Hydrolysis of hydro(pyrrolyl-1)borates

The hydrolysis of hydro(pyrrolyl-l)borates ([BH_n(NC₄H₄)_4-n]⁻, n = 1,2,3) can be treated as a kinetically one-step reaction outside of the mildly acidic region. In strongly acidic medium the hydrolysis takes place in a stepwise manner; the intermediates (boranes and the cationic boron compounds) being hydrolyzed more slowly than the borate anion. In the first step of the hydrolysis of [BH₃(NC₄H₄)]⁻ the B---H bond, while in case of [BH₂(NC₄H₄)₂]⁻ and [BH(NC₄H₄)₃]⁻ the B---N bond is breaking.In neutral and mildly alkaline medium, the hydrolysis is a general acid catalyzed reaction (A---S_E2 mechanism). It becomes to a special H⁺-ion catalyzed reaction (A-1 mechanism) in strongly alkaline region since the protonated intermediate can be reversed to the original borate upon reaction with the OH⁻ ion. The hydrolysis presumably takes place through an intermediate which is protonated on the pyrrolyl nitrogen. Concomitant to the hydrolysis an isotopic exchange reaction was observed on the C_α and C_β atoms of the pyrrolyl group in heavy water. In the hydrolysis of the [BH₃(NC₄H₄)]⁻-anion the N-protonated intermediate is assumed to be able to reverse to the original borate even in acidic or neutral region, at least in part.     

Trimacrocyclic hexasubstituted benzene linked by labile octahedral [X(CHCl3)6]− clusters

Crystalline supramolecular architectures mediated by cations, anions, ion pairs or neutral guest species are well established. However, the robust crystallization of a well-designed receptor mediated by labile anionic solvate clusters remains unexplored. Herein, we describe the synthesis and crystalline behaviors of a trimacrocyclic hexasubstituted benzene 2 in the presence of guanidium halide salts and chloroform. Halide hexasolvate clusters, viz. [Cl(CHCl₃)₆]⁻, [Br(CHCl₃)₆]⁻, and [I(CHCl₃)₆]⁻, were found to be critical to the crystallization process, as suggested by the single-crystal structures, X-ray powder diffraction (XRPD), thermogravimetric analysis (TGA), scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), and NMR spectroscopy. This study demonstrates the hitherto unexpected role that labile ionic solvate clusters can play in stabilizing supramolecular architectures.

We report the synthesis and robust crystallization of a trimacrocyclic hexasubstituted benzene and guanidium mediated by unprecedented labile halide hexasolvate clusters, viz. [Cl(CHCl₃)₆]⁻, [Br(CHCl₃)₆]⁻, [I(CHCl₃)₆]⁻, and [Br(CHBr₃)₆]⁻.     

Dipole‐bound anions supported by charge–transfer interaction: Anionic states of HnF3−nN → BH3 and H3N → BHnF3−n (n = 0, 1, 2, 3)

The possibility of electron binding to five molecules (i.e., F₃N → BH₃, H₂FN → BH₃, HF₂N → BH₃, H₃N → BH₂F, H₃N → BHF₂) was studied at the coupled cluster level of theory with single, double, and noniterative triple excitations and compared to earlier results for H₃N → BH₃ and H₃N → BF₃. All these neutral complexes involve dative bonds that are responsible for significant polarization of these species that generates large dipole moments. As a consequence, all of the neutral systems studied, except F₃N → BH₃, support electronically stable dipole‐bound anionic states whose calculated vertical electron detachment energies are 648 cm^?1 ([H₂FN → BH₃]^?), 234 cm^?1 ([HF₂N → BH₃]^?), 1207 cm^?1 ([H₃N → BH₂F]^?), and 1484 cm^?1 ([H₃N → BHF₂]^?). In addition, we present numerical results for a model designed to mimic charge–transfer (CT) and show that the electron binding energy correlates with the magnitude of the charge flow in the CT complex. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003     

