Superelectrophilic tetrakis(carbonyl)palladium(II)- and -platinum(II) undecafluorodiantimonate(V), [Pd(CO)4][Sb(2)F(11)]2 and [Pt(CO)4][Sb(2)F(11)]2: syntheses, physical and spectroscopic properties, their crystal, molecular, and extended structures, and density functional calculations: an experimental, computational, and comparative study

Homoleptic Transition Metal Carbonyl Cations: Synthetic Approaches, Characterization and Follow-Up Chemistry

ConspectusCarbon monoxide, CO, is one of the most important ligands in organometallic chemistry. It is an excellent π-acceptor and a moderate σ-donor. Therefore, most of the known transition metal carbonyls (TMCs) exhibit a zerovalent or even negative metal oxidation state (OS) of up to -4. However, given the right conditions, the carbonyl ligand also forms homoleptic cationic complexes with one or more transition metal atoms, the transition metal carbonyl cations (TMCCs), known with an OS of up to +3. Despite their long-standing history upon discovery of the first [M(CO)6]+ examples (M = Mn, Tc, Re) by E. O. Fischer in 1962 as well as their very fundamental nature, it took until the 1990s for the scope to be widened by Aubke, Strauss and Willner. Yet, many potential TMCC entries known from gas-phase mass spectrometry work remained unknown on preparative grounds. This is due to their high reactivity, which puts scientists to new challenges and encourages the development of suitable solvents, anions and oxidants, to cope with the demands of these fundamental salts─later referred to as pseudo-gas-phase conditions and innocent deelectronators and solvents.Hence, the utilization of extremely weakly coordinating perfluorinated alkoxyaluminates [Al(ORF)4]- and [F{Al(ORF)3}2]- (ORF = -OC(CF3)3) in combination with the polar but non- or weakly coordinating innocent solvents 1,2-difluorobenzene (oDFB) and 1,2,3,4-tetrafluorobenzene (TFB) yielded the first TMCC salts containing heptacoordinate [M(CO)7]+ (M = Nb, Ta) as well as paramagnetic [M(CO)6]+· (M = Cr, Mo, W) or [Ni(CO)4]+·. However, the use of typical inorganic oxidants Ag+, [NO]+ and Ag+/0.5 I2 regularly led to unwanted side reactions. For example, the Lewis acidic silver(I) cations form Lewis pairs with various Lewis basic TMCs yielding partly clustered [Agx{TMC}y]x+ complex salts, while nitrosonium cations may substitute for carbonyl ligands, forming [M(CO)x-1(NO)]+ complexes. The synergistic oxidizing reagent Ag+/0.5 X2 can add halonium ions X+ to the TMCs (X = Cl, Br, I). This prevented the synthesis of univalent group 8 TMCC salts. Yet, the application of radical cation salts of perfluorinated arenes as innocent deelectronators finally yielded salts of [Fe(CO)5]+· and [M3(CO)14]2+ (M = Ru, Os).TMCC salts are excellent starting materials, and the reaction of [Co(CO)5]+ and [Ni(CO)4]+· with benzene led to the previously unknown bis(benzene) sandwich complexes [Co(benzene)2]+ and [Ni(benzene)2]+·. Under the right conditions, even the very weakly bound oDFB-complex salts with [M(oDFB)2]+ (M = Co, Ni) cations form, useful as naked metal(I) synthons and for small-molecule activation.

Towards clustered carbonyl cations [M3(CO)14]2+ (M = Ru, Os): the need for innocent deelectronation

To access the hitherto almost unknown class of clustered transition metal carbonyl cations, the trimetal dodecacarbonyls M3(CO)12 (M = Ru, Os) were reacted with the oxidant Ag+[WCA]-, but yielded the silver complexes [Ag{M3(CO)12}2]+[WCA]- (WCA = [Al(ORF)4]-, [F{Al(ORF)3}2]-; RF = -OC(CF3)3). Addition of further diiodine I2 to increase the redox potential led for M = Ru non-specifically to divalent mixed iodo-RuII-carbonyl cations. With [NO]+, even the N-O bond was cleaved and led to the butterfly carbonyl complex cation [Ru4N(CO)13]+ in low yield. Obviously, ionization of M3(CO)12 with retention of its pseudo-binary composition including only M and CO is difficult and the inorganic reagents did react non-innocently. Yet, the radical cation of the commercially available perhalogenated anthracene derivative 9,10-dichlorooctafluoroanthracene (anthraceneHal) is a straightforward accessible innocent deelectronator with a half-wave potential E 1/2 of 1.42 V vs. Fc0/+. It deelectronates M3(CO)12 under a CO atmosphere and leads to the structurally characterized cluster salts [M3(CO)14]2+([WCA]-)2 including a linear M3 chain. The structural characterization as well as vibrational and NMR spectroscopies indicate the presence of three electronically independent sets of carbonyl ligands, which almost mimic M(CO)5, free CO and even [M(CO)6]2+ in one and the same cation.

trans-Carbonyl-chlorido-bis-(tri-ethyl-phosphane-κP)platinum(II) tetra-fluorido-borate

The chemical formulation of the title compound was established as trans-[PtCl{P(C2H5)3(CO)}BF4 by single-crystal X-ray analysis, in contrast to the five-coordinate tetra-fluoro-ethyl-ene complex that had been anti-cipated. The compound had been prepared by reaction of trans-PtHCl(P(C2H5)3)2 with C2F4 in the absence of air, and the presence of the carbonyl group was not suspected. The square-planar cations and BF4 - anions are linked by C-H⋯F and C-H⋯O inter-actions into thick wavy (010) sheets. The present crystal-structure refinement is based on the original intensity data recorded in 1967.

