The Parent Cyclopentadienyltin Cation,Its Toluene Adduct,and the Quadruple‐Decker [Sn3Cp4]2+

Truly cationic metallocenes with the parent cyclopentadienyl ligand are so far unknown for the Group 14 elements. Herein we report on an almost “naked” [SnCp]⁺ cation with the weakly coordinating [Al{OC(CF₃)₃}₄]⁻ and [{(F₃C)₃CO}₃Al−F−Al{OC(CF₃)₃}₃]⁻ anions. [SnCp][Al{OC(CF₃)₃}₄] was used to prepare the first main‐group quadruple‐decker cation [Sn₃Cp₄]²⁺ again as the [Al{OC(CF₃)₃}₄]⁻ salt. Additionally, the toluene adduct [CpSn(C₇H₈)][Al{OC(CF₃)₃}₄] was obtained.     

Reductive Elimination and Oxidative Addition of Hydrogen at Organostannylium and Organogermylium Cations

Bulkily substituted organodihydrogermylium and -stannylium cations [Ar*EH₂]⁺ (E=Ge, Sn; Ar*=2,6-Trip₂C₆H₃, Trip=2,4,6-triisopropylphenyl) were characterized as salts of the weakly coordinating perfluorinated alkoxyaluminate anion [Al{OC(CF₃)₃}₄]⁻. At room temperature, the stannylium cation liberates hydrogen to generate the low valent organotin cation [Ar*Sn]⁺. In contrast, the dihydrogermylium cation transfers the hydrogen atoms to an aryl moiety of the terphenyl ligand and oxidatively adds either hydrogen under an atmosphere of hydrogen or a sp² CH unit of the 1,2-difluorobenzene solvent.     

Homoleptic Phosphaalkyne Complexes of Silver(I)

By employing silver salts with a weakly coordinating anion Ag[A] ([A]=[FAl{OC₁₂F₁₅}₃], [Al{OC(CF₃)₃}₄]), two phosphaalkynes could be coordinated side‐on to a bare silver(I) center to form the unprecedented homoleptic complexes [Ag(η²‐P≡CtBu)₂][FAl{OC₁₂F₁₅}₃] ( 1 ) and [Ag(η²‐P≡CtBu)₂][Al{OC(CF₃)₃}₄] ( 2 ). DFT calculations show that the perpendicular arrangement in 1 is the minimum energy structure of the coordination of the two phosphaalkynes to a silver atom, whereas for 2 a unique square‐planar coordination mode of the phosphaalkynes at Ag⁺ was found. Reactions with donor molecules yield the trigonally planar coordinated silver salts [((CH₃)₂CO)Ag(η²‐P≡CtBu)₂][FAl{OC₁₂F₁₅}₃] ( 3 ) and [(C₇H₈)₂Ag(η²‐P≡CtBu)][FAl{OC₁₂F₁₅}₃] ( 4 ). All of the compounds were comprehensively characterized in solution and in the solid state.     

Silver–Ethene Complexes [Ag(η2‐C2H4)n][Al(ORF)4] with n=1, 2, 3 (RF=Fluorine‐Substituted Group)