Uncovering an oxide ion substitution for the OH− + CH3F reaction

Theoretical investigations on chemical reactions allow us to understand the dynamics of the possible pathways and identify new unexpected routes. Here, we develop a global analytical potential energy surface (PES) for the OH⁻ + CH₃F reaction in order to perform high-level dynamics simulations. Besides bimolecular nucleophilic substitution (S_N2) and proton abstraction, our quasi-classical trajectory computations reveal a novel oxide ion substitution leading to the HF + CH₃O⁻ products. This exothermic reaction pathway occurs via the CH₃OH⋯F⁻ deep potential well of the S_N2 product channel as a result of a proton abstraction from the hydroxyl group by the fluoride ion. The present detailed dynamics study of the OH⁻ + CH₃F reaction focusing on the surprising oxide ion substitution demonstrates how incomplete our knowledge is of fundamental chemical reactions.

Reaction dynamics simulations on a high-level ab initio analytical potential energy surface reveal a novel oxide ion substitution channel for the OH⁻ + CH₃F reaction.     

Kinetics of solvolysis and of formation of tetrachloroplatinate(II) in alcohol: Water mixtures

Summary Rate constants are reported for the reaction of [PtCl₄]^2– with hydrochloric-perchloric acid mixtures, in aqueous methanol and aqueous t-butanol at 308.2 K. The observed first-order rate constants are, from their dependence on chloride concentration, divisible into forward and reverse rate constants for the equilibrium: [PtCl₁₄]^2–+H₂O[PtCl₃(OH₂)]^–+Cl^–. The solvent dependence of aquation rates for [PtCl₄]^2– is compared with those for other chlorotransition metal complexes, and discussed in terms of the Grunwald-Winstein method of mechanism diagnosis in organic systems. The solvent dependence of rates of [PtCl₄]^2– formation is compared with the rates of formation of other metal complexes; differences between this platinum reaction and, for example, nickel(II) formation, are rationalised in terms of the reactant charge product difference and consequent solvent permittivity effects on rate trends.     

Kinetic,solvation and reactivity studies of iron(II) complexes of monoxime and dioxime ligands

Complexes of Fe^II with monoxime and dioxime ligands have been isolated and characterised. Kinetic results and rate laws are reported for acid aquation and base hydrolysis of these complexes in H₂O and in MeOH–H₂O mixtures. Kinetics of acid catalysed aquation of Fe^II–monoxime complexes follow a rate law with k_obs = k₂[H⁺] + k₃[H⁺]², while kinetics of acid dissociation and base hydrolysis of the Fe^II–dioxime complex follow rate laws with k_obs = k₂[H⁺] and k_obs = k₂[OH⁻]. Acid aquation and base hydrolysis mechanisms are proposed. The solubilities of Fe^II–monoxime and –dioxime complex salts are reported and transfer chemical potentials of their complex cations are calculated. Solvent effects on reactivity trends have been analysed into initial and transition state components. These are determined from transfer chemical potentials of reactant and kinetic data. Rate constant trends from these complexes are compared and discussed in terms of ligand structure and solvation properties. Our kinetic results give information relevant to the application of these ligands as analytical reagents for trace Fe^II in acidic and neutral media, in water and in aqueous alcohols.     

The preparation and characterisation of chromium(III) complexes of C-meso-5, 12-dimethyl-1, 4, 8, 11-tetraazacyclotetradecane (LM). Aquation and base hydrolysis kinetics ofcis- andtrans-[CrLMCl2]+

Summary The reaction of [CrCl₃(DMF)₃] with C-meso-5, 12-dimethyl-1, 4, 8, 11-tetra-azacyclotetradecane(L_M) in DMF gives a mixture ofcis-[CrL_MCl₂]Cl (ca. 90%) andtrans-[CrL_MCl₂]Cl (ca. 10%). These complexes are readily separated, as thecis-isomer is insoluble in warm methanol while thetrans-isomer is soluble. Using the dichlorocomplexes as precursors it has been possible to prepare a range ofcis-[CrL_MX₂]⁺ complexes (X=Br^–, NO ₃ ^– , N ₃ ^– , NCS^– and X₂=bidentate oxalate) and alsotrans-[CrL_MX₂]⁺ complexes (X=Br^–, H₂O or NCS^–). The spectroscopic properties and detailed stereochemistry of the complexes are discussed.The aquation and base hydrolysis kinetics ofcis- andtrans-[CrL_MCl₂]⁺ have been studied at 25° C. Base hydrolysis of thecis-complex is extremely rapid with K_OH =1.46×10⁵ dm³ mol^–1 at 25° C. This unusual reactivity appears to be associated with thetrans II stereochemistry of thesec-NH centres of the macrocycle. Base hydrolysis of thetrans complex with thetrans III chiral nitrogen stereochemistry is quite normal with k_OH =1.1 dm³ mol^–1 s^–1 at 25° C.     

