Modern Aspects of Pseudohalogen Chemistry: News from CN- and PN-Chemistry

Electrolyte design combining fluoro- with cyano-substitution solvents for anode-free Li metal batteries

Fluoro-substitution solvents have achieved great success in electrolyte engineering for high-energy lithium metal batteries, which, however, is beset by low solvating power, thermal and chemical instability, and possible battery swelling. Instead, we herein introduce cyanogen as the electron-withdrawing group to enhance the oxidative stability of ether solvents, in which cyanogen and ether oxygen form the chelating structure with Li+ not notably undermining the solvating power. Cyano-group strongly bonds with transition metals (TMs) of NCM811 cathode to attenuate the catalytic reactivity of TMs toward bulk electrolytes. Besides, a stable and uniform cathode-electrolyte interphase (CEI) inhibits the violent oxidation decomposition of electrolytes and guarantees the structural integrity of the NCM811 cathode. Also, a N-containing and LiF-rich solid-electrolyte interphase (SEI) in our electrolyte facilitates fast Li+ migration and dense Li deposition. Accordingly, our electrolyte enables a stable cycle of Li metal anode with Coulombic efficiency of 98.4% within 100 cycles. 81.8% capacity of 4.3 V NCM811 cathode remains after 200 cycles. Anode-free pouch cells with a capacity of 125 mAh maintain 76% capacity after 100 cycles, corresponding to an energy density of 397.5 Wh kg-1.

Synthesis, Structure and Reactivity of a Cyapho(dicyano)methanide Salt

We describe the synthesis of a cyapho(dicyano)methanide salt, [K(18-crown-6)][C(CN)2 (CP)], from reaction of [Na(18-crown-6)][PH2 ] (18-crown-6=1,4,7,10,13,16-hexaoxacyclooctadecane) with 1,1-diethoxy-2,2-dicyanoethylene (EtO)2 C=C(CN)2 . The reaction proceeds through a Michael addition-elimination pathway to afford [Na(18-crown-6)][HP{C(OEt)=C(CN)2 }]. Addition of a strong, non-nucleophilic base (KHMDS) to this intermediate results in the formation of [K(18-crown-6)][C(CN)2 (CP)]. Subsequent reactivity studies reveal that the cyapho(dicyano)methanide ion is susceptible to protonation with strong acids to afford the parent acid HC(CN)2 (CP). The reactivity of the cyaphide moiety in [C(CN)2 (CP)]- was explored through coordination to metal centers and in cycloaddition reactions with azides.

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.

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.

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.

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.

Computational study of the threshold energy for the 1,2-interchange of X and R (X, R = halogens, pseudohalogens, and monovalent hydrocarbon groups) on CH2XCH2R

Transition state geometries and threshold energies, E0, were computed for an unusual unimolecular isomerization reaction that exchanges two groups (X, R) on CH2XCH2R. An objective is to determine the most energetically feasible interchanges to guide experimental investigations. The interchanging species included halogens (F, Cl, Br) and pseudohalogens and monovalent hydrocarbons (H, SH, CH3, NH2, OH, OCF3, OCH3, CH=CH2, CH2CH3, CH2OH, C≡CH, CH2CF3, CCl3, CF3) attached to a two carbon backbone. Ground state and transition state geometries were optimized with the B3PW91 level of theory and 6-311+G(2d,p) basis set. The Br–Br interchange had the lowest E0 (141 kJ/mol), and CH3–H had the highest E0 (582 kJ/mol). In general, larger atoms or groups with lone pairs of electrons such as halogens, SH, OH, OCH3, OCF3, and NH2 tend to lower the E0 barrier for interchange, making them the most likely to be experimentally observed.

The reactivity of silylated amino(dichloro)phosphanes in the presence of silver salts

New cyclic and acylic phosphorus-nitrogen compounds have been synthesized in reactions of Hyp-N(SiMe3)PCl2 (hypersilyl = Hyp = (Me3Si)3Si) with silver salts of the perfluorinated anions [CF3CO2](-), [CF3SO3](-), and [C6F5](-). Depending on the choice of the silver salt, not only AgCl but also Me3SiCl elimination could be observed, leading to a transient highly reactive 1,3 dipole molecule. This 1,3 dipole molecule was found to be a key species, which can undergo [3 + 2] cyclization, when a dipolarophile such as acetonitrile is present. Also, dimerization or even cyclo-tetramerization are observed. The occurrence of different reaction channels demonstrates that the hypersilyl moiety can act as a highly reactive functional group. All new compounds have been characterized by single-crystal X-ray diffraction studies.