Unusual reactivity of tris(pyrazolyl)borate zirconium benzyl complexes

The synthesis and reactivity of [Tp*Zr(CH2Ph)2][B(C6F5)4] (2, Tp* = HB(3,5-Me2pz)3, pz = pyrazolyl) have been explored to probe the possible role of Tp'MR2+ species in group 4 metal Tp'MCl3/MAO olefin polymerization catalysts (Tp' = generic tris(pyrazolyl)borate). The reaction of Tp*Zr(CH2Ph)3 (1) with [Ph3C][B(C6F5)4] in CD2Cl2 at -60 degrees C yields 2. 2 rearranges rapidly to [{(PhCH2)(H)B(mu-Me2pz)2}Zr(eta2-Me2pz)(CH2Ph)][B(C6F5)4] (3) at 0 degrees C. Both 2 and 3 are highly active for ethylene polymerization and alkyne insertion. Reaction of 2 with excess 2-butyne yields the double insertion product [Tp*Zr(CH2Ph)(CMe=CMeCMe=CMeCH2Ph)][B(C6F5)4] (4). Reaction of 3 with excess 2-butyne yields [{(PhCH2)(H)B(mu-Me2pz)2}Zr(Cp*)(eta2-Me2pz)][B(C6F5)4] (6, Cp* = C5Me5) via three successive 2-butyne insertions, intramolecular insertion, chain walking, and beta-Cp* elimination.     

Spectrocoulometric study of the hydrolysis of the tris (1,10-phenanthroline)iron(III) complex ion

The spectrocoulometric technique reported earlier is applied to verify the mechanism and to evaluate the contributions k_Bi of the individual bases to the total rate constant k of the hydrolysis of the tris (1,10-phenanthroline) iron(III) complex, Fe (phen)³⁺₃. Both normal and “open-circuit” spectrocoulometric experiments are used. Partial rate constants for four bases in the acetate-buffered solutions are k_H2O=(3.4±1.2) × 10^?4s^?1 (k_H2O includes the H₂O concentration), k_OH=(1.20±0.06)×10⁷ mol^?1dm³s^?1, k_phen=(1.4±0.2) mol^?1dm³s^?1, k_Ac=(3.8±0.3)×10^?2 mol^?1dm³s^?1, at 25°C and ionic strength 0.5 mol dm^?3. The Fe(phen)³⁺³ hydrolysis, with (phen)₂ (H₂O) Fe-O-Fe (H₂O) (phen)⁴⁺² formation, is first order with respect to Fe (phen)³⁺³ and the bases present in the solution. The rate-determining step in the hydrolysis is the entry of a base to the coordinating sphere of the complex, as in the hydrolysis of the analogous 2,2′-bipyridyl complex.     

Kinetics of the reaction of tris(4,7-diphenyl-1,10-phenanthroline-disulphonate)iron(II) ion with hydroxide ion in water

Summary The kinetics of the hydrolysis of the tris(4,7-diphenyl-1,10-phenanthrolinedisulphonate)iron(II) ion has been studied. The results are consistent with a consecutive reaction mechanism with a reversible step, and from the analysis of the kinetic results the rate constants have been determined.     

Rhenium(I) carbonyl complexes derived from tris(3,5-dimethylpyrazolyl)borate ion

Treatment of [Re(CO)₄Cl]₂ with K[HB(3,5-Me₂C₃HN₂)₃] giving Re{HB(3,5-Me₂C₃HN₂)₃} (CO)₃ and Re(3,5-Me₂C₃HN₂)₂(CO)₃Cl, and bromination of the former to give Re{HB(3,5-Me₂-4-BrC₃N₂)₃}(CO)₃, without displacement of CO, is described.     

Redox-driven sulfate ion transfer between two tripodal tris(urea) receptors

Two anion receptors with the same tripodal scaffold but different signaling groups are employed to control intermolecular anion transfer via an electrochemical stimulus, which is detected by the change of the fluorescence intensity before and after electrochemical oxidation of the ferrocenyl units.     