Beiträge zur Chemie des Phosphors. 240 [1]. Zum reaktiven Verhalten von Diphosphan-boran,P2H4 · BH3

Contributions to the Chemistry of Phosphorus. 240. On the Reactive Behaviour of Diphosphane-borane, P₂H₄ · BH₃ Under mild temperature conditions, the thermal decomposition of diphosphane-borane ( 1 ) gives rise to the formation of phosphane-borane, PH₃ · BH₃, and triphosphane-2-borane, PH₂? PH(BH₃)? PH₂ ( 2 ). In the presence of diphosphane-1,2-bis(borane), triphosphane-1,3-bis(borane), BH₃? PH₂? PH? PH₂? BH₃ ( 3 ), is formed additionally. The thermolysis product at room temperature is a polymeric solid of varying composition which contains phosphorus, boron, and hydrogen. Compound 1 reacts with metalating agents such as n-BuLi, LiBH₄, and NaBH₄ to furnish the borane-trihydrogendiphosphide ion, [PH₂? PH? BH₃]^?, which immediately disproportionates to give the corresponding mono-and triphosphane derivatives. In the presence of an excess of THF-borane and in the case of a 1 : 1 molar ratio of 1 : NaBH₄, the disproportionation does not occur and the new diphosphide derivative sodium-1,1,2-tris(borane)-1,2,2-trihydrogendiphosphide, Na[(BH₃)₂PH? PH₂BH₃] ( 4 ) can be obtained. The action of additional NaBH₄ yields the diphosphide dianion with four coordinated BH₃ groups.     

Beiträge zur Chemie des Phosphors. 239 [1]. Reaktion von Diphosphan(4) mit Diboran(6) und mit THF-Boran: Bildung von Diphosphan-boran,P2H4 · BH3, und Diphosphan-1,2-bis(boran), BH3 · P2H4 · BH3

Contributions to the Chemistry of Phosphorus. 239. On the Reaction of Diphosphane(4) with Diborane(6) and with THF-Borane: Formation of Diphosphane-borane, P₂H₄ · BH₃, and Diphosphane-1,2-bis(borane), BH₃ · P₂H₄ · BH₃ Diphosphane(4) always reacts with diborane(6) in the temperature range of ?118 to ?78°C, to furnish a mixture of diphosphane-borane, P₂H₄ · BH₃ ( 1 ), and diphosphane-1,2-bis(borane), BH₃ · P₂H₄ · BH₃ ( 2 ), in addition to small amounts of triphosphane-1,3-bis(borane), BH₃ · P₃H₅ · BH₃, and phosphane-borane, BH₃ · PH₃, irrespective of the molar ratios of the reactants employed. The formation of the 1 : 1 adduct P₂H₄ · B₂H₆ reported in the literature [4] could not be confirmed. The structures of compounds 1 and 2 were investigated by nuclear magnetic resonance spectroscopy which revealed the complete, homolytic cleavage of diborane(6). As a result of the bonding of one BH₃ group to diphosphane(4), the Lewis basicity of the other PH₂ group is markedly reduced. Similar mixtures of products are obtained when the borane adduct THF · BH₃ is employed in an analogous reaction. In the case of a 1 : 1 molar ratio of P₂H₄ : THF · BH₃ at ?78°C, the reaction furnishes compound 1 exclusively. This product can be isolated in the pure state and is found to be appreciably more stable than diphosphane(4).     

