A Dimer of Hydrogen Cyanide Stabilized by a Lewis Acid

Hydrogen-Bonded π Complexes between Phosphaethyne and Hydrogen Chloride

The highly labile complexes between phosphaethyne (HCP) and hydrogen chloride (HCl) with 1:1 and 1:2 stoichiometries have been generated in Ar and N₂ matrices at 10 K through laser photolysis of the molecular precursors 1-chlorophosphaethene (CH₂PCl) and dichloromethylphosphine (CH₃PCl₂), respectively. The IR spectrum of the 1:1 complex suggests the preference of a single "T-shaped" structure in which HCl acts as the hydrogen donor that interacts with the electron-rich C≡P triple bond. In contrast, three isomeric structures for the 1:2 complex bearing a core structure of the "T-shaped" 1:1 complex are present in the matrix. The spectroscopic identification of these rare HCP π-electron complexes is supported by D-isotope labeling and the quantum chemical calculations at the CCSD(T)-F12a/cc-pVTZ-F12 level of theory.

A Lewis Acid Stabilized Ketenimine in an Unusual Variant of the Electrophilic Aromatic Substitution

Electrophilic aromatic substitution (EAS) can provide a straightforward approach to the efficient synthesis of functionalized complex aromatic molecules. In general, Lewis acids serve as a beneficial stimulus for the formation of a Wheland complex, the intermediate in the classical SE Ar mechanism of EAS, which is responsible for H/E (E=electrophile) substitution under formal H+ elimination. Herein, we report an unusual variant of EAS, in which a complex molecule such as the tricyanomethane, HC(CN)3 , is activated with a strong Lewis acid (B(C6 F5 )3 ) to the point where it can finally be used in an EAS. However, the Lewis acid here causes the isomerization of the tricyanomethane to the ketenimine, HN=C=C(CN)2 , which in turn directly attacks the aromatic species in the EAS, with simultaneous proton migration of the aromatic proton to the imino group, so that no elimination occurs that is otherwise observed in the SE Ar mechanism. By this method, it is possible to build up amino-malononitrile-substituted aromatic compounds in one step.

Main group cyanides: from hydrogen cyanide to cyanido-complexes

Homoleptic cyanide compounds exist of almost all main group elements. While the alkali metals and alkaline earth metals form cyanide salts, the cyanides of the lighter main group elements occur mainly as covalent compounds. This review gives an overview of the status quo of main group element cyanides and cyanido complexes. Information about syntheses are included as well as applications, special substance properties, bond lengths, spectroscopic characteristics and computations. Cyanide chemistry is presented mainly from the field of inorganic chemistry, but aspects of chemical biology and astrophysics are also discussed in relation to cyano compounds.

(Noble Gas)n -NC+ Molecular Ions in Noble Gas Matrices: Matrix Infrared Spectra and Electronic Structure Calculations

An investigation of pulsed‐laser‐ablated Zn, Cd and Hg metal atom reactions with HCN under excess argon during co‐deposition with laser‐ablated Hg atoms from a dental amalgam target also provided Hg emissions capable of photoionization of the CN photo‐dissociation product. A new band at 1933.4 cm⁻¹ in the region of the CN and CN⁺ gas‐phase fundamental absorptions that appeared upon annealing the matrix to 20 K after sample deposition, and disappeared upon UV photolysis is assigned to (Ar)_nCN⁺, our key finding. It is not possible to determine the n coefficient exactly, but structure calculations suggest that one, two, three or four argon atoms can solvate the CN⁺ cation in an argon matrix with C−N absorptions calculated (B3LYP) to be between 2317.2 and 2319.8 cm⁻¹. Similar bands were observed in solid krypton at 1920.5, in solid xenon at 1935.4 and in solid neon at 1947.8 cm⁻¹. H¹³CN reagent gave an 1892.3 absorption with shift instead, and a 12/13 isotopic frequency ratio–nearly the same as found for ¹³CN⁺ itself in the gas phase and in the argon matrix. The CN⁺ molecular ion serves as a useful infrared probe to examine Ng clusters. The following ion reactions are believed to occur here: the first step upon sample deposition is assisted by a focused pulsed YAG laser, and the second step occurs on sample annealing: (Ar)₂⁺+CN→Ar+CN⁺→(Ar)_nCN⁺.