Effects of Treatment Conditions on Pd Speciation in CHA and Beta Zeolites for Passive NO x Adsorption

The structure and evolution of Pd species in Pd-exchanged zeolite materials intended for use as passive NO _x adsorbers were examined under various pretreatment conditions. Using in situ CO-diffuse reflectance infrared spectroscopy, Pd structures were characterized after 500 °C pretreatments in inert (Ar), water (1-2% H₂O in Ar), oxidizing (air), and reducing (H₂, CO) atmospheres. Two zeolites of similar Si/Al ratios but different framework topologies (Beta, CHA) were found to show different distributions of Pd species, depending on the reducing agent used. Reduction in H₂ (500 °C; 10% H₂ in Ar) followed by re-oxidation (500 °C; air) led to higher amounts of single-site Pd ions on Pd-CHA than Pd-Beta, whereas high-temperature reduction in CO (500 °C; 1000 ppm CO in Ar) followed by re-oxidation (500 °C; air) led to significant loss of ionic Pd on both Pd-CHA and Pd-Beta, albeit H₂ temperature-programmed reduction and XPS experiments suggest that this phenomena may be limited to surface Pd. High-temperature treatments with water (500 °C; 1-2% H₂O in Ar) are shown to form either Pd metal or PdO particles, with Pd-Beta being more susceptible to these effects than Pd-CHA. This work suggests that the effects of CO are especially problematic with respect to the durability of these materials in passive NO _x adsorption applications, especially in the case of Beta zeolite.

Redox active Ni-Pd carbonyl alloy nanoclusters: syntheses, molecular structures and electrochemistry of [Ni22-xPd20+x(CO)48]6- (x = 0.62), [Ni29-xPd6+x(CO)42]6- (x = 0.09) and [Ni29+xPd6-x(CO)42]6- (x = 0.27)

A redox active Ni-Pd alloy nanocluster [Ni_22-xPd_20+x(CO)₄₈]^6- (x = 0.62) ([1]^6-) was obtained from the redox condensation of [NBu₄]₂[Ni₆(CO)₁₂] with 0.7-0.8 equivalents of Pd(Et₂S)₂Cl₂ in CH₂Cl₂. Conversely, [Ni_29-xPd_6+x(CO)₄₂]^6- (x = 0.09) ([2]^6-) and [Ni_29+xPd_6-x(CO)₄₂]^6- (x = 0.27) ([3]^6-) were obtained by employing [NEt₄]₂[Ni₆(CO)₁₂] and 0.6-0.7 equivalents of Pd(Et₂S)₂Cl₂ in CH₃CN. The molecular structures of these high nuclearity Ni-Pd carbonyl clusters were determined by single-crystal X-ray diffraction (SC-XRD). [1]^6- adopted an M₄₀ccp structure comprising five close-packed ABCAB layers capped by two additional Ni atoms. Conversely, [2]^6- and [3]^6- displayed an hcp M₃₅ metal core composed of three compact ABA layers. [1]^6-, [2]^6- and [3]^6- showed nanometric sizes, with the maximum lengths of their metal cores being 1.3 nm ([1]^6-) and 1.0 nm ([2]^6- and [3]^6-), which increased up to 1.9 and 1.5 nm, after including also the CO ligands. Ni-Pd distribution within their metal cores was achieved by avoiding terminal Pd-CO bonding and minimizing Pd-CO coordination. As a consequence, site preference and partial metal segregation were observed, as well as some substitutional and compositional disorders. Electrochemical and spectroelectrochemical studies revealed that [1]^6- and [2]^6- were redox active and displayed four and three stable oxidation states, respectively. Even though several redox active high nuclearity metal carbonyl clusters have been previously reported, the nanoclusters described herein represent the first examples of redox active Ni-Pd carbonyl alloy nanoclusters.

Stable salts of the hexacarbonyl chromium(I) cation and its pentacarbonyl-nitrosyl chromium(I) analogue

Homoleptic carbonyl radical cations are a textbook family of complexes hitherto unknown in the condensed phase, leaving their properties and applications fundamentally unexplored. Here we report on two stable 17-electron [Cr(CO)6]•+ salts that were synthesized by oxidation of Cr(CO)6 with [NO]+[Al(ORF)4]- (RF = C(CF3)3)) in CH2Cl2 and with removal of NO gas. Longer reaction times led to NO/CO ligand exchange and formation of the thermodynamically more stable 18-electron species [Cr(CO)5(NO)]+, which belongs to the family of heteroleptic chromium carbonyl/nitrosyl cations. All salts were fully characterized (IR, Raman, EPR, NMR, scXRD, pXRD, magnetics) and are stable at room temperature under inert conditions over months. The facile synthesis of these species enables the thorough investigation of their properties and applications to a broad scientific community.

