The homologous fluoride and hydroxide complexes of gold(III) [PPh4][(CF3)(3)AuX] [X = F (1), OH (2)] have been structurally characterized by single-crystal X-ray diffraction methods. Both of them crystallize in the P2(1)/n space group, yet they are not isomorphous. Despite the intrinsic difficulty to distinguish between F- and OH- by X-ray diffraction, the ability of the OH ligand in complex 2 to establish intramolecular O=H center dot center dot center dot F hydrogen bonding with one of the CF3 groups in cis position enables a clear differentiation from the fluoride complex 1. Given the tendency of late-transition metal fluorides to undergo hydrolysis, much caution should be taken when ascribing the identity of a fluoride ligand by X-ray diffraction methods, especially where unusual geometries are implied.

Multipurpose silver(III) fluoride. Access to the first silver(III) carbene complexes has been achieved by reaction of the fluoride [PPh4][(CF3)3AgF] precursor with different imidazolium salts. The novel methodology circumvents the use of free NHC molecules. This synthetic procedure is envisaged to enable access to carbene complexes of other late transition-metals in high oxidation states. More information can be found in the Research Article by M. Baya and co-workers (DOI: 10.1002/chem.202303937).

The homoleptic trifluoromethyl-palladium(II) complex [Pd(CF3)4]2- (1) is shown to be highly active towards amines. Thus, when treated with primary amines RNH2, it readily undergoes aminolysis of one of the CF3 ligands affording the isocyanide complexes [(CF3)3Pd(CNR)]- (R=aryl). In this process the original CF3 group undergoes total defluorination. Interestingly, the reaction of 1 with secondary amines R2NH proceeds with loss of just two F-substituents, whereby the Fischer-type fluoroaminocarbene complexes [(CF3)3Pd(CFNR2)]- are formed (R=Et, Ph). The reaction of 1 with diamines affords different [(CF3)3Pd(NHC)]- complexes containing sterically non-demanding NHC ligands. Representative examples of various topologies are reported based on the common imidazolidin-2-ylidene or benzimidazolin-2-ylidene rings as well as the expanded-ring perimidin-2-ylidene. This metal-tailored synthetic route, where a CF3 group acts as a pre-carbenic unit, is unprecedented in the vast NHC-chemistry. It takes place under very mild conditions and is envisaged to be extensible to other non-isolable NHC ligands. The key difluorocarbene intermediate [(CF3)3Pd(CF2)]- is experimentally detected.

We have synthesized the first silver(III) carbene complexes, (CF3)(3)Ag(NHC), by direct reaction of the silver(III) fluoride precursor complex [PPh4][(CF3)(3)AgF] with different imidazolium salts. This novel methodology circumvents the use of free NHC molecules. The silver(III) carbene complexes thus prepared are unprecedented and show remarkable thermal stabilities. They display square-planar or square-pyramidal geometry. Following our calculations, the electronic structure of a model representative complex exhibits Inverse Ligand Field (ILF). The compounds reported herein are synthetic analogues of the elusive difluorocarbene and carbonyl species proposed as intermediates in the acidic decomposition of [Ag(CF3)(4)](-). The synthetic procedure reported is envisaged to enable access to carbene complexes of other late transition-metals in high oxidation states.

The homoleptic phosphine with the bulky perchlorophenyl group, (C6Cl5)3P (1), exhibits trigonal pyramidal structure (TPY-3), yet considerably flattened: Sigma(C-P-C') = 321.0(1)degrees. Key steric and electronic properties of this simple organophosphorus species have been estimated by calculation. Attending to its characteristic features, 1 can be rated as a deactivated phosphine, where the less-basic P atom is sterically shielded by the bulky C6Cl5 groups. This marked inertness notwithstanding, it has been possible to obtain (under harsh conditions) derivatives with phosphorus in high oxidation state, namely the phosphine oxide (C6Cl5)3PO (2) and the difluorophosphorane (C6Cl5)3PF2 (3). These four- and five-substituted derivatives respectively exhibit trigonal pyramidal (TPY-4) and trigonal bipyramidal (TBPY-5) structures. The Sigma(C-P-C') value steadily increases along the series 1-3, according to the referred structural variation. The P-C bond length is, in turn, invariably maintained at about 185 pm regardless of the different oxidation state, the increasing number of substituents around the P atom and the overall geometry. The hypervalent difluorophosphorane (C6Cl5)3PF2 (3) dissociates one of the axial fluorides in the gas phase giving rise to the fluorophosphonium cation [(C6Cl5)3PF]+, as detected by mass spectrometry. This cation is identified as a Lewis superacid.