Tris(trimethylsilyl)silyl versus tris(trimethylsilyl)germyl: Radical reactivity and oxidation ability

A comparison of the tris(trimethylsilyl)silyl I and tris(trimethylsilyl)germyl II radical reactivity is provided. Their formation as well as their reactivity encountered in a large variety of chemical processes (addition to double bond, halogen abstraction, peroxyl radical formation…) is examined by laser flash photolysis, quantum mechanical calculations and electron spin resonance (ESR) experiments. The starting compound (TMS)₃GeH is more reactive than (TMS)₃SiH toward the t-butoxyl, the t-butylperoxyl and the phosphinoyl radicals. A similar behavior is noted for an aromatic ketone triplet state. II exhibits a lower absolute electronegativity: accordingly, the addition to electron rich alkenes is less efficient than for I. Radical II is also found less reactive for both the peroxylation and the halogen abstraction reactions. The rearrangement of is slower than for ; this is related to the respective exothermicity of the processes.     

Generation and reactivity of the dehydrotropylium-Co2(CO)6 ion

Dehydrotropylium-Co(2)(CO)(6) ion (2) has been generated by the Lewis acid mediated ionization of alcohol (3); it is attacked by relatively strong nucleophiles (N>1), but undergoes a radical homocoupling in the presence of weak nucleophiles (N<1).     

Synthesis and reactivity of ruthenium tetrazolate complexes containing a tris(pyrazolyl)borato (Tp) ligand

Facile ligand substitutions are observed when the neutral ruthenium cyclopropenyl complex (PPh₃)[Ru]-CC(Ph)CHCN (1, [Ru] = Tp(PPh₃)Ru) is treated with MeCN and pyrazole yielding the nitrile substituted ruthenium cyclopropenyl complex (MeCN)[Ru]-CC(Ph)CHCN (4a) and the ruthenium metallacyclic pyrazole complex (C₃H₃NN)[Ru]-CC(Ph)CH₂CN (7a), respectively. The reactions of Me₃SiN₃ with 1, 4a and 7a are investigated. Treatment of 1 with Me₃SiN₃ affords in high yield the cationic N-coordinated nitrile complex {(PPh₃)[Ru]NCCH(Ph)CH₂CN}N₃ (3). Interestingly, the reaction of 4a with Me₃SiN₃ in CH₂Cl₂ in the presence of NH₄PF₆ results in an insertion of four nitrogen atoms into the Ru-C_α bond to form a diastereomeric mixture of the bright yellow zwitterionic tetrazolate complex (MeCN)[Ru]-N₄CCH(Ph)CH₂CN (6a) in a 3:2 ratio. The reaction of 7a with Me₃SiN₃ gives the zwitterionic tetrazolate complex (C₃H₃NNH)[Ru]-N₄CCH(Ph)CH₂CN (9a). The two cationic tetrazolate complexes {(C₃H₃NNH)[Ru]-N₄(R)CCH(Ph)CH₂CN}⁺ (12a, R = CH₃, 12b, R = C₆H₅CH₂) are prepared by electrophilic addition of organic halides to 9a. All of the complexes are identified by spectroscopic methods as well as elemental analysis. Pathways for the synthesis of these compounds are proposed.     

Observations on the reactivity of pentafluorophenyl sulfonate esters

Studies on displacement reactions of alkyl pentafluorophenyl (PFP) sulfonates with amines are consistent with a mechanism involving an elimination-addition pathway; comparisons between the reactivity of PFP-sulfonates with sulfonyl chlorides and PFP-sulfonates with PFP-esters are also presented.     

Direct ion exchange of tris(2,2'-bipyridine)ruthenium(II) into an alpha-zirconium phosphate framework

The first direct ion exchange of a luminescent metal complex into an alpha-zirconium phosphate framework has been accomplished. A hydrated form of alpha-ZrP, with an expanded 10.3 A interlayer distance, has been used for the intercalation of Ru(bpy)(3)(2+), resulting in further expansion to 15.2 A. The Ru(bpy)(3)(2+) luminescence band is slightly blue-shifted. High Ru(bpy)(3)(2+) loadings lead to luminescence self-quenching.     