How does the Environment Influence a Given Cation? A Systematic Investigation of [Co(CO)5 ]+ in Gas Phase, Solution, and Solid State

IR spectroscopic studies of the gaseous metal carbonyl cations [Co(CO)₅ ]⁺ ⋅mCO (m=1-4) indicated that the weakly bound CO molecules in a second coordination sphere perturb the structure of [Co(CO)₅ ]⁺ causing the CO stretching frequencies ν(CO) to become noticeably redshifted. In this work, we aimed to establish the relationship between such gas phase IR spectra and those recorded in condensed phases, either as a solid salt or as a solution in the weakly basic solvent o-difluorobenzene. For this purpose, a series of [Co(CO)₅ ]⁺ [WCA]^- salts (WCA=weakly coordinating anion), with the counterions varying between more coordinating (WCA=F-Al(OR^F )₃ , (R^F O)₃ Al-F-Al(F)(OR^F )₂ ; R^F =C(CF₃ )₃ ) and almost non-coordinating (WCA=Al(OR^F )₄ , F{Al(OR^F )₃ }₂ ), were synthesized and characterized by vibrational spectroscopy as well as X-ray structure analysis. The experimental spectra differ considerably from that of the undisturbed gaseous [Co(CO)₅ ]⁺ ion, as the structural deformation of [Co(CO)₅ ]⁺ requires very little energy. Together with previously reported data, the perturbed condensed phase [Co(CO)₅ ]⁺ ions were analyzed and compared with the gaseous [Co(CO)₅ ]⁺ ⋅mCO ions. DFT calculations were performed on simply adapted [Co(CO)₅ ]⁺ structures to allow the assignment of all the ν(CO) modes and a qualitative interpretation of structural deformations by external influences as a function of the environment (ligands, solvation, crystal packing). The analysis showed that especially the degenerate E' mode ν_e and the averaged asymmetric equatorial CO stretch ν ‾ _e , which originates from a split of the E' mode, are a function of the interaction with the environment. Whereas for the more coordinating counterions ν ‾ _e values of 2112-2120 cm^-1 were obtained, for the less coordinating counterions ν ‾ _e values of up to 2133 cm^-1 were found, which is very close to that of gaseous [Co(CO)₅ ]⁺ ⋅4CO, with a ν ‾ _e value of 2135 cm^-1 . This indicates the possibility of approximating the gas phase conditions in the condensed phases with the [Co(CO)₅ ]⁺ ion probably being the prototypical probe molecule for investigating the strengths of interactions in different environments.

Zero-valent isocyanides of nickel, palladium and platinum as transition metal σ-type Lewis bases

Transition metal complexes that contain metal-to-ligand retrodative σ-bonds have become the subject of increasing studies over the last decade. Lewis acidic "Z-type ligands" can modulate the electronic structure of their resultant complexes in a manner distinct from 2e^- donor ligands, and can also engage in cooperative reactivity with a Lewis basic transition metal. In this Feature article, we summarize our work with transition metal isocyanide complexes of group 10 metals that have exploited metal-based σ-type Lewis basicity. While the complexes Ni(CNAr^Mes2)₃, Pd(CNAr^Dipp2)₂ and Pt(CNAr^Dipp2)₂ were initially targeted as analogues to unstable, low-coordinate metal carbonyls, it soon became apparent that these zero-valent metal centers bore appreciable Lewis basic qualities due largely to the enhanced σ-donor/π-acid ratio of isocyanides compared to CO. Detailed spectroscopic and structural studies of metal-only Lewis pairs (MOLPs) formed from these complexes have furthered our understanding of the electronic structure perturbations effected by Z-type ligand binding. In addition, the platinum (boryl)iminomethane (BIM) complex Pt(κ²-N,B-^Cy₂BIM)(CNAr^Dipp2) has illuminated a general ligand design strategy that can engender significant reverse-dative interactions with buttressed Lewis acids, and also has expanded the known scope of cooperative reactivity that can be realized at a transition metal-borane linkage.

The MOF-driven synthesis of supported palladium clusters with catalytic activity for carbene-mediated chemistry

The development of catalysts able to assist industrially important chemical processes is a topic of high importance. In view of the catalytic capabilities of small metal clusters, research efforts are being focused on the synthesis of novel catalysts bearing such active sites. Here we report a heterogeneous catalyst consisting of Pd₄ clusters with mixed-valence 0/+1 oxidation states, stabilized and homogeneously organized within the walls of a metal-organic framework (MOF). The resulting solid catalyst outperforms state-of-the-art metal catalysts in carbene-mediated reactions of diazoacetates, with high yields (>90%) and turnover numbers (up to 100,000). In addition, the MOF-supported Pd₄ clusters retain their catalytic activity in repeated batch and flow reactions (>20 cycles). Our findings demonstrate how this synthetic approach may now instruct the future design of heterogeneous catalysts with advantageous reaction capabilities for other important processes.

Synthesis, Structure, and Reactivity of the Sterically Crowded Th3+ Complex (C5Me5)3Th Including Formation of the Thorium Carbonyl, [(C5Me5)3Th(CO)][BPh4]

