Dismutation of Tricyanoboryllead Compounds: The Homoleptic Tetrakis(tricyanoboryl)plumbate Tetraanion.

A series of unprecedently air-stable (tricyanoboryl)plumbate anions was obtained by the reaction of the boron-centered nucleophile B(CN)3 2- with triorganyllead halides. Salts of the anions [R3 PbB(CN)3 ]- (R=Ph, Et) were isolated and found to be stable in air at room temperature. In the case of Me3 PbHal (Hal=Cl, Br), a mixture of the anions [Me4-n Pb{B(CN)3 }n ]n- (n=1, 2) was obtained. The [Et3 PbB(CN)3 ]- ion undergoes stepwise dismutation in aqueous solution to yield the plumbate anions [Et4-n Pb{B(CN)3 }n ]n- (n=1-4) and PbEt4 as by-product. The reaction rate increases with decreasing pH value of the aqueous solution or by bubbling O2 through the reaction mixture. Adjustment of the conditions allowed the selective formation and isolation of salts of all anions of the series [Et4-n Pb{B(CN)3 }n ]n- (n=2-4) including the homoleptic tetraanion [Pb{B(CN)3 }4 ]4- .

Thermal Decomposition and Hypergolic Reaction of a Dicyanoborohydride Ionic Liquid.

In this study, in situ infrared spectroscopy techniques and thermogravimetric analysis coupled with mass spectrometry (TGA-MS) are employed to characterize the reactivity of the ionic liquid, 1-butyl-3-methylimidazolium dicyanoborohydride (BMIM+DCBH-), in comparison to the well-characterized 1-butyl-3-methylimidazolium dicyanamide (BMIM+DCA-) ionic liquid. TGA measurements determined the enthalpy of vaporization (ΔHvap) to be 112.7 ± 12.3 kJ/mol at 298 K. A rapid scan Fourier transform infrared spectrometer was used to obtain vibrational information useful in tracking the appearance and disappearance of species in the hypergolic reactions of BMIM+DCBH- and BMIM+DCA- with white fuming nitric acid (WFNA) and in the thermal decomposition of these energetic ionic liquids. Attenuated total reflectance measurements recorded the infrared spectra of the reactant sample (BMIM+DCBH-) and the liquid reaction products after reacting with WFNA. Computational chemistry efforts, aided by the experimental results, were used to propose key reaction pathways leading to the hypergolic ignition of BMIM+DCBH- + WFNA. Experimental results indicate that the hypergolic reaction of BMIM+DCBH- with WFNA generates both common and unique intermediates as compared to previous BMIM+DCA- + WFNA investigations: nitrous oxide was generated during both hypergolic reactions indicating that it may play a crucial role in the hypergolic ignition process, NO2 was generated in significantly higher concentrations for BMIM+DCBH- than for BMIM+DCA-, CO2 was only generated for BMIM+DCA-, and HCN was only generated during thermal decomposition and hypergolic ignition of BMIM+DCBH-.

Hydroxytricyanoborate Anion: Synthetic Aspects and Structural, Chemical, and Spectroscopic Properties.

In recent years, salts of the hydridotricyanoborate anion [BH(CN)3]- (MHB) have become readily available. In spite of the unusually high stability of the MHB anion, it can be used as a valuable starting material for the preparation of selected tricyanoborates, for example, the boron-centered nucleophile B(CN)32-. A further unprecedented example is the hydroxytricyanoborate anion [B(OH)(CN)3]- that is accessible by oxidation of (H3O)MHB with elemental bromine in water. The Brønsted acid (H3O)[B(OH)(CN)3] was isolated as a crystalline solid. It serves as a versatile starting material for the synthesis of coordination compounds, metal salts, and ionic liquids. The [B(OH)(CN)3]- anion shows a rich coordination chemistry and a high tendency to form hydrogen-bonded motifs as demonstrated by a series of salts with different types of cations. Furthermore, the [B(OH)(CN)3]- anion itself serves as starting material for new tricyanoborates such as the unusual trianion [B{OB(CN)3}3]3- and the silylated anions [B(OSiR3)(CN)3]- (R = Me, Et, Ph). Some of these follow-up products have been characterized by single-crystal X-ray diffraction, e.g., [nBu4N]3[B{OB(CN)3}3] and [nBu4N][B(OSiPh3)(CN)3].

N-Heterocyclic Olefins as Electron Donors in Combination with Triarylborane Acceptors: Synthesis, Optical and Electronic Properties of D-π-A Compounds.