[Na · Triglyme]2[S(BH3)4]: Ein Salz des neuen Anions Tetrakis(boran)sulfat(2—) Kristallstruktur und theoretische Untersuchung der Molekülstruktur

[Na · Triglyme]₂[S(BH₃)₄]: a Salt of the New Anion Tetrakis(borane)sulfate(2? ). Crystal Structure and Theoretical Investigation of the Structure Na[H₃B-m?₂-S(B₂H₅)] 1 is produced by the reaction between NaSH and THF · BH₃, under dehydrogenation. 1 is also formed as the first ¹¹B-NMR-spectroscopically detectable reaction product by the reaction between anhydrous Na₂S and THF · BH₃. Adducts of BH₃ with the S^2? ion are not detectable in THF. The anion [S(BH₃)₄]^2? can however be obtained, by the addition of NaBH₄ to 1 in diglyme or triglyme respectively: [Na — Triglyme]₂[S(BH₃)₄] 2. 2 crystallizes in the monoclinic space group P2₁/n (Nr. 14). Structural data of 1 and 2 have been calculated by SCF methods. The anion of 2 may be viewed either as an adduct of B₂H₆ with S^2?, or as a bridge substituted thia derivative of B₂H₇^?; furthermore the anion of 2 is isoelectronic and isostructural with the SO ion.     

A free boratriptycene-type Lewis superacid

Bicyclic pyrazabole-bridged ferrocenes with BH groups at their bridgehead positions were prepared from [Li(thf)]₂[1,1′-fc(BH₃)₂] and pyrazole or 3,5-dimethylpyrazole in the presence of Me₃SiCl (1 or 1Me, respectively; 1,1′-fc = 1,1′-ferrocenylene); Me₃SiH and H₂ are released as byproducts. Treatment of 1 or 1Me with 1 eq. of the hydride scavenger [Ph₃C][B(C₆F₅)₄] afforded the borenium salts [2][B(C₆F₅)₄] (72%) and [2Me][B(C₆F₅)₄] (77%). According to X-ray crystallography, [2Me]⁺ contains one trigonal-planar borenium cation, the cyclopentadienyl (Cp) rings of the 1,1′-fc fragment remain parallel to each other, but the Cp–B bond vector is bent out of the Cp plane by an unprecedentedly large dip angle α* of 40.6°. The Fe⋯B(sp²) distance is very short (2.365(4) Å) and the ¹¹B NMR signal of the cationic B(sp²) center is remarkably upfield shifted (23.4 ppm), suggesting a direct Fe(3d) → B(2p) donor–acceptor interaction. Although this interpretation is confirmed by quantum-chemical calculations, the coupling between the associated orbitals corresponds to an energy of only 12 kJ mol⁻¹. Accordingly, both the experimental (e.g., Gutmann–Beckett acceptor number AN = 111) and theoretical assessment (e.g., Et₃PO and F⁻-ion affinities) of the Lewis acidity proves that [2]⁺ is among the strongest boron-based Lewis acids available to date.

An exceptionally strong ferrocene-containing, cationic boratriptycene-type Lewis acid is stabilized by a weak Fe⋯B through-space interaction.     

Boron Hydrogen Compounds: Hydrogen Storage and Battery Applications

About 25 years ago, Bogdanovic and Schwickardi (B. Bogdanovic, M. Schwickardi: J. Alloys Compd. 1–9, 253 (1997) discovered the catalyzed release of hydrogen from NaAlH₄. This discovery stimulated a vast research effort on light hydrides as hydrogen storage materials, in particular boron hydrogen compounds. Mg(BH₄)₂, with a hydrogen content of 14.9 wt %, has been extensively studied, and recent results shed new light on intermediate species formed during dehydrogenation. The chemistry of B₃H₈⁻, which is an important intermediate between BH₄⁻ and B₁₂H₁₂²⁻, is presented in detail. The discovery of high ionic conductivity in the high-temperature phases of LiBH₄ and Na₂B₁₂H₁₂ opened a new research direction. The high chemical and electrochemical stability of closo-hydroborates has stimulated new research for their applications in batteries. Very recently, an all-solid-state 4 V Na battery prototype using a Na₄(CB₁₁H₁₂)₂(B₁₂H₁₂) solid electrolyte has been demonstrated. In this review, we present the current knowledge of possible reaction pathways involved in the successive hydrogen release reactions from BH₄⁻ to B₁₂H₁₂²⁻, and a discussion of relevant necessary properties for high-ionic-conduction materials.     