The Th³⁺ complex, (C₅Me₅)₃Th, has been isolated despite the fact that tris(pentamethylcyclopentadienyl) complexes are highly reactive due to steric crowding and few crystallographically characterizable Th³⁺ complexes are known due to their highly reducing nature. Reaction of (C₅Me₅)₂ThMe₂ with [Et₃NH][BPh₄] produces the cationic thorium complex [(C₅Me₅)₂ThMe][BPh₄] that can be treated with KC₅Me₅ to generate (C₅Me₅)₃ThMe, 1. The methyl group on (C₅Me₅)₃ThMe can be removed with [Et₃NH][BPh₄] to form [(C₅Me₅)₃Th][BPh₄], 2, the first cationic tris(pentamethylcyclopentadienyl) metal complex, which can be reduced with KC₈ to yield (C₅Me₅)₃Th, 3. Complexes 1-3 have metrical parameters consistent with the extreme steric crowding that previously has given unusual (C₅Me₅)^- reactivity to (C₅Me₅)₃M complexes in reactions that form less crowded (C₅Me₅)₂M-containing products. However, neither sterically induced reduction nor (η¹-C₅Me₅)^- reactivity is observed for these complexes. (C₅Me₅)₃Th, which has a characteristic EPR spectrum consistent with a d¹ ground state, has the capacity for two-electron reduction via Th³⁺ and sterically induced reduction. However, it reacts with MeI to make two sterically more crowded complexes, (C₅Me₅)₃ThI, 4, and (C₅Me₅)₃ThMe, 1, rather than (C₅Me₅)₂Th(Me)I. Complex 3 also forms more crowded complexes in reactions with I₂, PhCl, and Al₂Me₆, which generate (C₅Me₅)₃ThI, (C₅Me₅)₃ThCl, and (C₅Me₅)₃ThMe, 1, respectively. The reaction of (C₅Me₅)₃Th, 3, with H₂ forms the known (C₅Me₅)₃ThH as the sole thorium-containing product. Surprisingly, (C₅Me₅)₃ThH is also observed when (C₅Me₅)₃Th is combined with 1,3,5,7-cyclooctatetraene. [(C₅Me₅)₃Th][BPh₄] reacts with tetrahydrofuran (THF) to make [(C₅Me₅)₃Th(THF)][BPh₄], 2-THF, which is the first (C₅Me₅)₃M of any kind that does not have a trigonal planar arrangement of the (C₅Me₅)^- rings. It is also the first (C₅Me₅)₃M complex that does not ring-open THF. [(C₅Me₅)₃Th][BPh₄], 2, reacts with CO to generate a product characterized as [(C₅Me₅)₃Th(CO)][BPh₄], 5, the first example of a molecular thorium carbonyl isolable at room temperature. These results have been analyzed using density functional theory calculations.

DFT Study of the Systematic Variations in Metal−Ligand Bond Lengths of Coordination Complexes: the Crucial Role of the Condensed Phase

The experimental M-A and M-B distances in several series of [MAnBm-n]-type complexes have been studied by DFT. Many of the structural features of the series, such as trans influences and sterically induced bond elongations, are not reproduced correctly in gas-phase DFT calculations. However, the correct trends are recovered by explicitly including environmental effects via the COSMO solvation model. These observations imply that the condensed-phase environment plays a critical role in determining the geometric structure of coordination complexes. Thus, any apparently satisfactory reproduction of the condensed-phase structure by an in vacuo calculation may mask an incorrect treatment of the interplay between different ligands attached to the same metal center.

Carbonyldinitrosyltris(fluorosulfato)tungstate(II) and -molybdate(II) anions: synthesis, spectroscopy, and density functional theory calculations

Carbonyldinitrosyltris(fluorosulfato)tungstate(II) and -molybdate-(II) anions, [fac-M(CO)(NO)2(SO3F)3]- (M=W, Mo), which are novel weakly coordinating anions that contain a metal carbonyl/nitrosyl moiety, have been generated in fluorosulfonic acid and completely characterized by multinuclear NMR, IR, and Raman spectroscopy as well as ESI mass spectrometry. ESI MS measurements performed for the first time on a superacidic solution system unambiguously reveal the formation of the monoanionic, mononuclear W and Mo complexes formulated as [M(CO)(NO)2(SO3F)3]- (M=W, Mo). Multinuclear NMR spectroscopic studies at natural abundance and 13C and 15N enrichment clearly indicate the presence of one CO ligand, two equivalent NO ligands, and two types of nonequivalent SO3F- groups in a 2:1 ratio. The IR and Raman spectra reveal that the two equivalent NO ligands have a cis conformation, thus indicating a fac structure. Density functional calculations at the B3LYP level of theory predict that these anions have a singlet ground state (1A) with a Cs symmetry along with C-O and N-O vibrational frequencies that are in agreement with the experimental observations. Mulliken population analysis shows that the monovalent negative charge is dispersed on the bulky sphere, the surface of which is covered by all the negatively charged O and F atoms with charge densities much lower than SO3F-, suggesting that [fac-M(CO)(NO)2(SO3F)3]- (M=W, Mo) are weakly nucleophilic and poorly coordinating anions.

Homoleptic, sigma-bonded octahedral superelectrophilic metal carbonyl cations of iron(II), ruthenium(II), and osmium(II). Part 2: Syntheses and characterizations of [M(CO)(6)][BF(4)](2) (M = Fe, Ru, Os)