A Phosphorus-Based Pacman Dication Generated by Cooperative Self-Activation of a Pacman Phosphane

Formal coordination of phosphorus(III) by a calix[4]pyrrole Schiff base ligand was achieved through the reaction of this ligand with PCl₃ under basic conditions. The reaction product adopts a Pacman conformation with two P-Cl moieties, one in exo and one in endo position. It represents the first non-metal compound of calix[4]pyrrole Schiff base ligands and of Pacman ligands in general. The spatial neighborhood of the two phosphorus atoms enables cooperative reactions. As a first example, the chloride abstraction with AgOTf is presented, yielding a macrocyclic dication with two embedded phosphorus(III) monocations, which both undergo a cooperative, internal activation reaction with an adjacent C=N double bond. This intramolecular redox process affords two pentacoordinated phosphorus(V) centers within the Pacman dication. All reaction products were fully characterized and all results are supported by computations.

NMR Properties of the Cyanide Anion, a Quasisymmetric Two-Faced Hydrogen Bonding Acceptor

The isotopically enriched cyanide anion, (13C≡15N)−, has a great potential as the NMR probe of non-covalent interactions. However, hydrogen cyanide is highly toxic and can decompose explosively. It is therefore desirable to be able to theoretically estimate any valuable results of certain experiments in advance in order to carry out experimental studies only for the most suitable molecular systems. We report the effect of hydrogen bonding on NMR properties of 15N≡13CH···X and 13C≡15NH···X hydrogen bonding complexes in solution, where X = 19F, 15N, and O=31P, calculated at the ωB97XD/def2tzvp and the polarizable continuum model (PCM) approximations. In many cases, the isotropic 13C and 15N chemical shieldings of the cyanide anion are not the most informative NMR properties of such complexes. Instead, the anisotropy of these chemical shieldings and the values of scalar coupling constants, including those across hydrogen bonds, can be used to characterize the geometry of such complexes in solids and solutions. 1J(15N13C) strongly correlates with the length of the N≡C bond.

Synthesis and Characterization of Poly(hydrogen halide) Halogenates (-I)

Herein, we report the synthesis and characterization of a variety of novel poly(hydrogen halide) halogenates (-I). The bifluoride ion, which is known to have the highest hydrogen bond energy of ≈160 kJ mol-1 , is the most famous among many examples of [X(HX)n ]- anions (X=F, Cl) known in the literature. In contrast, little is known about poly(hydrogen halide) halogenates containing two different halogens, ([X(HY)n ]- ). In this work we present the synthesis of anions of the type [X(HY)n ]- (X=Br, I, ClO4 ; Y=Cl, Br, CN) stabilized by the [PPh4 ]+ and [PPN]+ cation. The obtained compounds have been characterized by single-crystal X-ray diffraction, Raman spectroscopy and quantum-chemical calculations. In addition, the behavior of halide ions in hydrogen fluoride was investigated by using experimental and quantum-chemical methods in order to gain knowledge on the acidity of hydrogen halides in HF.

Trapping of Brønsted acids with a phosphorus-centered biradicaloid - synthesis of hydrogen pseudohalide addition products

The trapping of classical hydrogen pseudohalides (HX, X = pseudohalogen = CN, N3, NCO, NCS, and PCO) utilizing a phosphorus-centered cyclic biradicaloid, [P(μ-NTer)]2, is reported. These formal Brønsted acids were generated in situ as gases and passed over the trapping reagent, the biradicaloid [P(μ-NTer)]2, leading to the formation of the addition product [HP(μ-NTer)2PX] (successful for X = CN, N3, and NCO). In addition to this direct addition reaction, a two-step procedure was also applied because we failed in isolating HPCO and HNCS addition products. This two-step process comprises the generation and isolation of the highly reactive [HP(μ-NTer)2PX]+ cation as a [B(C6F5)4]- salt, followed by salt metathesis with salts such as [cat]X (cat = PPh4, n-Bu3NMe), which also gives the desired [HP(μ-NTer)2PX] product, with the exception of the reaction with the PCO- salt. In this case, proton migration was observed, finally affording the formation of a [3.1.1]-hetero-propellane-type cage compound, an OC(H)P isomer of a HPCO adduct. All discussed species were fully characterized.

