Moisture-sensitive Compounds Research Articles

Undirected C-H Bond Activation in Aluminium Hydrido Enaminonates.

Two new aluminium hydrido complexes were synthesized by reacting AlH3 with the enaminone ligand N-(4,4,4-trifluorobut-1-en-3-on)-6,6,6-trifluoroethylamine (HTFB-TFEA) in different molar ratios to obtain mono- and di-hydrido-aluminium enaminonates. Both air and moisture sensitive compounds could be purified via sublimation under reduced pressure. The spectroscopic analysis and structural motif of the monohydrido compound [H-Al(TFB-TBA)2] (3) showed a monomeric 5-coordinated Al(III) centre bearing two chelating enaminone units and a terminal hydride ligand. However, the dihydrido compound exhibited a rapid C-H bond activation and C-C bond formation in the resulting compound [(Al-TFB-TBA)-HCH2] (4a), which was confirmed by single crystal structural data. The intramolecular hydride shift involving the migration of a hydride ligand from aluminium centre to the alkenyl carbon of the enaminone ligand was probed and verified by multi-nuclear spectral studies (1H,1H NOESY, 13C, 19F, and 27Al NMR).

An Illustrated Guide to Schlenk Line Techniques

Schlenk lines are versatile pieces of laboratory equipment that enable the safe and convenient manipulation of air- and moisture-sensitive compounds. First pioneered in 1913 by Wilhelm Schlenk, the apparatus and techniques used today have evolved considerably, allowing more challenging and sensitive synthetic chemistry to be carried out on a routine basis. This tutorial, which is based on The Schlenk Line Survival Guide, aims to showcase and explain the key technical aspects of Schlenk line chemistry through a series of illustrated guides. It is hoped that this practical guide provides a useful introductory resource and teaching tool for beginner Schlenk line users, as well as a convenient go-to aid for chemists of all proficiency.

Handling considerations for the mass spectrometry of reactive organometallic compounds By Anuj Joshi, Charles Killeen, Tanner Thiessen, Harmen S. Zijlstra and J. Scott McIndoe

The Special Feature this month comes from J. Scott McIndoe and colleagues, Department of Chemistry, University of Victoria, British Columbia, Canada. It serves as a practical guide for the mass spectrometric analysis of reactive organometallic compounds, including air and moisture sensitive compounds. Although this Special Feature is focused exclusively on organometallic compounds, the approaches described here are more generally applicable to reactive compounds of any type. McIndoe and colleagues include numerous practical examples in their review, and they discuss mass spectrometric approaches applicable to a range of sample states (i.e., gas, liquid and solid samples), a range of sample introduction methods and various ionization techniques.

Facile Access to Polar-Functionalized Ultrahigh Molecular Weight Polyethylene at Ambient Conditions

Facile Access to Polar-Functionalized Ultrahigh Molecular Weight Polyethylene at Ambient Conditions

Synthesis and characterisation of two lithium-thiocyanate solvates with tetrahydrofuran: Li[SCN]·THF and Li[SCN]·2THF.

Li[SCN]·THF and Li[SCN]·2THF can be obtained from solutions of anhydrous Li[SCN] in tetrahydrofuran (C4H8O, THF). Both compounds are very hygroscopic and slowly decompose even at room temperature. At ambient conditions Li[SCN]·THF crystallizes in the monoclinic space group P21/c with the lattice parameters a = 574.41(2), b = 1643.11(6), c = 830.15(3) pm and β = 99.009(1)° for Z = 4 as determined by laboratory X-ray powder diffraction. Its crystal structure contains Li+ cations surrounded by one THF molecule and three thiocyanate anions [SCN]- forming {Li[NCS]2[SCN](OC4H8)}2- tetrahedra, which join together as pairs via shared N⋯N edges. CHNS combustion analysis and vibrational spectroscopy confirmed its composition, whereas differential scanning calorimetry and thermogravimetric analysis coupled with a mass spectrometer were applied to record its thermal behaviour. Li[SCN]·2THF crystallises in a primitive monoclinic lattice as well, but in the space group P21/n with the lattice parameters a = 1132.73(3), b = 1637.98(3), c = 1264.88(2) pm and β = 94.393(2)° for Z = 8 as determined from single-crystal X-ray diffraction data at 100 K. Its structure contains two crystallographically independent Li+-centred tetrahedra {Li[NCS]2(OC4H8)2}-, which form dimers {(C4H8O)2Li[μ2-NCS]2Li(OC4H8)2} via shared N⋯N edges. They are merely stabilised by weak agostic H⋯S interactions between some CH2-groups of the C4H8O molecules and the [NCS]- ligands.