As the first examples of homoleptic, sigma-bonded superelectrophilic metal carbonyl cations with tetrafluoroborate [BF(4)](-) as the counter anions three thermally stable salts of the composition [M(CO)(6)][BF(4)](2) (M = Fe, Ru, Os) have been synthesized and extensively characterized by thermochemical, structural, and spectroscopic methods. A common synthetic route, the oxidative carbonylation of either Fe(CO)(5) (XeF(2) as the oxidizer) or M(3)(CO)(12) (M = Ru, Os) (F(2) as the oxidizer) in the conjugate Bronsted-Lewis superacid HF/BF(3), was employed. The thermal behavior of the three salts, studied by differential scanning calorimetry (DSC) and gas-phase IR spectroscopy of the decomposition products, has been compared to that of the corresponding [SbF(6)](-) salts. The molecular structures of [M(CO)(6)][BF(4)](2) (M = Fe, Os) were obtained by single-crystal X-ray diffraction at 100 K. X-ray powder diffraction data for [M(CO)(6)][BF(4)](2) (M = Ru, Os) were obtained between 100 and 300 K in intervals of 50 K. All three salts are isostructural and crystallized in the tetragonal space group I4/m (No. 87). As for the corresponding [M(CO)(6)][SbF(6)](2) salts (M = Fe, Ru, Os), similar unit cell parameters and vibrational fundamentals were also found for the three [BF(4)](-) compounds. For the structurally characterized salts [M(CO)(6)][BF(4)](2) (M = Fe, Os), very similar bond parameters for both cations and anions were found. Hence, the invariance of structural and spectroscopic properties of [M(CO)(6)](2+) cations (M = Fe, Ru, Os) extended from the fluoroantimonates [Sb(2)F(11)](-) and [SbF(6)](-) as counteranions also to [BF(4)](-).

Homoleptic, sigma-bonded octahedral [M(CO)(6)](2+) cations of iron(II), ruthenium(II), and osmium(II). Part 1: Syntheses, thermochemical and vibrational characterizations, and molecular structures as [Sb(2)F(11)](-) and [SbF(6)](-) salts. A comprehensive, comparative study

Homoleptic octahedral, superelectrophilic sigma-bonded metal carbonyl cations of the type [M(CO)(6)](2+) (M = Ru, Os) are generated in the Bronsted-Lewis conjugate superacid HF/SbF(5) by reductive carbonylation of M(SO(3)F)(3) (M = Ru, Os) or OsF(6). Thermally stable salts form with either [Sb(2)F(11)](-) or [SbF(6)](-) as anion, just as for the previously reported [Fe(CO)(6)](2+) cation. The latter salts are generated by oxidative (XeF(2)) carbonylation of Fe(CO)(5) in HF/SbF(5). A rationale for the two diverging synthetic approaches is provided. The thermal stabilities of [M(CO)(6)][SbF(6)](2) salts, studied by DSC, range from 180 degrees C for M = Fe to 350 degrees C for M = Os before decarbonylation occurs. The two triads [M(CO)(6)][SbF(6)](2) and [M(CO)(6)][Sb(2)F(11)](2) (M = Fe, Ru, Os) are extensively characterized by single-crystal X-ray diffraction and vibrational and (13)C NMR spectroscopy, aided by computational studies of the cations. The three [M(CO)(6)][SbF(6)](2) salts (M = Fe, Ru, Os) crystallize in the tetragonal space group P4/mnc (No. 128), whereas the corresponding [Sb(2)F(11)](-) salts are monoclinic, crystallizing in space group P2(1)/n (No. 14). In both triads, the unit cell parameters are nearly invariant of the metal. Bond parameters for the anions [SbF(6)](-) and [Sb(2)F(11)](-) and their vibrational properties in the two triads are completely identical. In all six salts, the structural and vibrational properties of the [M(CO)(6)](2+) cations (M = Fe, Ru, Os) are independent of the counteranion and for the most part independent of M and nearly identical. Interionic C...F contacts are similarly weak in all six salts. Metal dependency is noted only in the (13)C NMR spectra, in the skeletal M-C vibrations, and to a much smaller extent in some of the C-O stretching fundamentals (A(1g) and T(1u)). The findings reported here are unprecedented among metal carbonyl cations and their salts.

Dynamic 13C NMR studies of ligand exchange in linear (d10) silver(I) and gold(I) and square-planar (d8) rhodium(I) homoleptic metal carbonyl cations in superacidic media

The dynamic CO exchange of the monovalent metal carbonyl cations [Ag(13CO)]+, [Au(13CO)2]+-Au(13CO) SO3F and [Rh(12CO)4-x(13CO)x]+ (x < or = 1) in superacidic solutions was studied by variable-temperature 13C NMR methods. The exchange rates are strongly dependent on the acidity of the solvent, the concentration of metal carbonyl cations and temperature. Whereas a suitable exchange rate of the Ag(I) system is only accessible in magic acid (HSO3F-SbF5), the more stable Au(I) and Rh(I) systems were studied in the less acidic fluorosulfuric acid. Selected solutions of Ag(I), Rh(I) and Au(I) yielded activation barriers deltaG* of 42.7, 43.5, and 56.2 kJ mol(-1) respectively.

Syntheses, structures and properties of 1-ethyl-3-methylimidazolium salts of fluorocomplex anions

Fluoroacid-base reactions of a room-temperature ionic liquid, 1-ethyl-3-methylimidazolium fluorohydrogenate (EMIm(HF)2.3F, EMIm = 1-ethyl-3-methylimidazolium cation), and Lewis fluoroacids (BF3, PF5, AsF5, NbF5, TaF5 and WF6) give EMIm salts of the corresponding fluorocomplex anions, EMImBF4, EMImPF6, EMImAsF6, EMImNbF6, EMImTaF6 and EMImWF7, respectively. Attempts to prepare EMImVF6 by both the acid-base reaction of EMIm(HF)2.3F with VF5 and the metathesis of EMImCl with KVF6 failed due to the strong oxidizing power of the pentavalent vanadium, whereas EMImSbF6 was successfully prepared only by the metathesis of EMImCl and KSbF6. EMImBF4, EMImSbF6, EMImNbF6, EMImTaF6 and EMImWF7 are liquids at room temperature whereas EMImPF6 and EMImAsF6 melts at around 330 K. Raman spectra of the obtained salts showed the existence of the EMIm cation and corresponding fluorocomplex anions. IR spectroscopy revealed that strong hydrogen bonds are not observed in these salts. EMImAsF6(mp 326 K) and EMImSbF6(mp 283 K) are isostructural with the previously reported EMImPF6. The melting point of the hexafluorocomplex EMIm salt decreases with the increase of the size of the anion (PF6- < AsF6- < SbF6- <NbF6- approximately TaF6-).