Compounds including the free or coordinated gas‐phase cations [Ag(η²‐C₂H₄)_n]⁺ (n=1–3) were stabilized with very weakly coordinating anions [A]^? (A=Al{OC(CH₃)(CF₃)₂}₄, n=1 ( 1 ); Al{OC(H)(CF₃)₂}₄, n=2 ( 3 ); Al{OC(CF₃)₃}₄, n=3 ( 5 ); {(F₃C)₃CO}₃Al‐F‐Al{OC(CF₃)₃}₃, n=3 ( 6 )). They were prepared by reaction of the respective silver(I) salts with stoichiometric amounts of ethene in CH₂Cl₂ solution. As a reference we also prepared the isobutene complex [(Me₂C?CH₂)Ag(Al{OC(CH₃)(CF₃)₂}₄)] ( 2 ). The compounds were characterized by multinuclear solution‐NMR, solid‐state MAS‐NMR, IR and Raman spectroscopy as well as by their single crystal X‐ray structures. MAS‐NMR spectroscopy shows that the [Ag(η²‐C₂H₄)₃]⁺ cation in its [Al{OC(CF₃)₃}₄]^? salt exhibits time‐averaged D_3h‐symmetry and freely rotates around its principal z‐axis in the solid state. All routine X‐ray structures (2θ_max.<55°) converged within the 3σ limit at C?C double bond lengths that were shorter or similar to that of free ethene. In contrast, the respective Raman active C?C stretching modes indicated red‐shifts of 38 to 45 cm^?1, suggesting a slight C?C bond elongation. This mismatch is owed to residual librational motion at 100 K, the temperature of the data collection, as well as the lack of high angular data owing to the anisotropic electron distribution in the ethene molecule. Therefore, a method for the extraction of the C?C distance in [M(C₂H₄)] complexes from experimental Raman data was developed and meaningful C?C distances were obtained. These spectroscopic C?C distances compare well to newly collected X‐ray data obtained at high resolution (2θ_max.=100°) and low temperature (100 K). To complement the experimental data as well as to obtain further insight into bond formation, the complexes with up to three ligands were studied theoretically. The calculations were performed with DFT (BP86/TZVPP, PBE0/TZVPP), MP2/TZVPP and partly CCSD(T)/AUG‐cc‐pVTZ methods. In most cases several isomers were considered. Additionally, [M(C₂H₄)₃] (M=Cu⁺, Ag⁺, Au⁺, Ni⁰, Pd⁰, Pt⁰, Na⁺) were investigated with AIM theory to substantiate the preference for a planar conformation and to estimate the importance of σ donation and π back donation. Comparing the group 10 and 11 analogues, we find that the lack of π back bonding in the group 11 cations is almost compensated by increased σ donation.     

One‐Dimensional Polymers Based on Silver(I) Cations and Organometallic cyclo‐P3 Ligand Complexes

The synthesis and characterization of the first supramolecular aggregates incorporating the organometallic cyclo‐P₃ ligand complexes [Cp^RMo(CO)₂(η³‐P₃)] (Cp^R=Cp (C₅H₅; 1a ), Cp* (C₅(CH₃)₅; 1b )) as linking units is described. The reaction of the Cp derivative 1a with AgX (X=CF₃SO₃, Al{OC(CF₃)₃}₄) yields the one‐dimensional (1D) coordination polymers [Ag{CpMo(CO)₂(μ,η³:η¹:η¹‐P₃)}₂]_n[Al{OC(CF₃)₃}₄]_n ( 2 ) and [Ag{CpMo(CO)₂(μ,η³:η¹:η¹‐P₃)}₃]_n[X]_n (X=CF₃SO₃ ( 3a ), Al{OC(CF₃)₃}₄ ( 3b )). The solid‐state structures of these polymers were revealed by X‐ray crystallography and shown to comprise polycationic chains well‐separated from the weakly coordinating anions. If AgCF₃SO₃ is used, polymer 3a is obtained regardless of reactant stoichiometry whereas in the case of Ag[Al{OC(CF₃)₃}₄], reactant stoichiometry plays a decisive role in determining the structure and composition of the resulting product. Moreover, polymers 3a, b are the first examples of homoleptic silver complexes in which Ag^I centers are found octahedrally coordinated to six phosphorus atoms. The Cp* derivative 1b reacts with Ag[Al{OC(CF₃)₃}₄] to yield the 1D polymer [Ag{Cp*Mo(CO)₂(μ,η³:η²:η¹‐P₃)}₂]_n[Al{OC(CF₃)₃}₄]_n ( 4 ), the crystal structure of which differs from that of polymer 2 in the coordination mode of the cyclo‐P₃ ligands: in 2 , the Ag⁺ cations are bridged by the cyclo‐P₃ ligands in a η¹:η¹ (edge bridging) fashion whereas in 4 , they are bridged exclusively in a η²:η¹ mode (face bridging). Thus, one third of the phosphorus atoms in 2 are not coordinated to silver while in 4 , all phosphorus atoms are engaged in coordination with silver. Comprehensive spectroscopic and analytical measurements revealed that the polymers 2 , 3a , b , and 4 depolymerize extensively upon dissolution and display dynamic behavior in solution, as evidenced in particular by variable temperature ³¹P NMR spectroscopy. Solid‐state ³¹P magic angle spinning (MAS) NMR measurements, performed on the polymers 2 , 3b , and 4 , demonstrated that the polymers 2 and 3b also display dynamic behavior in the solid state at room temperature. The X‐ray crystallographic characterisation of 1b is also reported.     