Self‐Assembly Reactions To Form Multinuclear Zirconium(III) and Titanium(III) Complexes with Imidazole Derivatives as Bridging Ligands

Self‐assembly reactions with low valent early transition metals, leading to neutral multinuclear complexes are rare. Mostly late transition metals like Pt, Pd or Ru together with N‐heterocycles or O‐donor‐based ligands are used to form supramolecular coordination complexes. This paper reports on self‐assembly reactions of low valent titanocene and zirconocene units and five‐membered N‐heterocycles as bridging ligands. These reactions lead to novel molecular triangles and rectangles with the metal centers marking the vertices. Five different imidazole derivatives and four different metallocene precursors were used. For the first time, molecular triangles and architectures with zirconocene as vertex units through self‐sorting effects are reported. Less sterically demanding substituents lead to the formation of molecular rectangles, whereas more sterically demanding substituents, e.g. Cp*‐ligands on the metal centers or phenyl groups on the bridging ligands lead to the formation of molecular triangles. The synthesis and properties of these air and moisture sensitive compounds are shown and discussed, and their molecular structures and geometries in the solid state were determined by single‐crystal X‐ray diffraction.

200 Years of Lithium and 100 Years of Organolithium Chemistry

The element lithium has been discovered 200 years ago. Due to its unique properties it has emerged to play a vital role in industry, esp. for energy storage, and lithium‐based products and processes support sustainable technological developments. In addition to the many uses of lithium in its inorganic forms, lithium has a rich organometallic chemistry. The development of organometallic chemistry has been hindered by synthetic problems from the start. When Wilhelm Schlenk developed the basic principles to handle and synthesize air‐ and moisture‐sensitive compounds, the road was open to further developments. After more information was available about the stability and solubility of such compounds, they started to play an essential role in other fields of chemistry as alkyl or aryl transfer reagents.

Analysis of air-, moisture- and solvent-sensitive chemical compounds by mass spectrometry using an inert atmospheric pressure solids analysis probe.

A novel method has been developed that enables chemical compounds to be transferred from an inert atmosphere glove box and into the atmospheric pressure ion source of a mass spectrometer whilst retaining a controlled chemical environment. This innovative method is simple and cheap to implement on some commercially available mass spectrometers. We have termed this approach inert atmospheric pressure solids analysis probe ( iASAP) and demonstrate the benefit of this methodology for two air-/moisture-sensitive chemical compounds whose characterisation by mass spectrometry is now possible and easily achieved. The simplicity of the design means that moving between iASAP and standard ASAP is straightforward and quick, providing a highly flexible platform with rapid sample turnaround.

Synthesis of 1,2-Azaborines and the Preparation of Their Protein Complexes with T4 Lysozyme Mutants.

We describe a general synthesis of 1,2-azaborines using standard air-free techniques and protein complex preparation with T4 lysozyme mutants by vapor diffusion. Oxygen- and moisture-sensitive compounds are prepared and isolated under an inert atmosphere (N2) using either a vacuum gas manifold or a glove box. As an example of azaborine synthesis, we demonstrate the synthesis and purification of the volatile N-H-B-ethyl-1,2-azaborine by a five-step sequence involving distillation and column chromatography for the isolation of products. T4 lysozyme mutants L99A and L99A/M102Q are expressed with Escherichia coli RR1 strain. Standard protocols for chemical cell lysis followed by purification using carboxymethyl ion exchange column affords protein of sufficiently high purity for crystallization. Protein crystallization is performed in various concentrations of precipitant at different pH ranges using the hanging drop vapor diffusion method. Complex preparation with the small molecules is carried out by vapor diffusion method under an inert atmosphere. X-ray diffraction analysis of the crystal complex provides unambiguous structural evidence of binding interactions between the protein binding site and 1,2-azaborines.

Electron ionization mass spectrometric analysis of air- and moisture-sensitive organometallic compounds.

Electron ionization (EI) is a reliable mass spectrometric method for the analysis of the vast majority of thermally stable and volatile compounds. In direct EI-MS, the sample is placed into the probe and introduced to the source. For air- and moisture-sensitive organometallic complexes, the sample introduction step is critical. A small quantity must be briefly exposed to the atmosphere, during which time decomposition can occur. Here we present a simple tool that allows convenient analysis of air- and moisture-sensitive organometallic species by direct probe methods: a small purge-able glove chamber affixed to the front end of the mass spectrometer. Using the upgraded mass spectrometer, we successfully characterized a series of air- and moisture-sensitive organometallic complexes, ranging from mildly to very air-sensitive.