Silver(I) Undecafluorodiantimonate(V)

The reaction between AgBF4 and excess of SbF5 in anhydrous hydrogen fluoride (aHF) yields the white solid AgSb2F11 after the solvent and the excess of SbF5 have been pumped off. Reaction between equimolar amounts of AgSb2F11 and AgBF4 yields AgSbF6. Meanwhile, oxidation of solvolyzed AgSb2F11 in aHF by elemental fluorine yields a clear blue solution of solvated Ag(II) cations and SbF6- anions. AgSb2F11 is orthorhombic, at 250 K, Pbca, with a=1091.80(7) pm, b=1246.28(8) pm, c=3880.2(3) pm, V=5.2797(6) nm3, and Z=24. The crystal structure of AgSb2F11 is related to the already known crystal structure of H3OSb2F11. Vibrational spectra of AgSb2F11 entirely match the literature-reported vibrational spectra of beta-Ag(SbF6)2, for which a formulation of a mixed-valence AgI/AgIII compound was suggested (AgIAgIII(SbF6)4). On the basis of obtained results it can be concluded that previously reported beta-Ag(SbF6)2 is in fact Ag(I) compound with composition AgSb2F11.

Fluorination of [Os3(CO)12] and [Ir4(CO)12]

Fluorination of [Os(3)CO(12)] in HF/SbF(5) affords [Os(CO)(4)(FSbF(5))(2)]. According to its crystal structure (orthorhombic, Pna2(1), a = 1590.3(3), b = 1036.6(1), c = 878.2(2) pm, Z = 4), the two SbF(6) units occupy cis positions in the octahedral environment around the Os atom. Fluorination of [Ir(4)(CO)(12)] in HF/SbF(5) produced three different compounds: (1) [Ir(4)(CO)(8)(mu-F)(2)(Sb(2)F(11))(2)] (tetragonal, P4n2, a = 1285.2(2), c = 952.9(1) pm, Z = 2). Here, two of the six edges of the Ir(4) tetrahedron in [Ir(4)CO(12)] are replaced by bridging fluorine atoms. (2) [fac-Ir(CO)(3)(FSbF(5))(2)HF]SbF(6).HF (orthorhombic, Pnma, a = 1250.6(1), b = 1340.7(2), c = 1092.6(2) ppm, Z = 4). The Ir(4) tetrahedron in Ir(4)(CO)(12) is completely broken down, but the facial Ir(CO)(3) configuration is retained. (3) [mer-Ir(CO)(3)F(FSbF(5))(2)] (triclinic, P1, a = 834.9(1), b = 86 4.9(1), c = 1060.0(1) pm, alpha = 69.173(4) degrees, beta = 77.139(4) degrees, gamma = 88.856(4) degrees, Z = 2).

Cationic carbonyl complexes of rhodium(I) and rhodium(III): syntheses, vibrational spectra, NMR studies, and molecular structures of tetrakis(carbonyl)rhodium(I) heptachlorodialuminate and -gallate, [Rh(CO)4][Al2Cl7] and [Rh(CO)4][Ga2Cl7]

Dimeric rhodium(I) bis(carbonyl) chloride, [Rh(CO)(2)(mu-Cl)](2), is found to be a useful and convenient starting material for the syntheses of new cationic carbonyl complexes of both rhodium(I) and rhodium(III). Its reaction with the Lewis acids AlCl(3) or GaCl(3) produces in a CO atmosphere at room temperature the salts [Rh(CO)(4)][M(2)Cl(7)] (M = Al, Ga), which are characterized by Raman spectroscopy and single-crystal X-ray diffraction. Crystal data for [Rh(CO)(4)][Al(2)Cl(7)]: triclinic, space group Ponemacr; (No. 2); a = 9.705(3), b = 9.800(2), c = 10.268(2) A; alpha = 76.52(2), beta = 76.05(2), gamma = 66.15(2) degrees; V = 856.7(5) A(3); Z = 2; T = 293 K; R(1) [I > 2sigma(I)] = 0.0524, wR(2) = 0.1586. Crystal data for [Rh(CO)(4)][Ga(2)Cl(7)]: triclinic, space group Ponemacr; (No. 2); a = 9.649(1), b = 9.624(1), c = 10.133(1) A; alpha = 77.38(1), beta = 76.13(1), gamma = 65.61(1) degrees; V = 824.4(2) A(3); Z = 2; T = 143 K; R(1) [I > 2sigma(I)] = 0.0358, wR(2) = 0.0792. Structural parameters for the square planar cation [Rh(CO)(4)](+) are compared to those of isoelectronic [Pd(CO)(4)](2+) and of [Pt(CO)(4)](2+). Dissolution of [Rh(CO)(2)Cl](2) in HSO(3)F in a CO atmosphere allows formation of [Rh(CO)(4)](+)((solv)). Oxidation of [Rh(CO)(2)Cl](2) by S(2)O(6)F(2) in HSO(3)F results in the formation of ClOSO(2)F and two seemingly oligomeric Rh(III) carbonyl fluorosulfato intermediates, which are easily reduced by CO addition to [Rh(CO)(4)](+)((solv)). Controlled oxidation of this solution with S(2)O(6)F(2) produces fac-Rh(CO)(3)(SO(3)F)(3) in about 95% yield. This Rh(III) complex can be reduced by CO at 25 degrees C in anhydrous HF to give [Rh(CO)(4)](+)((solv)); addition of SbF(5) at -40 degrees C to the resulting solution allows isolation of [Rh(CO)(4)][Sb(2)F(11)], which is found to have a highly symmetrical (D(4)(h)()) [Sb(2)F(11)](-) anion. Oxidation of [Rh(CO)(2)Cl](2) in anhydrous HF by F(2), followed in a second step by carbonylation in the presence of SbF(5), is found to be a simple, straightforward route to pure [Rh(CO)(5)Cl][Sb(2)F(11)](2), which has previously been structurally characterized by us. All new complexes are characterized by vibrational and NMR spectroscopy. Assignment of the vibrational spectra and interpretation of the structural data are supported by DFT calculations.