Darstellung und schwingungsspektroskopische Untersuchung von [H3B?Se?Se?BH3]2− und [H3B-μ2-Se(B2H5)]− Kristallstruktur und theoretische Untersuchung der Molekülstruktur von [H3B-μ2-Se(B2H5)]−

Synthesis and Vibrational Spectroscopic Investigation of [H₃B? Se? Se? BH₃]^2? and [H₃B-μ₂-Se(B₂H₅)]^? Crystal Structure and Theoretical Investigation of the Molecular Structure of [H₃B-μ₂-Se(B₂H₅)]^? M₂[H₃B? Se? Se? BH₃] 1 is produced by the reaction between elemental selenium and MBH₄ (1 : 1) in triglyme (diglyme), under dehydrogenation. 1 reacts with an excess of B₂H₆ to give M[H₃B-μ₂-Se(B₂H₅)] 2 which is also formed in the reaction of THF · BH₃ with 1 . These reactions proceed under cleavage of the Se? Se bond and hydrogen evolution. [(C₆H₅)₄]Br reacts with Na · 2 to form [(C₆H₅)₄P] · 2 which crystallizes in the tetragonal space group I4 (Nr. 82). An X-ray structure determination failed because of disordering of the cation and anion. ¹¹B, ⁷⁷Se NMR shifts and ¹J(¹¹B¹H) coupling constants as well as IR- and Raman spectroscopic investigations convey further structural information. Structural data of 2 have been calculated by SCF methods. The anion of 2 may be viewed either as an adduct of Se with B₃H₈^?, or as a bridge substituted selena derivative of B₂H₆.     

Pyridine Adducts of Tricyano- and Dicyanoboranes

Cyanoborane adducts of the Lewis acids B(CN)₃, BF(CN)₂, and BH(CN)₂ with pyridine and 4-cyanopyridine have been obtained in high yields. The syntheses were accomplished by oxidation of the readily available potassium salts of the cyano(hydrido)borate anions [BH(CN)₃]⁻ ( MHB ), [BFH(CN)₂]⁻ ( FHB ), and [BH₂(CN)₂]⁻ ( DHB ) with bromine in the presence of the respective pyridine derivative C₅H₅N or 4-CN-C₅H₄N as starting material. All six cyanoborane adducts have been characterized by NMR and vibrational spectroscopy, elemental analysis, and single-crystal X-ray diffraction. The reduction of the cyanoborane adducts has been investigated by cyclic voltammetry and the Lewis acidity of the different cyanoboranes has been assessed using the Gutmann-Beckett method. Selected experimental data and trends are compared to theoretical ones, for example fluoride ion affinities (FIAs).     

Optimization of crystal packing in semiconducting spin-crossover materials with fractionally charged TCNQδ− anions (0 < δ < 1)

Co-crystallization of the prominent Fe(ii) spin-crossover (SCO) cation, [Fe(3-bpp)₂]²⁺ (3-bpp = 2,6-bis(pyrazol-3-yl)pyridine), with a fractionally charged TCNQ^δ− radical anion has afforded a hybrid complex [Fe(3-bpp)₂](TCNQ)₃·5MeCN (1·5MeCN, where δ = −0.67). The partially desolvated material shows semiconducting behavior, with the room temperature conductivity σ_RT = 3.1 × 10⁻³ S cm⁻¹, and weak modulation of conducting properties in the region of the spin transition. The complete desolvation, however, results in the loss of hysteretic behavior and a very gradual SCO that spans the temperature range of 200 K. A related complex with integer-charged TCNQ⁻ anions, [Fe(3-bpp)₂](TCNQ)₂·3MeCN (2·3MeCN), readily loses the interstitial solvent to afford desolvated complex 2 that undergoes an abrupt and hysteretic spin transition centered at 106 K, with an 11 K thermal hysteresis. Complex 2 also exhibits a temperature-induced excited spin-state trapping (TIESST) effect, upon which a metastable high-spin state is trapped by flash-cooling from room temperature to 10 K. Heating above 85 K restores the ground-state low-spin configuration. An approach to improve the structural stability of such complexes is demonstrated by using a related ligand 2,6-bis(benzimidazol-2′-yl)pyridine (bzimpy) to obtain [Fe(bzimpy)₂](TCNQ)₆·2Me₂CO (4) and [Fe(bzimpy)₂](TCNQ)₅·5MeCN (5), both of which exist as LS complexes up to 400 K and exhibit semiconducting behavior, with σ_RT = 9.1 × 10⁻² S cm⁻¹ and 1.8 × 10⁻³ S cm⁻¹, respectively.