Pseudohalide HCN aggregate ions: [N3(HCN)3]-, [OCN(HCN)3]-, [SCN(HCN)2]- and [P(CN·HCN)2]-

In the presence of μ-nitridobis(triphenylphosphonium) cation, [PPN]+, it was possible to stabilize and isolate [PPN]+-salts bearing the highly labile hydrogen cyanide aggregate anions of pseudohalides X (X = N3, OCN and SCN). From a concentrated solution of the [PPN]X salts in HCN, crystals of [PPN][X(HCN)3] (X = N3, OCN) or [PPN][SCN(HCN)2] could be obtained, when the crystallization was carried out fast and at low temperatures. The reaction of liquid HCN with the PCO- salt led to formation of dicyanophosphide, which crystallized as HCN disolvate [P(CN·HCN)2]-. All synthesized salts with hydrogen-bridged pseudohalide solvate anions are thermally unstable. Immediate loss of HCN was observed in the crystals outside the HCN solution. Oligomerization begins at ambient temperature, even in HCN solution. All discussed species were characterized by means of Raman spectroscopy, single crystal X-ray analysis and quantum-chemical calculations.

Salts of HCN-Cyanide Aggregates: [CN(HCN)2 ]- and [CN(HCN)3 ]. Angew Chem Int Ed Engl 2020;59:10508-10513. [PMID: 32027458 PMCID: PMC7317722 DOI: 10.1002/anie.201915206]

Although pure hydrogen cyanide can spontaneously polymerize or even explode, when initiated by small amounts of bases (e.g. CN- ), the reaction of liquid HCN with [WCC]CN (WCC=weakly coordinating cation=Ph4 P, Ph3 PNPPh3 =PNP) was investigated. Depending on the cation, it was possible to extract salts containing the formal dihydrogen tricyanide [CN(HCN)2 ]- and trihydrogen tetracyanide ions [CN(HCN)3 ]- from liquid HCN when a fast crystallization was carried out at low temperatures. X-ray structure elucidation revealed hydrogen-bridged linear [CN(HCN)2 ]- and Y-shaped [CN(HCN)3 ]- molecular ions in the crystal. Both anions can be considered members of highly labile cyanide-HCN solvates of the type [CN(HCN)n ]- (n=1, 2, 3 …) as well as formal polypseudohalide ions.

Borane Adducts of Hydrazoic Acid and Organic Azides: Intermediates for the Formation of Aminoboranes

The reaction of HN₃ with the strong Lewis acid B(C₆ F₅ )₃ led to the formation of a very labile HN₃ ⋅B(C₆ F₅ )₃ adduct, which decomposed to an aminoborane, H(C₆ F₅ )NB(C₆ F₅ )₂ , above -20 °C with release of molecular nitrogen and simultaneous migration of a C₆ F₅ group from boron to the nitrogen atom. The intermediary formation of azide-borane adducts with B(C₆ F₅ )₃ was also demonstrated for a series of organic azides, RN₃ (R=Me₃ Si, Ph, 3,5-(CF₃ )₂ C₆ H₃ ), which also underwent Staudinger-like decomposition along with C₆ F₅ group migration. In accord with experiment, computations revealed rather small barriers towards nitrogen release for these highly labile azide adducts for all organic substituents except R=Me₃ Si (m.p. 120 °C, T_dec =189 °C). Hydrolysis of the aminoboranes provided C₆ F₅ -substituted amines, HN(R)(C₆ F₅ ), in good yields.