Tris(trifluoromethyl)borane carbonyl, (CF3)3BCO-synthesis, physical, chemical and spectroscopic properties, gas phase, and solid state structure

Tris(trifluoromethyl)borane carbonyl, (CF(3))(3)BCO, is obtained in high yield by the solvolysis of K[B(CF(3))(4)] in concentrated sulfuric acid. The in situ hydrolysis of a single bonded CF(3) group is found to be a simple, unprecedented route to a new borane carbonyl. The related, thermally unstable borane carbonyl, (C(6)F(5))(3)BCO, is synthesized for comparison purposes by the isolation of (C(6)F(5))(3)B in a matrix of solid CO at 16 K and subsequent evaporation of excess CO at 40 K. The colorless liquid and vapor of (CF(3))(3)BCO decomposes slowly at room temperature. In the gas phase t(1/2) is found to be 45 min. In the presence of a large excess of (13)CO, the carbonyl substituent at boron undergoes exchange, which follows a first-order rate law. Its temperature dependence yields an activation energy (E(A)) of 112 kJ mol(-)(1). Low-pressure flash thermolysis of (CF(3))(3)BCO with subsequent isolation of the products in low-temperature matrixes, indicates a lower thermal stability of the (CF(3))(3)B fragment, than is found for (CF(3))(3)BCO. Toward nucleophiles (CF(3))(3)BCO reacts in two different ways: Depending on the nucleophilicity of the reagent and the stability of the adducts formed, nucleophilic substitution of CO or nucleophilic addition to the C atom of the carbonyl group are observed. A number of examples for both reaction types are presented in an overview. The molecular structure of (CF(3))(3)BCO in the gas phase is obtained by a combined microwave-electron diffraction analysis and in the solid state by single-crystal X-ray diffraction. The molecule possesses C(3) symmetry, since the three CF(3) groups are rotated off the two possible positions required for C(3)(v)() symmetry. All bond parameters, determined in the gas phase or in the solid state, are within their standard deviations in fair agreement, except for internuclear distances most noticeably the B-CO bond lengths, which is 1.69(2) A in the solid state and 1.617(12) A in the gas phase. A corresponding shift of nu(CO) from 2267 cm(-)(1) in the solid state to 2251 cm(-)(1) in the gas phase is noted in the vibrational spectra. The structural and vibrational study is supported by DFT calculations, which provide, in addition to the equilibrium structure, confirmation of experimental vibrational wavenumbers, IR-band intensities, atomic charge distribution, the dipole moment, the B-CO bond energy, and energies for the elimination of CF(2) from (CF(3))(x)()BF(3)(-)(x)(), x = 1-3. In the vibrational analysis 21 of the expected 26 fundamentals are observed experimentally. The (11)B-, (13)C-, and (19)F-NMR data, as well as the structural parameters of (CF(3))(3)BCO, are compared with those of related compounds.

Structures of the BrF(4)(+) and IF(4)(+) cations

The large discrepancies between the calculated and observed structures for BrF(4)(+) and IF(4)(+) (Christe, K. O.; Zhang, X.; Sheehy, J. A.; Bau, R. J. Am. Chem. Soc. 2001, 123, 6338) prompted a redetermination of the crystal structures of BrF(4)(+)Sb(2)F(11)(-) (monoclinic, P2(1)/c, a = 5.2289(6) A, b = 14.510(2) A, c = 14.194(2) A, beta = 90.280(1) degrees, Z = 4) and IF(4)(+)SbF(6)(-) (orthorhombic, Ibca, a = 8.2702(9) A, b = 8.3115(9) A, c = 20.607(2) A, Z = 8). It is shown that for BrF(4)(+), the large differences were mainly due to large errors in the original experimental data. For IF(4)(+)SbF(6)(-), the geometry previously reported for IF(4)(+) was reasonably close to that found in this study despite a very large R-factor of 0.15 and a refinement in an incorrect space group. The general agreement between the calculated and the redetermined geometries of BrF(4)(+) and IF(4)(+) is excellent, except for the preferential compression of one bond angle in each ion due to the influence of interionic fluorine bridges. In BrF(4)(+), the fluorine bridges are equatorial and compress this angle. In IF(4)(+), the nature of the fluorine bridges depends on the counterion, and either the axial (in IF(4)(+)SbF(6)(-)) or the equatorial (in IF(4)(+)Sb(2)F(11)(-)) bond angle is preferentially compressed. Therefore, the geometries of the free ions are best described by the theoretical calculations.

