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.

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.

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.

Arsenic-Mediated C-C Coupling of Cyanides Leading to Cyanido Arsazolide [AsC4 N4 ].

The chemistry of arsenic cyanides has been investigated and is found to be completely different to the chemistry of the heavier analogs antimony and bismuth as well as phosphorus. The reaction of As(CN)3 with cyanide salts resulted in the formation of an unknown cyanido arsazolide heterocycle, which represents a structure isomer of the desired [As(CN)4 ]- . The structure, bonding, and formation of this unusual heterocycle is discussed featuring an arsenic mediated C-C coupling of cyanides. [AsC4 N4 ]- salts with different counterions such as [PPh4 ]+ , [PPN]+ =[Ph3 P-N-PPh3 ]+ , Ag+ , and [BMIm]+ are reported with [BMIm][AsC4 N4 ] being a low-temperature ionic liquid (Tm =-62 °C).

Cyanido Antimonate(III) and Bismuthate(III) Anions.

The reaction of in situ generated E(CN)3 (E = Sb, Bi) with different amounts of [Ph4P]CN and [PPN]CN ([PPN]+ = [Ph3P-N-PPh3]+) was studied, affording salts bearing the novel ions [E(CN)5]2-, [Bi2(CN)11]5-, and [Bi(CN)6]3-. The valence lone pair of electrons on the central atom of antimony and bismuth(III) compounds can be either sterically active in an unsymmetric fashion (three shorter bonds + x longer bonds) or symmetric (with rather long averaged bonds). In the presence of weakly coordinating cations (e.g., [Ph4P]+ and [PPN]+), the solid-state structures of salts with [E(CN)5]2- anions contain well-separated cations and monomeric anions, which display a sterically active lone pair and a monomeric square-based pyramidal (pseudo-octahedral) structure. The [Bi(CN)5·MeCN]2- acetonitrile adduct ion exhibits a strongly distorted octahedral structure, which is better understood as a [5 + 1] coordination. The intriguing [Ph4P]6[Bi2(CN)11]CN salt consists of separated cations and anions as well as well-separated [Bi2(CN)11]5- and CN- ions. The structure of the molecular [Bi2(CN)11]5- ion can be described as two square-based-pyramidal [Bi(CN)5]2- fragments connected by a disordered bridging CN- ion, thereby leading to a distorted-octahedral environment around the two Bi centers. Here the steric effect of the lone pair is much less pronounced but still present.

Molecular E(CN)3 (E=Sb, Bi) Species Synthesized from Ionic Liquids as Solvates.

The heavy pnictogen tricyanides, E(CN)3 (E=Sb, Bi), were synthesized from EF3 and Me3 SiCN in ionic liquids, for example, 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([BMIm][OTf]), which prevents the oligomerization of the molecular E(CN)3 species by formation of [BMIm][E(CN)3 (OTf)] salts in solution. Recrystallization of [BMIm][E(CN)3 (OTf)] from THF led to the isolation and full characterization of the molecular species E(CN)3 ⋅2 THF.

Tetracyanido(difluorido)phosphates M(+) [PF2 (CN)4 ](.).

The systematic study of the reaction of M[PF6 ] salts and Me3 SiCN led to a synthetic method for the synthesis and isolation of a series of salts containing the unprecedented [PF2 (CN)4 ](-) ion in good yields. The reaction temperature, pressure, and stoichiometry were optimized. The crystal structures of M[PF2 (CN)4 ] (M=[nBu4 N](+) , Ag(+) , K(+) , Li(+) , H5 O2 (+) ) were determined. X-ray crystallography showed the exclusive formation of the cis isomer in accord with (31) P and (19) F solution NMR spectroscopy data. Starting with the K[PF2 (CN)4 ] the room temperature ionic liquid EMIm[PF2 (CN)4 ] was prepared exhibiting a rather low viscosity.