Low-Valent MxAl3 Cluster Salts with Tetrahedral [SiAl3]+ and Trigonal-Bipyramidal [M2Al3]2+ Cores (M=Si/Ge)

Schnöckel's [(AlCp*)₄] and Jutzi's [SiCp*][B(C₆F₅)₄] (Cp*=C₅Me₅) are landmarks in modern main-group chemistry with diverse applications in synthesis and catalysis. Despite the isoelectronic relationship between the AlCp* and the [SiCp*]⁺ fragments, their mutual reactivity is hitherto unknown. Here, we report on their reaction giving the complex salts [Cp*Si(AlCp*)₃][WCA] ([WCA]⁻=[Al(OR^F)₄]⁻ and [F{Al(OR^F)₃}₂]⁻; R^F=C(CF₃)₃). The tetrahedral [SiAl₃]⁺ core not only represents a rare example of a low-valent silicon-doped aluminium-cluster, but also—due to its facile accessibility and high stability—provides a convenient preparative entry towards low-valent Si−Al clusters in general. For example, an elusive binuclear [Si₂(AlCp*)₅]²⁺ with extremely short Al−Si bonds and a high negative partial charge at the Si atoms was structurally characterised and its bonding situation analysed by DFT. Crystals of the isostructural [Ge₂(AlCp*)₅]²⁺ dication were also obtained and represent the first mixed Al−Ge cluster.     

Synthesis and Characterization of a Stable Nickelocenium Dication Salt

We report the synthesis and characterization of the nickelocenium cations [NiCp₂]⋅⁺ and [NiCp₂]²⁺ as their [F-{Al(OR^F)₃}₂]⁻ (Cp = C₅H₅; R^F=C(CF₃)₃) salts. Diamagnetic [NiCp₂]²⁺ represents the first example for the isolation of an unsubstituted parent metallocene dication. Both salts were generated by reacting neutral NiCp₂ with [NO]⁺[F-{Al(OR^F)₃}₂]⁻ in 1,2,3,4-tetrafluorobenzene (4FB). The salts were characterized by single crystal X-ray diffraction (XRD), indicating shorter metal-ligand bond lengths for the higher charged salt. Powder XRD shows the salts to be phase pure, cyclic voltammetry in 4FB gave quasi reversible redox waves at −0.44 (0→1) and +1.17 V (1→2) vs Fc/Fc⁺. The ¹H NMR of [NiCp₂]²⁺ is a singlet at 8.6 ppm, whereas paramagnetic [NiCp₂]⋅⁺ is significantly shifted upfield to −103.1 ppm.     

Hydrodefluorination of non-activated C-F bonds by diisobutyl-aluminiumhydride via the aluminium cation [i-Bu2Al]

A novel system for the hydrodefluorination (HDF) of non-activated C-F bonds at room-temperature is described. The reaction of i-Bu₂AlH with [Ph₃C][B(C₆F₅)₄] (1), [Ph₃C][Al(C₆F₅)₄] (2) and [Ph₃C][Al{OC(CF₃)₃}₄] (3) as precatalysts leads under formation of triphenylmethane to the aluminium cation [i-Bu₂Al]⁺ and the non-coordinating anions [M(C₆F₅)₄]⁻ (M = B, Al) and [Al{OC(CF₃)₃}₄]⁻. The formed aluminium cation is very reactive towards C-F bonds and easily forms i-Bu₂AlF releasing a carbocation that abstracts the hydride of excess i-Bu₂AlH and yields the corresponding hydrocarbon. Thereby, the active species [i-Bu₂Al]⁺ is regenerated and can realize a catalytic cycle. For 1-fluorohexane as an example including non-activated C-F bonds different activities were found (TON: 1: 20; 2: 12; 3: 30) in cyclohexane as solvent.     

