrate interactions prior to reduction. Results with NaN(3), 1-adamantyl azide, acetone, benzophenone, phenanthroline, pyridine, azobenzene, and phenazine are described. Not only were coordination complexes isolated, but substrate reduction by (BPh(4))(-) was also observed. Complex 1 reacts with NaN(3) to form the azide [(C(5)Me(5))(2)YN(3)](x), 3, which crystallizes as [(C(5)Me(5))(2)Y(μ-N(3))](3), 4, when obtained from 1 and 1-adamantyl azide. The samarium analogue [(C(5)Me(5))(2)SmN(3)](x), 5, can be produced similarly from 2 and NaN(3) and crystallized from MeCN as [(C(5)Me(5))(2)Sm(NCMe)(μ-N(3))](3), 6, and {[(C(5)Me(5))(2)Sm(μ-N(3))][(C(5)Me(5))(2)Sm(NCMe)(μ-N(3))]}(n), 7. Complexes 1 and 2 react with stoichiometric amounts of acetone and benzophenone to form the ketone adducts [(C(5)Me(5))(2)Ln(OCMe(2))(2)][BPh(4)] (Ln = Y, 8; Sm, 9) and [(C(5)Me(5))(2)Ln(OCPh(2))(2)][BPh(4)] (Ln = Y, 10; Sm, 11), respectively. Phenanthroline (phen) coordinates to 1 to form [(C(5)Me(5))(2)Y(phen)][BPh(4)], 12. Complexes 1 and 2 react with pyridine (py) to form [(C(5)Me(5))(2)Ln(py)(2)][BPh(4)], (Ln = Y, 13; Sm, 14). Complexes 3, 8, 10, and 12 can also be made from the solvated cation [(C(5)Me(5))(2)Y(THF)(2)][BPh(4)]. The reaction of 1 with PhNNPh yields the diamagnetic adduct [(C(5)Me(5))(2)Y(PhNNPh)][BPh(4)], 15, which transforms in benzene to the radical anion complex (C(5)Me(5))(2)Y(PhNNPh), 16, via a one electron reduction by (BPh(4))(-). Complex 1 similarly reacts with phenazine (phz) to produce the first rare earth phenazine radical anion complex {[(C(5)Me(5))(2)Y](2)(phz)}{BPh(4)}, 17. Further reduction of phenazine by (BPh(4))(-) in 17 yields [(C(5)Me(5))(2)Y](2)(phz), 18, which contains the common (phz)(2-) dianion. The reduction of fluorenone by (BPh(4))(-) is also reported.     

Structural diversity in metal complexes with a dinucleating ligand containing carboxyamidopyridyl groups

The synthesis of a (carboxyamido)pyridinepyrazolate (H(5)bppap) dinucleating ligand is described. Bimetallic iron and cobalt complexes of H(5)bppap ([M(II)(2)H(2)bppap](+)) showed structural differences in both their primary and secondary coordination spheres. The binding of small molecules into the preorganized ligand cavity is verified by the hydration of [Fe(II)(2)H(2)bppap](+) and [Co(II)(2)H(2)bppap](+), leading to the formation of complexes [{Co(II)(OH)}Co(II)H(3)bppap](+) and [{Fe(II)(OH)}Fe(II)H(3)bppap](+), in which one of the metal centers has a terminal hydroxo ligand.     

Nitric Oxide Insertion Reactivity with the Bismuth–Carbon Bond: Formation of the Oximate Anion, [ON(C6H2tBu2O)]−, from the Oxyaryl Dianion, (C6H2tBu2O)2−

The first example of NO insertion into a Bi?C bond has been found in the direct reaction of NO with a Bi³⁺ complex of the unusual (C₆H₂tBu₂‐3,5‐O‐4)^2? oxyaryl dianionic ligand, namely, Ar′Bi(C₆H₂tBu₂‐3,5‐O‐4) [Ar′=2,6‐(Me₂NCH₂)₂C₆H₃] ( 1 ). The oximate complexes [Ar′Bi(ONC₆H₂‐3,5‐tBu₂‐4‐O)]₂(μ‐O) ( 3 ) and Ar′Bi(ONC₆H₂‐3,5‐tBu₂‐4‐O)₂ ( 4 ) were formed as a mixture, but can be isolated in pure form by reaction of NO with a Bi³⁺ complex of the [O₂C(C₆H₂tBu₂‐3‐5‐O‐4]^2? oxyarylcarboxy dianion, namely, Ar′Bi[O₂C(C₆H₂tBu₂‐3‐5‐O‐4)‐κ²O,O’]. Reaction of 1 with Ph₃CSNO gave an oximate product with (Ph₃CS)^1? as an ancillary ligand, (Ph₃CS)(Ar′)Bi(ONC₆H₂‐3,5‐tBu₂‐4‐O) ( 5 ).     

