Cyclic Arsenic−Nitrogen Cations

Single-Bonded Cubic AsN from High-Pressure and High-Temperature Chemical Reactivity of Arsenic and Nitrogen

Chemical reactivity between As and N2 , leading to the synthesis of crystalline arsenic nitride, is here reported under high pressure and high temperature conditions generated by laser heating in a diamond anvil cell. Single-crystal synchrotron X-ray diffraction at different pressures between 30 and 40 GPa provides evidence for the synthesis of a covalent compound of AsN stoichiometry, crystallizing in a cubic P21 3 space group, in which each of the two elements is single-bonded to three atoms of the other and hosts an electron lone pair, in a tetrahedral anisotropic coordination. The identification of characteristic structural motifs highlights the key role played by the directional repulsive interactions between non-bonding electron lone pairs in the formation of the AsN structure. Additional data indicate the existence of AsN at room temperature from 9.8 up to 50 GPa. Implications concern fundamental aspects of pnictogens chemistry and the synthesis of innovative advanced materials.

An Acyclic Arsenium Cation Stabilised by a Single P-As π-Interaction and a Cyclic Diphosphinophosphonium Salt

Stable acyclic arsenium cations R₂ As⁺ , isoelectronic analogues of germylenes, are rare in comparison to the corresponding phosphenium cations. The first example of a diphosphaarsenium salt, [{(Dipp)₂ P}₂ As][Al{OC(CF₃ )₃ }₄ ]⋅1 1 / 2  PhMe, is described. This salt exhibits remarkable stability due to the delocalisation of a lone pair from a planar phosphorus centre into the vacant p-orbital at arsenic; the bonding in 2 has been probed by DFT calculations. An attempt to synthesise an analogous diphosphaphosphenium salt unexpectedly generated the cyclic phosphonium salt [cyclo-{(Mes)P}₂ P(Mes)₂ ][BAr^F ₄ ]⋅CyMe through the cyclisation of a putative phosphine-substituted diphosphene cation intermediate.

Synthesis and characterization of a stable non-cyclic bis(amino)arsenium cation

The reaction of Li[Mes*NH] (1, Mes* = 2,4,6-tri-tert-butylphenyl) with aminoarsane Mes*N(H)AsCl2 (2, Mes* = 2,4,6-t-Bu3C6H2) at −80 °C resulted in the formation of bisamino(chloro)arsane (Mes*NH)2AsCl (3Cl) by elimination of LiCl. 3Cl reacted with the Lewis acids such as AlCl3, GaCl3, and Ag[X] (X = AsF6−, OTf−, BF4−; OTf = trifluoromethanesulfonate = OSO2CF3−) upon chloride ion abstraction to give salts bearing the cation [(Mes*NH)2As]+ (3[X]; X = AsF6−, OTf−, BF4−, ECl4; E = Al, Ga). 3+ represents the first NH-functionalized acyclic bis(amino)arsenium cation. The formation of the salts bearing 3+ could also be observed in the reaction of cyclo-1,3-diarsa-2,4-diazane [ClAs(μ-NMes*)]2 (4) with Lewis acids (AlCl3, GaCl3) in the presence of proton sources in solution. All presented salts 3[X] were stable at room temperature and fully characterized.

Reactive p-block cations stabilized by weakly coordinating anions

The chemistry of the p-block elements is a huge playground for fundamental and applied work. With their bonding from electron deficient to hypercoordinate and formally hypervalent, the p-block elements represent an area to find terra incognita. Often, the formation of cations that contain p-block elements as central ingredient is desired, for example to make a compound more Lewis acidic for an application or simply to prove an idea. This review has collected the reactive p-block cations (rPBC) with a comprehensive focus on those that have been published since the year 2000, but including the milestones and key citations of earlier work. We include an overview on the weakly coordinating anions (WCAs) used to stabilize the rPBC and give an overview to WCA selection, ionization strategies for rPBC-formation and finally list the rPBC ordered in their respective group from 13 to 18. However, typical, often more organic ion classes that constitute for example ionic liquids (imidazolium, ammonium, etc.) were omitted, as were those that do not fulfill the - naturally subjective -"reactive"-criterion of the rPBC. As a rule, we only included rPBC with crystal structure and only rarely refer to important cations published without crystal structure. This collection is intended for those who are simply interested what has been done or what is possible, as well as those who seek advice on preparative issues, up to people having a certain application in mind, where the knowledge on the existence of a rPBC that might play a role as an intermediate or active center may be useful.

Extremely bulky amide ligands in main group chemistry

The development of extremely sterically demanding, monodentate amide ligands facilitates the isolation of main group species with new and highly reactive coordination modes. An outstanding feature of these ligands is the ability to tune their steric demands. Reactivity investigations highlight the potential for small molecule activation chemistry and catalysis for these compounds.