Finally Stable and Homoleptic: Isolation and Characterization of {Cu[Fe(CO)5]2}+ Stabilized with Perfluoroalkoxyaluminate Anion, [Al(OC(CF3)3)4]−

Developments in the chemistry of weakly coordinating anions enabled isolation of numerous unique metal complexes with unusual ligands. An important example is the family of metal-Fe(CO)₅ complexes. In the current paper we present synthesis and thorough characterization of the first truly homoleptic {Cu[Fe(CO)₅]₂}⁺ cation obtained as a salt of weakly coordinating [Al(OR^F)₄]⁻ (R^F=C(CF₃)₃) anion. TGA/DSC/MS study show that its decomposition becomes noticeable only above 110 °C, thus it can be stored as powder in air-free conditions for months. The crystal structure of {Cu[Fe(CO)₅]₂}⁺ shows strong asymmetry of the cation and very short Cu-CO bonds in comparison to analogous {M[Fe(CO)₅]₂}⁺ where M=Ag or Au. Characterization is complemented with analysis of vibrational spectra and extensive DFT calculations which give insight into the energetics of Cu⁺-Fe(CO)₅ systems. Our results show that {Cu[Fe(CO)₅]₂}⁺ is homoleptic only as salt of [Al(OR^F)₄]⁻. Furthermore, in the presence of additional, even weakly basic ligands, the Cu⁺-Fe(CO)₅ bond strength decreases what may contribute to the complex's instability in liquid SO₂ or in the presence of [SbF₆]⁻. These conclusions point at the key role of selection of proper anion and solvent in stabilization of these types of complexes.     

Reaction of S2CC(PPh3)2 with Silver Salts Containing Weakly Coordinating Anions; Preparation and Crystal Structures of [Ag6{S2CC(PPh3)2}4][BF4]6 · 9.75CH2CL2 and [Ag4{S2CC(PPh3)2}4][Al{OC(CF3)3}4]4 · 4.25C2H4Cl2

The betain‐like carbodiphosphorane CS₂ adduct S₂CC(PPh₃)₂ ( 1 ) reacts with Ag(I) salts which contain weakly coordinating anions such as [BF₄]^? or [Al{OC(CF₃)₃}₄]^? to produce the cluster compounds [Ag₆{S₂CC(PPh₃)₂}₄][BF₄]₆ ( 2 ) and [Ag₄{S₂CC(PPh₃)₂}₄][Al{OC(CF₃)₃}₄]₄ ( 3 ), respectively, as orange yellow crystals containing solvent molecules. In the solid state the Ag₄ unit in 3 forms a tetrahedron, and in the Ag₆ core of 2 two of the opposite edges of the tetrahedron are bridged by Ag⁺ ions. The clusters are held together by argentophilic interactions, and each sulfur atom of 1 is coordinated to four (as in 2 ) or three (as in 3 ) silver atoms. The compounds are characterized by IR and ³¹P NMR spectroscopic studies and by X‐ray diffraction analyses.     

The metathesis reactions of [SNS][SbF6] and [SN][AsF6] with Li[Al(OC(CF3)3)4] in liquid SO2

The small di- and triatomic molecules [SN]⁺ and [SNS]⁺ have shown versatile chemistries and [SNS]⁺ is an important starting reagent for many sulfur-nitrogen radicals. However, their chemistry is limited to the more polar solvents (e.g. SO₂). In this work an attempt is made to increase their solubility in less polar solvents by exchange of the usual [MF₆]⁻ (M = As, Sb) anions by the large and weakly coordinating [Al(OC(CF₃)₃)₄]⁻. As expected the metathesis reactions of [SN][AsF₆] and [SNS][SbF₆] with Li[Al(OC(CF₃)₃)₄] in liquid sulfur dioxide resulted in the formation of the insoluble Li[SbF₆], which is the driving force for these metathesis reactions. The characterization of the compounds by IR and multinuclear NMR revealed that [SNS]⁺ formed a [Al(OC(CF₃)₃)₄]⁻ salt in a clean reaction. A preliminary crystal structure of [SNS][Al(OC(CF₃)₃)₄] is presented. The solubility of [SNS][Al(OC(CF₃)₃)₄] in CH₂Cl₂ is significantly increased with respect to the corresponding [MF₆]⁻ salts, and potentially opens up new areas of [SNS]⁺ chemistry. The reaction of the more reactive [SN]⁺ with Li[Al(OC(CF₃)₃)₄] was less clear. Multinuclear NMR and IR spectra were consistent with the formation of [SN][Al(OC(CF₃)₃)₄], which also showed significant decomposition.     

