Pseudohalogen Chemistry in Ionic Liquids with Non-innocent Cations and Anions.

Within the second funding period of the SPP 1708 "Material Synthesis near Room Temperature",which started in 2017, we were able to synthesize novel anionic species utilizing Ionic Liquids (ILs) both, as reaction media and reactant. ILs, bearing the decomposable and non-innocent methyl carbonate anion [CO3 Me]- , served as starting material and enabled facile access to pseudohalide salts by reaction with Me3 Si-X (X=CN, N3 , OCN, SCN). Starting with the synthesized Room temperature Ionic Liquid (RT-IL) [nBu3 MeN][B(OMe)3 (CN)], we were able to crystallize the double salt [nBu3 MeN]2 [B(OMe)3 (CN)](CN). Furthermore, we studied the reaction of [WCC]SCN and [WCC]CN (WCC=weakly coordinating cation) with their corresponding protic acids HX (X=SCN, CN), which resulted in formation of [H(NCS)2 ]- and the temperature labile solvate anions [CN(HCN)n ]- (n=2, 3). In addition, the highly labile anionic HCN solvates were obtained from [PPN]X ([PPN]=µ-nitridobis(triphenylphosphonium), X=N3 , OCN, SCN and OCP) and HCN. Crystals of [PPN][X(HCN)3 ] (X=N3 , OCN) and [PPN][SCN(HCN)2 ] were obtained when the crystallization was carried out at low temperatures. Interestingly, reaction of [PPN]OCP with HCN was noticed, which led to the formation of [P(CN)2 ]- , crystallizing as HCN disolvate [PPN][P(CN⋅HCN)2 ]. Furthermore, we were able to isolate the novel cyanido(halido) silicate dianions of the type [SiCl0.78 (CN)5.22 ]2- and [SiF(CN)5 ]2- and the hexa-substituted [Si(CN)6 ]2- by temperature controlled halide/cyanide exchange reactions. By facile neutralization reactions with the non-innocent cation of [Et3 HN]2 [Si(CN)6 ] with MOH (M=Li, K), Li2 [Si(CN)6 ] ⋅ 2 H2 O and K2 [Si(CN)6 ] were obtained, which form three dimensional coordination polymers. From salt metathesis processes of M2 [Si(CN)6 ] with different imidazolium bromides, we were able to isolate new imidazolium salts and the ionic liquid [BMIm]2 [Si(CN)6 ]. When reacting [Mes(nBu)Im]2 [Si(CN)6 ] with an excess of the strong Lewis acid B(C6 F5 )3 , the voluminous adduct anion {Si[CN⋅B(C6 F5 )3 ]6 }2- was obtained.

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.

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.

Salts of HCN-Cyanide Aggregates: [CN(HCN)2 ]- and [CN(HCN)3 ].

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.

Cyanidosilicates-Synthesis and Structure.

Starting from fluoridosilicate precursors in neat cyanotrimethylsilane, Me3 Si-CN, a series of different ammonium salts [R3 NMe]+ (R=Et, n Pr, n Bu) with the novel [SiF(CN)5 ]2- and [Si(CN)6 ]2- dianions was synthesized in facile, temperature controlled F- /CN- exchange reactions. Utilizing decomposable, non-innocent cations, such as [R3 NH]+ , it was possible to generate metal salts of the type M2 [Si(CN)6 ] (M+ =Li+ , K+ ) via neutralization reactions with the corresponding metal hydroxides. The ionic liquid [BMIm]2 [Si(CN)6 ] (m.p.=72 °C, BMIm=1-butyl-3-methylimidazolium) was obtained by a salt metathesis reaction. All the synthesized salts could be isolated in good yields and were fully characterized.