The synthesis, vibrational spectra, and molecular structure of [Ir(CO)(6)][SbF(6)](3).4HF - the first structurally characterized salt with a tripositive, homoleptic metal carbonyl cation and the first example of a tetrahedral hydrogen-bonded (HF)(4) cluster

The reductive carbonylation of IrF(6) in a dilute solution of SbF(5) in anhydrous HF (1:6 by volume) produces surprisingly at 25 degrees C and 1.5 atm CO the complex salt [Ir(CO)(6)][SbF(6)](3).4HF, while [Ir(CO)(6)][Sb(2)F(11)](3) is obtained in liquid SbF(5) under similar conditions. Vibrational spectra in the CO stretching range for both salts and [Ir(CO)(6)](3+)((solv)) are identical within error limits, and nu(CO)(av) is with 2269 cm(-1) the highest average stretching frequency so far observed for octahedral metal carbonyl cations. A vibrational assignment supported by DFT calculations is presented, and the vibrational fundamentals are compared to those of [Os(CO)(6)](2+). The molecular structure of [Ir(CO)(6)][SbF(6)](3).4HF is determined by single-crystal X-ray diffraction. Crystal data for [Ir(CO)(6)][SbF(6)](3).4HF: rhombohedral, R3c (No. 161), a = 14.630(4) A, c = 18.377(7) A, V = 3406.4(18) A(3), Z = 6, T = 150 K, R(1) = 0.0338 [I > 2sigma (I)], wR(2) = 0.0797). The average Ir-C bond length in the octahedral [Ir(CO)(6)](3+) cation is with 2.029(10) the longest observed for iridium carbonyl derivatives, consistent with the absence of Ir --> CO pi-back-bonding. The four solvate HF molecules form a tetrahedron via long, asymmetric, and partly delocalized hydrogen bonds with F-F edge lengths of 2.857 (3x) and 2.914 (3x) A. There is no precedent for a polyhedral (HF)(n) cluster in the gas, liquid, or solid phase. The four F atoms of the (HF)(4) cluster are coordinated to the C atoms of the six CO ligands of the cation, which again is without precedent. The coordination of one of the F atoms to three C atoms in a iso-tridentate mode with contact distances C-F(8) of 2.641(10) A is most unusual. The observed tight C-F coordination in [Ir(CO)(6)][SbF(6)](3).4HF provides conclusive evidence for the presence of electrophilic carbon in the cation and illustrates how superelectrophilic cations such as [Ir(CO)(6)](3+) are solvent stabilized in the conjugate Brønsted-Lewis superacid HF-SbF(5).

Synthesis and characterization of the first examples of perfluoroalkyl-substituted trialkyloxonium salts, [(CH3)2OCF3]+[Sb2F11]- and [(CH3)2OCF(CF3)2]+[Sb2F11]-

In the superacidic HF/SbF(5) system, methyl trifluoromethyl ether forms at -78 degrees C the new tertiary oxonium salt [(CH(3))(2)OCF(3)](+)[Sb(2)F(11)](-), which was characterized by Raman and multinuclear NMR spectroscopy and its crystal structure. The same oxonium salt was also obtained by methylation of CH(3)OCF(3) with CH(3)F and SbF(5) in HF solution at -30 to -10 degrees C. Replacement of one methyl group in the trimethyloxonium cation by the bulkier and more electronegative trifluoromethyl group increases the remaining O-CH(3) bond lengths by 0.037(1) A and the sum of the C-O-C bond angles by about 4.5 degrees. Methylation of CH(3)OCF(CF(3))(2) with CH(3)F in HF/SbF(5) solution at -30 degrees C produces [(CH(3))(2)OCF(CF(3))(2)](+)[Sb(2)F(11)](-). The observed structure and vibrational and NMR spectra were confirmed by theoretical studies at the B3LYP/6-311++G(2d,2p) and the MP2/6-311++G(2d,p) levels.

Polynitrogen chemistry. Synthesis, characterization, and crystal structure of surprisingly stable fluoroantimonate salts of N5+

The new N5+ salt, N5+ SbF(6)(-), was prepared from N(2)F(+)SbF(6)(-) and HN(3) in anhydrous HF solution. The white solid is surprisingly stable, decomposing only at 70 degrees C, and is relatively insensitive to impact. Its vibrational spectrum exhibits all nine fundamentals with frequencies that are in excellent agreement with the theoretical calculations for a five-atomic V-shaped ion of C(2)(v)symmetry. The N5+ Sb(2)F(11)(-) salt was also prepared, and its crystal structure was determined. The geometry previously predicted for free gaseous N5+ from theoretical calculations was confirmed within experimental error. The Sb(2)F(11)(-) anions exhibit an unusual geometry with eclipsed SbF(4) groups due to interionic bridging with the N5+ cations. The N5+ cation is a powerful one-electron oxidizer. It readily oxidizes NO, NO(2), and Br(2) but fails to oxidize Cl(2), Xe, or O(2).