Perfluorinated Trialkoxysilanol with Dramatically Increased Brønsted Acidity

The Brønsted acidity of the perfluorinated trialkoxysilanol {(F₃C)₃CO}₃SiOH is more than 13 orders of magnitude higher than that of orthosilicic acid, Si(OH)₄, and even more for most previously known silanols. It is easily deprotonated by simple amines and pyridines to give the conjugate silanolates [OSi{OC(CF₃)₃}₃]⁻, which possess extremely short Si−O bonds, comparable to those of silanones.     

Low-Temperature Isolation of a Labile Silylated Hydrazinium-yl Radical Cation, [(Me3Si)2N−N(H)SiMe3].+

The oxidation of silylated hydrazine, (Me₃Si)₂N−N(H)SiMe₃, with silver salts led to the formation of a highly labile hydrazinium-yl radical cation, [(Me₃Si)₂N−N(H)SiMe₃]^.+, at very low temperatures (decomposition > −40 °C). EPR, NMR, DFT and Raman studies revealed the formation of a nitrogen-centered radical cation along the N−N unit of the hydrazine. In the presence of the weakly coordinating anion [Al{OCH(CF₃)₂}₄]⁻, crystallization and structural characterization in the solid state were achieved. The hydrazinium-yl radical cation has a significantly shortened N−N bond and a nearly planar N₂Si₃ framework, in contrast to the starting material. According to DFT calculations, the shortened N−N bond has a total bond order of 1.5 with a π-bond order of 0.5. The π bond can be regarded as a three-π-electron, two-center bond.     

Hydridotetrylene [Ar*EH] (E = Ge,Sn, Pb) coordination at tantalum,tungsten, and zirconium

In a reaction of tantalocene trihydride with the low valent aryl tin cation [Ar*Sn(C₆H₆)][Al(OC{CF₃}₃)₄] (1a) the hydridostannylene complex [Cp₂TaH₂–Sn(H)Ar*][Al(OC{CF₃}₃)₄] (2) was synthesized. Hydride bridged adducts [Cp₂WH₂EAr*][Al(OC{CF₃}₃)₄] (E = Sn 3a, Pb 3b) were isolated as products of the reaction between Cp₂WH₂ and cations [Ar*E(C₆H₆)][Al(OC{CF₃}₃)₄] (E = Sn 1a, Pb 1b). The tin adduct 3a exhibits a proton migration to give the hydridostannylene complex [Cp₂W(H) Sn(H)Ar*][Al(OC{CF₃}₃)₄] 4a. The cationic complex 4a is deprotonated at the tin atom in reaction with base ^MeNHC at 80 °C to give a hydrido-tungstenostannylene [Cp₂W(H)SnAr*] 5a. Reprotonation of metallostannylene 5a with acid [H(Et₂O)₂][BAr^F] provides an alternative route to hydridotetrylene coordination. Complex 4a adds hydride to give the dihydrostannyl complex [Cp₂W(H)–SnH₂Ar*] (7). With styrene 4a shows formation of a hydrostannylation product [Cp₂W(H) Sn(CH₂CH₂Ph)Ar*][Al(OC{CF₃}₃)₄] (8). The lead adduct 3b was deprotonated with ^MeNHC to give plumbylene 5b [Cp₂W(H)PbAr*]. Protonation of 5b with [H(Et₂O)₂][Al(OC{CF₃}₃)₄] at −40 °C followed by low temperature NMR spectroscopy indicates a hydridoplumbylene intermediate [Cp₂W(H) Pb(H)Ar*]⁺ (4b). Hydrido-tungstenotetrylenes of elements Ge (5c), Sn (5a) and Pb (5b) were also synthesized reacting the salt [Cp₂W(H)Li]₄ with organotetrylene halides. The metallogermylene [Cp₂W(H)GeAr*] (5c) shows an isomerization via 1,2-H-migration to give the hydridogermylene [Cp₂W Ge(H)Ar*] (9), which is accelerated by addition of AIBN. 9 is at rt photochemically transferred back to 5c under light of a mercury vapor lamp. Zirconocene dihydride [Cp₂ZrH₂]₂ reacts with tin cation 1a to give the trinuclear hydridostannylene adduct 10 [({Cp₂Zr}₂{μ-H})(μ-H)₂μ-Sn(H)Ar*][Al(OC{CF₃}₃)₄]. Deprotonation of 10 was carried out using benzyl potassium to give neutral [({Cp₂Zr}₂{μ-H})(μ-H)μ-Sn(H)Ar*] (11). 11 was also obtained from the reaction of low valent tin hydride [Ar*SnH]₂ with two equivalents of [Cp₂ZrH₂]₂. The trihydride Ar*SnH₃ reacts with half of an equivalent of [Cp₂ZrH₂]₂ under evolution of hydrogen and formation of a dihydrostannyl complex 13 [Cp₂Zr(μ-H)SnH₂Ar*]₂ and with further equivalents of Ar*SnH₃ to give bis(hydridostannylene) complex [Cp₂Zr{Sn(H)Ar*}₂].