Dosage delivery of sensitive reagents enables glove-box-free synthesis.

Contemporary organic chemists employ a broad range of catalytic and stoichiometric methods to construct molecules for applications in many fields, including material sciences1, pharmaceuticals2–5, agrochemicals, and sensors6. The potential utility of a synthetic method can be greatly reduced if it relies on the use of air- and/or moisture-sensitive reagents or catalysts. Furthermore, many synthetic chemistry laboratories have numerous containers of partially used reagents that have been spoiled by exposure to the ambient atmosphere. This is exceptionally wasteful from both an environmental and a cost perspective. In this manuscript, we report an encapsulation method through which air- and moisture-sensitive sensitive compounds can be rendered stable and stored on a laboratory bench top. We demonstrate this approach in three contexts, by describing single use capsules that contain all of the reagents (i.e., catalysts, ligands, and bases) necessary for palladium-catalyzed carbon–fluorine7–9, carbon–nitrogen10,11, and carbon–carbon12 bond forming reactions. The strategy described in this paper should be broadly applicable to a wide range of reagents and catalysts and should have the power to be transformative in preparative organic chemistry, particularly for inexperienced chemists. In addition, this approach will reduce the amount of tedious and time-consuming weighing procedures for the synthetic chemist performing these techniques on a large number of substrate combinations.

Reactivity control using a Schlenk line

Schlenk line (SL) techniques are very common for manipulating air and/or moisture sensitive compounds in organic, inorganic and bioorganic chemistry. Physical and chemical hazards such as pressure burst, explosions, and implosions are usually associated with the SL manipulations due to the use of inert gas, vacuum, liquid nitrogen and chemicals. Therefore researchers require skills in using the Schlenk line for chemical manipulations. This manuscript describes about the SL set-up, its use for controlling reactivity of hydrogenation and moisture sensitive chemicals, and the hazards associated with manipulations.

Spin Density Distribution in Iron(II) and Cobalt(II) Alkyl Complexes Containing 1,3-Bis(2-pyridylimino)isoindolate Ligands

Iron(II) and cobalt(II) alkyl complexes using tridentate bis(pyridylimino)isoindolates as ancillary ligands have been synthesized from the pyridine alkyl precursor complexes [(py)2Fe(CH2SiMe3)2] and [(py)2Co(CH2SiMe3)2]. The extremely air- and moisture-sensitive compounds were structurally characterized in the solid state by X-ray diffraction as well as in solution by paramagnetic NMR spectroscopy. It is demonstrated that the paramagnetic shifts in the 13C NMR spectra are dominated by strong Fermi-contact interactions. All 13C NMR signals can be assigned by correlation with DFT-calculated spin-density distributions.

Pressurized Sample Infusion for the Continuous Analysis of Air- And Moisture-Sensitive Reactions Using Electrospray Ionization Mass Spectrometry

Air- and moisture-sensitive compounds pose handling difficulties for chemists requiring mass spectrometric analysis. A simple pressurized sample infusion (PSI) system for electrospray ionization mass spectrometry using a Schlenk flask is presented, which allows straightforward one-off analyses as well as continuous reaction monitoring at any temperature up to the boiling point of the solvent.

A System for Cooling Inside a Glove Box

An easy, efficient, reliable, and low-cost method of constructing a cooling system using a simple circulating pump is described. The system is employed in conjunction with an inert atmosphere glove box to achieve the synthesis of air- and moisture-sensitive compounds inside the glove box at controlled, low temperatures without contaminating the glovebox purification system. The system can also be used in an inert atmosphere glovebag.

Convenient route to water-sensitive sol–gel precursors using click chemistry

The CuAAC-'click' reaction under anhydrous conditions is reported as a new tool for the preparation of moisture-sensitive triethoxysilyl compounds that are obtained in 5 minutes in excellent yield with simple purification.

A Simple Double-Chamber NMR Tube for the Monitoring of Chemical Reactions by NMR Spectroscopy

The development of a simple piece of equipment for monitoring chemical reactions by NMR (nuclear magnetic resonance) spectroscopy is reported. The kit provides full control of the reaction temperature at any time and can be operated in the temperature range from −80 to 130 °C. The core component is a double-chamber coaxial tube consisting of a 5 mm screw-cap tube and a 3 mm glass insert, which allows two reactant solutions to be placed separately in one NMR tube. The tube can be operated from outside the magnet by additional hardware, which affords the mixing of two reactants inside the sensitive coils region of the NMR probe. The tube kit can be used without any expensive hardware modifications at the NMR instrument and is compatible with the uptake of air- and moisture-sensitive compounds. The potential of the device is demonstrated by two low-temperature experiments involving highly reactive silicon(II) species.