A new method for the spectrophotometric determination of pertechnetate with tris(1,10-phenanthroline)iron(II) ion

A new spectrophotometric determination of technetium has been developed by means of the solvent extraction of tris(1,10-phenanthroline)iron(II) ([Fe(phen)₃ ²⁺]) with pertechnetate into nitrobenzene. The concentration of technetium can be determined by measuring the characteristic absorbance at 516 nm (=11,700M^–1·cm^–1) in the organic phase. An important feature of the proposed method is that the concentration of pertechnetate can be determined without complicated processes such as the reduction of pertechnetate and the subsequent formation of a colored chelate.     

Reactivity of the triple ion and separated ion pair of tris(trimethylsilyl)methyllithium with aldehydes: a RINMR study

Low-temperature rapid-injection NMR (RINMR) experiments were performed on tris(trimethylsilyl)methyllithium. In THF/Me2O solutions, the separated ion (1S) reacted faster than can be measured at -130 degrees C with MeI and substituted benzaldehydes (k >/= 2 s -1), whereas the contact ion (1C) dissociated to 1S before reacting. Unexpectedly, the triple ion reacted faster with electron-rich benzaldehydes relative to electron-deficient ones. The addition of HMPA had no effect on the rate of reaction of the triple ion with p-diethylaminobenzaldehyde, and the immediate product of the reaction was the HMPA-solvated separated ion 1S, with the Peterson product forming only slowly. Thus, the aldehyde is catalyzing the dissociation of the triple ion. HMPA greatly decelerated the reaction of 1S (<10 -10), providing an estimate of the Lewis acid activating effect of a THF-solvated lithium cation in an organolithium addition to an aldehyde.     

Oxidation of N-(2-hydroxyethyl)ethylenediamine triacetate by tris(polypyridy)iron(III) complexes and the dodecatungstocobaltate(III) ion

Summary The stoichiometry, kinetics and mechanism of oxidation of N-(2-hydroxyethyl)ethylenediamine triacetate by K₅Co^IIIW₁₂O₄₀, Fe(phen) _inf3 ^sup3+ and Fe(bipy) _inf3 ^sup3+ have been studied. Each reaction is first order with respect to the oxidant and the reductant, but retarded by [H⁺] in the 0.20–1.60 mol dm ^–3 range. Simple electron exchanges are thought to occur, leading to the decarboxylation of the substrate.     

Ruthenium(II) tris(bipyridyl) ion as a luminescent probe for oxygen uptake on the catalyzed oxidation of HSO(3)(-)

The present work describes an alternative technique for monitoring the rate of oxygen consumption during the oxidation of HSO(3)(-) catalyzed by manganese and iron ions. The method is based on the spectrofluorimetric monitoring of the quenching effect of molecular oxygen on the emission of the photoexcited [Ru(bipy)(3)](2+) ion, added to the reaction mixtures. The effects of Fe(III), at very low concentrations, and of Mn(II) on the oxidation of HSO(3)(-) by dissolved oxygen, have been investigated. The metal ions in the trivalent oxidation state react with HSO(3)(-) to initiate a radical chain reaction in which HSO(3)(-) is oxidized to sulfate and the metal ion is reduced to the divalent state. The synergistic effect of Mn(II) and Fe(III) was clearly evaluated. Possible parallel reactions with the oxygen indicator, [Ru(bipy)(3)](2+), are considered.     