Low valent cations of tin and lead were used to form hydridotetrylene coordination compounds. The mobility of the hydrogen substituent was investigated in deprotonation equilibria as well as in 1,2-H-shift reactions.     

Going Homoleptic: Synthesis and Full Characterization of Stable Manganese Tetranitrosyl Cation Salts

Although similar to carbon monoxide, the chemistry of homoleptic nitrogen monoxide complexes is fundamentally unexplored compared to their carbonyl analogues. Herein we report the synthesis of the first truly homoleptic transition‐metal nitrosyl cation as the salt of the weakly coordinating anions (WCAs) [Al(OR^F)₄]^? and [F{Al(OR^F)₃}₂]^? (R^F=C(CF₃)₃). These salts are easily accessible in good yields, phase pure, and were fully characterized by IR/Raman, NMR and UV/Vis spectroscopy as well as single‐crystal and powder X‐ray diffraction. They may serve as unprecedented simple model systems for theoretical and experimental studies of nitrosyl complexes.     

Chemical Bonding in Homoleptic Carbonyl Cations [M{Fe(CO)5}2]+ (M=Cu,Ag, Au)

Syntheses of the copper and gold complexes [Cu{Fe(CO)₅}₂][SbF₆] and [Au{Fe(CO)₅}₂][HOB{3,5-(CF₃)₂C₆H₃}₃] containing the homoleptic carbonyl cations [M{Fe(CO)₅}₂]⁺ (M=Cu, Au) are reported. Structural data of the rare, trimetallic Cu₂Fe, Ag₂Fe and Au₂Fe complexes [Cu{Fe(CO)₅}₂][SbF₆], [Ag{Fe(CO)₅}₂][SbF₆] and [Au{Fe(CO)₅}₂][HOB{3,5-(CF₃)₂C₆H₃}₃] are also given. The silver and gold cations [M{Fe(CO)₅}₂]⁺ (M=Ag, Au) possess a nearly linear Fe-M-Fe’ moiety but the Fe-Cu-Fe’ in [Cu{Fe(CO)₅}₂][SbF₆] exhibits a significant bending angle of 147° due to the strong interaction with the [SbF₆]⁻ anion. The Fe(CO)₅ ligands adopt a distorted square-pyramidal geometry in the cations [M{Fe(CO)₅}₂]⁺, with the basal CO groups inclined towards M. The geometry optimization with DFT methods of the cations [M{Fe(CO)₅}₂]⁺ (M=Cu, Ag, Au) gives equilibrium structures with linear Fe-M-Fe’ fragments and D₂ symmetry for the copper and silver cations and D_4d symmetry for the gold cation. There is nearly free rotation of the Fe(CO)₅ ligands around the Fe-M-Fe’ axis. The calculated bond dissociation energies for the loss of both Fe(CO)₅ ligands from the cations [M{Fe(CO)₅}₂]⁺ show the order M=Au (D_e=137.2 kcal mol⁻¹)>Cu (D_e=109.0 kcal mol⁻¹)>Ag (D_e=92.4 kcal mol⁻¹). The QTAIM analysis shows bond paths and bond critical points for the M−Fe linkage but not between M and the CO ligands. The EDA-NOCV calculations suggest that the [Fe(CO)₅]→M⁺←[Fe(CO)₅] donation is significantly stronger than the [Fe(CO)₅]←M⁺→[Fe(CO)₅] backdonation. Inspection of the pairwise orbital interactions identifies four contributions for the charge donation of the Fe(CO)₅ ligands into the vacant (n)s and (n)p AOs of M⁺ and five components for the backdonation from the occupied (n-1)d AOs of M⁺ into vacant ligand orbitals.     