Since gold is located well beyond the oxo wall, chemical species with terminal Au-N and Au-O units are extremely rare and limited to low coordination numbers. We report here that these unusual units can be trapped within a suitable organometallic frame. Thus, the terminal auronitrene and auroxyl derivatives [(CF3 )3 AuN]- and [(CF3 )3 AuO]- were identified as local minima by calculation. These open-shell, high-energy ions were experimentally detected by tandem mass spectrometry (MS2 ): They respectively arise by N2 or NO2 dissociation from the corresponding precursor species [(CF3 )3 Au(N3 )]- and [(CF3 )3 Au(ONO2 )]- in the gas phase. Together with the known fluoride derivative [(CF3 )3 AuF]- , they form an interesting series of isoleptic and alloelectronic complexes of the highly acidic organogold(iii) moiety (CF3 )3 Au with singly charged anions X- of the most electronegative elements (X=F, O, N). Ligand-field inversion in all these [(CF3 )3 AuX]- species results in the localization of unpaired electrons at the N and O atoms.

Neutral Ag(III) complexes stabilised with just monodentate ligands are here unambiguously established. In a series of square-planar (CF3)3Ag(L) compounds with hard and soft Group 15 donor ligands, L, the metal center has been found to exhibit substantial acidity favouring apical coordination of an additional ligand under no coordination constraints.

The involvement of silver in two-electron Ag-I/Ag-III processes is currently emerging. However, the range of stability of the required and uncommon Ag-III species is virtually unknown. Here, the stability of Ag-III towards the whole set of halide ligands in the organosilver(III) complex frame [(CF3)(3)AgX](-) (X=F, Cl, Br, I, At) is theoretically analyzed. The results obtained depend on a single factor: the nature of X. Even the softest and least electronegative halides (I and At) are found to form reasonably stable Ag-III-X bonds. Our estimates were confirmed by experiment. The whole series of nonradiative halide complexes [PPh4][(CF3)(3)AgX] (X=F, Cl, Br, I) has been experimentally prepared and all its constituents have been isolated in pure form. The pseudohalides [PPh4][(CF3)(3)AgCN] and [PPh4][(CF3)(3)Ag(N-3)] have also been isolated, the latter being the first silver(III) azido complex. Except for the iodo compound, all the crystal and molecular structures have been established by single-crystal X-ray diffraction methods. The decomposition paths of the [(CF3)(3)AgX](-) entities at the unimolecular level have been examined in the gas phase by multistage mass spectrometry (MSn). The experimental detection of the two series of mixed complexes [CF3AgX](-) and [FAgX](-) arising from the corresponding parent species [(CF3)(3)AgX](-) demonstrate that the Ag-X bond is particularly robust. Our experimental observations are rationalized with the aid of theoretical methods. Smooth variation with the electronegativity of X is also observed in the thermolyses of bulk samples. The thermal stability in the solid state gradually decreases from X=F (145 degrees C, dec.) to X=I (78 degrees C, dec.) The experimentally established compatibility of Ag-III with the heaviest halides is of particular relevance to silver-mediated or silver-catalyzed processes.

By using suitable synthetic procedures, we have first isolated the square-planar organosilver(III) compounds [PPh 4 ][ trans -(CF 3 ) 2 AgX 2 ] [X=Cl ( 1 a ), Br ( 2 a )]. The geometry and stereochemistry of the chloro-derivative 1 a have been unambiguously established by single-crystal X-ray diffraction (SC-XRD) methods. Following our calculations on the relative stability of the cis -/ trans -[(CF 3 ) 2 AgX 2 ] − couples (X=F, Cl, Br, I), the experimentally obtained compounds 1 a and 2 a appear to be kinetically favored stereoisomers. They display some tendency to associate an additional X − ligand affording rare five-coordinate Ag III species [(CF 3 ) 2 AgX 3 ] 2− . Interestingly, compound [PPh 4 ] 2 [(CF 3 ) 2 AgBr 3 ] ( 3 ) has been identified by SC-XRD methods as the first Ag III derivative with trigonal symmetry in general and trigonal bipyramidal geometry in particular. This unusual five-coordinate species also exhibits inverted ligand field.

Surprising silver: The binary silver(I) halides, AgX, are well-known chemical species. In contrast, the only binary halide of silver(III) currently known is the fluoride AgF3. The CF3 group provides a suitable frame to stabilise silver(III) compounds with every halogen; these have been isolated and thoroughly characterised. Multistage unimolecular fragmentation experiments demonstrate that the Ag−X bond is surprisingly robust. The sobriety of silver thus perfectly matches the colourful variety of halogens. More information can be found in the Full Paper by B. Menjón et al. (DOI: 10.1002/chem.202101859).