Co-crystallization of the cationic complex [Fe(3-bpp)2]²⁺ with fractionally charged TCNQ^δ− anions (0 < δ < 1) affords semiconducting spin-crossover (SCO) materials. The abruptness of SCO is strongly dependent on the interstitial solvent content.     

Self-Assembly of Antiferromagnetically-Coupled Copper(II) Supramolecular Architectures with Diverse Structural Complexities

The self-assembly of 2,6-diformyl-4-methylphenol (DFMP) and 1-amino-2-propanol (AP)/2-amino-1,3-propanediol (APD) in the presence of copper(II) ions results in the formation of six new supramolecular architectures containing two versatile double Schiff base ligands (H₃L and H₅L1) with one-, two-, or three-dimensional structures involving diverse nuclearities: tetranuclear [Cu₄(HL²⁻)₂(N₃)₄]·4CH₃OH·56H₂O (1) and [Cu₄(L³⁻)₂(OH)₂(H₂O)₂] (2), dinuclear [Cu₂(H₃L1²⁻)(N₃)(H₂O)(NO₃)] (3), polynuclear {[Cu₂(H₃L1²⁻)(H₂O)(BF₄)(N₃)]·H₂O}_n (4), heptanuclear [Cu₇(H₃L1²⁻)₂(O)₂(C₆H₅CO₂)₆]·6CH₃OH·44H₂O (5), and decanuclear [Cu₁₀(H₃L1²⁻)₄(O)₂(OH)₂(C₆H₅CO₂)₄] (C₆H₅CO₂)₂·20H₂O (6). X-ray studies have revealed that the basic building block in 1, 3, and 4 is comprised of two copper centers bridged through one μ-phenolate oxygen atom from HL²⁻ or H₃L1²⁻, and one μ-1,1-azido (N₃⁻) ion and in 2, 5, and 6 by μ-phenoxide oxygen of L³⁻ or H₃L1²⁻ and μ-O²⁻ or μ₃-O²⁻ ions. H-bonding involving coordinated/uncoordinated hydroxy groups of the ligands generates fascinating supramolecular architectures with 1D-single chains (1 and 6), 2D-sheets (3), and 3D-structures (4). In 5, benzoate ions display four different coordination modes, which, in our opinion, is unprecedented and constitutes a new discovery. In 1, 3, and 5, Cu(II) ions in [Cu₂] units are antiferromagnetically coupled, with J ranging from −177 to −278 cm⁻¹.     

Preparation of High-Purity Ammonium Tetrakis(pentafluorophenyl)borate for the Activation of Olefin Polymerization Catalysts