Role of Y,C,Y-Chelating Ligands in Control Hydrolysis of Diorganotin Compounds

The potential use of Y,C,Y-chelating ligands in control hydrolysis of diorganotin(IV) compounds of general formula L1,2SnPhX2 (L1 = 2,6-(Me2NCH2)2C6H3, L2 = 2,6-(MeOCH2)2C6H3, and X = Cl, CF3SO3, and [1-CB11H12]) is reported. The hydrolysis of moisture-sensitive compounds L1SnPh(OTf)2 (3) and L2SnPh(OTf)2 (4) gave organotin(IV) cations {[L1SnPh(OH2)(OTf)]+[OTf]−} (5) and {[L2SnPh(OH2)(OTf)]+[OTf]−} (6). Reported is also the preparation of diorganotin(IV) cations {[L1SnPhCl]+ [1-CB11H12]−} (7) and {[L2SnPhCl]+ [1-CB11H12]−} (8) and the isolation of [PhL2Sn-μ-(OH)2-SnL2Ph]2+ 2*[1-CB11H12]− (9), the final hydrolytic product of 8. The products were characterized by 1H, 11B, 13C, and 119Sn NMR and IR spectroscopy, ESI/MS, and elemental analyses, and the structures of compounds 3 and 6 were determined by X-ray diffraction studies.

Titanium‐Based Molecular Squares and Rectangles: Syntheses by Self‐Assembly Reactions of Titanocene Fragments and Aromatic N‐Heterocycles

This paper reports on the potential of titanium compounds as building blocks for supramolecular polygons. Self-assembly reactions of low-valent titanocene units and N-heterocyclic bridging ligands lead to novel titanium-based supramolecular squares. Pyrazine (3), 4,4'-bipyridine (4), and tetrazine (5) were used as bridging ligands, and the acetylene complexes [Cp2Ti{eta2-C2(SiMe3)2}] (1) and [(tBuCp)2Ti{eta2-C2(SiMe3)2}] (2) as sources of titanocene fragments. Molecular rectangles can be synthesized by stepwise reduction of the titanocene dichlorides [Cp(2)TiCl2] and [(tBuCp)2TiCl2] and consecutive coordination of two different bridging ligands. The resulting complexes are the first examples of molecular rectangles containing bent metallocene corner units. Single-crystal X-ray analyses of the tetranuclear compounds revealed the geometric properties of the molecular polygons in the solid state. Comparison of bond lengths and angles in coordinated and free ligands reveals the reduced state of the bridging ligand in the low-valent titanium compounds. The syntheses and properties of these novel, highly air- and moisture-sensitive compounds are discussed.

Polysulfonylamine, CXLVII [1]. Die ersten N,N-disulfonylierten Thioharnstoffe: Synthese von (RSO2)2N-C(S)-NMe2 (R = Me, 4-Me-C6H4) und Kristallstruktur der Ditosylverbindung / Polysulfonylamines, CXLVII [1]. The First N,N-Disulfonylated Thioureas: Synthesis of (RSO2)2N-C(S)-NMe2 (R = Me, 4-Me-C6H4) and Crystal Structure of the Ditosyl Compound

The moisture-sensitive title compounds were obtained in good yields by treating the corresponding silver salts AgN(SO2R)2 with the thiocarbamoyl chloride Me2NC(S)Cl in acetonitrile. In the NMR solution spectra of the novel thioureas, as recorded at room temperature for 13C and up to 120 °C for 1H, the Me2N group invariably gives rise to two distinct resonances, reflecting unusually high barriers to rotation about the C(S)-NMe2 bond. The crystal structure of the ditosyl compound (triclinic, space group P1̅, X-ray diffraction at -130 °C) contains two independent molecules A and B, in which the bond lengths and angles are nearly identical, whereas the conformations exhibit pronounced discrepancies. The amide N and thiocarbonyl C atoms have trigonal-planar environments, but the S -N -S planes are strikingly rotated into approximately perpendicular orientations relative to the planar C2N-C(S)-N moieties. Other remarkable features of the molecular structures are the exceedingly long C(S)-NS2 bonds [mean: 145.4(3) pm] and the concomitantly short C -S and C(S)-NC2 bonds [mean values: 164.8(2), 132.6(3) pm]. The packing is governed by a three-dimensional system of weak hydrogen bonds and may be viewed as a self-clathrate, in which (B)2 dimers constructed from C-H···S=C interactions are inserted as guest species into parallel tunnels between (A)∞ tapes based upon short C-H···O=S contacts.