Cationic titanium alkyls as alkene polymerisation catalysts: Solvent and anion dependence

The ethylene polymerisation activity of [(Ind)₂TiMe]BPh₄ decreases with decreasing solvent polarity but is enhanced if BPh₄⁻ is replaced by the less basic anion [B{C₆H₃(CF₃)₂}₄]⁻. The reaction of [PhNHMe₂]BPh₄ with Cp*₂TiMe₂ gives [Cp*₂TiMe]BPh₄, the first isolable 14-electron titanium alkyl cation complex (Ind = indenyl, Cp* = C₅Me₅).     

Group 6 Hexacarbonyls as Ligands for the Silver Cation: Syntheses,Characterization, and Analysis of the Bonding Compared with the Isoelectronic Group 5 Hexacarbonylates

The syntheses of the two novel complexes [Ag{Mo/W(CO)₆}₂]⁺[F-{Al(OR^F)₃}₂]⁻ (R^F=C(CF₃)₃) are reported along with their structural and spectroscopic characterization. The X-ray structure shows that three carbonyl ligands from each M(CO)₆ fragment bend towards the silver atom within binding Ag−C distance range. DFT calculations of the free cations [Ag{M(CO)₆}₂]⁺ (M=Cr, Mo, W) in the electronic singlet state give equilibrium structures with C₂ symmetry with two bridging carbonyl groups from each hexacarbonyl ligand. Similar structures with C₂ symmetry (M=Nb) and D₂ symmetry (M=V, Ta) are calculated for the isoelectronic group 5 anions [Ag{M(CO)₆}₂]⁻ (M=V, Nb, Ta). The electronic structure of the cations is analyzed with the QTAIM and EDA-NOCV methods, which provide detailed information about the nature of the chemical bonds between Ag⁺ and the {M(CO)₆}₂^q (q = −2, M = V, Nb, Ta; q = 0, M = Cr, Mo, W) ligands.     

Pyridine-Stabilized Cationic Silanethione Tungsten Complexes: Synthesis,Structures, and Reactivity

Silanethione compounds, R₂Si=S, have been recognized as highly reactive species. One reliable way to stabilize silanethione is its coordination to transition metal fragments to convert silanethione-coordinated transition metal complexes. Herein, we report the synthesis, structure, and reactivity of a second cationic silanethione tungsten complex [Cp*(OC)₃W{S=SiR₂(py)}]TFPB (R=Me ( 5 a ), Ph ( 5 b ), Cp*: η⁵-C₅Me₅, py: pyridine, and TFPB⁻: [B{3,5-(CF₃)₂C₆H₃}₄]⁻). Complex 5 was obtained by H⁻ abstraction from the Si atom in the corresponding silylsulfanyl complex Cp*(OC)₃W(SSiR₂H) ( 4 ) with Ph₃CTFPB, followed by the addition of pyridine. The reaction of 5 with PhNCS and PMe₃ produced [Cp*(OC)₃W{SSiR₂N(Ph)C(PMe₃)₂}]TFPB (R=Me ( 6 a ), Ph ( 6 b )) via the elimination of pyridine and the addition of the 1,3-dipolar species PhNC(PMe₃)₂ ( A ) to the Si atom.     

A Cationic NHC-Supported Borole

This work describes the synthesis and characterization of a highly reactive cationic borole. Halide abstraction with Li{Al[OC(CF₃)₃]₄} from the NHC-chloroborole adduct yields the first stable NHC-supported 1-(^MeNHC)-2,5-(SiMe₃)₂-3,4-(Ph*)₂-borole cation. Electronically, it features both a five-membered cyclic conjugated 4 π-electron system and a cationic charge and thus resembles the yet elusive cyclopentadienyl cation. The borole cation was characterized crystallographically, spectroscopically (NMR, UV/Vis), by cyclovoltammetry, microanalysis and mass-spectrometry and its electronic structure was probed computationally. The cation reacts with tolane and reversibly binds carbon monoxide. Direct comparison with the structurally related, yet neutral, 1-mesityl borole reveals strong Lewis acidity, reduced HOMO–LUMO gaps, and increased anti-aromatic character.