Homogeneous olefin polymerization catalysts are activated in situ with a co-catalyst ([PhN(Me)₂-H]⁺[B(C₆F₅)₄]⁻ or [Ph₃C]⁺[B(C₆F₅)₄]⁻) in bulk polymerization media. These co-catalysts are insoluble in hydrocarbon solvents, requiring excess co-catalyst (>3 eq.). Feeding the activated species as a solution in an aliphatic hydrocarbon solvent may be advantageous over the in situ activation method. In this study, highly pure and soluble ammonium tetrakis(pentafluorophenyl)borates ([Me(C₁₈H₃₇)₂N-H]⁺[B(C₆F₅)₄]⁻ and [(C₁₈H₃₇)₂NH₂]⁺[B(C₆F₅)₄]⁻) containing neither water nor Cl⁻ salt impurities were prepared easily via the acid–base reaction of [PhN(Me)₂-H]⁺[B(C₆F₅)₄]⁻ and the corresponding amine. Using the prepared ammonium salts, the activation reactions of commercial-process-relevant metallocene (rac-[ethylenebis(tetrahydroindenyl)]Zr(Me)₂ (1-ZrMe₂), [Ph₂C(Cp)(3,6-^tBu₂Flu)]Hf(Me)₂ (3-HfMe₂), [Ph₂C(Cp)(2,7-^tBu₂Flu)]Hf(Me)₂ (4-HfMe₂)) and half-metallocene complexes ([(η⁵-Me₄C₅)Si(Me)₂(κ-N^tBu)]Ti(Me)₂ (5-TiMe₂), [(η⁵-Me₄C₅)(C₉H₉(κ-N))]Ti(Me)₂ (6-TiMe₂), and [(η⁵-Me₃C₇H₁S)(C₁₀H₁₁(κ-N))]Ti(Me)₂ (7-TiMe₂)) were monitored in C₆D₁₂ with ¹H NMR spectroscopy. Stable [L-M(Me)(NMe(C₁₈H₃₇)₂)]⁺[B(C₆F₅)₄]⁻ species were cleanly generated from 1-ZrMe₂, 3-HfMe₂, and 4-HfMe₂, while the species types generated from 5-TiMe₂, 6-TiMe₂, and 7-TiMe₂ were unstable for subsequent transformation to other species (presumably, [L-Ti(CH₂N(C₁₈H₃₇)₂)]⁺[B(C₆F₅)₄]⁻-type species). [L-TiCl(N(H)(C₁₈H₃₇)₂)]⁺[B(C₆F₅)₄]⁻-type species were also prepared from 5-TiCl(Me) and 6-TiCl(Me), which were newly prepared in this study. The prepared [L-M(Me)(NMe(C₁₈H₃₇)₂)]⁺[B(C₆F₅)₄]⁻-, [L-Ti(CH₂N(C₁₈H₃₇)₂)]⁺[B(C₆F₅)₄]⁻-, and [L-TiCl(N(H)(C₁₈H₃₇)₂)]⁺[B(C₆F₅)₄]⁻-type species, which are soluble and stable in aliphatic hydrocarbon solvents, were highly active in ethylene/1-octene copolymerization performed in aliphatic hydrocarbon solvents.     

Versatile Reactivity of MnII Complexes in Reactions with N-Donor Heterocycles: Metamorphosis of Labile Homometallic Pivalates vs. Assembling of Endurable Heterometallic Acetates

Reaction of 2,2′-bipyridine (2,2′-bipy) or 1,10-phenantroline (phen) with [Mn(Piv)₂(EtOH)]_n led to the formation of binuclear complexes [Mn₂(Piv)₄L₂] (L = 2,2′-bipy (1), phen (2); Piv⁻ is the anion of pivalic acid). Oxidation of 1 or 2 by air oxygen resulted in the formation of tetranuclear Mn^II/III complexes [Mn₄O₂(Piv)₆L₂] (L = 2,2′-bipy (3), phen (4)). The hexanuclear complex [Mn₆(OH)₂(Piv)₁₀(pym)₄] (5) was formed in the reaction of [Mn(Piv)₂(EtOH)]_n with pyrimidine (pym), while oxidation of 5 produced the coordination polymer [Mn₆O₂(Piv)₁₀(pym)₂]_n (6). Use of pyrazine (pz) instead of pyrimidine led to the 2D-coordination polymer [Mn₄(OH)(Piv)₇(µ₂-pz)₂]_n (7). Interaction of [Mn(Piv)₂(EtOH)]_n with FeCl₃ resulted in the formation of the hexanuclear complex [Mn^II₄Fe^III₂O₂(Piv)₁₀(MeCN)₂(HPiv)₂] (8). The reactions of [MnFe₂O(OAc)₆(H₂O)₃] with 4,4′-bipyridine (4,4′-bipy) or trans-1,2-(4-pyridyl)ethylene (bpe) led to the formation of 1D-polymers [MnFe₂O(OAc)₆L₂]_n·2nDMF, where L = 4,4′-bipy (9·2DMF), bpe (10·2DMF) and [MnFe₂O(OAc)₆(bpe)(DMF)]_n·3.5nDMF (11·3.5DMF). All complexes were characterized by single-crystal X-ray diffraction. Desolvation of 11·3.5DMF led to a collapse of the porous crystal lattice that was confirmed by PXRD and N₂ sorption measurements, while alcohol adsorption led to porous structure restoration. Weak antiferromagnetic exchange was found in the case of binuclear Mn^II complexes (J_Mn-Mn = −1.03 cm⁻¹ for 1 and 2). According to magnetic data analysis (J_Mn-Mn = −(2.69 ÷ 0.42) cm⁻¹) and DFT calculations (J_Mn-Mn = −(6.9 ÷ 0.9) cm⁻¹) weak antiferromagnetic coupling between Mn^II ions also occurred in the tetranuclear {Mn₄(OH)(Piv)₇} unit of the 2D polymer 7. In contrast, strong antiferromagnetic coupling was found in oxo-bridged trinuclear fragment {MnFe₂O(OAc)₆} in 11·3.5DMF (J_Fe-Fe = −57.8 cm⁻¹, J_Fe-Mn = −20.12 cm⁻¹).     