A monomeric Mn(III)-peroxo complex derived directly from dioxygen

The binding and activation of dioxygen by transition metal complexes is a fundamentally and practically important process in chemistry. Often the initial steps involve formation of peroxometal species that is difficult to observe because of their inherent reactivity. The interaction of dioxygen with a manganese(II) complex (1) of bis[(N'-tert-butylurealy)-N-ethyl]-(6-pivalamido-2-pyridylmethyl)amine was investigated, leading to the detection of a new intermediate that is a peroxomanganese(III) complex (2). This complex is high-spin (S = 2) with a g value of 8.2 and D = -2.0(5) as determined by parallel-mode electron paramagnetic resonance spectroscopy. The coordination of a peroxo ligand was established using Fourier transform infrared spectroscopy that reveals a new signal at 885 cm-1 for 2 when formed from 16O2-this band shifts to 837 cm-1 when 18O2 is used in the preparation. Moreover, electrospray ionization mass spectra contain a strong ion at an m/z of 576.2703 for the 16O-isotopomer that shifts to 580.2794 in the 18O-isotopomer. Complex 2 also is capable of oxidatively deformylating aldehydes, which is a known reaction of peroxometal complexes. The similarities of 2 to the peroxo intermediates in cytochrome P450 are noted.     

Group IV imino-semiquinone complexes obtained by oxidative addition of halogens

An isostructural series of titanium, zirconium, and hafnium complexes, M[ap] 2L 2 (M = Ti, Zr, Hf; L = THF, pyridine), of the redox-active 4,6-di- tert-butyl-2- tert-butylamidophenolate ligand ([ap] (2-)) have been prepared. The zirconium and hafnium derivatives react readily with halogen oxidants such as XeF 2, PhICl 2, and Br 2, leading to products in which one-electron oxidation of each [ap] (2-) ligand accompanies halide addition to the metal center. Iodine proved to be too weak of an oxidant to yield the corresponding oxidative addition product, and under no conditions could halogen oxidative addition products be obtained for titanium. According to X-ray crystallographic studies, the zirconium and hafnium oxidation products are best formulated as MX 2[isq.] 2 ([isq.] (-) = 4,6-di- tert-butyl-2- tert-butylimino-semiquinonate; M = Zr, Hf; X = F, Cl, Br) species, in which the molecule is symmetric with each redox-active ligand in the semiquinone oxidation state. Temperature-dependent magnetization measurements suggest a singlet ( S = 0) ground-state for the diradical complexes with a thermally accessible triplet ( S = 1) excited state. Solution electron paramagnetic resonance (EPR) spectra are consistent with this assignment, showing both Delta m s = 1 and Delta m s = 2 transitions for the antiferromagnetically coupled electrons.     

Lithium-alkyl, -aryl, and -amido ligand-exchange dynamics of dianionic zirconium(IV) complexes with chelating amidophenolate ligands

The synthesis, characterization, and solution behavior of a series of six-coordinate zirconium(IV) dianions [ZrX2(ap)2]2- (ap = 2,4-di-tert-butyl-6-(tert-butylamido)phenolate; X = Ph, 3a; X = p-tolyl, 3b; X = Me, 4; X = NMe2, 5) are described. Complexes 3-5 were prepared by treating the neutral zirconium complex Zr(ap)2(THF)2 (1) with 2 equiv of LiX or by the direct reaction of apLi2 and LiX with ZrCl4. The complexes were isolated as lithium-etherate salts, and they were characterized by NMR spectroscopy and single-crystal X-ray diffraction. In non-coordinating solvents such as benzene-d6, complexes 3-5 are robust in solution, but in coordinating solvents such as THF-d8, dissociation of LiX was observed. The rate of LiX loss was evaluated by exchange reactions; the reaction rate constants span nine orders of magnitude at 298 K, with the slowest reaction being the dissociation of PhLi from 3a (tau1/2 = 4 h) and the fastest reaction being the dissociation of LiNMe2 from 5 (tau1/2 = 53 mus). In the case of LiNMe2 dissociation from 5, activation parameters suggest that the rate-determining step is purely dissociative; however, for diphenyl and dimethyl complexes 3a and 4, respectively, activation parameters suggest a solvent-assisted rate-determining step.     

Synthesis, structure, and magnetism of an f element nitrosyl complex, (C5Me4H)3UNO

(C(5)Me(4)H)(3)U, 1, reacts with 1 equiv of NO to form the first f element nitrosyl complex (C(5)Me(4)H)(3)UNO, 2. X-ray crystallography revealed a 180° U-N-O bond angle, typical for (NO)(1+) complexes. However, 2 has a 1.231(5) ? N═O distance in the range for (NO)(1-) complexes and a short 2.013(4) ? U-N bond like the U═N bond of uranium imido complexes. Structural, spectroscopic, and magnetic data as well as DFT calculations suggest that reduction of NO by U(3+) has occurred to form a U(4+) complex of (NO)(1-) that has π interactions between uranium 5f orbitals and NO π* orbitals. These bonding interactions account for the linear geometry and short U-N bond. The complex displays temperature-independent paramagnetism with a magnetic moment of 1.36 μ(B) at room temperature. Complex 2 reacts with Al(2)Me(6) to form the adduct (C(5)Me(4)H)(3)UNO(AlMe(3)), 3.