Gold Teflates Revisited: From the Lewis Superacid [Au(OTeF5 )3 ] to the Anion [Au(OTeF5 )4 ]. Chemistry 2023;29:e202203634. [PMID: 36598847 DOI: 10.1002/chem.202203634] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

A new synthetic access to the Lewis acid [Au(OTeF₅ )₃ ] and the preparation of the related, unprecedented anion [Au(OTeF₅ )₄ ]^- with inorganic or organic cations starting from commercially available and easy-to-handle gold chlorides are presented. In this first extensive study of the Lewis acidity of a transition-metal teflate complex by using different experimental and quantum chemical methods, [Au(OTeF₅ )₃ ] was classified as a Lewis superacid. The solid-state structure of the triphenylphosphine oxide adduct [Au(OPPh₃ )(OTeF₅ )₃ ] was determined, representing the first structural characterization of an adduct of this highly reactive [Au(OTeF₅ )₃ ]. Therein, the coordination environment around the gold center slightly deviates from the typical square planar geometry. The [Au(OTeF₅ )₄ ]^- anion shows a similar coordination motif.

A Versatile Silver(I) Pentafluorooxosulfate Reagent for the Synthesis of OSF5 Compounds

Herein, we report the preparation of silver(I) pentafluorooxosulfate from commercially available AgF and OSF₄. The compound is surprisingly stable in a MeCN solution. Apart from that, AgOSF₅ has been stabilised by the addition of 2,2′‐bipyridine ligands. Starting from solutions of the unstabilised silver(I) salt, OSF₅ complexes with Ni^II, Cu^I, and Cu^II‐centres have been obtained. In addition, AgOSF₅ has proven to be generally capable of mediating the transfer of OSF₅ groups to aryne moieties, thus furnishing a new and safe method for the preparation of OSF₅‐substituted arenes. X‐ray crystal structure analysis of selected transition‐metal OSF₅ compounds have revealed distorted octahedral [OSF₅]⁻ anions which are extensively stabilised by hydrogen bonding.

Can Weakly Coordinating Anions Stabilize Mercury in Its Oxidation State +IV?

While the thermochemical stability of gas-phase HgF4 against F2 elimination was predicted by accurate quantum chemical calculations more than a decade ago, experimental verification of "truly transition-metal" mercury(IV) chemistry is still lacking. This work uses detailed density functional calculations to explore alternative species that might provide access to condensed-phase Hg(IV) chemistry. The structures and thermochemical stabilities of complexes Hg(IV)X4 and Hg(IV)F2X2 (X- = AlF4-, Al2F7-, AsF6-, SbF6-, As2F11-, Sb2F11-, OSeF5-, OTeF5-) have been assessed and are compared with each other, with smaller gas-phase HgX4 complexes, and with known related noble gas compounds. Most species eliminate F2 exothermically, with energies ranging from only about -60 kJ mol(-1) to appreciable -180 kJ mol(-1). The lower stability of these species compared to gas-phase HgF4 is due to relatively high coordination numbers of six in the resulting Hg(II) complexes that stabilize the elimination products. Complexes with AsF6 ligands appear more promising than their SbF6 analogues, due to differential aggregation effects in the Hg(II) and Hg(IV) states. HgF2X2 complexes with X- = OSeF5- or OTeF5- exhibit endothermic fluorine elimination and relatively weak interactions in the Hg(II) products. However, elimination of the peroxidic (OEF5)2 coupling products of these ligands provides an alternative exothermic elimination pathway with energies between -120 and -130 kJ mol(-1). While all of the complexes investigated here thus have one exothermic decomposition channel, there is indirect evidence that the reactions should exhibit nonnegligible activation barriers. A number of possible synthetic pathways towards the most interesting condensed-phase Hg(IV) target complexes are proposed.

Methyl Tin(IV) Derivatives of HOTeF5 and HN(SO2CF3)2: A Solution Multinuclear NMR Study and the X-ray Crystal Structures of (CH3)2SnCl(OTeF5) and [(CH3)3Sn(H2O)2][N(SO2CF3)2]