HSAB principle and nickel(II) ion reactivity towards 1-methyhydantoin

1-Methylhydantoin and its novel nickel(II) complex [Ni(H₂O)₄(1-mhyd)₂] were prepared and identified, by elemental analysis, single crystal X-ray determination and MS methods. In addition, the complex was characterized by spectroscopic (IR, UV-Vis), magnetic and thermal techniques. The ligand reveals an interesting supramolecular architecture with both classical and non-conventional extended HB bonding networks. All rings and chains formed due to this HB bonding are embedded into the undulated pattern. A single crystal X-ray diffraction analysis of the complex shows that the nickel ion is coordinated by deprotonated hydantoin and water ligands in a N₂O₄ tetragonal arrangement. In the [Ni(H₂O)₄(1-mhyd)₂] structure both inter and intramolecular hydrogen bonds are created with the participation of water molecules.The ESI-MS method confirmed mono-nuclearity of the complex while electronic spectroscopy proved the tetragonal and pseudooctahedral geometries around the metal ion in the solid state and solution, respectively. By application of the “average environment rule”, 10Dq parameters were obtained for the hypothetical, hexa-coordinate [Ni(1-mhyd)₆] approximation or rather more realistic [Ni(1-mhyd)₃] chelate. Based on this the mhyd ligand was ranked in the spectrochemical series close to ammonia. The general consideration of the structure of the hydantoin complexes as a function of the metal ion hardness within the framework of the HSAB theory has been provided. Both the ligand and the complex were found to be non-toxic agents against breast (MCF-7), lung carcinoma epithelial (A549) and mouse fibroblasts (Balb/3T3) cancer cell lines.     

Substituent effects on carbocation stability: the pK(R) for p-quinone methide

A value of k(H) = 1.5 x 10(-)(3) M(-)(1) s(-)(1) has been determined for the generation of simple p-quinone methide by the acid-catalyzed cleavage of 4-hydroxybenzyl alcohol in water at 25 degrees C and I = 1.0 (NaClO(4)). This was combined with k(s) = 5.8 x 10(6) s(-)(1) for the reverse addition of solvent water to the 4-hydroxybenzyl carbocation [J. Am. Chem. Soc. 2002, 124, 6349-6356] to give pK(R) = -9.6 as the Lewis acidity constant of O-protonated p-quinone methide. Values of pK(R) = 2.3 for the Lewis acidity constant of neutral p-quinone methide and pK(add) = -7.6 for the overall addition of solvent water to p-quinone methide to form 4-hydroxybenzyl alcohol are also reported. The thermodynamic driving force for transfer of the elements of water from formaldehyde hydrate to p-quinone methide to form formaldehyde and p-(hydroxymethyl)phenol (4-hydroxybenzyl alcohol) is determined as 6 kcal/mol. This relatively small driving force represents the balance between the much stronger chemical bonds to oxygen at the reactant formaldehyde hydrate than at the product p-(hydroxymethyl)phenol and the large stabilization of product arising from the aromatization that accompanies solvent addition to p-quinone methide. The Marcus intrinsic barrier for nucleophilic addition of solvent water to the "extended" carbonyl group at p-quinone methide is estimated to be 4.5 kcal/mol larger than that for the addition of water to the simple carbonyl group of formaldehyde. O-Alkylation of p-quinone methide to give the 4-methoxybenzyl carbocation and of formaldehyde to give a simple oxocarbenium ion results in very little change in the relative Marcus intrinsic barriers for the addition of solvent water to these electrophiles.     

Using stannous ion as an excellent inorganic ECL coreactant for tris(2,2'-bipyridyl) ruthenium(II)

It was found that stannous chloride (SnCl(2)), as a popular inorganic reducing reagent, could obviously enhance the electrochemiluminescence (ECL) of tris(2,2'-bipyridyl) ruthenium(II) (Ru(bpy)(3)(2+)) in aqueous solution. Some factors affecting the ECL reactions between Ru(bpy)(3)(2+) and Sn(2+), including pH, concentrations of coreactant, and electrode materials, were investigated by comparison with a classic ECL coreactant tripropylamine (TPA). The Ru(bpy)(3)(2+)-Sn(2+) ECL coreactant system produces stronger and more stable ECL signals, can keep its excellent ECL activity over a wider pH range and has more choices in using electrode materials than the Ru(bpy)(3)(2+)-TPA ECL coreactant system. The ECL mechanism of the Ru(bpy)(3)(2+)-Sn(2+) coreactant system was also studied in detail.