N,N'-dialkylimidazolium chloroplatinate(II), chloroplatinate(IV), and chloroiridate(IV) salts and an N-heterocyclic carbene complex of platinum(II): synthesis in ionic liquids and crystal structures

Piperidinium and Pyrrolidinium Ionic Liquids as Precursors in the Synthesis of New Platinum Catalysts for Hydrosilylation

Six new air-stable anionic platinum complexes were synthesized in simple reactions of piperidinium [BMPip]Cl or pyrrolidinium [BMPyrr]Cl ionic liquids with platinum compounds ([Pt(cod)Cl2] or K2[PtCl6]). All these compounds were subjected to isolation and spectrometric characterization using NMR and ESI-MS techniques. Furthermore, the determination of melting points and thermal stability of the above derivatives was performed with the use of thermogravimetric analysis. The catalytic performance of the synthesized complexes was tested in hydrosilylation of 1-octene and allyl glycidyl ether with 1,1,1,3,5,5,5-heptamethyltrisiloxane. The study has shown that they have high catalytic activity and are insoluble in the reaction medium which enabled them to isolate and reuse them in consecutive catalytic cycles. The most active complex [BMPip]2[PtCl6] makes it possible to conduct at least 10 catalytic runs without losing activity which makes it an attractive alternative not only to commonly used homogeneous catalysts, but also to heterogeneous catalysts for hydrosilylation processes. The activity of the studied catalysts is also affected by the kind of anion and, to some extent, the kind of cation.

Crystallographic Insights into the Behavior of Highly Acidic Metal Cations in Ionic Liquids from Reactions of Titanium Tetrachloride with [1-Butyl-3-Methylimidazolium][X] Ionic Liquids (X = Chloride, Bromide, Tetrafluoroborate)

Highly charged metal ions are difficult to investigate in weakly coordinating ionic liquids (ILs) because of the insolubility of their solid forms, but the molecular liquid TiCl₄ offers a way to react tetravalent metal ions in an IL. Reactions of TiCl₄ with 1-butyl-3-methylimidazolium ([C₄mim]⁺)-based ILs containing chloride or bromide lead to mixtures of highly metastable amorphous solids and small amounts of crystalline chlorotitanate salts including [C₄mim]₂[TiCl₆] and two polymorphs of [C₄mim]₂[Ti₂Cl₁₀] in a manner not well correlated with stoichiometry or anion identity. The reaction of TiCl₄ with [C₄mim][BF₄] yields crystals of the mixed fluoro-chloro complex [C₄mim]₂[Ti₄F₆Cl₁₂], indicating spontaneous reaction of the IL ions to generate HF in situ. These unusual behaviors are explained in terms of the exceptionally high acidity of Ti⁴⁺ and the unusual behavior of TiCl₄ among metal halides as a nonpolar molecular compound.

Hydrogen Adsorption Properties of Carbon Nanotubes and Platinum Nanoparticles from a New Ammonium-Ethylimidazolium Chloroplatinate Salt

Self-supporting membranes built entirely of carbon nanotubes have been prepared by wet methods and characterized by Raman spectroscopy. The membranes are used as supports for the electrodeposition of Pt nanoparticles without the use of additional additives and/or stabilizers. The Pt precursor is an ad hoc synthesized ammonium-ethylimidazolium chloroplatinate(IV) salt, [NH3 (CH2 )2 MIM)][PtCl6 ]. The Pt complex was characterized using NMR spectroscopy, XRD, ESI-MS, and FTIR spectroscopy. The interaction between the Pt-carbon nanotubes nanocomposites and hydrogen is analyzed using electrochemical and quartz microbalance measurements under near-ambient conditions. The contribution of the Pt phase to the hydrogen adsorption on nanotube is found and explained by a kinetic model that takes into account a spillover event. Such a phenomenon may be exploited conveniently for catalysis and electrocatalysis applications in which the hybrid systems could act as a hydrogen transfer agent in specific hydrogenation reactions.