The structure and energetics of arsenic(III) oxide intercalated by ionic azides

Unprecedented intercalates of arsenic(iii) oxide with potassium azide and ammonium azide have been obtained and characterized by single crystal X-ray diffraction. The compounds are built of As2O3 sheets separated by charged layers of cations and azide anions perpendicular to the sheets. The intercalates are an interesting example of hybrid materials whose structure is governed by covalent bonds in two directions and ionic bond in the third one. The obtained compounds are the first examples of As2O3 intercalates containing linear pseudohalogen anions. Periodic DFT calculations of interlayer interaction energies were carried out with the B3LYP-D* functional. The layers are held together mainly by ionic bonds, although the computations indicate that interactions between cations and As2O3 sheets also play a significant role. A comparison of cation and anion interaction energies with neutral As2O3 sheets sheds light on the crystallisation process, indicating the templating effect of potassium and ammonium cations. It consist in the formation of sandwich complexes of cations with crown-ether-resembling As6O12 rings. Raman spectra of both compounds are recorded and computed ab initio and all vibrational bands are assigned.

Low-Temperature Isolation of the Bicyclic Phosphinophosphonium Salt [Mes*2P4Cl][GaCl4]

The reaction of [ClP(μ-PMes*)]2 (1) with the Lewis acid GaCl3 yielded a hitherto unknown tetraphosphabicyclo[1.1.0]butan-2-ium salt, [Mes*P4(Cl)Mes*][GaCl4] (3[GaCl4]), which incorporates a positively charged phosphonium center within its bicyclic P4 scaffold. The formation of the title compound was studied by means of low-temperature NMR experiments. This led to the identification of an intermediate cyclotetraphosphenium cation, which was trapped by reaction with dimethylbutadiene (dmb). All of the compounds were fully characterized by experimental and computational methods.

A neutral low-coordinate heterocyclic bismuth-tin species

The reaction of cyclodistannadiazane with an excess of antimonytrichloride led to the formation of tetrachlorodistibanes, while in the reaction with bismuthtrichloride a carbenoid bismuth species was obtained which can be regarded as a heavy atom analog of NHCs.

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.

Second order non-linear optical activity of arsenic and antimony dithiolene complexes

Synthesis and characterization of dithiolene complexes of arsenic and antimony in trivalent state have been reported. A four coordinated structural motif results in a ladder like arrangement in the arsenic complex due to the inter-anionic As-S interaction which is replaced by Sb-π interaction with the counter cation in the solid state structure of the similar antimony complex. Electronic structure calculations on ground state geometries and the time-dependent density functional theoretical calculations were performed in order to characterize the absorption spectra incorporating solvent effects. Notably, both the complexes display intense second order optical non-linearity as has been determined using hyper-Rayleigh scattering technique in dichloromethane solution and the results are corroborated by DFT calculations.

Structure and bonding of novel acyclic bisaminoarsenium cations

The synthesis and characterization of a salt bearing a labile bisaminoarsenium cation of the type {[(Me3Si)2N]2As}(+) (9a) are described, which was obtained in the reaction of the chloroarsane [(Me3Si)2N]2AsCl (8) with GaCl3. Reacting 8 with AgOTf did not yield an arsenium salt, but the cyclo-diarsadiazane [(Me3Si)2NAs-μ-NSiMe3]2 (11) was obtained in excellent yields. Moreover, the reactivity of the analogous antimony species [(Me3Si)2N]2SbCl (12) was studied. In the reaction with GaCl3, the aminochlorostibenium salt [(Me3Si)2NSbCl](+)[(Me3Si)2N(GaCl3)2](-) (5) was isolated. In the reaction with AgOTf, substitution of the chlorine in 12 resulted in the formation of [(Me3Si)2N]2SbOTf (13), a compound with significant stibenium character. All new compounds have been fully characterized by means of X-ray, vibrational spectroscopy, CHN analysis, and NMR experiments. All compounds were further investigated by means of density functional theory and the bonding situation was accessed by natural bond orbital (NBO) analysis.

On the synthesis and reactivity of highly labile pseudohalogen phosphenium ions

The synthesis and characterization of salts bearing highly labile pseudohalogen-substituted aminophosphenium cations of the type [(Me3Si)2NPX][GaCl4] (X = NCO, NCS, O(SiMe3)) and their respective reactivity toward Lewis bases (4-dimethylaminopyridine, dmap) and dienes (2,3-dimethyl-1,3-butadiene, dmb; 1,3-cyclo-hexadiene, chd) are described. As π-acidic species, aminophosphenium cations react with dmap at low temperatures to yield adduct salts of the type [(Me3Si)2NP(dmap)X][GaCl4] (X = Cl, N3, NCO) which were fully characterized. In the reaction with dienes at -50 °C, salts bearing phospholenium cations were obtained that could be structurally characterized. The crystal structures of novel 7-phosphanorbornenium cations of the type [(Me3Si)2NP(C6H8)X][GaCl4] (X = Cl, N3, NCO) are reported. All compounds were further investigated by means of density functional theory, and the bonding situation was accessed by Natural Bond Orbital (NBO) analysis.