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Electron-rich, late transition metals are known to act as hydrogen-bonding (HBd) acceptors. In this regard, Pt(ii) centres in square-planar environments are particularly efficient. It is however puzzling that no convincing experimental evidence is currently available for the isoelectronic neighbour Au(iii) being involved in HBd interactions. We report now on the synthesis and characterisation of two series of isoleptic and isoelectronic (d8) compounds [(CF3)3Pt(L)]- and (CF3)3Au(L), where the L ligands are based on the quinoline frame and have been selected to favour HBd with the metal centre. Strong HBd interactions were actually found in the Pt(ii) compounds, based on structural and spectroscopic evidence, and they were further confirmed by theoretical calculations. In contrast, no evidence was obtained in the Au(iii) case. In order to find the reason underlying this general disparity, we undertook a detailed theoretical analysis of the model systems [(CF3)3Pt(py)]- and (CF3)3Au(py). This study revealed that the filled dz2 orbital is the HOMO in the case of Pt(ii), but is buried in the lower energy levels in the case of Au(iii). The sharply different electronic configurations involve ligand-field inversion on going from Pt to the next element Au. This is not a gradual but an abrupt change, which invalidates Au(iii) as a HBd-acceptor wherever ligand-field inversion occurs.

Organosilver(III) fluoride complexes have been assigned a key role in different fluorination processes. To the best of our knowledge, however, none of them seem to have been isolated or even detected thus far. Here we report on the successful synthesis of the trifluoromethyl derivative [PPh4][(CF3)(3)AgF], which has been isolated in high yield. The thermodynamic stability of the Ag-F bond is shown by calculation and demonstrated by multistage mass spectrometry (MSn) under collision-induced dissociation (CID) conditions. Nevertheless, the substantial elongation found in the Ag-F bond (X-ray) is correlated with a marked nucleophilic character of the terminal F ligand. This Ag-F bond is, in fact, quite reactive: it suffers hydrolysis and is also solvolyzed by thiols.

No organosilver(III) fluoride was known hitherto. Now the first representative of this important class of compound is reported here, namely [PPh4][(CF3)3AgF] (cover image, center). This compound exhibits an interesting combination of stability and reactivity. Thus, the CF3 groups confer the compound substantial stability approaching that of the homoleptic, all-organometallic compound [PPh4][(CF3)4Ag] (right). Concurrently, the Ag−F moiety is reactive, yet not as violently as for the purely inorganic anion [AgF4]− (left). A kind of advantageous “silvery mean”, i.e., argentea mediocritas, is therefore achieved. More information can be found in the Communication by B. Menjón et al. on page 4471.

AbstractA comparative study of the homoleptic [M(CF3)4]− complexes of all three coinage metals (M=Cu, Ag, Au) reveals that homolytic M−C bond cleavage is favoured in every case upon excitation in the gas phase (CID‐MS2). Homolysis also occurs in solution by photochemical excitation. Transfer of the photogenerated CF3. radicals to both aryl and alkyl carbon atoms was also confirmed. The observed behaviour was rationalized by considering the electronic structure of the involved species, which all show ligand‐field inversion. Moreover, the homolytic pathway constitutes experimental evidence for the marked covalent character of the M−C bond. The relative stability of these M−C bonds was evaluated by energy‐resolved mass spectrometry (ERMS) and follows the order Cu

The improved synthesis of the homoleptic perchlorophenyl stibine (C6Cl5)(3)Sb (1a) has enabled us to obtain detailed spectroscopic and structural information. In contrast to the planar structure shown by the nitrogen homologue (C6Cl5)(3)N, the antimony compound 1a shows unmistakable pyramidal structure (C-Sb-C 100.9(2)degrees, av.) with slightly elongated Sb-C bonds (219.6(4) pm, av.) with respect to the non-chlorinated model compound Ph3Sb. The Sb-C bonds shorten upon oxidation, as it is found in the oxidized compound (C6Cl5)(3)SbCl2 (2a). A single isomer is stereoselectively obtained for this hypervalent compound 2a, namely that with the Cl ligands in axial positions. This neutral, hypervalent compound (2a) is found to dissociate chloride in the gas phase (MS) giving rise to the [(C6Cl5)(3)SbCl](+) cation (3a). According to theoretical calculations this cation should have nearly tetrahedral structure and behave as a Lewis superacid. The structural properties and Lewis acidity of compounds 1a-3a are compared with those calculated for their corresponding isoelectronic tin derivatives (1b-3b). (c) 2019 Elsevier B.V. All rights reserved.

Resumen del trabajo presentado al 22nd International Symposium on Fluorine Chemistry, celebrado en Oxford (UK) del 22 al 27 de julio de 2018.

The homoleptic silver(I) compound [PPh4 ][CF3 AgCF3 ] (1) provides a convenient entry to the homoleptic silver(III) derivative [PPh4 ][Ag(CF3 )4 ] (2). Once isolated as pure substances, these compounds exhibit marked thermal stabilities. Their structural and spectroscopic properties have been experimentally established. Moreover, their electronic structures have been calculated by theoretical methods. The electronic structure of the oxidized species [Ag(CF3 )4 ]- provides a new case of ligand-field inversion caused by the CF3 ligands.

Resumen del trabajo presentado al XXXVI GEQO Congress Organometallic Chemistry Group, celebrado en Zaragoza (Espana) del 5 al 7 de septiembre de 2018.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.