Metal-free, ionic liquid-mediated synthesis of functionalized quinolines

An expedient and metal-free synthetic protocol for construction of substituted quinolines has been developed from anilines and phenylacetaldehydes using imidazolium cation-based ionic liquids as the reaction medium. Mechanistic analysis indicated that the reaction occurs through C-C and C-N bond formation to produce isolable 2,3-disubstituted quinoline intermediates, which undergo C-C bond cleavage to produce 3-substituted quinolines. The reaction proceeds smoothly with a range of functionalities in good to excellent yields. Advantages of this protocol include metal-free, environmentally friendly, recyclable reaction media, higher yields and shorter reaction times, and thus is promising for the efficient combinatorial synthesis of structurally diverse 2,3-disubstituted and 3-substituted quinolines.

Selective synthesis of cis- and trans-[(NHCMe)2PtCl2] and [NHCMePt(cod)Cl][NHCMePtCl3] using NHCMeSiCl4

NHC^MeSiCl₄ was used to selectively synthesise cis and trans-[(NHC^Me)₂PtCl₂], as well as [NHC^MePt(cod)Cl][NHC^MePtCl₃], which revealed the first ever N-heterocyclic carbene analogue of the Cossa's salt anion.

Solidification of Ionic Liquids: Theory and Techniques

Ionic liquids (ILs) have become an important class of solvents and soft materials over the past decades. Despite being salts built by discrete cations and anions, many of them are liquid at room temperature and below. They have been used in a wide variety of applications such as electrochemistry, separation science, chemical synthesis and catalysis, for breaking azeotropes, as thermal fluids, lubricants and additives, for gas storage, for cellulose processing, and photovoltaics. It has been realized that the true advantage of ILs is their modular character. Each specific cation–anion combination is characterized by a unique, characteristic set of chemical and physical properties. Although ILs have been known for roughly a century, they are still a novel class of compounds to exploit due to the vast number of possible ion combinations and one fundamental question remains still inadequately answered: why do certain salts like ILs have such a low melting point and do not crystallize readily? This Review aims to give an insight into the liquid–solid phase transition of ILs from the viewpoint of a solid-state chemist and hopes to contribute to a better understanding of this intriguing class of compounds. It will introduce the fundamental theories of liquid–solid-phase transition and crystallization from melt and solution. Aside form the formation of ideal crystals the development of solid phases with disorder and of lower order like plastic crystals and liquid crystals by ionic liquid compounds are addressed. The formation of ionic liquid glasses is discussed and finally practical techniques, strategies and methods for crystallization of ionic liquids are given.

Bis(phenanthridinium) hexa-chloridoplatinate(IV) dimethyl sulfoxide disolvate

The asymmetric unit of the title compound, (C(13)H(10)N)(2)[PtCl(6)]·2C(2)H(6)OS, contains one independent protonated phenanthridinium cation, half of a centrosymmetric [PtCl(6)](2-)anion and one dimethyl sulfoxide solvent mol-ecule. Intra-molecular N-H⋯O and inter-molecular C-H⋯Cl hydrogen-bonding inter-actions seem to be effective in the stabilization of the structure.

Bis(2,4,6-trimethyl-pyridinium) hexa-chloridoplatinate(IV)

The asymmetric unit of the title compound, (C(8)H(12)N)(2)[PtCl(6)], contains one independent protonated 2,4,6-trimethyl-pyridinium cation and one half of a centrosymmetric [PtCl(6)](2-) anion. The Pt ion has an almost ideal octa-hedral coordination. In the crystal structure, intra-molecular N-H⋯Cl and inter-molecular C-H⋯Cl hydrogen bonds result in the formation of a supra-molecular structure.

Bis(2,6-dimethyl-pyridinium) hexa-chlorido-platinate(IV)

The asymmetric unit of the title compound, (C(7)H(10)N)(2)[PtCl(6)], contains one independent protonated 2,6-dimethyl-pyridinium cation and half of a centrosymmetric [PtCl(6)](2-) anion. The Pt atom has an octa-hedral coordination. In the crystal structure, inter-molecular N-H⋯Cl and C-H⋯Cl hydrogen bonds result in the formation of a supra-molecular structure. There is a π-π contact between the pyridine rings [centroid-centroid distance = 4.235 (1) Å].