N-heterocyclic olefins (NHOs), relatives of N-heterocyclic carbenes (NHCs), exhibit high nucleophilicity and soft Lewis basic character. To investigate their π-electron donating ability, NHOs were attached to triarylborane π-acceptors (A) giving donor (D)-π-A compounds 1-3. In addition, an enamine π-donor analogue (4) was synthesized for comparison. UV-visible absorption studies show a larger red shift for the NHO-containing boranes than for the enamine analogue, a relative of cyclic (alkyl)(amino) carbenes (CAACs). Solvent-dependent emission studies indicate that 1-4 have moderate intramolecular charge-transfer (ICT) behavior. Electrochemical investigations reveal that the NHO-containing boranes have extremely low reversible oxidation potentials (e.g., for 3, E ox 1 / 2 =-0.40 V vs. ferrocene/ferrocenium, Fc/Fc+ , in THF). Time-dependent (TD) DFT calculations show that the HOMOs of 1-3 are much more destabilized than that of the enamine-containing 4, which confirms the stronger donating ability of NHOs.

Bis(amidinato)- and bis(guanidinato)silylenes and silylenes with one sterically demanding amidinato or guanidinato ligand: synthesis and reactivity.

This article deals with the synthesis and reactivity of the bis(amidinato)silylene [iPrNC(Ph)NiPr]2Si (5), the bis(guanidinato)silylene [iPrNC(NiPr2)NiPr]2Si (6), the mono(amidinato)silylene [DippNC(Ph)NDipp]SiNMe2 (Dipp = 2,6-diisopropylphenyl) (8) and the mono(guanidinato)silylene [DippNC(NMe2)NDipp]SiN(SiMe3)2 (9). The reactions studied include (i) nucleophilic substitutions, (ii) Lewis acid/base reactions, (iii) Brønsted acid/base reactions, (iv) oxidative additions (bond activations, small-molecule activations), (v) cycloaddition reactions with unsaturated organic substrates, (vi) reductions and (vii) radical formation by muonium addition. Silylenes 5, 6, 8 and 9 have been demonstrated to display unique reactivity profiles and to be versatile precursors for the synthesis of novel four- or five-coordinate silicon(ii) and four-, five- or six-coordinate silicon(iv) complexes with unprecedented structural motifs. This article also deals with the structural characterisation of all the new silicon(ii) and silicon(iv) compounds synthesised. Crystal structure analyses and 29Si NMR spectroscopic studies in the solid state and in solution were used to characterise the silicon coordination polyhedra of these compounds.

Anhydrous, Homoleptic Lanthanide Frameworks with the Pentafluoroethyltricyanoborate Anion.

Pentafluoroethyltricyanoborate frameworks of rare-earth metal ions of the general formula [Ln{C2F5B(CN)3}3(OH2)n] (Ln = La, Eu, Ho; n = 0, 3; [Ln13(OH2)n]) were synthesized using the oxonium salt (H3O)[C2F5B(CN)3] ((H3O)1) and lanthanide chlorides LnCl3·nH2O as starting compounds. Single-crystals of ∞3[La{C2F5B(CN)3}3] (∞3[La13]) are obtained from the room temperature ionic liquid (RTIL) [EMIm]1 using either a ionothermal approach or by recrystallization of anhydrous microcrystalline [La13] that is obtained from reactions in aqueous media after drying in a vacuum. Removal of water from [Ln13(OH2)3] (Ln = Eu, Ho) to give microcrystalline ∞3[Ln13] is achieved in a vacuum at elevated temperatures. All compounds were characterized by vibrational and NMR spectroscopy, thermogravimetry, and elemental analysis. The structures of the three-dimensional coordination polymers ∞3[Eu13(OH2)3] and ∞3[La13] were elucidated by single-crystal X-ray-diffraction. According to powder diffraction studies on anhydrous ∞3[Ln13] (Ln = La, Eu, Ho), the three compounds are isotypic. A study of the photoluminescence properties reveals that both Eu3+ compounds, [Eu13] and [Eu13(OH2)3], are strongly luminescent, the emission of the anhydrous framework being significantly more intense than the one of the hydrate. The Eu-compounds benefit from a sensitizer effect of the anion. In contrast, the Ho-containing framework ∞3[Ho13] exhibits separate chromophores and a strong reabsorption of the fluorescence by the Ho3+ ions.