The new tin(IV) species (CH(3))(2)SnCl(OTeF(5)) was prepared via either the solvolysis of (CH(3))(3)SnCl in HOTeF(5) or the reaction of (CH(3))(3)SnCl with ClOTeF(5). It was characterized by NMR and vibrational spectroscopy, mass spectrometry, and single crystal X-ray diffraction. (CH(3))(2)SnCl(OTeF(5)) crystallizes in the monoclinic space group P2(1)/n (a = 5.8204(8) A, b =10.782(1) A, c =15.493(2) A, beta = 91.958(2) degrees, V = 971.7(2) A(3), Z = 4). NMR spectroscopy of (CH(3))(3)SnX, prepared from excess Sn(CH(3))(4) and HX (X = OTeF(5) or N(SO(2)CF(3))(2)), revealed a tetracoordinate tin environment using (CH(3))(3)SnX as a neat liquid or in dichloromethane-d(2) (CD(2)Cl(2)) solutions. In acetone-d(6) and acetonitrile-d(3) (CD(3)CN) solutions, the tin atom in (CH(3))(3)SnOTeF(5) was found to extend its coordination number to five by adding one solvent molecule. In the strong donor solvent DMSO, the Sn-OTeF(5) bond is broken and the (CH(3))(3)Sn(O=S(CH(3))(2))(2)(+) cation and the OTeF(5)(-) anion are formed. (CH(3))(3)SnOTeF(5) and (CH(3))(3)SnN(SO(2)CF(3))(2) react differently with water. While the Te-F bonds in the OTeF(5) group of (CH(3))(3)SnOTeF(5) undergo complete hydrolysis that results in the formation of [(CH(3))(3)Sn(H(2)O)(2)](2)SiF(6), (CH(3))(3)SnN(SO(2)CF(3))(2) forms the stable hydrate salt [(CH(3))(3)Sn(H(2)O)(2)][N(SO(2)CF(3))(2)]. This salt crystallizes in the monoclinic space group P2(1)/c (a = 7.3072(1) A, b =13.4649(2) A, c =16.821(2) A, beta = 98.705(1) degrees, V = 1636.00(3) A(3), Z = 4) and was also characterized by NMR and vibrational spectroscopy.

The facile preparation of weakly coordinating anions: structure and characterisation of silverpolyfluoroalkoxyaluminates AgAl(ORF)4, calculation of the alkoxide ion affinity

Purified LiAlH4 reacts with fluorinated alcohols HORF to give LiAl(ORF)4 (RF=-CH(CF3)2, 2a; -C(CH3)(CF3)2, 2b; -C(CF3)3, 2c) in 77 to 90% yield. The crude lithium aluminates LiAl(ORF)4 react metathetically with AgF to give the silver aluminates AgAl(ORF)4 (RF=-CH(CF3)2, 3a; -C(CH3)(CF3)2, 3b; -C(CF3)3, 3c) in almost quantitative yield. The solid-state structures of solvated 3a-c showed that the silver cation is only weakly coordinated (CN(Ag)=6-10; CN = coordination number) by the solvent and/or weak cation - anion contacts Ag-X (X=O, F, Cl, C). The strength of the Ag-X contacts of 3a-c was analysed by Brown's bond-valence method and then compared with other silver salts of weakly coordinating anions (WCAs), for example [CB11H6Cl6]- and [M(OTeF5)n]- (M=B, Sb, n=4, 6). Based on this quantitative picture we showed that the Al[OC(CF3)3]4 anion is one of the most weakly coordinating anions known. Moreover, the AgAl(ORF)4 species are certainly the easiest WCAs to access preparatively (20 g in two days), additionally at low cost. The Al-O bond length of Al(ORF)4- is shortest in the sterically congested Al[OC(CF3)3]4- anion-which is stable in H2O and aqueous HNO3 (35 weight%)--and indicates a strong and highly polar Al-O bond that is resistant towards heterolytic alkoxide ion abstraction. This observation was supported by a series of HF-DFT calculations of OR-, Al(OR)3 and Al(OR)4- at the MPW1PW91 and B3LYP levels (R= CH3, CF3, C(CF3)3). The alkoxide ion affinity (AIA) is highest for R=CF3 (AlA=384 +/- 9 kJ x mol(-1)) and R= C(CF3)3 (AIA=390 +/- 3 kJ x mol(-1)), but lowest for R=CH3 (AIA=363 +/- 7 kJ X mol(-1)). The gaseous AL(ORF)4-anions are stable against the action of the strong Lewis acid ALF3(g) by 88.5 +/- 2.5 (RF=CF3) and 63 +/- 12 kJ X mol(-1) (RF=C(CF3)3), while AL(OCH3)4- decomposes with -91 +/- 2 kJ X mol(-1). Therefore the presented fluorinated aluminates AL(ORF)4- appear to be ideal candidates when large and resistant WCAs are needed, for example, in cationic homogenous catalysis, for highly electrophilic cations or for weak cationic Lewis acid/base complexes.