Heavy Neutral and Anionic Pnictogen Thiocyanates

When [PPN]SCN (1; PPN = [Ph₃P-N-PPh₃]) is treated with Me₃Si-SCN in methanol, [PPN][H(NCS)₂] (2), a hydrogen diisothiocyanate salt bearing the [H(NCS)₂]^- anion, was generated, isolated, and fully characterized. Pure heavy E(NCS)₃ [E = Sb (3), Bi (4)] species were obtained from the reaction of EF₃ and an excess of Me₃Si-SCN, while the tetrahydrofuran (THF) solvates E(NCS)₃·THF were isolated when the product was recrystallized from THF. When 2 equiv of 1 was combined with Me₃Si-SCN and SbF₃, [PPN]₂[Sb(NCS)₅] (5) could be isolated. When 1 was added to BiF₃, [PPN]₂[Bi(NCS)₃(SCN)₂·THF] (6·THF), containing three SCN^- ions coordinating via the N atom and two coordinating via the S atom, was isolated after recrystallization from THF. The structures of 1, 2, 3·THF, 4·THF, 5, and 6·THF were determined. 3·THF displayed a typical [3 + 3] coordination mode with a trigonal-pyramidal environment in the first coordination sphere of the Sb³⁺ ion, and the dianion of 5, [Sb(NCS)₅]^2-, featured a classical square-pyramidal molecular geometry around the Sb³⁺ ion with one additional Menshutkin-type interaction to one aryl ring of the [PPN]⁺ cation. 4·THF exhibited a distorted pentagonal-bipyramidal structure within a two-dimensional network, while in 6·THF, an octahedrally surrounded Bi³⁺ ion was observed.

Lewis adduct formation of hydrogen cyanide and nitriles with arsenic and antimony pentafluoride

The reactions of hydrogen cyanide, butyronitrile, cyclopropanecarbonitrile, pivalonitrile and benzonitrile with arsenic pentafluoride and antimony pentafluoride result in the formation of 1 : 1 Lewis adducts, while malononitrile yielded both 1 : 1 and 1 : 2 Lewis adducts.

Grignard synthesis of fluorinated nanoporous element organic frameworks based on the heteroatoms P, B, Si, Sn and Ge

We present the synthesis and characterization of fluorinated polymers based on P, B, Si, Sn and Ge as heteroatoms via Grignard activation.

Fundamental Vibrational Analyses of the HCN Monomer, Dimer and Associated Isotopologues

In this work we provide high level ab initio treatments of the structures, vibrational frequencies, and electronic energies of the HCN monomer and dimer systems along with several isotopologues. The plethora of information related to this system within the literature is summarized and serves as a basis for comparison with the results of this paper. The geometry of the dimer and monomer are reported at the all electroncoupled-cluster singles, doubles, and perturbative triples level of theory [AE-CCSD(T)] with the correlation consistent quadruple-zeta quality basis sets with extra core functions (cc-pCVQZ) from Dunning. The theoretical geometries and electronic structures are further analyzed through the use of the Natural Bond Orbital (NBO) method and Natural Resonance Theory (NRT). At the AE-CCSD(T)/cc-pCVQZ level of theory, the full cubic with semi-diagonal quartic force field for nine dimer and four monomer isotopologues (the parent isotopologue along with 15 N, 13 C, and D derivatives) were obtained to treat the anharmonicity of the vibrations via second order vibrational perturbation theory (VPT2). Lastly, the enthalpy change associated with the formation of the dimer from two monomer units was determined using the focal point analysis. Computations including coupled-cluster through perturbative quadruples as well as basis sets up to six-zeta quality, including core functions (cc-pCVXZ, X=D,T,Q,5,6) were used to extrapolate to the AE-CCSDT(Q)/CBS energy associated with this hydrogen-bond forming process. After appending anharmonic zero-point vibrational, relativistic, and diagonal Born-Oppenheimer corrections, we report a value of -3.93 kcal mol-1 for the enthalpy of formation. To our knowledge, each set of results (geometries, vibrational frequencies, and energetics) reported in this study represents the highest-level and most reliable theoretical predictions reported for this system.

Group 15 biradicals: synthesis and reactivity of cyclobutane-1,3-diyl and cyclopentane-1,3-diyl analogues

Synthesis, structure and reactivity of cyclobutane-1,3-diyl and cyclopentane-1,3-diyl analogues are discussed along with their application as molecular switches or reagents to activate or trap small molecules with single or multiple bonds.