Reduction of iodine by hydroxylamine within the pH range 0.7–3.5

The reduction of iodine by hydroxylamine within the [H⁺] range 3×10⁻¹–3×10⁻⁴ mol.L⁻¹ was first studied until completion of the reaction. In most cases, the concentration of iodine decreased monotonically. However, within a narrow range of reagent concentrations ([NH₃OH⁺]₀/[I₂]₀ ratio below 15, [H⁺] around 0.1 mol.L⁻¹, and ionic strength around 0.1 mol.L⁻¹), the [I₂] and [I₃⁻] vs. time curves showed 2 and 3 extrema, respectively. This peculiar phenomenon is discussed using a 4 reaction scheme (I₂+I⁻⇔︁I₃⁻, 2 I₂+NH₃OH⁺+H₂O→HNO₂+4 I⁻+5 H⁺, NH₃OH⁺+HNO₂→N₂O+2 H₂O+H⁺, and 2 HNO₂+2 I⁻+2 H⁺→2 NO+I₂+2 H₂O). In a flow reactor, sustained oscillations in redox potential were recorded with an extremely long period (around 24 h). The kinetics of the reaction was then investigated in the starting conditions. The proposed rate equation points out a reinforcement of the inhibition by hydrogen ions when [H⁺] is above 4×10⁻² mol.L⁻¹ at 25°C. A mechanism based on ion-transfer reactions is postulated. It involves both NH₂OH and NH₃OH⁺ as the reducing reactive species. The additional rate suppression by H⁺ at low pH would be connected to the existence of H₂OI⁺ in the reactive medium. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 785–797, 1998     

Base hydrolysis ofcis-(methyl/ethylamine)bis(ethylenediamine) (salicylato)cobalt(III) complexes

The kinetics of the base hydrolysis ofcis-[Co(en)₂(RNH₂)-(SalH)]²⁺ (R=Me or Et; SalH=HOC₆H₄CO ₂ ⁻ ) were investigated in aqueous ClO ₄ ⁻ in the 0.004–0.450 mol dm⁻³ [OH⁻] range, I=0.50 mol dm⁻³ at 30–40°C. The phenoxide species is hydrolysed via [OH⁻]-independent and [OH⁻]-dependent paths, the latter being first order in [OH⁻]. The high rate of alkali-independent hydrolysis of the phenoxide species is associated with high ΔH^≠ and ΔS^≠ values, in keeping with the SNICB mechanism involving an amido conjugate base generated by the phenoxide-assisted NH-deprotonation of the coordinated amine. The [OH⁻]-dependent path also involves the conventional SN₁ CB mechanism. The rate constant, k₁, for the SNICB path exhibits a steric acceleration with the increasing size of the non-labile alkylamine, whereas the rate constant, k₂, for the SN₁CB path shows a reverse trend. TMC 2578